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.

Paul Fritz wrote:
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.

A bit of physics here... with the hull on plane, the energy required to
lift the boat is coming from the engine.

It's possible that gas mileage for light planing hulls has improved in
recent years. But the efficiency curve still isn't going to go backwards
to any significant degree, and adding any load to the boat is going to
make the curve steeper (ie higher penalty on mileage at higher speeds).

Motorboaters deny it to their dying breath, but it's like arguing
against gravity. Speed costs. Sorry to be the bearer of bad news.

Fair Skies
Doug King

Doesn't seem unusual to me at all. At around 2500 rpms is about where
mine drops off plane and essentiallly plows water....

Ok, let's say your boat drops off plane at 2500 RPM. (Are we talking OB motor?)

Let's say that just off plane in your boat is
9 mph.

At 2600 rpm we'll say you're back on plane at 10-11 mph. Adding 400 rpm to that
will bring you to 25 mph?

Something is fracturing my paradigm. Very light boats, outboard motors, or
something else I don't typically experience.

"Gould 0738" wrote in message
...
Doesn't seem unusual to me at all. At around 2500 rpms is about where
mine drops off plane and essentiallly plows water....

Ok, let's say your boat drops off plane at 2500 RPM. (Are we talking OB
motor?)

Let's say that just off plane in your boat is
9 mph.

At 2600 rpm we'll say you're back on plane at 10-11 mph.

My 17' Whaler can stay on plane at about 13mph. Very few v-bottom boats can
plane at that slow a speed...so I doubt the Triumph is back on plane at 2600
rpm and a speed of 10-11mph.

Adding 400 rpm to that
will bring you to 25 mph?

An engine needs to run at a higher RPM to initially jump onto plane than it
does to maintain planing speed. However, I think you're incorrectly
assuming that the boat started planing at 10-11mph.




Something is fracturing my paradigm. Very light boats, outboard motors, or
something else I don't typically experience.


Light boats, yes. Outboards? Probably no different from an
I/O...definitely different from an inboard.

I think what you're missing is that there is less drag on a boat when it is
running fast and high out of the water, then when it's running at a speed
off-plane or just on-plane.

It's the same reason a boat runs faster with the engine trimmed out. Less
drag.

"Gould 0738" wrote in message
...
Doesn't seem unusual to me at all. At around 2500 rpms is about where
mine drops off plane and essentiallly plows water....

Ok, let's say your boat drops off plane at 2500 RPM. (Are we talking OB
motor?)

I/O on a 28ft Wellcraft Monte Carlo. :-)


Let's say that just off plane in your boat is
9 mph.

At 2600 rpm we'll say you're back on plane at 10-11 mph. Adding 400 rpm to
that
will bring you to 25 mph?

I don't stay on plane at 10-11, it pops out of the hole somewhere around 20.
At about 3000 rpm, I run at about 25 mph, at full throttle on flat water I
max at about 38.






Something is fracturing my paradigm. Very light boats, outboard motors, or
something else I don't typically experience.

"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?

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

At 1500rpm (5.7mph) : 6.7mpg

At 4000rpm (27.2mph): 7.22mpg

Now that seems more reasonable.
A 2500 rpm increase taking the boat from
6 mph to 27 is more believable (to me) than a 500 rpm increase taking the boat
from 9mph to 25.