Trim tabs on a catarmaran

[razzle]

I have gone crazy trying to stop the porpoising with my catarmaran i've tried COG and lowering the strut all the way down and pointing the prop downwards as far as it could go, also moving the batteries forward and nothing helps can trim tabs be used on a cat. Has anyone used them on a cat...would they help?

[dana]

Have you tried moving the strut all the way up?

[brooks93]

move the strut up or move your battery's forward. Can you post some pics of your setup?

[razzle]

I've tried moving the strut all the way up and moving the batteries forward...The attached picture is from my first run when the strut was level with the bottom of sponsons, when the strut was level like this just touching the throttle the boat nearly does a backflip. I have also tried a smaller prop but hardly any difference...maybe it is just the hull is designed not to go that fast...I've seen trim tabs on the super surge crusher do you think they will work?P1040047.JPGP1040054.JPG

[dana]

Try putting the strut 1/4" and sponson bottoms

[Fluid]

Some cats will just porpoise because of faulty design - I am not familiar with that particular hull but it may always run poorly.....or not. Sometimes more speed will get the boat past the porpoising stage. Move the strut up in 1/8" steps, not just shoving it to the top otr bottom. It takes time to dial in some cats.

[RandyatBBY]

Have you tried a little more power?

[Old Sloppy]

[QUOTE=Fluid;407358
It takes time to dial in some cats.[/QUOTE]

I want to add that sometimes a smaller diameter prop (with increased pitch ) will aid with "Dial In".

the increased pitch lifts the transom.

the decreased diameter reduces the bow lift.

I didn't see your rpm reading , so I don't know if it is too low or too high.

Stay away from trim tabs, there are better ideas available........

Harry

[razzle]

Is the grimracer L38 × 63 lifter prop worth a try?

[dana]

Nope

[razzle]

octura x637 dia 37mm pitch 59.2mm?

[D for Dummy]

There are only three other things to try to stop porposing, you have listed many of the common fixes.

1) Raise the RPM with your current setup (through a variety of ways: de-tonguing the prop, larger motor, smaller prop, less pitch)
2) Cup your current prop (This will reduce the thrust cone, creating less lift at the prop, and lift the nose of the boat)
3) True your hull (add camber if possible to each sponson)

Side note:
The motley Crew hull is nearly perfect in size, shape, step, camber, trueness. I've yet to experience a better out of the box experience. Many Proboat Miss Gieco and Mystic guys are spending weeks trying to find their ideal setup. I've added a GrimRacer 42x55, My strut is aprox 4mm below the hull. Running two GrimRacer 2s 5000mAh 40C. See my video links on my profile page.

[JIM MARCUM]

One unmentioned fix is to mount two trim tabs on the transom large enough to fit between the rudder and shaft struts ( cut a slot to fit the rudder strut), Bend the tabs down at about a 15-20% angle. The tabs will act like the horizontal stabalizers on the tail of an airplane & force the bow down. Increase/decrease trim tabs angle to find the sweet spot at max speed. JIM