"basskisser" wrote in message
om...
"Joe" wrote in message news:Pgstb.58486
All *planning hulls* will see *some* improvement in efficiency at
various
speeds. This improvement will mostly be realized in slow to midrange
speeds.

So, JoeTechnician, are you trying to say that trim tabs, when extended
into the water, don't create drag?

I never said they didn't.
I said "But, if the drag they do create is less than the drag they reduce
(stern
dive, pushing a wall of water against the bottom of the hull), and
inefficient prop angle (wasted energy pushing the bow up instead of the boat
forward) then the overall decrease in drag will result in increased fuel
efficiency."

And this is the case on a planing hull in slow to moderate speeds. I have
never seen a planing hull that didn't benefit from the addition of trim
tabs. Put them on a displacement hull and you'd probably *only* create drag.

My contention is a properly trimmed boat, ie: weight distribution, etc. is
correct, wouldn't need trim
tabs.

Distribution of weight will not create lift. It can help, but can not equal
the benefit of the tabs.

Why would a company build a hull that was engineered to give a
unefficient ride??

A planing hull can not be designed to operate efficiently throughout the
range of operation. They are designed to be efficient at higher speeds.

I can see the use of trim tabs to get on plane, but
after that, they ARE creating drag, and a good bit.

They may create some drag but this drag is reducing the overall drag of the
boat. At midrange power most boats can not stay on plane without them. If
you retract them fully at those speeds the stern drops,the bow rises, and
efficiency is lost.

Do this, take a plate of material the same size as the TWO trim tabs, fill
your
bathtub full of water, and try to pull those through the water. Now
using some simple math, you'd see that at planning speed, that drag is
quite a bit.

Tabs are not *pulled* through the water, nor angled down into the water at
the same angles as aircraft tabs. On my boat, you can barely tell the
difference in angle between full up, and the angle needed to hold plane at
slower speeds.

Again, I suggest you take a ride with someone who has them.