Thinking of fitting a Benett ATC Trim Tab unit to your boat?

Submitted: Thursday, Sep 23, 2010 at 18:03

ThreadID: 81513 Views:5292 Replies:1 FollowUps:1

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Tonyfish#58

To all the boating enthusiasts. I recently purchased a set of Bennett M80 Sports tabs to trim up my Cairns Custom Craft Tri hull. I though I would go with the ATC Unit which auto trims the boat.

To cut a long an time consuming short, the ATC control module was supplied new in a faulty condition. Bennett support Australia were good with advice and did supply a new one that did work, but it does not recover the hours of fault finding an rewiring that had to be done.

So if you purchase this unit make sure you wire the unit up and test it before going to the effort to install it in the boat.

To others that may have fitted trim tabs and because of transom design the tabs do not line up to the keel, have a look at the photo below that shows a cut and shut method of realigning the trim tabs.

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Reply By: Maîneÿ . . .- Thursday, Sep 23, 2010 at 21:58

Thursday, Sep 23, 2010 at 21:58

Tony,
Are you sure you have the trims on the correct sides ?

They look like they are reversed left to Right, just my thought as the far outside edge is higher up than the inside edge is and the usual method is to have the trailing edge parallel with the surface of the water so as they go deeper into the water they give stable lift vertically.

Maîneÿ . . .

AnswerID: 431266

Follow Up By: Tonyfish#58 - Sunday, Sep 26, 2010 at 17:25

Sunday, Sep 26, 2010 at 17:25

Mainey - Thanks for that - Yes they are on the correct side :-)

This is a Tri Hull boat and you will notice it has considerable deadrise on the outer Keels.

The trim tabs must follow the plane and line of the keel, which they now do. The front edge of the tab is set 1/2" above the bottom of the boat and the trailing edge 5/8".

The problem I had and as do some others is that the stern of the boat is not parallel to the keel. You will notice in the first photo the trim tab is out of parallel by 30mm. This was the same on both sides. This would have meant the tabs would have wanted to steer the boat. Not the desirable outcome :-)

Once mounted you have a lot of holes drilled to fit the tabs and actuator, you can not move these holes. So to put a wedge behind the tab was out of question and it would have been a large wedge.

So the solution was the second photo. cut the inside angles and flaps off and weld them to the outer side of the opposite tab. Cut the outside flaps off and weld them to the inside of the opposite tabs.

I now have tabs that sit parallel to the keel and I can now tell you they operate excellent. It has made this boat twice as good to drive.

I needed to keep the flaps on each tab as this was designed to give extra lift, they are only a small tab. Otherwise I could have just cut these flaps off.

I did a bit of research about this issue, there were other fixes quoted on online forums but it was basically new tabs needed. As this was one of those moments "hey I can do this another way & easy "I posted this to let others know you can fix them without drilling more holes or getting new flaps.

Regards & cheers Tony

FollowupID: 702257