why doesnt most cats have trim tabs?
 

?????

By nature cats tend to run flat from side to side because of the air cushion in the tunnel, and the tabs typically won't have near the effect on angle of attack that a tunnel tab will for that same reason. So if they need trim that the drives can't provide a tunnel tab makes more sense.

Yep. . . . . . What Ted said. We have them on the race boat and I have never used them once. Tunnel tab comes in handy once in a while though.

They dont need trims but if you dont have one in the tunnel good luck gettin on plane....

i see

thanks

Not all cats need or would benefit from a tunnel tab.
Mine gets on plane just fine without a tunnel tab.
I do use my trim tabs a small amount in rougher conditions

what is tunnel tabs? any pics?

i think it is a large tab between the 2 hulls ?? paul

A Tunnel Tab looks like a giant Trim Tab mounted at the rear of the tunnel between the sponsons. It re-directs air more so than water because of it's location. Drop it down and you pack more air in the tunnel - which gives you more lift. On a center pod tunnel (Eliminator cats for instance), it works more like a single Trim Tab.

oh yes ive seen one of these before on a American Offshore i think

Many builders are not using them any more because the hull doesn't need it. They can get you in HUGE trouble if they are left down as your speed increases. My buddies MTI has one that is fixed just about 2 inches down from level. Usually they will keep the cat from porpoising at the speed just before the hull normally packs air.

For the rest of the story

www.PerformanceBoatSchool.com

This is a tunnel tab

the big pallet in the middle...

http://www.limestonedev.com/mti/11.jpg

My Nor-Tech has trim tabs....use them mostly for getting on plane and then pretty much leave them alone at neutral....