Help - Motor Height on Pods / Cat

[Grand_Marlin]

G'day All,

I couldn't help myself, and have bought another Cat ... but just a little one this time ;D

It is a 5m Sharkcat Sportsman, with twin 70 Yammies on Pods.

The problem I have is I am getting cavitation when I try to trim the motors out (up) and therefore aren't getting enough bow up attitude for the boat.

I assume I will have to drop the motors by a hole or two, but wanted to check with others first, as I have to redrill holes in the pods.

The current measurements:
from the bottom of the sponson to the bottom of pod = 80mm
from the bottom of the sponson to the cav plate = 50mm

Therefore the cav plate is 50mm higher than the bottom of the sponson, and 30mm below the bottom of the pod.

Slight cavitiation can be noticed at 4500 revs or 25 knots, even with the motors trimmed right in / down.

Also, when the motors are trimmed right in, the cavitation plate and bottom of hull / pod are essentially dead level, there is no negative trim angle.
I dont think this is a concern as I am chasing up trim, not down.

What are your thoughts?

Cheers

Pete

[Grand_Marlin]

Cat

[Kerry]

Some thing strange looking about those pods? Fitted standard or home made add on? Something has been added on somewhere!

Those pods definately look as if they stand the motor bracket straight up and down? If this is the case then effectively you might have trim (compared to normal fitted angle) even though the motor is trimmed right in?

As for the cavplate being 50 mm above sponson, that in theory would be about right, with a 600mm long pod extension.

Did this boat originally have conventional outboard wells? Something doesn't look right?

Regards, Kerry.

[blaze]

Hi Pete
I would think maybe the bottom of your pod is poorly designed and not matching up to the hull, looks like they have partieal tried to make a full pontoon shaped pod but the boat would ride with the pods partially submerged creating dirty water. Maybe the option would be to shape the pods to the shape of the hull. Maywell be wrong but worth a thought.
cheers
blaze

[blaze]

ps
forgot to add
If you like Pete bring her down with you and I sort it out for you over the next couple of years
cheers
blaze

[Spaniard_King]

Pete,

I woulda thought those engines to be deep enough, as Blaze says most likely to be dirty nwater off the pods/hull. Dropping is going to help. Do you have to cut down the top of the pods as well as re drilling??

4 blade props may also help, not sure if they make em for 70 yammies tho

Garry

[seatime]

My, what a big pair of pods you have there Pete.

Not sure of the fine details or if it helps, but a 560 that I'm familiar with needed larger pods fabricated to carry replacement motors. The new pods didn't have enough angle on the back, were larger than the originals, and the motors couldn't be trimmed in enough. The solution that finally worked was to attach trim tabs to the bottom of the pods. These are a fixed tab, really just angled alloy plate screwed to the back of the pod, so the angled part extends about 50-60mm below the bottom of the pod at something like 20 degrees. There was a bit of fiddling around, but they got it working in the end.
I think the cav plates are lower than your's appear, and not sure if they had cavitation problems.
That hasn't helped at all has it? though sort of interesting.
Are they the original pods?

regards
Steve.

[fishingrod]

I saw that photo of the Freedom targa and thought it was sitting next to a smallish cat :o

Ive got a few photos of 5m Sportsmans ive collected.
One with pods.

Not sure if they help. (sorry i dont have any better resolution, you can zoom a bit on your own computer)

http://i31.photobucket.com/albums/c369/fishingbasket/5.jpg
http://i31.photobucket.com/albums/c369/fishingbasket/5mIluka.jpg
http://i31.photobucket.com/albums/c369/fishingbasket/23_1151549023.jpg

[Grand_Marlin]

G'day Kerry,

The boat and pods are 93 model, and were made by Noosacat.
I couldnt say whether they were playing around with things at the time or not, but they are factory standard.

BUT in saying that, look at the photo of the first cat fishingrod posted ... these are standard factory podsa as well, but are a lot smaller and higher on the transom.

Cheers

Pete

[Grand_Marlin]

G'day Blaze,

The bottom of the pod is flat, and is level with the chines.
I agree that it would still be in the water when on the plane.

Interesting also, the quicker you go, the more "up" trim you can get.

So, this is definitely part of the problem.

Keep in mind it isnt a huge problem, but it could be better.

ps - you already have a boat ... it is only twin hull envy you have ;D ... just like Troy :o

Cheers

Pete

[Grand_Marlin]

G'day Gary,

I dont have to cut down the top lip of the pods, just redrill holes.

I have room to drop 2 holes if needed.

I think this will have to be the starting point, as redesigning / replacing pods is major work, quite a few $$$, and I want to go fishing over Christmas ;)

Thats why I bought her, cos the big ones not finished 8-)

Cheers

Pete

[Grand_Marlin]

G'day Gelsec,

Absolutely no help at all, but an interesting story ;D ;D ;D

I have to go the opposite and get the nose up a bit more.

When I trim the motors up, I start to get cavitation before I get any trim angle.

Cheers

Pete

[Grand_Marlin]

G'day Fishingrod,

Mate I think you could spot a cat anywhere :o

Yes the targa pic was taken up against the little cat.

Thank you for those pics - the Green one with pods is what I was looking for to compare to mine.

I have been out in that boat, and it performs perfectly, so I might call in and see if I can take some measurements.

The boat lives at Redcliffe ... is the owners name Geoff?? I cant remember.

Cheers

Pete

[finga64]

Cat owners. They're worse then Kingswood owners ;D

[BaysideMarine]

Marlin,

I don't really like the shape of those pods with those sharp corners.

I'm wondering if the pressure wave as it leaves the rearmost point of the hull and rises up then hits the pod and is deflected back down into into the prop stream.

Also, what props does it have on it? I would expect 17 inch or possibly even 15's for a heavy rig like that.

It looks as if it was a sterndrive model, yes? no? I wonder also if its too light in the arse now, although 2 donks hanging off the back has to be comparable in weight to a heavy sterndrive sitting in the boat.

Engine heights look about right to me. Usually 1 inch up for every foot from the back of the boat as a very basic, rough guide.

I would try dropping the engines but I don't think that will fix the problem. A couple of cupped props should help you a great deal as thats the whole point of cupping a prop, so it has better grip in turbulent water.

Cheers

[Grand_Marlin]

G'day BM,

I think you may be right with the pressure wave theory.

The props are 17-K Yamaha props.

These little 5m cats were never made in sterndrive configuration - only ever twin outboards.

All the first of the 500 series were outboard wells, and the last model made had pods.
Noosacat actually still makes this exact hull now ... it has either twins on pods or a single centremounted engine (merc 90 with hi 5 prop)

According to the formula, the motors are set at the right height.

Are the cupped props a Yamaha item, or are they made by others (like Solas)

Cheers

Pete

[Grand_Marlin]

If I made a false bottom on the pod to match the exact shape of the bottom of the boat hull, then dropped the motors to suit, would this fix it?

Effectively then what I have done is extended the hull.

Cheers

Pete

[fishingrod]

G'day Fishingrod,
Mate I think you could spot a cat anywhere :o

My mate said to me yesterday when we were following a boat in traffic that its sad when you can identify a brand and model only by looking at the transom ::)

I love cats. Except I cant tow one ! I was looking for a 5m second hand cat or Hydrofoil, Hookem, Maxicat etc but they are pretty border line with my 1600kg tow capacity.



The boat lives at Redcliffe ... is the owners name Geoff?? I cant remember.


Ive never seen that boat in real life. It has been advertised for sale some time in the last 12 months. Thats where I got the photo from. (pinched it off the advert)

Its a nice little toy you got there. Hope you have some fun over summer. A simple fix might be to stay below 4500rpm ;D

:)

[BaysideMarine]

If Yam dont have one as a listed part any other manufacturer will be able to provide them. Or get yours cupped.

If you extend the hull bottom right through then that should work well. Drop the engines back to normal height (since its now effectively the same as a normal transom mounted engine) and see how it fares.

Cheers

[seatime]

G'day Gelsec,

Absolutely no help at all, but an interesting story #;D ;D ;D

I have to go the opposite and get the nose up a bit more.

When I trim the motors up, I start to get cavitation before I get any trim angle.

Cheers

Pete

Yeah, the one I'm referring to had too much weight on the back and too much nose up attitude.
You can see that the problem is reversed, your's looks too light, or the pods might be too big and too low, giving the stern too much floation. So maybe the solution is reversed.
I agree with the bottom shape of the pods looking too square, someone was acting out their design theories by the look of it.

Add ballast to the pods, problem solved ;D ;D

merry xmas :)
Steve

[Grand_Marlin]

Add ballast to the pods, problem solved #;D ;D

Steve


... and I suppose you suggested ballast is 2 healthy blokes standing down the back of the cat holding Tiagra 50w's?? ;D :o ;D

Cheers

Pete

[Grand_Marlin]

A simple fix might be to stay below 4500rpm #;D

:)



Sorry, not an option ;D ;D ;D

Cheers

Pete

[Grand_Marlin]

Thanks BM, I will give Colin at Performance Propellors a call and see what he can do.

Cheers

Pete

[Grand_Marlin]

I have also sent an email / pics to Noosacat, but they are rarely much help.

Cheers

Pete

[Kerry]

GM,

Height in theory is ok, Pod design is questionable and it doesn't surprise me that they have some issues, from just looking at it!

The Pod on the Green cat is more the design/style of what one would expect. Similar to this one which works extremelly well and has no issues with pressure waves or the like but the clearance is quite different and so is the sponson shape. So is the angle of the engine mount?
http://www.cqnet.com.au/~user\aitken\gen\stb_sx.jpg


If I made a false bottom on the pod to match the exact shape of the bottom of the boat hull, then dropped the motors to suit, would this fix it? dunno? but from the rake of the pods the motors are still too vertical or is this just an illusion from the pic?

One of the things with NC's, there's been quite a bit of playing around gone on over the years?

Regards, Kerry.

[ahoj]

Quiet finga ;)

about the 25 -(30) tohatsu any resolution?

[ahoj]

How much space have you got between the cat hull and the pod? if its more then 25 mm then you creating soda water you have to fill the gap and increase your pod transom slope min 15 degrees in

The rule still applies-- level of hull to outboard leg should stand 90 degrees each outboard already is made to accomodate 15 degrees incline, so if the transom is standing 90 degrees? the outboard is looking outward thus some cavitation.


This will be a small project for marlin after hollidays , in the meantime have a good xmas and lots of fishing cheers Ahoj

[ahoj]

If I made a false bottom on the pod to match the exact shape of the bottom of the boat hull, then dropped the motors to suit, would this fix it?

Effectively then what I have done is extended the hull.

Cheers

Pete

Yes that will stop the soda water and you have a smoother power and better ride

[Grand_Marlin]

G'day All,

Thanks for you ideas and help.

I got the Yamaha props cupped.
Colin at performance propellors did the job.
He said the standard prop didnt have enough cup in it anyway ... so with a bit of blacksmith work, the props were done.

And...

Worked perfectly ... just as I wanted and very happy with the result.

It has dropped the max revs from 5500 to 5300, but the top speed has gone up by 4 knots !

Footnotes:

As suggested Noosacat were a pack of unhelpful pricks

the pods are standard noosacat pods and they are the same design as what appears on the 2300 walkaround, which is the current model

Cheers, and thanks very much again,

Pete

[jimbo59]

[quote author=Grand_Marlin link=1166349316/15#28 date=11672

As suggested Noosacat were a pack of unhelpful pricks


Bruce harris went in for a visit one day when he was in the area and was promptly kicked out,you think they would have at least shown him around the factory and offered him a cup of tea!