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?

Thanks!

Larger trim tabs will help the boat to stay on plane at lower speeds but
they will create more drag which will defeat the purpose. For best fuel
economy - you need to use minimal tabs (just enough to keep the boat level)
and use enough throttle to keep the boat on plane. Throttle gives you more
speed. Tabs create less speed due to drag. Speed vs throttle setting is
what controls fuel economy. The more speed you have for a given throttle
setting the better fuel economy you will have. W/ tabs buried to stay on
plane you are creating a lot of drag and load on the engine. This really
reduces economy.
At least that is my (and several friends) experience w/ larger boats.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"Big Daddy" wrote in message
m...
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?

Thanks!

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?

Thanks!

I use no tabs unless I want the bow down for rough water, i.e., to
give a little smoother ride while on plane.

John H

On the 'PocoLoco' out of Deale, MD,
on the beautiful Chesapeake Bay!

"JohnH" 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?

Thanks!

I use no tabs unless I want the bow down for rough water, i.e., to
give a little smoother ride while on plane.

John H

How does this answer his question?

Brian

On Mon, 22 Nov 2004 10:58:57 -0000, "BrianR"
wrote:


"JohnH" 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?

Thanks!

I use no tabs unless I want the bow down for rough water, i.e., to
give a little smoother ride while on plane.

John H

How does this answer his question?

Brian


Better than your post!

John H

On the 'PocoLoco' out of Deale, MD,
on the beautiful Chesapeake Bay!

BD,
Since your question about getting the boat on plane is really about optimal
fuel use, I'm wondering if you have fuel flow meters on the engines. If
not, check out this link where several different manufacturer's products are
shown:
http://www.boatersland.com/fuelflow.html


"Big Daddy" wrote in message
m...
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?

Thanks!

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

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

IMO and personal experience, the results of using trim tabs and probably
their optimum size varies from boat to boat, so there is no generic answer.
Like Tom pointed out, trim tabs are primarily for lateral positioning due to
heeling into the wind or unbalanced lateral loads. Many boats that are
under or marginally powered benefit from lowering the tabs to help get on
plane, but it is a balance of lifting the stern and generating more drag.

If the OP's boat is underpowered, my guess would be that larger tabs might
help lift the stern to get on plane which will the significantly reduce
overall hull drag. Once on plane, he should slowly raise the tabs back up,
while watching his tach until he finds the "sweet spot" of max RPM for a
fixed throttle setting.

Somewhere I think I remember reading that tabs should have an inch of width
for every foot of boat length.

Just my opinion.

Eisboch

On Mon, 22 Nov 2004 13:13:13 GMT, "Eisboch"
wrote:
Many boats that are
under or marginally powered benefit from lowering the tabs to help get on
plane, but it is a balance of lifting the stern and generating more drag.

I went through this exercise with my previous boat (Bertram 33
sportfish). With a full load of fuel and a lot of gear on board it
was difficult to get the bow down to the correct attitude. The boat
was planing but cruising speed was a knot or two short of what it
should have been and the boat didn't feel quite right. The folks at
Bennet tabs were helpful in recommending the correct size:

http://www.bennetttrimtabs.com/

If the OP's boat is underpowered, my guess would be that larger tabs might
help lift the stern to get on plane which will the significantly reduce
overall hull drag. Once on plane, he should slowly raise the tabs back up,
while watching his tach until he finds the "sweet spot" of max RPM for a
fixed throttle setting.

That's about right. I would start by setting my throttles at correct
cruising RPMs and then adjust the tabs for best speed. That usually
causes RPMs to increase so I would then throttle back slightly and
readjust.

Whether or not a particular boat will be helped by larger tabs is
somewhat problematic. It depends on the boat, how it is powered, how
heavily it is loaded, and weight distribution.

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