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gtphantom
07-11-2009, 08:22 PM
a question for the cat frat? what can cause one hull to rise higher on the plane if both are trimmed identically and the static trim port-starb is neutral I seem to have a situation where once I get to around 30+knts the port hull wants to lift any suggestions ?

Plastic_Magic
07-11-2009, 08:53 PM
What sort of cat? Are your engines couter rotating?

gtphantom
07-11-2009, 10:04 PM
6m leisurecat counter 115 suzi's

Angla
07-11-2009, 10:12 PM
Is it possible that it is to do with the wind direction?

Do you experience this in poor conditions or in glass conditions or even wondering if the effect is more noticeable in stronger wind conditions?

Cheers
Chris

gtphantom
08-11-2009, 03:16 AM
on glass!! if I travel at 4000-4500rpm and trim @ 25-28 knts then it seems to fly straight and level but if I push the throttles open to over 5000rpm and 30+knts then i get this situation where the port hull wants to lift -- for want of a better explanation, even tried with the bimini removed, thought it may have been a contributing factor -- but not! no apparent issues when travelling in a normal swell/sea, but then again I don't normally travel at 30+knts under those circumstances-- have played with the O/B hieghts and prop pitches found four blades seem to give the best result but I don't have much room for adjustments on the PTT before it cavitates

battleon
08-11-2009, 06:37 AM
Could it be possible there is more weight in one hull than the other? Fuel or storage of items and the difference only becomes more noticable when speed increases.

Are your motors aligned correctly.Ie when motors are centered is the distance measured from inside centre leg of one motor to inside leg of other motor the same as the outside centres?

Just 2 possibles that might cause this.

Laraby
08-11-2009, 07:45 AM
Just wondering ,when you say both are trimmed identical, is this coming from trim gauges- maybe they are reading slightly different. Just a slight amount of trim doing those speeds can make a big difference to how a cat can run-mine is very sensitive to trim.I have found now that i know the boat i dont even use the trim gauges,just go by feel.
Laraby.

insideout
08-11-2009, 08:04 AM
does ur cat sit flat at rest? make sure you have a good look, for even with weight on one side , they still look like they are sitting flat. Use a spirt level if you have to.( this is to make sure you do not have water in one of the hulls,,ect)
This of course changes when underway, for i believe most cats are trim sensitive.

Finnatical
08-11-2009, 04:01 PM
I agree with Laraby that sometimes the trim gauges can be slightly out and what appears to be them being equally trimmed could be that one is slightly higher than the other. I just normally go by feel and use the gauges as a guide as even the smallest load distribution difference will change the trim characteristics.

Cheers,

SnapHead101
08-11-2009, 06:03 PM
Do you have a large transducer unit on your port hull that could lift it?? I agree with above and trim gauges not being absolutely correct. I would trim the engines for your 30 knot cruise so they are equal on the gauges, then measure the engines to see if they really are equally trimmed.

gtphantom
09-11-2009, 02:52 PM
gday fellas -- yep done all this even had the boat stripped down ,2POB, fuel tanks full and only safety gear on board nothing at all else only differance port to starb is house battery on starb side The T/D is in the starb hull at the rear most , but I've got the bait pump and deck wash mounted low in the port hull at the rear as well , as far as O/B trim-- as is I can only get minimal trim out as is wants to cavitate and if I lower the O/B's another hole on the mounts to get more range in the trim, the engines, I think are to low in the water and we have experienced other issues in following seas with this boat with the O/B's on the lower mount holes.

cormorant
09-11-2009, 04:15 PM
2 more suggestions

Damage on one of the props ( get em propscanned if worried)
Engine mount holes in the transom on either side not the same height or not vertical. Use a straightedge on bottom of hull and measure up to the cav plate on each motor accurately with them trimmed teh same - use a bubble level

Steering. Under torque load if hydraulic steering ha sair in one motors ram it will change the geometry. This is moreso if trim tabs behind props are not set correctly...

Hook in hull on one side.
Gearcase with a different shape or damage on fin
Trim tab behind each prop. Many people don't set them up properly and I have even them swapped between normal and CR motors. Are they the same setting.

Are your rev counters accurate. Are both motors reaching teh same WOT settings
Toe in , toe out of motors. Are you sure your test runs are actually straight and you aren't "crabbing" as you go.
Water in hull of foam or in one of the compartments if they are sealed.

Can you correct it with trim?

Chimo
09-11-2009, 04:19 PM
Hi gtphantom

Have you checked your motors toe-in / toe-out measurements?
Ie the motors should not be set exactly parallel to each other.

You need good tight motor linkages as you are looking for 10 to 15 mm differences.

These could be out and could be causing your problem.

Cheers
Chimo

gtphantom
09-11-2009, 07:48 PM
g'day fellas -- have already measured the cav plate hieght at parralell to the keel-- both are within 1-2mm of each other , acceptable i would think? we have tried with three sets of props , the set supplied from Suzuki, 14" dia 20"pitch , solas 14' dia 21" pitch -- both three blades ,and 13 7/8"dia 21" pitch solas four blades . the four blades seem to be a lot better but still tends to want to lift the port hull. the thrust tabs have been all over the place with setting ,initially they were set at dead astern -- how they came out of the box , L/C want the port tab set at full port and the starb on full starb ? after I've done some test and recording all this seems to do is take up-to 3knts off at different RPM's can't see any advantage the best I've had it is with the four blade props and the thrust/trim tabs removed -- at the minute I've got the 21" pitch solas three blade on with flat tabs and the limiting bar on the PTT to stop the leg going into to much reverse trim- this combination seems not to bad but as I said before I seem to only have a very small margin of positive trim before the props cavitate
the steering is hydrive units with the cat valve -- I've bled the system thoroghly and have nice smooth steering -- I hav'nt had to reset the hydraulic line valve since the initial install and the O/B's have about 10-15mm toe-in this hasn't altered and Iv'e not had to top up the fluid level-- no obvious leaks
both O/Bs are getting the right WOT@ 5900-6000rpm
trimming the O/B's independantly in or out isn't succesfull cos it cavitates
when the PTT is on the limiting bar both trim gauges read the same

Noelm
10-11-2009, 07:17 AM
boats of all types are different at different speeds, that's why you have power trim in the first place! absolutely NO boat has a "set and forget" trim system, all sorts of "things" vary at speed, steering, trim, everything changes all the time, adjust the trim to suit, unless, there is something drasticaly wrong with the setup (which I kind of doubt)as for the silly trim gauges, they are only (as the name implies) a gauge, not the absolute measuremnet of each motor ,in fact, I am not sure why they even make them, if you don't know if your motor is up or down, you should not own a boat!

kitty_cat
10-11-2009, 07:48 AM
hey mate noelms right not worth the stress you are going through i dont even look at my trim guages its all by feel.
wayne

Chimo
10-11-2009, 10:23 AM
GT

Have you tried toe-out as a contrast to your present set up?

You do need to "feel" what the boat is doing so as others have said the guages perhaps should only be the 'indicators" at the beginning of each assessment run.


Experience from others is as below
"Toe in to me means the nosecone of the gearboxes are closer together and the exhaut hubs further apart. That is props are angles outwards.

Toe out is obviously the reverse.

Have found that very little is best for a start and that on high speed running on flat water you can get more porpoiseing with toe out but a more stable lateral ride when not hammering at top speed .

Slight Toe in- is more predictable offshore and stops the boat trying to turn ( tip sponson in ) when running along swells on your beam"


Cheers
Chimo

Dean1
10-11-2009, 03:57 PM
Yeah Like Noelm and Kitty cat said is correct, I have never looked at my trim gauges ever either, just trim to suit the speed/conditions, even a quick glance at the motors gives you an idea what the hull should or will be doing. Sounds like you need more practice!! ;D

gtphantom
10-11-2009, 04:57 PM
thanks to all-- much appreciated everyones input ,experience and advice -- a lot more help than the builder!! a few more things to take on board and try . as I have said I have'nt had much time on cats -- the last 15 years on mono's -- med to large platey's so it's all been a steep learning curve on the cat . cheers

Laraby
10-11-2009, 09:14 PM
I'm assuming that when you are trying to trim the boat you are triming the Port engine out & the Starboard engine in ? This may sound back-to-front ,but this is how cats work . By trimming in, it lifts the transome on that side up thus the whole hull. By trimming out, it forces the transome down along with that hull.
Try a bit of negative trim on your Starboard side & some positive trim on your Port side. Once you have the boat sitting level then you can adjust your overall trim like a mono by trimming both engines at the same time- trim out to lift the nose of the boat or trim in to lower the nose.
You may already know all of this - just thought i would mention this incase you are getting all crossed up.
Laraby

bassfan
11-11-2009, 07:53 PM
a question for the cat frat? what can cause one hull to rise higher on the plane if both are trimmed identically and the static trim port-starb is neutral I seem to have a situation where once I get to around 30+knts the port hull wants to lift any suggestions ?

Buy a mono hull:P

On a serious note this is not uncommon on cats, particularly narrow beam ones such as the Leasurecats. I use (but don't own) a 7m L/cat which has recently been repowered with 150 suzukis. I never noticed this before with the 140s it had but then it would only top 28 knots, now it gets to 38 kts but the stbd bow digs in at more than 30kts. It gets a bit hairy at the higher speeds & I have tried all sorts of trim settings to no avail. Now I'm thinking it's the narrow beam that may be the cause.

gtphantom
11-11-2009, 10:03 PM
how old is the 7m you got? was that you that Leisurecat gave you the advice about the props and trimming a couple weeks ago?

cormorant
11-11-2009, 10:41 PM
Can I guess you guys are running bladed props?

gtphantom
12-11-2009, 12:47 PM
Can I guess you guys are running bladed props?
don't understand the question ?

cormorant
12-11-2009, 01:46 PM
Sorry didn't have number lock on on the keyoard

It should have read 4 bladed props? .

In some hulls the extra lift they create mean the hulls at the rear are not "settled "in the water well at high speed. The back walks about making it feel out of balance.

Well set up a boat and good hull design shouldn't rely or need a prop that lifts the transom and the power can be better used pushing rather than lifting. Interesting to hear if someone has had this hull at even higher speed and how it performed. A lot of issues that are minor at usual speeds get very serious at higher speeds although that is not what it is designed for.

What props have been tried and what difference have any of them made?

gtphantom
12-11-2009, 04:28 PM
Sorry didn't have number lock on on the keyoard

It should have read 4 bladed props? .

In some hulls the extra lift they create meand the hulls at the rear are not "settled "in the water well at high speed. The back walks about making it feel out of balance.

Well set up a boat and good hull design shouldn't rely or need a prop that lifts the transom and the power can be better used pushing rather than lifting. Interesting to hear if someone has had this hull at even higher speed and how it performed. A lot of issues that are minor at usual speeds get very serious at higher speeds although that is not what it is designed for.

What props have been tried and what difference have any ov them made?
G'day fellas -- have already measured the cav plate hieght at parralell to the keel-- both are within 1-2mm of each other , acceptable i would think? We have tried with three sets of props , the set supplied from Suzuki, 14" dia 20"pitch , solas 14' dia 21" pitch -- both three blades ,and 13 7/8"dia 21" pitch solas four blades . The four blades seem to be a lot better but still tends to want to lift the port hull. The thrust tabs have been all over the place with setting ,initially they were set at dead astern -- how they came out of the box , L/C want the port tab set at full port and the starb on full starb ? After I've done some test and recording all this seems to do is take up-to 3knts off at different RPM's can't see any advantage the best I've had it is with the four blade props and the thrust/trim tabs removed -- at the minute I've got the 21" pitch solas three blade on with flat tabs and the limiting bar on the PTT to stop the leg going into to much reverse trim- this combination seems not to bad but as I said before I seem to only have a very small margin of positive trim before the props cavitate
the steering is hydrive units with the cat valve -- I've bled the system thoroghly and have nice smooth steering -- I hav'nt had to reset the hydraulic line valve since the initial install and the O/B's have about 10-15mm toe-in this hasn't altered and Iv'e not had to top up the fluid level-- no obvious leaks
both O/Bs are getting the right WOT@ 5900-6000rpm
trimming the O/B's independantly in or out isn't succesfull cos it cavitates
when the PTT is on the limiting bar both trim gauges read the same

Chimo
12-11-2009, 05:18 PM
Have you tried toe out of at least 15 mm?

Cheers
Chimo

cormorant
12-11-2009, 09:53 PM
OK . Is it the whole hull , sponson that feels like it is lifting or are you referring to the bow lifting higher on the port side?

Just trying to clarify what you mean.

If sitting at rest is the boat level?

Hpw much tilt are we talking about and are you noticing it as you see the bow rail against the horizon or is it just the brain and eyes?


My last suggestion is that the limit pins are possibly allowing no negative trim ( some boat sellers set it up like that so people don't get into nasty trouble in following seas) and for whatever reason on the plane the trim needs to be negative rather than trimmed out. Triming - if port hull bow is lifting then 2 choices. Trim out port motor or trim in starboard motor. Yep it is the opposide to what you think as other have said.

Not sure if your motors are set back from the trailing edge of the transom but for every 6 inches a 1 inch rise in the cav plate approx is the norm to have the motors at the right height. If too heigh you may get constant airation of prop as you try and trim out.

Chimos toe out is how I have set em up before as well.

LC suggestions of tabs goes against everything I know. They only exist to stop torque steer. With hydraulic set up or a tiebar they are not really required but some will like them to take the weight off the steering rams and the main steering bearing and so if you have a tie bar failure a motor will still point straight ahead.

gtphantom
12-11-2009, 11:11 PM
the faster you travel the more the port hull rises -- the crew has also commented and it feels as though it will go over in conditions we were ski buisciting!!
as far a neg trim I have none at all with the limit pins in and as I said before , only limited pos trim -- this isn't how L/C set it up

julian1
13-11-2009, 11:39 AM
you were towing a ski buscuit with a 18' cat ????????????? are you allowing for driver weight ? is the ski buscuit tied to the starboard side of the hull ??

Noelm
13-11-2009, 11:59 AM
Jesus, skiing with a cat, I bet the turns would be exciting, not that it can't be done, I have towed skiers with mine, but you need a bloody big lake to give them a "whip" but back to the question, seems kind of strange that it should keep lifting (or at least appear to) as you go faster, might need to adjust the trim stop bar to get more trim range (maybe), have you been back to the motor installers, and/or the manufacturers to help you sort it out? and is there any others with the same setup as you?

gtphantom
13-11-2009, 02:48 PM
bridled from tow pionts between the O/Bs only travelling at about 20-25 knts when it did this and was glassed off- only ones biscuiting at the time-- no sharp turns-- three POB-- all the other times it has done it when travelling to/from fishing pionts

John Buoy
13-11-2009, 07:01 PM
Trim both motors in totally and do a diagonal measurement
from identical points on both motors and check to see if they
are equal.
A misaligned engine can also cause a sponson to lift.

Regards Frank

fly_1
14-11-2009, 07:33 AM
Have seen skiers behind a Kcat 7.2m with twin styers!!!! Yes the rope was bloody long, but we still managed to do it. It was a laugh to see a skier behind a sportfishing boat off Mooloolaba!!!

Fed
14-11-2009, 09:41 AM
Too heavy in the front, too light in the bum, not enough trim to keep the front up, combined with glassy/oily surface can tend to want to make one hull 'stick' to the water and go into a sort of ploughing mode.

What height are the cav plates in relation to the bottom of the hulls?
I think you need to change the running attitude of the boat, I had a similar problem with my old cat.

bassfan
15-11-2009, 05:04 PM
how old is the 7m you got? was that you that Leisurecat gave you the advice about the props and trimming a couple weeks ago?

The boat is about 4 years old and has just had the 140 susies replaced with 150s. Nope it wasn't me that got advice from leasurecat a couple of weeks ago.

Hell Boy
15-11-2009, 06:38 PM
I find the best way to trim cats is to set the lawnmower on high and then reduce height to desired length::) well i'm off to have another rum and coke:D for the cat lovers out there, only joking, im not going to waste fuel on a cat:P

gtphantom
15-11-2009, 09:53 PM
was that with a reel mower or a slasher?

bassfan
16-11-2009, 12:25 PM
I find the best way to trim cats is to set the lawnmower on high and then reduce height to desired length::) well i'm off to have another rum and coke:D for the cat lovers out there, only joking, im not going to waste fuel on a cat:P

Great idea, I also like the lead poisoning method (calibre of your choice)....!;)

Hell Boy
16-11-2009, 12:44 PM
was that with a reel mower or a slasher?

both would be acceptable:) but i'm thinking the Reel mower would be the best choice due to it's ability to produce a fine cut;D nothing worse than a mangled pussy8-)

Hell Boy
16-11-2009, 12:53 PM
Great idea, I also like the lead poisoning method (calibre of your choice)....!;)

I never thought about lead poisoning, bassfan. But i'm about animal welfare and i'm not sure it would be good for the environment when the lead leaches out the cat while i'm using it for crabbing:P

Well i better let you guys get back to the topic, Trimming the meow

gtphantom
16-11-2009, 08:18 PM
they make great cray bait a well ---- a bit upsetting seeing those sad little eyes as they go over the side in the pot!! but hey gotta do some thing to keep the native fauna safe!! bit of a shame that the WA fisheries wont let you use hair or hide anymore--- hard work skinning a live mog!!