Slower than what? Planing hulls going slower than planing speed are much
less efficient.

Actually, i am not so sure about that, I have a 44 marine trader with twin
270
hp lemans, I cruise at 9 mph (knots are for sailors with lots of time on
their

Your 44 Marine Trader is not a planing hull.

It's a semi-displacement trawler.

At what rpm do you make 8 kt? (about 9 mph)

Experiment with slowing down to 7 kt, and you might realize a 25-30 percent
increase in fuel economy. I have experienced that kind of results in the past,
in a smaller hull with similar characteristics.

Caveat: Running a diesel engine too slowly for an extended period of time is
not generally recommended. As you know, they thrive on exercise.

Make sure if running twins that they are in sync.

Find your boats sweet spot. On most planeing hulls idle speed is probably most
efficient but if I wanted to go that slow I would have purchased a sailboat.

On my boat for example the "sweet spot" is 3100 RPM with the drives trimmed
slightly up. This gets me, depending on conditions anywhere from 28 to 30 MPH
and a fuel burn of just under 11 GPH. Of course wind, load and currents can
affect this but these are my averages over 5 seasons of usage.

BTW, gasoline at my marina is $2.339 for 89 octane, on the street anywhere from
$1.999 to $2.299 for 87 octane. Not to shabby. Other marinas are charging from
$2.45 to $2.75 per gallon. My marina and the other marina in my harbor have
always been lower than the norm for some reason. Maybe that is why both are
full.

I get 9 mph at 14oo rpm.

"Florida Keyz" wrote in message
...
Slower than what? Planing hulls going slower than planing speed are much
less efficient.

Actually, i am not so sure about that, I have a 44 marine trader

A Marine Trader is not a "planing hull".

"DSK" wrote in message
...
actually, it's pretty simple, go slower


NOYB wrote:
Slower than what? Planing hulls going slower than planing speed are
much
less efficient.

Nope. This is a common motorboater's misconception.

If you doubt it, look at the fuel test results commonly printed in
magazines.

Just checked June 2004 Powerboat Reports, page 13

Boat/engine: Triumph 210 Chaos center console with single Honda 4-stroke
150hp

Mileage at 1500 rpm (6mph): approximately 6.2mpg
Mileage at 2500 rpm(9mph): approximately 3.5 mpg
Mileage at 3000 rpm(25mph): approximately 6.5mpg

So in this example, the most efficient (best mpg) speed is when the boat is
on plane at 25 mph. In two-strokes, the difference would be even more
dramatic since two-strokes consume significantly more gas than 4-strokes
when travelling at trolling speed.

Mileage at 1500 rpm (6mph): approximately 6.2mpg
Mileage at 2500 rpm(9mph): approximately 3.5 mpg
Mileage at 3000 rpm(25mph): approximately 6.5mpg


TILT!

(occurs to me you kids don't fully appreciate that term).......

The performance curve seems out of whack.

The boat travels 6 mph at 1500 rpm.
Seems really slow, but let's use that.
It ought to do 6mph at a fast idle, one would think.

2500 rpm is only 9 mph? Still seems really, really, really slow, but let's use
that.

If 2500 rpm is propelling this vessel at 9mph, it stretches the imagination to
consider that adding 500 rpm will increase the speed by a factor of 2 1/2
times, or an additional 16mph.

Not saying it isn't so, just that it seems very unusual.

Sure the 2500 rpm isn't 19 mph, instead of
9?

My experience with my 4 stroke merc 60 is it uses less than 1 GPH at "slow"
(AKA "manatee zone") speed. Since I always end up right back where I started
and I don't really have a mission at the other end of the ride, who cares how
fast I go getting there or how far "there" is ?

"Gould 0738" wrote in message
...
Mileage at 1500 rpm (6mph): approximately 6.2mpg
Mileage at 2500 rpm(9mph): approximately 3.5 mpg
Mileage at 3000 rpm(25mph): approximately 6.5mpg


TILT!

(occurs to me you kids don't fully appreciate that term).......

The performance curve seems out of whack.

The boat travels 6 mph at 1500 rpm.
Seems really slow, but let's use that.
It ought to do 6mph at a fast idle, one would think.

2500 rpm is only 9 mph? Still seems really, really, really slow, but
let's use
that.

If 2500 rpm is propelling this vessel at 9mph, it stretches the
imagination to
consider that adding 500 rpm will increase the speed by a factor of 2
1/2
times, or an additional 16mph.

Not saying it isn't so, just that it seems very unusual.

Sure the 2500 rpm isn't 19 mph, instead of
9?

Doesn't seem unusual to me at all. At around 2500 rpms is about where
mine drops off plane and essentiallly plows water.....much of the energy
produced by the engines is being used to push water out of the way, not move
the boat forward. At rpms around 1500, more energy is moving the boat
forward than pushing water,(less wake for example) and the same is true at
3000 with the hull on plane.

"Gould 0738" wrote in message
...
Mileage at 1500 rpm (6mph): approximately 6.2mpg
Mileage at 2500 rpm(9mph): approximately 3.5 mpg
Mileage at 3000 rpm(25mph): approximately 6.5mpg


TILT!

(occurs to me you kids don't fully appreciate that term).......

The performance curve seems out of whack.

The boat travels 6 mph at 1500 rpm.
Seems really slow, but let's use that.
It ought to do 6mph at a fast idle, one would think.

2500 rpm is only 9 mph? Still seems really, really, really slow, but let's
use
that.

If 2500 rpm is propelling this vessel at 9mph, it stretches the
imagination to
consider that adding 500 rpm will increase the speed by a factor of 2 1/2
times, or an additional 16mph.

Not saying it isn't so, just that it seems very unusual.

Sure the 2500 rpm isn't 19 mph, instead of
9?


I dunno, Gould. Those are the numbers in the article I cited. You could go
to Yamaha Motor's website and look at others, but I don't have time right
now. Check the "Performance Data" section. I'll check later if I get a
chance.

Here's one for you:
http://www.yamaha-motor.com/products...triumph/bullet
in_otb_4StrokePerf_MidThrustJetPort_115hp_03-48-TPH-C.pdf

Best economy is at 1000RPM (4.3mph): 10.33mpg

At 1500rpm (5.7mph) : 6.7mpg

At 4000rpm (27.2mph): 7.22mpg

The Powerboats Report article doesn't list mpg below 1500rpm, where, for a
four-stroke, you get the best efficiency.
On two-strokes, it could be very different. I'll check later.



"Gould 0738" wrote in message
...
Mileage at 1500 rpm (6mph): approximately 6.2mpg
Mileage at 2500 rpm(9mph): approximately 3.5 mpg
Mileage at 3000 rpm(25mph): approximately 6.5mpg


TILT!

(occurs to me you kids don't fully appreciate that term).......

The performance curve seems out of whack.

The boat travels 6 mph at 1500 rpm.
Seems really slow, but let's use that.
It ought to do 6mph at a fast idle, one would think.

2500 rpm is only 9 mph? Still seems really, really, really slow, but let's
use
that.

If 2500 rpm is propelling this vessel at 9mph, it stretches the
imagination to
consider that adding 500 rpm will increase the speed by a factor of 2 1/2
times, or an additional 16mph.

Not saying it isn't so, just that it seems very unusual.

Sure the 2500 rpm isn't 19 mph, instead of
9?