Trim tabs and transom plates?

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MarcusBrown

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Can't anyone explain in terms for a novice how trim tabs and transom plates work and what they do to the boat. In particular how they would affect 12ft v hull aluminium boat with outboard no console (at the moment I'm only running a 4hp mercury outboard but looking to upgrade to around a 9.8hp on spring)


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Quite simply tabs whether affixed to the back of the transom or fins put off the lower unit of the OB, add lift to the rear of the boat. This lift, however, is actually created as a result of 'drag' and various designs are better at minimizing the drag than others.

For such a small boat, I'd go with a fin off the OB lower unit, but not on the 4hp. For small tins where the bow rises uncomfortably while planing out I've always used the hydrofoil fins; some are really great and some work, but at a huge decrease in speed.

The better OB-foil designs optimize speed and make the hull really perform, at least by my actual testing (my boat club has a fleet of a few dozen small boats and I help manage the boats, motors and docks). A larger hull could use those Smart Tabs. See these posts for more info on both types:

https://forum.tinboats.net/viewtopic.php?f=4&t=40090

https://forum.tinboats.net/viewtopic.php?f=3&t=39462
 
Before I did any of that I would try to rearrange the weight in the boat, weight distribution in a small boat is a huge factor.

A transom plate will enable you to raise the motor if it is mounted too low and will also provide some set back which will enable higher mounting as well. Good for more clearance but also the further the motor is in the water the more drag there is as well.
 

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