trim tabs on a cat

[ozzie-crawl]

i havent been able to find a answer to wether i can put trim tabs on a cat. the hull in question is a blackjack, the reason i was thinking trim tabs is this will be for straight line speed only and thought they will help keep it on the water a bit better
here are some pics of the build so far.

[crrcboatz]

I have seen it done in gas on a am conquest to settle it down. I think the person had the wrong prop on it but anyway he said it helped. The boat did run nice and smooth. NOT an everyday thing though.

Curt

[Boatman]

There simply is no better solution than filling in the last set of steps on that hull. I do not know how to explain it but I would very highly suggest it.

[Jeff Wohlt]

Back to the post title.

Think of it as additional hull length. It can reduce porpoising, keep the rear end up in the corners, reduce chine walk, etc. Do we want to use them...not really as it is one more thing to have to adjust when working on CG and running but if you get used to them they can have a big effect on running in many conditions....especially V hulls.

Most big (4o' +) racing cats have them so they can adjust the rear end lift and handling and keep the nose down....their CG is usually very much in the rear (twin blown 1500 hp Sterling motors/drives,etc...yeah baby!) Also they can keep the boat running level when weight is more to one side (more for big Vs with people in them). When you trim a real boat to run nose high and reduce resistance it simply pushes the transom down so tabs can get the rear end back to running lighter. For us we have to use CG for that...more than thrust angle.

In our instance we do not have optional trim (working on that one) so running them with slight down can have a big effect on the nose and ride attitude and down the straights.

I have seen some cats have a center tab in the tunnel from the factory. Get them out of the hole faster.

[Boatman]

the hull in question is a blackjack,

Back to topic. I dont really know if Jeff has put trim tabs on the blackjack or not as it doesnt mention the hull in his post but I have. They do nothing but make you want to throw it all in the rubbish. I cant say filling the the steps is a secret but whether you are going for saw or offshore it just seems to calm everything down and with fullers inline hardware it really plants the hull and doesnt want to roll especially across your or others wakes.

[Jeff Wohlt]

No...not on a BJ. The hull is too short. Use them on larger cats. The BJ is a good looking hull but not built for real speed unless modified and filling the step in probably is the best option....to much air under the hull and steps to be able to control it and the sponsons are too flat. Some are getting 50 mph but that would be on perfect water...which I never get.

I was trying to let you know about what they can do for hulls.

[ozzie-crawl]

thanks guys just wanted to know if it was a option as i had seen them on larger cats,but will give them a miss and look at filling the last step

[785boats]

Hi Scott.
If you're going for straight out speed trim tabs will slow you down. The attitude on a blackjack is a matter of prop angle & COG.
A tunnel tab or wedge would help lift the hull a bit without the drag.
I was under the impression that filling in the last step was more for solving cornering problems. It also tends to slow the hull in a straight line.
Here's the procedure on a Drifter hull in the 'Tips & info' section on this site.

http://www.offshoreelectrics.com/inf...fters-turn.php

I can vouch for the wedge because it certainly made the 32" cat run a bit drier but may have been part of my cornering issues.
Just my thoughts.
Paul.

[ozzie-crawl]

thanks paul i will leave filling in the step for now and see how it runs