2 yr headach!!! almost resolved...thanks to GOFISHIN

[bannana]

I just thought id put this up incase anyone else has had the same boat with the same problem. Or at the very least if someone who has a similar boat has this problem in the future they can refer back to this.


Ive been running into cavitation problems with my Noosacat 3100 since I bought it new 2 years ago. At one stage i used 350lts of fuel to travel 68k's!!!! yes just a little over 5ltrs per k...

These issues have been a headache to say the least leaving me boat less for at least 50% of the time. At first I thought it was a prop problem and then an engine height issue and then a weight distribution problem and then finally last year Nooscat lifted the pods because they thought it was a pod height problem. Well as many are aware its never easy to get the right height engine combined with the best prop and then to mix in pod height makes life real hard. Well after testing multiple props given to me by yamaha last year I stuck with a pair of 17t's and combined with the pod lift and the engines getting drowned these props stopped the cavitation issues but unfortunately left me with an absolute pig of a boat.

Now with the engines at least 2 holes too deep and the incorrect props on the boat the boat drags its arse through the water. Any time i was in a 15 knott head sea i wish i was in my tinny (thats the truth!!! it would easily ride better). Id have to say in a head sea it was one of the worst rides I have experienced because the arse end of the boat would drag through the water and the bow was up in the air with every wave pounding the tunnel. Unless she was doing 30 knots it road like shit because it couldn't plane at low speed of 23 knots or less. Anyway i have gone to solas and tried multiple different props offered and will be trying a few merc props this week but after yesterday talking in detail with Brendan (Gofishin) and jason (Soulfish) I have a far better understanding and now can be confident I'm heading in the right direction as far as a solution is concerned.

Step 1... Try as many props as possible (recommended by yamaha, solas, Merc etc ) with a loaded boat to simulate a typical trip to ensure i have the best prop for the boat. To date the solas 3 blade 16, 17's have been the best and by a long way. looking forward to the mercs rev 4's
Step 2... Go through the motions of raising the engines one hole at a time (this week) and repeat the prop tests with the best 3 props found so I can be sure of engine height combined with props
Step 3... Add to the existing pods (flat bottom alloy pods currently) temporary ply sheets (20mm thick) to pack down the pods back to original pod height. Once the best height is found and the boat is riding like it should then look for a more permanent solution to remove the ply. Wayne from Noosacat explained that the Nooscats have a flat pod for a reason and that is the pods should skim the water giving the boat stability. My boat after having the pods raised has lifted the pods out of the water so when traveling at speed it makes the boat real unsteady and rolls from side to side in flat conditions on the big rounded sponsons. Once i get the pods back to the right height this should give me stability and a flatter ride.
Step 4... Enjoy fishing again!!!!

Id just like to say a big thank you To Gofishin (Brendan) for giving his time yesterday and coming out for a run and helping me sort some ongoing issues i have had with my boat. Heres a guy I have never met yet after a Pm I sent him last week was willing to help me and give his own time for no other reason other than just a good person helping someone who's got no idea. I know Brendan has offered plenty of advice on this forum and he obviously knows his stuff but to sacrifice half your saturday for someone who you don't know in my opinion is up there and i really appreciated the time he gave.


I also like to thank Soulfish for always helping me out when it comes to boating and once again he was there yesterday helping work through the problems. cheers mate.


Fingers crossed Im heading in the right direction finally and can get back out on the water a little more regularly.


I'll post up all the props Ive tested and outcomes when i finalise whats best for my boat.

Cheers

[myusernam]

I can't understand how noosacat can sell u a new boat and not have all that sorted.

[mitc69]

bad salesman :)

[scottar]

You know Keith , if you had just bought a mono :-X. Good to hear you are finally getting on top of it. It is surprising given the number of VMR rigs that are around at about that size that Noosacat don't have any answers.

[gofishin]

Sh!t Keith, nothing like a bit of pressure on now.... :)

In my mind we still have a long way to go to get your rig to what I would call an optimum setup, but with the right approach to this sort of problem, and the willingness to tweak/try everything - as you indeed have - I am sure we can get that awesome rig humming along as she should.

Just hope like cr@p the ensuing trials and tweaks deliver....!
cheers

[Horse]

That's the best thing about groups like AF. There is a huge amount of information and help available for those in need. Your current issue is going to be a brain twister working on all three parameters. As you increase the stern lift by changing the pods you are going to impact on drag as will raising the legs. This will mean your choice of props may no longer be optimal. Have you also ruled out the use of permatrims etc to help with the trim

[bannana]

Neil, I have looked at foils multiple times but they will be the last case scenario.

Scotty,

The biggest problem i have had was i keep my boat in my shed at 1770 and I had no where to keep it in Brisbane. I didn't want to anti-foul the boat so each time I brought it down to get work done on it i would then have to return it to 1770. Whats worse is a short run up noosa river doesn't give you a true sense of how the boats going to perform considering its running empty on fuel and gear. Fully loaded with another tonne of fuel and water never mind 4 big blokes and all their gear for an over nighter. So Id take the boat back to 1770 thinking I had the boat fixed each time and it would come back worse than it left once loaded and a bit of sea and swell was involved. In Noosacats defence they are busy and Wayne did ask me to keep my boat down here and use it down here until we got it sorted and I was unable too. So i can't blame them!!

So this time I decided to buy a seapenn (23k) and leave my boat in the water down at aquatic making it easy to access and get work done on the boat in Brisbane. I talked with wayne on saturday and he was really helpful. I'll keep in touch with him and talk through what we are doing so he knows and can also help steer me in the right direction.

The best part is i have now met someone who is actually interested in helping me and has loads of knowledge in this department and happy to point me in the right direction as well. Thanks to ausfish and the many members who contribute in this fashion. All the advice that goes back and forth is truly great. Theres guys on here that I don't agree with for one reason or another or have a blue with here and there but one things for sure they mostly all will give a lending hand and offer advice when needed. Its a breath of fresh air to meet guys like Brendan who are willing to share their knowledge and lend a hand for no return.....(a few good red marks are coming your way Brendan).

[robothefisho]

Id give Mercury's new enertia eco props a go. Big diameter for heavy boats with big four strokes. Also I've never had a boat with a pod work well without additional cupping being added to even stainless propellers. I would run the motors a tiny bit lower than a normal hull also to get good water flow. Ie cav plates having shallow water flow over instead of none at cruise. I would run the merc props with vent plugs solid

Australian prop repairs at the goldy have been excellent every time I get work done there. I really don't think you will get any prop to work without this extra cupping.

[Fed]

I think recording all the numbers after every change was a very good idea.

See graphs in post below.
http://www.ausfish.com.au/vforum/showthread.php?200609-Prop-test-advice

[chris69]

Hi Bannana ive read your problem with the set up and was thinking how some interseptors would go on the hulls you would get some stability while traveling as they would lift the ass.

[battleon]

What size/make motors are on it, I didn't notice it mentioned. Possibly not suited to the vessel???

[Back In Black]

Bananna, I thought we reached an agreement that before you hit the send button, Megs was going to check your spelling for you??

You didn't even get past the title of the post you knob!! LOL

Your spellcheck friend,

Beaker

[bannana]

Tony,

Im not worried about being a dyslexic dick mate. Im use to it and it all makes good sense to me.





Battleon,

Mate I'm running twin 300 yammies. I wish i went with Verado's like I was going to before getting talked out of it.




Chris 69,

Whats interceptors?? Do you mean foils?


Fed,

mate I'm going to fill my boat with fuel and water and redo tests again so the boat is as close to loaded as possible and take full figures including trimmed in and maximum trim out and of course optimum trim. So basically i will take 3 sets of figures for each prop at each engine height and compare all data at the end. Its not just about economy, revs or best cruising performance for me its as much about getting my boat to lift at lower speeds and get its arse out of the water. i might be asking a bit but until I try everything I just wont know. If I can achieve a big reduction in cavitation I'll be happy and start from there.


Robthefisho,

Yeah mate Ive never heard about the vent plugs solid so thank you for raising it. Otherwise I would of got the props and have no clue as to what they are. I still don't fully understand what they do but i will look into it a little more. Thanks. As for cupping solas gave me a set of four blades and then they cupped them last week for me and they still cavitate terribly. Im looking forward to trying the rev4's and also the Merc guy recommended a mirage prop so keen to see how that goes. Soulfish is a big fan of the enertia prop as well so I'll definitely give those three a crack for starters. thanks for your advice.

[chris69]

No Bannana not foils its a long thin wedge that goes across the hull at the stern between the strakes the water is push down at that point,they put them on a few big bass boats being very stern heavy with large motors and live well tanks,have a google about them.

[Fed]

Did you have a previous thread on this Bannana, I've looked & couldn't find anything?
How do you know you're getting cavitation, it sounds more like ventilation combined with a lot of prop slip.

If you're not looking for any additional input on this tell me to bugger off I'm sure gofishin has a handle on it but sometimes it helps to kick things around.

[bannana]

Fed,

Mate please offer as much advice as possible and i will defiantly take it on board. I'v learnt so much in the last week about what has been a pain in the arse of a problem only to find how little I actually knew about this topic. For example I don't know the difference between ventilation, cavitation and slippage.....I thought they were the same!! until I just read your last post..so thank you.

No I haven't had a previous thread because i didn't want people thinking I am shit canning Noosacat...and Im not. If I had done what Noosacat had asked me to do and that was keep my boat down here when i first got it and worked through the problems Im sure I wouldn't be in this position. They would of had more time to help resolve and to tell you the truth Id rather go through this process myself so i get exactly what i want and what feels good to me. Im not after the best economy or top end or even hole shot. i just want the best ride i can get with a fully loaded boat in 15-25 knot conditions because I have been caught out multiple times in this and when you 160 k's from port she's a long run home when it turns to shit and this is what I'm chasing.

I do think some of the guys on this forum are better equipped to help me resolve my issue than the so called experts anyway so I will always take others advice on board and it is truly appreciated.



Just a couple of questions



1. Whats the difference between ventilation, slippage and cavitation????

2. If yamaha 300's have a rev range of 5000-6000 and I can only achieve a maximum revs fully loaded of say 5200 yet the boat performs perfect for my liking...does this damage the engine????

For example the last set of props I have tried are a 16 diameter and 17 pitch from solas. Hole shot was great, top end at 46 knots, fuel economy best I've had, most outward trim I have had, I couldn't feel any cavitation, planeing at 19 knots at 3400rpm and 29.5 knots at 3900rpm (this is my cruise speed). However maximum revs only came up to 5400 with 5500 at max trim out. My boat was light with at least another 1200kgs to go in it for an overnighter...extra 2 guys, 800 litre fuel, 150lts water, food, drink, bait, ice, tackle, bedding, rods reels etc. So I don't know what or how many revs I will drop.

But my question is lets say I drop 300 revs and when i lift my engines a hole or two and pick back up 100 revs....IF I'm pulling say 5200-5300 revs will this damage my engine or shorten the life of the engine when the rev range is stated at 5000-6000...& Why


Thanks

keith

[gofishin]

Yes Fed, and others, by all means offer up… don’t let the title put you off by any means.

I am certainly not the messiah of props, or indeed the savour to this problem/condition. The best advice Keith can get is from someone that’s had/experienced this situation with the same/a very similar setup – because that can rule out a lot of trial & error. However, even though different rigs/power/setups etc can change things a lot, especially with props, mostly the tried & proven theories hold without too much deviation - so any prop trials/setup fixes with V6 4/ donks may help.

Although I have only just met him, he seems to be the sort of guy that takes everything on board – from everyone, learns enough about what he doesn’t know (very quickly), and puts that knowledge to good use (with the help of good mates etc, like Jason).

PS. Yes, I did say in an email to him that it was ventilation…however he is probably going through 'information overload' at this time, hence I have since left it be … (and I thought Kerry would put us all straight anyway :) ).

Cheers
Brendon

[Fed]

Gotta be quick the wife has got me working...

Ventilation is sucking air down from the water surface, the anti-ventilation plate gives it a longer path to travel which helps stop this.

Slippage is the difference between theoretical & actual distance a prop moves a boat.
EG, 1 turn of a 17" prop without slip would move a boat 17" whereas with slip 1 turn of a 17" prop may only move the boat 15".
Slip is usually around 10%.

Cavitation is water boiling off on the low pressure side (front) of the prop, it looks like corrosion.

Will post back with question 2 but have to say I always prefer to be near the top end of RPM when lightly loaded... gotta run.

[TheRealPoMo]

WAY out of my depth here as you have obviously spent some serious money, but I have to ask:
Looking at the specs, twin 250HP is the max rated but this is not mentioned ? Captain Obvious here....
Why not leave the rig with Noosacat until it is sorted ? Surely they are best placed to sort out teething issues ?

Cheers and hope it works out.

Too much money to have not working properly....

[Camhawk88]

MAte seeing as you are dealing with prop issues, pod issues and engine height issues simultaneously, have you given thought to using jacking plates? It sounds like the pods are best left at the original height so with the jacking plates you could adjust motor height on the go while trialing different props. It would give you the ability to change the height and compare the handling, and cavitation/ventilation/slip while underway in a matter of seconds/minutes rather than days. You would be able to fine tune it on the run and being able to compare immediately, you would get a better feel for the difference various heights bring to the table. Then you could trial all props at all heights on the same day.

[Fed]

Sorry about that I'm married to the hoarder from hell and in a moment of weakness she decided to have a tidy up... an opportunity I couldn't afford to miss out on.

But my question is lets say I drop 300 revs and when i lift my engines a hole or two and pick back up 100 revs....IF I'm pulling say 5200-5300 revs will this damage my engine or shorten the life of the engine when the rev range is stated at 5000-6000...& Why
I don't think running 5200-5300 when fully loaded would hurt anything but why would you choose to when you could be running 5500 fully loaded and 6000 light load.
The motors would be happier and responsive boats are much more fun to drive.

Fear of lugging as they called it stems back to old tech 2 strokes that had mechanically controlled timing advance, controlled from the throttle with no regard at all for engine RPM. I'd like to think modern computer controlled motors have overcome.... maybe not?

Either way you're still inside the recommended RPM.

I'd start with the pods in the lower position to help stern lift and stability
then with the best props to date raise the motors as high as possible without having them ventilate, this will help reduce bow lift.

After that it's fine tuning the props to get good WOT RPM, with the right props you may even be able to go up another hole.

Anyway I think your best way forward is to get the pods back down.

[scottar]

So reading between the lines mate - shes too fat to get her bum out of the water at less than 20 odd knots????. Having just been through similar set-up issues with the Victory but chasing specifically slow speed planing performance at an economical fuel burn, the things that made the biggest difference were the trim tabs. Not really practicle on a cat I know. The next best was a Permatrim foil which was removed once the tabs went on (The holes left in the AV plate are an annoyance I have since learnt to live with) . I agree with the other guys that to correct your instability issue the pods do need to go back down or be modified to the correct depth if you want to run the motors higher. I found that all the variations ( motor height, 4 blader - tried 3 before I got the right one by luck) did make a difference but by nowhere near as much. A small gain was made with each one to add icing on the cake so to speak. What I had before the tweaking was a hull that apart from slow speed plane worked fine but in choppy conditions when you had to slow down was unbalanced due to outboard weight and adopted a very poor attitude with the bow pointing skywards and as such burned a heap of fuel due to prop slip as the thing was always teetering on the edge of falling off the plane.

While a 4 blade prop saw a change in the slip at the rpms I was travelling at what it effectively did was increase boat speed for the given RPM and simply shifted the issue to a lower RPM bracket. I still needed to go slower to suit the sea conditions. The only way was to shed transom weight or generate lift to get the balance right.

As for the RPM side of things, my very basic understanding is that by running over propped you are basically increasing the load on the motor. This will lead to higher combustion chamber temps and EGT's. At what point they actually start to become an issue and do damage is probably only known to the manufacturers (and even then sometimes you would wonder) but personally I would be at least trying to shoot for the high side of the allowable RPM band

[Blackened]

G'day

Keith, Have you had a look at the Hysucat foils? http://hysucatmarine.co.za/

We had some on both the Noosacat 4400's I used to work on back in the day They made a great boat brilliant. I also spotted some on a Coral Sea 55 that I detailed recently.

Dave

[bannana]

Thanks guys...info over load but i will absorb all this over time and put it to good use. As for today i trailed another set of 4 blades from solas that were terrible so i put the 16d 17p props they supplied back on. I have then put 900lts fuel in the boat, 150ltrs water and about 200 kg's of gear so i could then test the boat fully loaded. I even filled up both live bait tanks on the transom (about 150ltrs of water) to see how the boat went. First of all id like to say the outboards are down and down a long way!!! but even after loading the boat up to this degree the boat still pulled the same revs as it did the previous day unloaded. So i am shocked at after putting in over a tonne that the revs stayed similar. Hole shot was down, cruise speed was down and top end speed was down to 42 knots but still good. What I didn't like about this was that the boat would not plane at lower revs/speeds and for the boat to feel like it was working well it had to be above 27knots in speed. It would just drag its butt otherwise. At full noise there was an immense amount of spray around the engines and i couldn't see the cav plats. So taking on Fed's and Gofishings advice tomorrow I'm going to pull my boat out at RQ public ramp and lift the engines 2 holes and then add a temporary ply packer of 50mm underneath the pods (to get back to the original pod height in line with the chine) and re test the same props and see what happens. If all is good and the props don't ventilate then happy days . On Thursday the guys from merc are going to provide me with a few different props and come for a run and see what they think. If the engines are too high I can always drop them but at the moment I think they are too low going by what I'm told and read on here and as a result are contributing to the drag.

I will definitely put some stats up latter in the week when i get a chance. I'll let you guys know how the pod lower and engine lift goes tomorrow with the same props that appear to be ok other than the inability to get the boat going well at lower speeds under load.

Once again thanks for the feed back and don't think for one second that I'm not taking on board what is written. For example I called Solas this afternoon about the jackplates and they said my outboards are already to far back and by adding jack plates could potentially make the situation worst because it is moving the outboards back another 150mm. I still haven't crossed these out but do want to get the engine s as close to the best height first with props that are not ventilating and the pods at the optimal heights.

Fingers crossed tomorrow.

Cheers for the advice guys.



thank you

keith

[scottar]

Just one thing to consider with all the experimentation - do you have water pressure gauges so you can keep an eye on the cooling situation. If not, make sure you keep a very close eye on the temp gauges. Probably not an issue while the donks are low but something to be mindful of as you lift them up.

[Darren Mc]

Can I ask why we're the 4 blades so terrible?

[gofishin]

Yes, were they the small diam props Keith?

Scott, I don't think cooling will be an issue at all. To give you an idea how buried the motors are, I could only get a clear view of where the donks/plates were when we were above 40kn. At 28 even the 127mm extensions were buried in that much spray it was difficult to even see them. The Yams have additional cooling grates at the leading point of the gear housing/prop tube too.

A big factor is of course the motors being ~650mm behind the transom.

Sent from my iPhone using Tapatalk

[bannana]

Can I ask why we're the 4 blades so terrible?


Darren,

Ive tried 3 different sets of 4 blade props, 1 set of five blade and now 3 sets of 3 blades and on Thursday another set of four blades and two more different 3 blades from Merc. So all up that will be 10 sets of props and all recommended by the experts...Sloas, Yamaha and Mercury.

So to answer your question the first set of four blades were Turbos supplied by yamaha last year and they vibrated pretty bad. They also ventilated really bad. The second set was from solas and I have tried them twice. Once uncupped and then again cupped with Gofishing on the boat for the cupped run. Once again terrible cavitation/ventilation/???. As for the third set well that was today with a loaded boat and they struggled to get past 5000 revs so i didn't bother going any further. I'll write down all the names of the props tomorrow and sizes and retry them again once I lift engines and pack pods. But to date the big surface area 3 blades seem to grip the best but unfortunately I'm still dragging my bum. But to date the pick has been the Yamaha 17T 15 1/2 & The Solas 16 diamiter and 17 pitch. Both 3 blade props.

Im really interested to see what happens tomorrow and again on thursday when Merc brings up 3 different props to try.

[bannana]

Yes, were they the small diam props Keith?

Scott, I don't think cooling will be an issue at all. To give you an idea how buried the motors are, I could only get a clear view of where the donks/plates were when we were above 40kn. At 28 even the 100mm extensions were buried in that much spray it was difficult to even see them. The Yams have additional cooling grates at the leading point of the gear housing/prop tube too.

A big factor is of course the motors being ~650mm behind the transom.

Sent from my iPhone using Tapatalk


Yeah they were mate...struggled even getting to 5000 revs!! it was a slug out of the hole and the boat sat low in the water. Didn't even get past the third set of beacons and just turned around.

[overdraft]

Sounds like you are heading in the right direction Keith. Just a quick question to anyone who might know why my fuel economy has gone so bad. I used to use about .8 litres per km and now I am using around 1.2 litres per km. Would love to get a bit of advice on if changing to a different prop will help.
(PS I might have to borrow some of those props Keith)
Danny

[Darren Mc]

Wow you have been busy. I'm really surprised how bad the four blade props have performed. Normally the right four blade would help your situation. That is slower planing speeds, more stern lift, better grip hence great holeshot.
I will keep following this thread to find out how you go.
Best of luck with it, hope you get it sorted soon.

[Dicktracey]

Keith for what its worth this is how I set up the 6.5M Evo. 200hp suzuki 16" stainless 3 blade
With the use of a gopro i set the engine height first so the cav plate on the leg was on the water surface when at half trim.
After i had the engine at the right height i then tested props swinging the biggest prop i could & still reaching max revs.
After decided on prop i calculated prop slip finding i had about 15%, had prop scanned to find high point "lump" on a brand new Suzuki/Solas prop.
Spent $400 grinding and de pitching prop by 1/2" to give me 7-1/2" % propslip & increase in fuel econ from 1km/L up to 1.2km/L
This is the second boat I have set up like this after similar frustration & been happy with result.
Hope it can help
Dick

[gofishin]

..it was difficult to even see them. ... and by this I meant I could only see the top of the 127mm leg extension in one donk, not even this in the other. I.e. The plates were buried under ~150mm of spray/white water.

Edit: extension height corrected.

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[gofishin]

Dick, good info. A prop scan/tune/balance can prove very worthwhile sometimes. And yes, this will be looked at when we are down to the last prop - if Keith wants to go that far.



de pitching prop by 1/2" to give me 7-1/2" % propslip & increase in fuel econ from 1km/L up to 1.2km/L... This is very interesting, and that is a marked improvement in performance. I have found & heard often that de-pitching can lead to increased ventilation. Is this the case? Who did the work out of interest, Brisbane or Goldy?

Danny/overdraft could be a chunk/dent out of the gear case/prop, but could also be a mechanical/motor issue, or a simple issue of partial blockage of the pitot hole in the leg. Is this indicated economy or calculated economy from fuel used/dist travelled, or both? Any noticable drop in zuke gauge speed? When's the next service due? Did you hit anything? Any vibration or changes to WOT? Get a propscan done, might pay off regardless.


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[Dicktracey]

and by this I meant I could only see the top of the 100mm leg extension in one donk, not even this in the other. I.e. The plates were buried under ~150mm of spray/white water.


Sent from my iPhone using Tapatalk
Brendon i depitched prop to kovr rev range when planning to allow better use of engine torqur curve,prop guy in Brisbane pm me your number mate ilk give you a call later on just finished night shift
Dick

Dick, good info. A prop scan/tune/balance can prove very worthwhile sometimes. And yes, this will be looked at when we are down to the last prop - if Keith wants to go that far.

This is very interesting, and that is a marked improvement in performance. I have found & heard often that de-pitching can lead to increased ventilation. Is this the case? Who did the work out of interest, Brisbane or Goldy?

Danny/overdraft could be a chunk/dent out of the gear case/prop, but could also be a mechanical/motor issue. When's the next service due? Did you hit anything? Any vibration or changes to WOT? Get a propscan done, might pay off regardless.


Sent from my iPhone using Tapatalk

[robothefisho]

Just thought id clarify that the mercury enertias will be useless in this setup. You want the mercury enertia eco's which are 16 inch diameter far better suited to the high hp high load application you have here.

[gofishin]

Robbo,
They would obviously be an option to try, however unless they have brought out a 17”p or even 15/16”p they would be a waste of time (19”p way too big at this diam), unless of course they are a very ‘short’ prop, meaning the pitch size is overstated. From what I can see, they are working on a 17, but haven’t released it yet (maybe Mr Mercury will have a prototype with him tomorrow?)

Here is a bit of my thinking…

There are many attributes to a ‘propeller design’, but most important are diameter and pitch. The ‘size’ of a propeller is a combination of its diameter and pitch. Designers also use a term called ‘pitch ratio’, which is the pitch of a prop divided by its diameter. Different types of craft require different pitch ratios, and each has a ‘range’ of pitch ratios which ‘should’ provide an appropriate propeller depending on the speed, fitted power, load, and the number of blades etc.

At lower speeds, available torque (thrust) is more important to overcome the load imposed by a certain diameter prop. At high speeds/WOT, HP comes into play, and pitch more so over diameter.

While the theory you state (re large diams/heavy load) is generally true, i.e. select a prop on the lower end of the preferred ‘pitch ratio’ range, we also need to consider the prop speed required to get the boat to a certain speed.

At 6000 engine rpm’s Keith’s props are doing 3429 rpm. If he had Zuke 300’s on the bum the props would only be doing 2885 rpm. The props on the Yams are spinning 19% faster! That ‘generally’ means that you need to err slightly toward the size of pitch rather than diameter – so two identical boats with these motors would not only end up with different pitch props, but possibly different diams too and even different styles of props – if you wanted to get the absolute best out of the rig for ‘your’preferred operating conditions.

Atthe moment it seems the 16” diam SOLAS props are the pick, but with a bit of boat trim/motor height corrections to come.

AlthoughI have not propped anything like this rig with outboards, or any twin outboard rigs for that matter, what I believe we will find is that as the motors come up (and/or the pods dropped/boards added below the pods), the larger diameter props will suffer a bit more from ventilation – from my experience. Why? Well my theory is that the prop tips on a bigger props are closer to the surface of the water, hence easier to drag air/disturbed water into the prop.

However, I have been wrong before JJ ... and have found instances with props/propping where practice does not follow theory with diameters … and I can’t explain it. Whatever happens, it will be a very interesting and learning experience for all, and that includes me!
Cheers
Brendon

[Fed]

Just in passing I Googled the ratio & found 2 different answers...

1.75:1 and also 2.33:1

Buggered if I know, not up with this new fangled stuff.
What are we dealing with?
Bottom of the page in both links.
http://www.yamaha-motor.com.au/sites/yamaha-motor/files/brochures/2010-yamaha-motor-australia-4-stroke-hi-power-brochure.pdf

http://www.yamaha-motor.com/outboard/Hot_Sheets/June_2010_Hotsheets/V-6%20Offshore%20Hot%20Sheet%20FINAL%20FINAL%20%28v2 %29.pdf

I'm off to search for an app that will graph my rpm vs speed, gotta love those apps.:)

[gofishin]

Fed,very interesting!

Didn’t even knowanother ratio existed, but maybe only in another part of the world?

By Keith’s GPS speeds and revs he has posted,he definitely has the 1.75 ratios – no questions about it.
Cheers

PS. Oh, and if the 46kn @5500 rpm was average GPS speed in both directions from the 16"d x 17"p props (post #16), the props aren't 17"p, they are actually bigger. For these conditions/parameters and 0% slip, speed is 44kn not 46kn - unless my fat fingers have pushed the wrong button on the calculator!

[Fed]

By Keith’s GPS speeds and revs he has posted,he definitely has the 1.75 ratios – no questions about it.
Good thinking it never struck me to do the sums.


Another thought, could the pods be sucking themselves to the water surface like the old Haines Sigs where they had to put a large hole through the hull and raised well above the waterline to break the suction?

It seems to me KC have never had this combination of boat, motors & weight before otherwise they would know the answer, it may not of happened with any previous boats.

[robothefisho]

The motors sound like they are way too deep which it sounds like you guys are addressing. Id do that and see if those solas dont gain 2-300rpm. They sound like they are more a 19pitch prop from those numbers. were they heavily cupped? Huge cupping could account for that. I dont see anything under 15 diameter in a 3 blade working. Im guessing the boat would be around 6 ton. Which should turn 19s with 600hp.

Maybe suzuki genuine props would be a good match I think they're pretty large too.

Ideally you want the smallest diameter largest pitch that runs high in rev range and low slip numbers. If they are to small diameter it will be obvious in quick revving with boat speed lagging behind. More revs to maintain slow plane. But normally look ok towards WOT when drag reduces.

[bannana]

ok guys,

thank you for all the advise and comments... F%&k me what an effort and what a science this is. I hit the ramp early today and put my yamaha props (17's) on first and gave them a run so i could get a feel of them again. Then at the ramp I lifted the engines two holes (one to go if needed) and took the yamaha props for another run. All that happened was they ventilated like no tomorrow...in turns and even in straight runs. the bum was dragging and once again i couldn't get the boat going well unless it was doing 27-28 knots or above. it was a pig!!

I then put on the solas 16d 17p that have to date been the best props and to my surprise once again no increase in revs but a massive increase in lower planning speed. I could now plane at 21-22 knots comfortably which is what I've been looking for. I then took the boat back to the ramp and fitted a sheet of 25mm thick ply to the underside of each pod and retested the solas prop. before testing the prop we realised it was damaged. I'm not sure how as I didn't feel like I had hit anything but the port prop was damaged. it had nicks out of each blade some as large as half a finger nail. Stuffs me how this happened!!! Skeg untouched!!

When retesting these props with the ply fitted to the underside of the pods we noticed a huge improvement in the stability of the boat and additional lower speed planing. i could now plane around 16knotts. without feeling that the boat was dragging through the water.

However one note to mention is that we still cannot see the cavitation plate!!!! its still that buried. All the splashing around the engines also cleared up once the ply was fitted. We realised the majority of the splashing was coming from the live bait pick up that is now clear of the water thanks to the lift created by the ply.


Also one thing to note is revs have remained the same loaded or unloaded and even the same once the engines have been raised.... yet another thing i don't understand.

Tomorrow the merc man Dallas is bring up rev 4's in both 15's & 17's. He's also now bringing up enertias...not sure what size. Looking forward to seeing where this takes me. i think the ply heights is good for the solas 16's because at cruise speed the ply just touches the water and at WOT the ply just sits of the water. An additional 25mm like it was when i got the boat would only raise the stern and lower the bow further and at present it feels comfortable so i will wait and see how the merc props go first.



Getting close.. thanks fellas.

[FNQCairns]

Bannana

Reads like you have a couple bucks at your disposal, what about fitting a couple of hydraulic jack plates?..also wedges as needed. Would make for a more customisable rig in real time anyway. I am not up there on cats but performance numbers always speak the truth if able to CONSTANT them through time.

Really big O/Bs are out of my interest these days but if there is a jack unit that might handle them it will make your life better on the water, even if with the bit of extra setback I expect.

good luck and sad to hear of your problems...that fuel usage you mentioned early is so far out there I wonder how the boat was even usable.

[rocklobster]

Bannana,
If you havent ried everything Solas has try these . HR Titans 14 and a half inch diameter and 15 inch pitch. These will lift the stern and get the revs up .

[bannana]

Merc prop failure!!!!

Unfortunately the enertia and rev 4's all cavitated poorly. The rev 4 15 pitch weren't too bad in the cavitation stakes but they did cavitate. they also performed poorly when stacked up against the solas 3 blade 16d 17p prop. The revs were good at 6000-6100 and while the top end speed was sitting at 38 knots the most disappointing thing was the cruise speed was down to low 20 knots and chewing up the fuel. The economy was sitting around 400-450k's per tank (1000lt tank) while the solas were sitting at 600-700 k's a tank. When we tried the 17 pitch rev 4's they caveatted terribly when turning but there cruise speed was up at 26-27 knots with top end just a tad over 40. Economy for this prop was 500-550k's per tank. The best thing about this prop was the boat would plane at low speeds and the boat felt great. it sat high and stable with good acceleration however it still caveatted when turning hard and even when accelerating too quickly.

All in all a little confused today and disappointed. I'll get the current solas 3 blades that are the only props out of 11 tested over the last two years to have not cavitated in an obvious way. I will use these props for the next couple of trips and see how i go.

this is so frustrating. You would think that theres multiple props i could test that would work and it would be a matter of picking out the best performance and economy combination to suit the particular owner. In my case I can't find any props to choose from so Im seriously thinking that the props are not the problem and I have to take the next step.....Pods!!!! How do i deliver clean water to my props???? Especially when the big round sponsons on my 3100 seriously depend on a flat pod to stabilise the boat while under way. I can't extend my hull because the current shape is just about rounded and the boat when the pods are clear of the water just rolls around uncontrollably.

[gofishin]

Well that's a big downer Keith!

I really thought the 17's would be in the top two in terms of grip and greatly reduce your ventilation issues. I was wrong. The lift and low speed planing characteristic benefits are as per expected.... but .... these results are damn frustrating.

Did you take a photo of the hulls/pods by chance when you lifted the donks/had the boat out of the water?

Did the Merc guy have any comment about current plate height when cruising etc? Or how long till they release the Enertia ECO 17's?

That is a bummer!


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[gofishin]

One thing I think we can deduce/assume(?), even though you were told that the small SOLAS 4 bld and the 3 x 16 x 17 SOLAS had no additional cupping, the figures tell us different!

If so, this explains why you're getting such good grip with the big 3 bld.

If they can't fix the dings, and have to replace it with a new one, I guess we'll know for sure if one side performs different to the other!
Cheers


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[grahams]

This may not help, but I used to run a couple of Voyager 11m cats with high speed diesels.
i very quickly learnt the horsepower wasn,t the issue, it was all about torque. Big boats behave differently, you "push" them thru the water unlike a little planing hull. My boat with less horsepower lower max revs steeper pitch props went a lot better and faster than the one with more horsepower, because the power was only at much higher revs which meant I put smaller pitch props on that spun faster, the faster they spun the more slip/ inefficiency i got. If I had kept the boats I would have swapped the gear box on the bigger motors to get a much slower prop speed.
I suspect a 3100 Noosa cat probably works more like a displaning hull than planing hull. If you approach the problem this way it might help.
there is no way a big boat is going to keep going forward at the rate the prop is spinning, that happens with my little 485 haines, but not with my 9 tonne cats.
we were running steyrs diesels around 200 HP and achieving top speeds around 20 knots ( which is meaningless) we were cruising around 17 knots at good economy and by "normal standards" way over propped, not a chance in hell of getting to max revs. I think the best boat would only rev out at to 3300 instead of 3600. but if we proped it to get to max revs our cruise speed would have been 10 knots!
It was all about getting in the right torque band

have you tried grossly over propping? Can you change the gear ratio on the big yammies?

[robothefisho]

Mate,

Don't stress about damaging the prop. It will cost about a hundred bucks to fix (yes easily fixed) and you won't even know it was damaged. While it's there ask them to put it on a pitch block and find out what pitch it actually is.
If they are still gripping well lift the motors the final hole it may improve again and costs nothing.

The merc prop tests only confirm you need large props, if your happy with the solas props keep them and be content that at 46 knots its close to as fast as possible anyway and at 0.6-0.7 km per litre not bad going.

If you find a prop that works great but slips a little in turns just get the blade tips cupped a bit more about 50$ per prop and it will fix this.

imho this boat with 300's should turn 19's as the same boat with yamaha 250's does albeit only to mid 5's. If it was me I would use it with those solas props as high as u can lift the motors because it is free. If they start to slip in turns cup them a little bit. If you are very keen to ring the most out of it try the 19 enertia eco's. I really think they are one of the few props which will work. These might require a bit extra cup to.

Btw I have seen your boat around and it sounds awesome those big four strokes humming along. Just enjoy it knowing that at 46 knots you are at 98% of what it will do anyway and you may keep searching forever trying to find the extra 2%.

[chris69]

What i dont understand with all of this is why the hull designer did not have any imput into this as the software they have can calculate the best prop for the load and speed.

[ozynorts]

What i dont understand with all of this is why the hull designer did not have any imput into this as the software they have can calculate the best prop for the load and speed.

They can go even further. They can advise the best gear box ratio as well which when matched with the right prop should give the desired results.

[Horse]

Keith, I think you are trying to make the tail wag the dog. You are trying to use your pods to stabilize your hull. For them to have any impact on your hull stability they must be applying considerable force to the water immediately in front of your props and this is whats causing all of your concerns. I would knock up a mould off your hull and make a couple of temporary pod extensions that follow your hull lines and work your antiventilation plate height off these. Permatrims will provide a lot more stability than flat pods that have intermittent contact with the water.

[bannana]

What I'll do horse is when I get the damaged props back from solas I'll give the perms trims a crack. If this fails and the mirage plus props fail I'll also get a mould made to fill in under my pods to remove any air that may be getting sucked in. If this works ill get a more permanent mould made up. Trial and error I know. I am keen to try the over proping as suggested.

Thanks for for all the advice everyone. I'll keep changing this around until I can get the cavitation to a minimum or even better to disappear.

im defiantly thinking differently after processing all this feedback and it's much appreciated. Hopefully problem is sorted soon!!

cheers

[myusernam]

Surely noosacat have built these before? What do they say. Why aren't they more invested? They should have had this motor boat combo before?

[Chimo]

Noosacat as I understand it, have supplied a heap of similar sized cats to the NSW Police. They are supposed to go like cut cats so how is your set up different from theirs?

[bannana]

Wayne from Noosacat said when I first picked up my boat to use it in Brisbane for a while and resolve any teething issues. Its not the easiest boat to house so I just worked through any issues while keeping the boat at 1770. At first I thought it was a prop issue or engine height issue so I was able to do these adjustments myself. When these didn't fix the problem I took the boat back but they thought it best to raise the pods further sinking my engines to stop the cavitation....this didn't work. All it done was make the boat a pig at low speeds and an unstable boat at high speed. Every time I do a change then do a trip it's about a 6-8 week turn around. So this is the reason I brought my boat back to Brisbane and bit the bullet and put it in a sea pen until I can get it resolved. Now I can make changes every week and easily test....as Noosacat origanaly asked.
what did Noosacat say? Well they are unsure of what the problem is. They think it could be water in the hull somewhere...the rep for Yanaha thinks it's a weight distrubution problem in the hull... Noosacat said its one if the heaviest boats they have built in this size also. I Don't feel like it's water in the hull but I do know there is a problem so in not ruling anything out until I have tested it myself.
All this aside I feel more confident talking to as many people as possible and absorbing there two bob. For example I cannot understand if an engine has been sunk to the degree mine have just how can they cavitates??? There are more 3100's getting around with yammies on the back but I don't have their details to contact or I would. What I do know is some of the advice on here is better than that of the so called experts.

Another important issue is I seriously doubt a large majority of people would realise there is an issue. If you just did day trips if Moreton you probably wouldn't know there was a problem. But when you've spent a 1000 hrs in a few cats and get to know how they perform in different conditions you get to know what to expect. This boat of mine does not ride right because of the cavitation issues and what's been done to mask these problem in itself has created a larger problem that will be easily fixed once the pods are packed back down to the original height. This only takes me back to the origanaly starting point and where all other 3100 pods have been set up. The best I can expect from Noosacat is advice in areas if asked. They did organise prop tests with mercury the other day and have helped. But as far as dropping the boat of and picking it up how I want well that's a long story!!
im best just keeping in touch with Wayne and talking to you guys and eliminating what ever reason I can until I find the best solution... I feel like it's just around the corner..

[gofishin]

Keith, water in cat hulls (I.e places where it shouldn't be) is not a rare problem in cats. There have been a few posts about this over the years, and I recall hearing about a few others 15 - 20yrs ago when I was still active in the game fishing scene down here. Here is a recent thread that I remembered, and it also details my experience with this very problem - albeit a long time ago.

http://www.ausfish.com.au/vforum/archive/index.php/t-198526.html

Checking to see if this is indeed a 'contributing factor' to your current problems should not be too hard.



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[hinchy]

Hi Keith

PM sent.

Regards Hinchy

[bannana]

WATER IN HULL!!!!

Is there any way of finding out if water is in my hull without cutting inspection holes into every sealed compartment? Is there an affordable exray solution. I don't really have an accurate weight of my boat when purchased so I cannot depend on scales.

??????

[FisHard]

When the dude bought my last boat, he had in professionally inspected (don't think the word survey really covers it) and the guy that did the job had an instrument that measured moisture in the transom (to see if it was rotten). I don't know if the same device would measure water trapped in hull?

[scottar]

WATER IN HULL!!!!

Is there any way of finding out if water is in my hull without cutting inspection holes into every sealed compartment? Is there an affordable exray solution. I don't really have an accurate weight of my boat when purchased so I cannot depend on scales.

??????

I got a battery drill next time its on the trailer.;D. Sorry mate - little help I know but it had to be said. Either that or turn it upside down and give it a shake.

[gofishin]

Talk to a marine surveyor Keith. I think what FisHard is referring to only works when you can get inside the transom/structure etc. Too much glass and gel coat from the outside. But maybe they have better moisture meters these days.

I have never heard of this technology being used for this purpose before, however I would look at using thermal imaging. With a guy that really knows his stuff, I can't see why it wouldn't work. Boat would have to come out of water though, but then you would need to do this for Scottar to use his drill too :).

With a hull the spends 99% of its time in the water lately, any water that is in the hulls would attain (or close to it) the temp of the surrounding canal water (~25 deg ??). Pull the boat out in the morning, hose off hulls and shammy down. Leave for a few hrs until nice hot midday sun.

Water inside the hull(s) has thermal mass, air does not. The glass hull sides will warm up fairly uniformly and try and meet the ~30 deg ambient, except of course if it has water behind it that is at ~25 deg.

Thermal imaging cameras these days accurately pick up temp differences of 'points' of a degree, let alone 3 to 5 etc.

Well worth a shot talking to a few 'providers' I would think!

Edit:
PS. Don't lose sight of the big picture mate. 'If' you find any water in there, it may be contributing to your problems, but I doubt it is the major cause of your ventilation issues.

PSS. Did your ventilation (and handling ??) issues suddenly get worse when your T/D popped out and the compartment filled up with water - and then the boat did - at 1770 that time?


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[Horse]

Keith, pull it out on your trailer and give it a good tap all over with a wooden/rubber mallet. You will hear the difference if a compartment is full. I guess I'm a bit of a control freak but I have a need to know whats happening under my floor. I have three spinouts and two inspection ports in my little 17'er

[myusernam]

Ultrasound....

[Gon Fishun]

Put it on the trailer, grab a stethoscope and rock the boat from side to side. I have found water in the side pockets of an old Haines by this method.

[Jarrah Jack]

When the dude bought my last boat, he had in professionally inspected (don't think the word survey really covers it) and the guy that did the job had an instrument that measured moisture in the transom (to see if it was rotten). I don't know if the same device would measure water trapped in hull?

The moisture meter is a probe with two prongs used for timber, it wouldn't work in underfloor cavities.

[mutineer]

Get a couple bungs glassed into pods , 2 year old kevlakat (mates boat ) always was bum heavy with the Yamahas almost drowning at all times , lucky he has those little brass plugs , it was just a feeling by a mechanic undid them and it drained for hrs with an estimated1000 + litres in the hulls , meant to be sealed as you know , reading all this it does seem unusual ly bum heavy drill and bung cant hurt

[gofishin]

Horse, in the instance I referred to it was impossible for us to know 100% there was water in the hull compartments by knocking. This only told me how long each compartment was re placement of full height (supposedly) bulkheads. I'm pretty sure I didn't find the 1/3 height b/heads this way though (bulkhead top was too close to the chine).

The hull list I mentioned obviously showed something was not right, as it was increasing over time.

It was not until a serious look and tapping session throughout the floor inside that I found the suspect floor area under/within the battery box, over the most aft u/floor compartment. A small pilot hole confirmed this flour area needed some replacement work so I got out a decent hole saw... And the rest is history.

The most aft compartment had water approx 8" above the port hull chines (from memory, but we are talking ~20yrs ago!).

When I could see the water there thru the cutout I went back outside to see if I could 'knock' for the level, determining if water was there by knocking let alone where the level was. Nope, no way! And, as I later found out, this aft compartment had the highest level too (but was very short in length, hence stiff panels).

The PC's had a very low tunnel in comparison to Keith's model, and a step out in the sides of the hulls, combined with relatively short spacings b/w bulkheads meant the hull side panels were fairly rigid, and with the water level quite close to the chines (very strong), I believe this made it very difficult/impossible to tell if there was water in there by knocking.

The NC3100 has a lot higher tunnel than the PC (taller hulls), so possibly a larger panel area could get more movement/effect/noise change from knocking (if there is water behind it). Obviously a good thing to try before spending $'s.

As for the stethoscope, yes we used this for similar water situations in dad's workshop/boat business, but with a lot smaller boats. Certainly try that too, but getting a sufficient rock up (to slosh water about down low in the hulls) in a ~4 & 1/2 tonne plus (??) rig in Keith's case is not going to happen with a few men 'rocking the boat'. Need a crane to lift a side a bit then drop, or drive one side of trailer off a 100mm slab etc etc. In our case we had ~8t to rock. It didn't happen!

Not trying to be negative, just that you might need plans A, B, C... ready to go as determining 100% (without physically inspecting/viewing that there is water there - by drilling/cutting something out), is going to be very hard.

PS. You might chuckle at Scottar's drill a hole suggestion, but Peter Webster actually wrote a bit about water in his PC328 ' Tracey J IV' in Australian Boating approx mid to late 80's. They suspected it (also a hull list), but no one was sure, so they eventually just drilled holes in the hull compartments!

Found water, then went looking for the source. Can't remember too well but I think they found an accidental hole someone drilled in the floor!!

Cheers


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[bannana]

Talk to a marine surveyor Keith. I think what FisHard is referring to only works when you can get inside the transom/structure etc. Too much glass and gel coat from the outside. But maybe they have better moisture meters these days.

I have never heard of this technology being used for this purpose before, however I would look at using thermal imaging. With a guy that really knows his stuff, I can't see why it wouldn't work. Boat would have to come out of water though, but then you would need to do this for Scottar to use his drill too :).

With a hull the spends 99% of its time in the water lately, any water that is in the hulls would attain (or close to it) the temp of the surrounding canal water (~25 deg ??). Pull the boat out in the morning, hose off hulls and shammy down. Leave for a few hrs until nice hot midday sun.

Water inside the hull(s) has thermal mass, air does not. The glass hull sides will warm up fairly uniformly and try and meet the ~30 deg ambient, except of course if it has water behind it that is at ~25 deg.

Thermal imaging cameras these days accurately pick up temp differences of 'points' of a degree, let alone 3 to 5 etc.

Well worth a shot talking to a few 'providers' I would think!

Edit:
PS. Don't lose sight of the big picture mate. 'If' you find any water in there, it may be contributing to your problems, but I doubt it is the major cause of your ventilation issues.

PSS. Did your ventilation (and handling ??) issues suddenly get worse when your T/D popped out and the compartment filled up with water - and then the boat did - at 1770 that time?


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Brendan it just remained the same. The worst cavitation issues were before Wayne lifted the pods. but as you seen they are still pretty bad to say the least.

[bannana]

I'll stick with the inspection port in every department I think. Thanks Scotty the silliest suggestion is probably the one that will get used. i would love bungs in my cat but that would only be one compartment and she has quite a few.

i think my boats going to be Brisbane based for a few months to come.



106690106691106692

[bannana]

106693106694106695106696

[bluefin59]

What about one of those 12v engine inspection cameras , maybe someone on here willing to let you borrow one . You would need to drill a couple of holes in the floor to fit the camera so you could look inside the hulls , the holes wouldn't have to be so big maybe 20 mm and the cameras normally have an led light so you can get a decent view . Matt

[chris69]

Very interesting Keith the pics give a better idea of what your fighting with,theres a blade on that prop that looks like its been cavititeing.

To me the bottom of the hull needs to be extended to the end of the pod and the pod needs to match the hull shape so the props get clean water to them,the motor looks to be a fair distance behind the hull.

[bannana]

Yeah thats not a bad Idea Matt!!! I have mats glue over the floor so i should be able to lift the mats and then glass back over the holes and glue the floor mats back down.

Cheers.



106697106698

[bannana]

Chris,

The pods are 700mm long so yeah she's a long way back.


106699106700

[Horse]

Well those legs are well and truly deep enough. They should be at least 1" higher for every foot behind the hull. I think your on the right track with the options we talked about. Hopefully you get it sorted quickly

[bannana]

New game plan.

Im going to try a final set of props so i can narrow down the preferred props. Mirage plus!!!

Secondly a pod infill. I will look at getting a couple of different foam moulds made......Any suggestions ....Brendan????

Then if this is not working I will try a permatrim. Does anyone else have experienced or used one of these???? Especially any other cat owners??

Lastly take the boat back to Noosacat early next year and get them to weight the boat and start moving weight around. Maybe move tanks back and look at repositioning batteries etc.


If this works then i will put the piss on for anyone and everyone.....



If this doesn't work I will sink the boat in the bay and start using it as an arti and fish in my sons tinny.....probably more fun anyway.

Cheers fellas.

[cormorant]

Does every watertight bulkhead area not have a bilge pump pipe that comes to deck level or a manifold? I just find it amazing that there is no means of determining if any area is not full of water, fuel etc. Look at steber boats and the 8 pipes manifold they have into every compartment all next to a bilge pumps that can suck from any or from the crash bilge as well if required or petrol pump can be connected to manifold. Does your boat have a crash bilge all along the keel below the watertight compartments with limber holes and just a single bilge pump each side?


Just an opinion and probably totally wrong

Water coming off trailing edge of hull at old transom, rising and striking that dog ( I don't understand it) of a pod and airating sucking in air from tunnel and props not getting bite . Prove it . If the boat will plane on one motor or you can get it planing and idle one motor you will see all the water in that side still airated before it gets to prop? Pod is not high enough to clear water at rear as water rises 1-2 inched every foot it goes back after going under keel. Can't understand that pod design on such a large boat. IMO opinion it would be acting like a stepped hull in a monohull
http://www.navaldesign.co.za/articles.html


Don't waste any more time. idiots guide to weight is simply measure distance to water at marina from coaming or rubber at hull joint or other known point on side of hull at transom and point at bow. Give it to wayne, displacement of bow and stern can be quickly calculated as he has hull shape in CAD I'm sure. You could use load cells at a marina or even fork with scales to determine weight distribution if you think that is the issue. Some of the newer straddle lifts have electronic controls and automatically measure weights via load cells on pulleys so they can't be overloaded .

Find a sister boat. get photos Fly wherever and go for a ride in it and check it's setup . Boat builder should know details of sistercraft they have built. Even if the sistercraft are carrying less transom weight load one up with a couple of waterbags at stern to same as yours and confirm ride, attitude and performance. Who owns randycat now? http://www.noosacat.com.au/Noosa_Cat/Reports_files/Noosacat%202012%20Brochure%20.pdf


Video from a 2nd boat from side or shore your next test run. Video over the transom at rest, idle semiplane and full plane . I dislike the attitude of some cat designs but they are riding correctly when you see them from the outside . They have set the floor so it is flat at rest but on plane floor is no longer level due to lift in hull shape.

No one has mentioned much about trim but since you have hours in boats I guess you are right on top of that and the motors are actually running through their trim range under load.

Don't spend more money till you have actually narrowed down the underlying issues .

About the photos . Are those tanks the same sizes and the same positions as sistercraft?

Just some dumb thoughts

Same hull? http://www.boatsales.com.au/boats-for-sale/private/SSE-AD-2796786/2000-Noosa-Cat-3100-STANDARD-CABIN

[bluefin59]

Supercheap sell a usb camera with 7 mt of lead for $60 and is only 10 mm at least that would eliminate the unlikely event your holding water, the rest of your problem is beyond me but I still don't understand the pod thing and why it doesn't follow the hull lines if you know what I mean but I'll leave you with that .. Matt

[gofishin]

Chris, hull extensions were one of the first things we discussed on the trial the other day, however NC did not like the idea at all, so it was put on the back burner. It's good to hear they are back on the table.

Keith, it's good to see the hull shape/pods out of the water. I will give you a contact or two that can knock up a couple of one piece HD foam blocks that will be cheap but good enough for a trial or five - but not long term.

Those deflection plates NC added do not make any sense to me at all!!! The pods were raised, tending towards a true 'clear-water' pod, thus reducing or maybe eliminating most of the dynamic lift the pods previously created.... but then these deflection plates were added to force lift. WT?

You know I personally don't like pods, but this even more!

All they do in my mind, due to the angle they are on, is force disturbed/aerated water up under the pod... But the idea of a clear-water pod is to not have any of this, and especially all this disturbed water hitting the underside of the pod and the exposed part of the leg above the plate. That totally negates any benefit of this concept of pods, and creates drag.

I am sure this is why there is so much chaos going on under there now.... IMHO.

PS. Nice structure under the floor, looks like no timber at all? Why are some compartments flocoated, do you have access to these for storage already?

PSS. Not on a cat, but as discussed previously I have used permatrims very successfully to combat ventilation in big tinny's with an exposed keel, including one of my own. They would help right now, but I would recommend they be kept for the last hurrah. Get it as good as it can be, and motors as high as possible without ventilation, then if still not quite right whack them on, then you may be able to go up again!
Cheers





Sent from my iPhone using Tapatalk

[robothefisho]

Those spray? rails on the outside of pod. Can't say I've seen them before, are these a recent thing? Anyway I can see them causing dirty water big time and possibly dragging the rear down. Also the motors look way to deep.
Mirage plus should go alright. I'm very keen to hear how they go.
if those pods are on water at speed the cav plates should be at least level with these if not 20mm above.

[Darren J]

New game plan.

Then if this is not working I will try a permatrim. Does anyone else have experienced or used one of these???? Especially any other cat owners??

Cheers fellas.

Keith,
I sent you a PM earlier today re these, but your inbox is full. I have just fitted a set on the Glacier Bay. Hopefully will se how they improve stability in the next week or two when I get it out.

Cheers,
Darren

[bannana]

Keith,
I sent you a PM earlier today re these, but your inbox is full. I have just fitted a set on the Glacier Bay. Hopefully will se how they improve stability in the next week or two when I get it out.

Cheers,
Darren


Really interested to here Darren.

Ive since cleaned up my inbox. Thanks

[bannana]

Supercheap sell a usb camera with 7 mt of lead for $60 and is only 10 mm at least that would eliminate the unlikely event your holding water, the rest of your problem is beyond me but I still don't understand the pod thing and why it doesn't follow the hull lines if you know what I mean but I'll leave you with that .. Matt


I'll grab one tomorrow Matt. I need to get a couple things done by a fibreglass guy so he can patch the holes at the same time.

just need to know one way or an other if the hull is holding water. If not I can reseal and know for sure that its not in the equation. I will also get the boat weighed so in the future I can just re weight the boat and check this way.

cheers

[bannana]

Those spray? rails on the outside of pod. Can't say I've seen them before, are these a recent thing? Anyway I can see them causing dirty water big time and possibly dragging the rear down. Also the motors look way to deep.
Mirage plus should go alright. I'm very keen to hear how they go.
if those pods are on water at speed the cav plates should be at least level with these if not 20mm above.

Noosacat installed those rails when i took the boat back after testing it when the pods were raised. The boat just fell from side to side once the pods were clear of the water at speed. So wayne decided to install these rails to add stability. They do work but not real well and also the boat cavitated before these were installed and of course after.

[bannana]

Chris, hull extensions were one of the first things we discussed on the trial the other day, however NC did not like the idea at all, so it was put on the back burner. It's good to hear they are back on the table.

Keith, it's good to see the hull shape/pods out of the water. I will give you a contact or two that can knock up a couple of one piece HD foam blocks that will be cheap but good enough for a trial or five - but not long term.

Those deflection plates NC added do not make any sense to me at all!!! The pods were raised, tending towards a true 'clear-water' pod, thus reducing or maybe eliminating most of the dynamic lift the pods previously created.... but then these deflection plates were added to force lift. WT?

You know I personally don't like pods, but this even more!

All they do in my mind, due to the angle they are on, is force disturbed/aerated water up under the pod... But the idea of a clear-water pod is to not have any of this, and especially all this disturbed water hitting the underside of the pod and the exposed part of the leg above the plate. That totally negates any benefit of this concept of pods, and creates drag.

I am sure this is why there is so much chaos going on under there now.... IMHO.

PS. Nice structure under the floor, looks like no timber at all? Why are some compartments flocoated, do you have access to these for storage already?

PSS. Not on a cat, but as discussed previously I have used permatrims very successfully to combat ventilation in big tinny's with an exposed keel, including one of my own. They would help right now, but I would recommend they be kept for the last hurrah. Get it as good as it can be, and motors as high as possible without ventilation, then if still not quite right whack them on, then you may be able to go up again!
Cheers




Sent from my iPhone using Tapatalk

Brendan so far mate you have been on it!!! Send me through the name and number of the guy for the pod infill and I'll get onto him tomorrow.

The side rails were not installed for lift they were installed for stability. They do work but not that well.

Looking forward to trying the infill to see if this cleans up the water around the props. Fingers crossed!!!

I have a few things to check but sounds like an easy check now to see if water has made its way into the hull, just about got the props narrowed down to 3 that should go well if I can clean up the aeration, infills shouldn't be a problem to test and permatrims for last case senario....although no matter how good or badly the boat performs I will still give them a crack. I will still look at getting the boat weighed at the marina for future tests and to check the balance of the boat compared to others that Noosacat have weighed.

cheers

keith

[bannana]

Cormorant,

Mate no he has no access into any sealed compartment other than the transducer compartment and an inspection port over each of the fuel tanks.

No bilge pumps what so ever installed.

Tanks 500ltrs each (sister crafts 400ltrs) and about 100kgs empty heavier and 170kgs full heavier each. Also the tanks are slightly more forward because of a large fish box on the back deck that he compensated for. I believe the tanks should of been further back and this is also the belief of the yamaha rep at the time of the test.

As far as trim goes there isn't a lot because the boat starts to cavitate. But with the props I have from solas there is far more than I have had. It could be better.

As far as $$ goes it wont cost a lot to test different hull infills, props, drill a few holes and check the hull for water and adjust engine heights. Ive only just started over the last couple of weeks by having the boat down here and with the advice I'm getting from you guys and some good ideas to try its worth a crack. if I can get it sorted doing this then great. If not she's going to be a weight problem for sure and its a big job to cut up the floor and move back fuel tanks and what ever else. So i'll just try what i can first and go from there. once again fingers crossed!!

Cheers

[cormorant]

Don't drill holes. If it is out of balance or overweight in a massive way let the builder or his surveyor / shipwright do it. With weights it has to be compared against a real boat that was really weighed not just a materials plus accessories estimate by a builder.

If infills work with motors raised and it starts to perform that will be interesting and then the challenge is that the stress on the rear planing edge ( normally transom) just moved back well behind the strength of the transom which is why they will have designed the stepped up 3/4 pods. I don't think I want to go into the issues of a boat destroying itself in chop and big seas but full pods are a huge stress when bolted on so new fully glassed hull extension may be a answer or removing pods.

It still begs the question of what is different with your boat to sisterships and do the others ride and perform as badly as you say yours does? A few hunderd kg on a boat that weight shouldn't worry it. ya havent got the titanics anchor chain hidden in the bow by any chance?

[bannana]

Well as far as the cavitation and performance at low speed goes I'm happy to take anyone out for a run....she cavitates!!!

difference from my boat to others is that mine is heavier apparently... I'm not convinced but that's what Noosacat are telling me. I have a lot of electronics, Kab seats, large fish box, anchor drum winch (that I didn't want) and close foam cell blocks under the floor. I realised last night that because of these blocks drilling a hole wouldn't allow me to see water under the floor anyway if it was there.

whats different.... Just the larger tanks and them being forward..so they think it could be a weight forward issue. So I'm trying to fix it first because it could take forever to get them to get my boat back in there. There trying to finish 5 boats at the moment and one of them is a 48 thats been going for 7 years!!!!! I'm not going to hold my breath. My boats been down here for 4 mths ready to go but they can't get me in. So I've decided to just move forward trying what I can and if push comes to shove I'll rip the floor up and move the tanks back... What's different with my boat is if it's poorly balanced then I would of thought it would sit nose down in the water and I don't think it does. But I will get a few pics taken and see what she looks like underway, at rest, loaded, unloaded..

cheers

[scottar]

So as you go up through the rev range, what happens? Does the bow lift at any point before she starts to plane? Is the cavitation there all the time or only during the transition between displacement and planing? Does creeping rpm on very slowly have any effect on the cavitation? When you are trying to travel slower and the ride is no good - what sort of attitude is the boat adopting and thus causing the issue?

[hinchy]

Hi Keith
Do you want to PM me your phone No.Have fitted permatrims to a small cat and can offer some advice.

Regards hinchy

[Fed]

After seeing the pictures I'm still in the pod suction camp bannana.

They want the pods to act like big trim tabs giving lift & stability but in doing so they have created two stepped hulls that are glueing the pods to the water.

[mutineer]

With that many compartments it seem highly unlikely that there would be enough water in several compartments before it would bother you ... unless there was a serious delamination of the floor .hmmmm well it's nearly got to be the pod , if continuing with the water thing it would only need 1 hole at 2 mm , stick in a prod and if it's wet then you could do more , but that wouldn't be necessary anyway..mine is only a mono but drive's like a whale without the tabs as my pod is also not following hull and very long could try wedges to get the legs under for lift , I don't believe that the 4 blade will do stuff all if it's that bad anyway ....with my very limited knowledge I'm going with the pod

[hookinin]

emailed a couple of pics for you

[cormorant]

So as you go up through the rev range, what happens? Does the bow lift at any point before she starts to plane? Is the cavitation there all the time or only during the transition between displacement and planing? Does creeping rpm on very slowly have any effect on the cavitation? When you are trying to travel slower and the ride is no good - what sort of attitude is the boat adopting and thus causing the issue?


Exactly why I want to see photos and video of the boat running and different trim settings not that trim affects these larger cats like it does smaller ones.. As you make changes you can then see any significant difference .
If it is a weight issue it wouldn't be the same with empty tanks so I wouldn't be cutting and moving anything. Measure your raft against a sistership to confirm weight.

Keep it simple but if you can do pot infills it will be interesting to see the results but they have to be good infills

[bannana]

Exactly why I want to see photos and video of the boat running and different trim settings not that trim affects these larger cats like it does smaller ones.. As you make changes you can then see any significant difference .
If it is a weight issue it wouldn't be the same with empty tanks so I wouldn't be cutting and moving anything. Measure your raft against a sistership to confirm weight.

Keep it simple but if you can do pot infills it will be interesting to see the results but they have to be good infills


hey guys,

Its been a full on week so been unable to do anything over the last few days. i have organised a guy to add aluminium infills that match the hull identically and just tack them on to start with with an additional sicca to the pod to extension joint.

ill give them a run and see how she goes. unfortunately he can't fit me in this side of xmas but will do it in january. i'll let you know how it goes.

cheers

keith

[Fed]

i have organised a guy to add aluminium infills that match the hull identically and just tack them on to start with with an additional sicca to the pod to extension joint.
Will the infills run parallel to the hull all the way to the end of the pods?

[bannana]

Will the infills run parallel to the hull all the way to the end of the pods?


Yes this his is what I was going to do.

[FNQCairns]

What a headache....here is what I would have done right from the getgo for what it's worth these days....buy a cheap battery drill and 2mm drill bit.

lay down on my back under the trailer and start drilling little holes along each hull at organised centres....say .5m or whatever an expert on the model might consider, ...careful of experts n fuel tanks lol

Waited to see water any water at any time....would start the process at the rear back and forth across hulls.

If water...well the top needs opening to sort.

If no water would get holes preped and epoxy repaired (a fix way better/stronger than new) then gelcoat obviously (yes polyester gelcoat sticks very well to epoxy), then....back on water after 2 weeks max....cheap as chips too.

Phase two if no water and I still wanted the boat:

Fit hydraulic jack plates (wouldn't touch permatrims/etc with a 10 foot pole) AND wedges.

Boat will perform if the power is there and the wedges are enough, can add two together.

Go boating n fishing.

good luck.

[Gr0wler]

How did you end up getting on with this Keith ? Very keen to see if you got it sorted and how ? photo's might be deceiving but the chines on the sponsons look small (narrow) compared to my old 7m sharkcat, and for what it's worth I would've been having the pods made to match the shape of the sponsons and the cav plates should line up with the keels when trimmed to the same angle and if this solved the problem compensation should be in order as they have started building the sponsons longer so the bolt on pod is gone and the sponson becomes the pod so to speak (as you prob already know).

[bannana]

Guys she's been a long haul but well worth the time and effort. Ive got to thank a few guys for the help and advice I have received over this period and a special thanks goes to Soulfish and guys like Gofishin who spent there time to come down to help someone they don't know. All the advice thats been given at the very least has made me think about things differently helping me bring this frustrating situation to an end. Instead of having a boat that was a bucket of shit its now a boat that punches well above its weight... Its brilliant. Best boat i have ever owned or been in for that matter.

At the end of the day weight has played a big part as expected in fixing the issues. I have removed batteries front under driver and passengers seat boxes and the factory has rebuilt new boxes at the rear to take these. I have also removed another 100kgs in driver and passenger suspension seat after replacing them with a lighter model and shifted unnecessary weight towards the rear where possible. All in all about 350kgs has moved from the front of my boat with a large portion of this weight moved towards the rear or removed all together.

Although even after doing this the cavitation continued!! We then changed the tow of the motors back to a neutral position and lifted the motors to original heights. the pods remained 50mm higher than when fitted. We then changed the gear boxes around so the propellers spun opposite to how they would normal be fitted and also fitted wedges to give move negative trim.................FIXED,,,, Its going excellent!!! Sounds simple but I went through every possible senario with engine heights, pod heights, props etc before coming to this.

Everything from planning at low speeds now and the boat riding flat to going 35 knots.... Its awesome and the boat that I originally expected to own is now in my garage. The flat pods are perfect for the boat and give the big girl sensational stability at both slow and high speeds as they work like massive stabilisers on the rear of the hull. Its not until I get up around the 40 knots or above that the pods lift themselves completely out of the water and then the boat walks a little from side to side. It doesn't make to much difference but needs to be driven if this happens. So far Ive only had it in 20 knot winds but even then it handled brilliantly while I was sitting on 30 knots travelling either with the sea, beam on or into the sea. I cannot ask for more. Its going great.

Now Im back fishing after a year and a half of problems.... I'm pumped.

Thanks again to all the guys for the advice from everyone and the time you guys take to write down your advice and thoughts. None of it has fallen on deaf ears and in the end its this advice that helped me over the line and its very much appreciated.

Also the main reason Ausfish is head and shoulders over any other fishing site Ive seen.

Cheers

Keith

[gofishin]

Well done Keith, sounds like persistence (and some very hard work) paid off big-time in the end. Great to hear that NC got stuck in too and got it sorted for you.

Sounds like she is now the weapon she should be!

Cheers
Brendon
PS. By the number of trips you have been doing lately, including massive day trips down to Sandy Cape (??? :) ), I figured that could only mean one thing - you were really enjoying her :)


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[Gr0wler]

Great to hear Banana, As terrible (in my opinion) as it is that you had to go through all of this after forking out all that coin for a new boat and it not being right when delivered I would sought of also see it as a good thing in a way. By going through the whole nightmare you have now sorted out all the dramas but you know how it was sorted and you will have a very good understanding of what is going on with the hull in different conditions and even on other boats (if you didn't already) and will be able to drive it more comfortably and safer as a result of your ordeal.

I have not been on AF long but the overwhelming support and help you guys offer is what gets me, I'm really proud to call myself an ausfish member.....ok, a newbie then ;D oh and just to make sure it is running perfectly I will have to insist I do decky duties on one of your next trips to see if there is any possible improvements to be had ;D lol.



no really.......I'm serious.

[bannana]

Any time mate I'm always happy to take guys for a fish.

[robothefisho]

Hi mate,

Curious as to what performance and props you ended up getting?

[bannana]

I'm currently using the Yamaha 17t (I think that's what they are called) these came with the boat

5600 revs fully loaded
42 knots fully loaded
2 Litres a k fully loaded


when fully loaded with four blokes to spend a couple of nights on the reef compared to just taking the family to tangalooma there's about 1400kgs difference in fuel water, bait, food, fishing gear, and fish... Big difference in performance and even bigger in economy with the difference in weight.

this has been one of the trickier components to manage when trying to get the boat right.... Weight and the distrubution of that weights as the load changes throuout a trip... It's sorted now but now that I don't have any cavitation issues when I bring my boat back down to brissy in the next few months I'll go threw the prop testing scenario again to see if I can get the economy back down to where it should possible be.

[Cods Whallup]

I'm currently using the Yamaha 17t (I think that's what they are called) these came with the boat

5600 revs fully loaded
42 knots fully loaded
2 Litres a k fully loaded


when fully loaded with four blokes to spend a couple of nights on the reef compared to just taking the family to tangalooma there's about 1400kgs difference in fuel water, bait, food, fishing gear, and fish... Big difference in performance and even bigger in economy with the difference in weight.

this has been one of the trickier components to manage when trying to get the boat right.... Weight and the distrubution of that weights as the load changes throuout a trip... It's sorted now but now that I don't have any cavitation issues when I bring my boat back down to brissy in the next few months I'll go threw the prop testing scenario again to see if I can get the economy back down to where it should possible be.

Gday Keith, I take that ( 2 litres per k) as 1 litre per k per motor, that seems pretty reasonable for that size boat and motors and for those revs. What kind of figures would you be trying to achieve by tuning the props?

Cheers andrew