Wow. Thanks for all the great comments. Let me clarify a few
things...
I don't even need to use the trim tabs to get on plane, even with full
tank and many people. I guess the duoprop twin outdrives do the
trick.
I will check into the flowmeters, but I think the reason I don't buy
them is that I'd like to get good at finding what you have all called
"the sweet spot" by watching the gps speed vs rpm while making
adjustments. All I can think of is all the gas I can buy for the 2 or
3 hundred dollars for flow meters for my twins! (I hope that isn't a
dumb answer).
What I really should have asked is; Would I get better fuel mileage
by running on plane at a slower speed with larger trim tabs versus
running at a faster minimum planing speed with the tabs I have now.
I think you have all answered my question. Leave it alone. The tabs
are Bennet and installed new on the boat. The boat runs great the way
it is. I really like the advice to watch rpm and speed while changing
things.

Thanks a lot.

Hey, one more quick one. Has anyone else noticed in some of the
magazine boat reviews where they show the rpm, boat angle, and mpg
that in some tests, the best mpg that they measure is when the boat
angle is at it's steepest, like 5 degrees? That seems odd to me.
That, I would think is the very worst angle for good gas mileage and
yet they show it as the best.

Thanks
Wayne

Short Wave Sportfishing wrote in message . ..
On 21 Nov 2004 17:35:54 -0800, (Big Daddy) wrote:

Hello. I have a 29' Chaparral (great boat) with twin v-6's and Volvo
duoprops. It comes on plane extremely fast if I work the trim tabs
full and use the outdrive tilt. You almost don't even know the bow is
raising!

My question is...in lieu of the damn gas prices, I'm wondering if I
could get better mileage if I added larger trim tabs so that the boat
would plane at a slower speed. Right now, I have to get it to 3,000
rpm's to bring it down on plane.

Any thoughts?

Based on my experience, I've never used trim tabs to bring a boat on
or off plane. On my Contender, it's more a question of lateral
balance in unfavorable sea conditions and for keeping proper bow entry
in seas. Then again, I have outboards, so the conditions may be
different.

I don't think larger trim tabs are going to help much because of drag
issues. I'm not all that familiar with I/Os, but with outboards,
plane is more a function of proper engine trim and throttle setting.
On my Ranger, a 20 footer which doesn't have trim tabs, it's all
about engine angle and throttle setting. On the Contender, I hardly
twitch the tabs unless I absolutely have to.

I would think that larger trim tabs would create more drag, thus less
performance, thus more gas used.

Later,

Tom