****, here we go again, JoeTechnician, I even have to explain what to
hell YOU responded to. Read the second sentence of the original post:
They create a lot of drag to force the bow down at slower speeds.
Of course you can raise them and get the efficiency back.

I know exactly what I responded to and stand by my statement.

At slower speeds, they definately DO create more drag. AT SLOWER
SPEEDS, get it? You are plunging a planar piece of material, at an
angle, into the water. Do you think that is creating drag, yes or no
please.

If not correctly adjusted they might (extended too far).
Here's a shocker for you, they usually work better at slower speeds and
rougher seas than they do at higher speeds and calmer seas.
I'm not talking about idle speeds when I say "slower speeds" but they will
begin to be efficient approximately at the point that you can plane with the
tabs adjusted down.

Here's real world scenario for you- On my boat (21.5' CC 200hp), at 3000rpm
the boat will ride with a bow high attitude with stern dive. As I actuate
the trim tabs the stern rises, the bow lowers and the boat planes. Once
planed the rpm's will immediately climb (without touching the throttle) and
my speed increases. I then can reduce throttle back to 3000rpm and continue
along on a plane.

Now, tell me, do you think my boat is more, or less efficient at 3000rpm's
with my tabs down or tabs up?

Now, that in turn, pushes the bow down, again, we are AT
SLOWER SPEEDS. So, you are essentially putting more of the hull in
contact with the water. Do you not think this, AT SLOWER SPEEDS,
creates drag? Yes or no, please.

Trim tabs, when activated, will *always* add some drag, and as 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."


Here's some reading for you.

http://www.bennetttrimtabs.com/whatdo.htm
http://www.trimmaster.net/id114.htm
http://www.boatus.com/boattech/trimtabs.htm
http://www.powerandmotoryacht.com/fe...abs/index.html
http://www.h-ri.com/Product/Duraplane/Duraplane_01.html