On 23 Nov 2004 15:31:50 -0800, (Big Daddy) wrote:

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).

Yes and no. It would seem a wasteful purchase and I should know - I
had to be convinced that it would help with my Contender. I have to
admit that I was wrong. The fuel flow meters help because they can
show you if, all things being equal, you might have a problem. And
you can pretty much keep track of how much fuel you are using at any
one time. The ones I have keep track of total fuel usage also.

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.

Ah - it if works, it works. My motto. :)

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.

Once again, depends on the type of hull. I would bet that those boats
at that angle don't have a great deal of deal rise.

Later,

Tom

On Tue, 23 Nov 2004 18:47:36 -0500, Wayne.B
wrote:

On Tue, 23 Nov 2004 10:24:06 -0500, Harry Krause
wrote:
With a smaller, open boat, you can see when you are on plane. On the
Parker, that's pretty much impossible, though there are certain "feels"
at various speeds.

================================================= ===

It's been my experience that the transition point gets much fuzzier as
boat weight and length increase. With something like a Hatteras 53
weighing 50,000 pounds or so, they never really look or feel like they
are on plane even when going 20 knots.

My Bertram 33 weighed about 23,000 pounds and was clearly on plane at
13 to 14 knots with a little help from the trim tabs. It really
didn't FEEL like it was on plane however until it got over 20 kts. At
that point the hull was well out of the water and it had the feel of
gliding over the water instead of plowing it aside.

AH HA!!!

See - "gliding"....

WHOO HOO!!!! I love it when I'm right. :)

Later,

Tom

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!

On Sun, 21 Nov 2004 22:11:43 -0500, Harry Krause
wrote:

JohnH wrote:
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


Nice that you have tabs and only use them on rough water, Herring,
but...that isn't what the poster asked. Oh...and his boat is much
heavier than yours, and is powered differently. D'oh.

I can see that this response is much more your style, Harry. Do you
think it helped answer his question?

John H

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

On Wed, 24 Nov 2004 00:00:19 GMT, Short Wave Sportfishing
wrote:

AH HA!!!

See - "gliding"....

=========================

Yes, that light feeling of skipping across the wave tops. I know it
well, and like it as much as anyone else, BUT many heavy boats are
truly "on plane" well before that point is reached. And many heavy
boats never reach that point even though they start planing somewhere
between 13 and 20 knots.

Which brings us back to the original question in a circular sort of
way: When is a boat "on plane" ? I'd be inclined to vote for 2.5X
the theoretical hull speed. Easy enough to calculate, and sort of
intuitive. It may not be dead right for every boat but it should be
in the ball park.

On 23 Nov 2004 15:31:50 -0800, (Big Daddy) wrote:
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.

============================

Depends on the boat and how it is loaded. 5 degrees is not all that
much but it is probably enough to get the forward third of the boat
out of the water and thus reducing hull friction. If you increase the
angle too much the stern squats and digs in, creating a different kind
of drag.

I would also expect that a certain amount of bow rise helps the boat
climb onto the surface of the water just as a small angle of attack
helps an airplane climb through the air. In each case the downward
flow deflection creates an upward lifting force.

Wayne.B wrote in message
...
On Tue, 23 Nov 2004 10:24:06 -0500, Harry Krause
wrote:
With a smaller, open boat, you can see when you are on plane. On the
Parker, that's pretty much impossible, though there are certain "feels"
at various speeds.

================================================== ==

It's been my experience that the transition point gets much fuzzier as
boat weight and length increase. With something like a Hatteras 53
weighing 50,000 pounds or so, they never really look or feel like they
are on plane even when going 20 knots.

My Bertram 33 weighed about 23,000 pounds and was clearly on plane at
13 to 14 knots with a little help from the trim tabs. It really
didn't FEEL like it was on plane however until it got over 20 kts. At
that point the hull was well out of the water and it had the feel of
gliding over the water instead of plowing it aside.


I get a similar feel with the Navigator. At 15 knots or so I can sense that
it is making a transition, and at 19 to 20 knots it sort of glides and will
bank into turns. I tweak with the tabs until the boat "feels good" and it
usually will add a knot or so to my speed. The Navigator has very little bow
rise however, compared to a Hat that typically takes a bow to the sky
attitude. The Navigator hull seems to lift uniformly and maintains a similar
attitude at 19 knots as it does sitting in the slip. One of the claims of
fame of the designer, Jules Marshall, is an efficient hull design that
allows a decent cruise speed with smaller engines. At 19 knots it burns
approximately 26 gals/hr with the twin 370 hp Volvo's and displacing
somewhere around 42000 lbs loaded up.

Eisboch

On Wed, 24 Nov 2004 05:07:52 GMT, "Eisboch"
wrote:

At 19 knots it burns
approximately 26 gals/hr with the twin 370 hp Volvo's and displacing
somewhere around 42000 lbs loaded up.

====================================

That is excellent fuel economy for a boat that size going 19 kts.
Most Hatt 53s would be burning over 40 gph.

Wayne.B wrote in message
...
On Wed, 24 Nov 2004 05:07:52 GMT, "Eisboch"
wrote:

At 19 knots it burns
approximately 26 gals/hr with the twin 370 hp Volvo's and displacing
somewhere around 42000 lbs loaded up.

====================================

That is excellent fuel economy for a boat that size going 19 kts.
Most Hatt 53s would be burning over 40 gph.


It really is and it verified the fuel burn graph provided by Navigator when
I bought the boat. I was a little dubious of it at first but made several
checks on our trip to Florida when we would spend 8 hours or so at an
average of 19 knots. The graph was right on the money.

Eisboch

Wayne.B wrote in message
...
On Wed, 24 Nov 2004 05:07:52 GMT, "Eisboch"
wrote:

At 19 knots it burns
approximately 26 gals/hr with the twin 370 hp Volvo's and displacing
somewhere around 42000 lbs loaded up.

====================================

That is excellent fuel economy for a boat that size going 19 kts.
Most Hatt 53s would be burning over 40 gph.


A Hatt 53 is also significantly heavier I think.

Eisboch