Trim Tab Sizing

[ChrisN67]

I have a 36 foot with diesel and surface drives. I have two options, a 12x 24 or 12x18 with a taper where as the end is only 10" wide. Is it preferable to have a longer tab? What is the benefit of added length over width?

Thanks

[keysdisease]

Hello Chris,

With trim tabs more is always better (within reason)

This is because it is more efficient to deploy a larger tab a little to get the desired effect than to deploy a smaller tab a lot for the same effect. It's a lift vs drag question.

Tabs are described as having width and chord. Chord is the fore to aft dimension. Just like an airplane more width is more efficient at lift than more chord. Think of what a gliders wings look like, very wide with a very small "chord." Trim tabs provide lift just like a gliders wings.

You will see performance tabs with a larger chord like some K planes. These are a compromise because the hulls they usually end up on are long skinny go fast hulls with twin or triple engines, no room left for wide tabs. These type tabs are the answer to a real estate problem.

Exactly what kind of 36ft diesel surface drive boat are we talking about and what brand style tab??

Steve

[ChrisN67]

Its an Intrepid 339 with outboard bracket removed, stretched 24" and (2) yanmar 6ly2 (440hp) installed with 2 speed ZF ATS gear and surface drives. Its been a work in process for 2 years

[keysdisease]

Way cool, my Father in Law has a 28 Intrepid and I have great admiration for their product.

Sounds like neat project.

Steve