Trim Tabs

[steve157]

My trim tabs are not working and I cant figure out why as the pumps ok and there is plenty of fluid in the tank, my question is do they make a vast difference to the perfomance of the boat or is it ok just to trim it on the legs, I have heard some people fix the trim tabs in one position. Oh they are fully retracted...

 

[BrendanS]

They can make a huge difference to some boats in terms of perfomance and comfort, and maybe even safety depending what conditions you are likely to be out in. What make and model boat do you have? For those of us not familiar with Oz boats, the type, size, engine etc will probably help.

generally if you have a boat with high hull and superstructure for instance, a cross wind will be a lot more comfortable if you have tabs. On my own boat, they would make no difference, though on a boat I helped move to its new home some weeks ago it made a hell of a difference. Sometimes in boats that are not highly powered, they can help onto the plane. In some boats, they can be used differently if going downwind/wave or into wind/wave to adjust that level of attack of the boat to the waves - downwind/wave in some boats this can significantly change the behaviour of the boats handling.

All generalisations tho. Hence why we need to know the type of boat

On the other hand, you'll probably be able to sort out the problem here if you provide enough info. Mechanics isn't my area tho!

 

[steve157]

The boat is a 28ft Carver flybridge with twin 130hp volvo diesels, am only getting 20knots out of the boat and wondered if the tabs would make a difference or does that speed sound about right with the engines thats in her.....

 

[Callisto]

you only have one pipe to the ram assuming they are Bennet type tabs so the problem is hydraulic. If the pump runs, but you get no oil into th rams the valves are not opening to allow it in. IIRC, the bennet tab uses hydraulic pressure to drive it down and then it returns on a big spring in the ram.

If you try this, do it carefully as the pressure can be very high, slacken the nut on the feed to the ram and run the pump, if oil exits the joint, the problem is in the ram and its either jammed or letting oil past in which case you will see a slick behind you as there is no return to the tank. If you get no oil out, the valves in the pump are at fault.

don't forget to re tighten anything you have slackened off.

20 knots seems low for the boat too. I assume that you are pulling the full 3900 rpm that the VP AD31 should give, I'm guessing that they are AD31 as that would seem abot the right age of boat for them and they were 130hp.

it could be a prop issue or with the defective tabs, you may not be fully planing and the boat cant pick up speed. the carver 28 is a heavyish boat for 130hp motors. I get 30kn tops from my Falcon but she's just under 28 ft with no flybridge.
hope this helps

JH