Gould,
Since you boat with a trawler I think you have forgotten what happens when a
planning hull is no longer planning but is "muscling" it's way through the
water. Most boats drop off of planning at 2200 rpm to 2800 rpm.
The numbers do look reasonable for a "planning hull".


"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?

On Thu, 03 Jun 2004 15:03:10 GMT, "John Smith"
wrote:
Gould,
Since you boat with a trawler I think you have forgotten what happens when a
planning hull is no longer planning but is "muscling" it's way through the
water. Most boats drop off of planning at 2200 rpm to 2800 rpm.
The numbers do look reasonable for a "planning hull".


"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

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

The numbers are reasonable for a planing hull, problem is that they
didn't test at lower than 1500 RPM. At 1500 the boat is already
exceeding its hull speed by a considerable margin and leaving a big
wake. If they had tested at 1000 RPM the results would have been as
expected and shown the best fuel economy. No one wants to travel at
that speed with a planing hull of course, but that is where the best
economy is.

"Wayne.B" wrote in message
...
On Thu, 03 Jun 2004 15:03:10 GMT, "John Smith"
wrote:
Gould,
Since you boat with a trawler I think you have forgotten what happens
when a
planning hull is no longer planning but is "muscling" it's way through
the
water. Most boats drop off of planning at 2200 rpm to 2800 rpm.
The numbers do look reasonable for a "planning hull".


"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

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

The numbers are reasonable for a planing hull, problem is that they
didn't test at lower than 1500 RPM. At 1500 the boat is already
exceeding its hull speed by a considerable margin and leaving a big
wake. If they had tested at 1000 RPM the results would have been as
expected and shown the best fuel economy. No one wants to travel at
that speed with a planing hull of course, but that is where the best
economy is.


Exactly!

Gould,
Since you boat with a trawler I think you have forgotten what happens when a
planning hull is no longer planning but is "muscling" it's way through the
water. Most boats drop off of planning at 2200 rpm to 2800 rpm.
The numbers do look reasonable for a "planning hull".

Once a month I do test runs on a wide variety of different boats. A number of
them are planing hulls. I cannot remember a boat where an increase of 500 rpm
would have brought the boat from 9mph to 25mph. As I said, I'm not in a
position to comment on that specific boat, but the numbers seem strange to me.

Once a boat is over the bow wake and on plane, (which should be occuring
somewhere in the low to mid teens speed wise), in most cases fuel consumption
goes up exponentially to obtain additional speed. It would be interesting to
view a speed/fuel chart for the boat NOYB is referring to.

A boat with the operating characteristics NOYB described would be frustrating
as hell. A difference of 500 RPM increases the speed by 2 1/2 times? Unless you
wanted to run (and the conditions permitted) 25mph, you'd have a dickens of a
time setting the throttle for a speed somewhere between 9mph and 25mph and
keeping the boat there. Everytime a mosquito landed on the throttle lever you'd
pick up or lose a couple of miles an hour. :-)

"Gould 0738" wrote in message
...
Everytime a mosquito landed on the throttle lever you'd
pick up or lose a couple of miles an hour. :-)


Well it seems like the answer is to keep mosquitoes off the throttle lever.
: - )

On 03 Jun 2004 16:12:17 GMT, (Gould 0738) wrote:
A boat with the operating characteristics NOYB described would be frustrating
as hell. A difference of 500 RPM increases the speed by 2 1/2 times? Unless you
wanted to run (and the conditions permitted) 25mph, you'd have a dickens of a
time setting the throttle for a speed somewhere between 9mph and 25mph and
keeping the boat there.

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

Actually, that's just about how my 5,000 lb, 24 ft I/O performs. From
1000 RPM up to 2500 the boat is just pushing water and making waves.
Speed climbs from around 5.5 kts to about 8. Starting at 2500 the
boat will come up on a slow, labored plane at about 15 kts which is
useful only for running in a nasty chop with the bow up. Starting at
2800 it comes up onto a semi-comfortable plane with a speed of 18 to
19 kts which can be sustained with minor throttle tweaking. At 3000
RPM and 20 kts the bow comes down, the boat trims out nicely, and it
gains about 1 knot for every 100 RPM thereafter. Anything under 3000
RPM is not really fun for very long.

Obviously these characteristics vary a great deal depending on the
length and weight of the boat, and the type of motor.. My 12 foot
inflatable for example will come up onto a nice stable plane at about
12 knots because of its light weight and short length.

Wayne.B wrote:

On 03 Jun 2004 16:12:17 GMT, (Gould 0738) wrote:

A boat with the operating characteristics NOYB described would be frustrating
as hell. A difference of 500 RPM increases the speed by 2 1/2 times? Unless you
wanted to run (and the conditions permitted) 25mph, you'd have a dickens of a
time setting the throttle for a speed somewhere between 9mph and 25mph and
keeping the boat there.


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

Actually, that's just about how my 5,000 lb, 24 ft I/O performs. From
1000 RPM up to 2500 the boat is just pushing water and making waves.
Speed climbs from around 5.5 kts to about 8. Starting at 2500 the
boat will come up on a slow, labored plane at about 15 kts which is
useful only for running in a nasty chop with the bow up. Starting at
2800 it comes up onto a semi-comfortable plane with a speed of 18 to
19 kts which can be sustained with minor throttle tweaking. At 3000
RPM and 20 kts the bow comes down, the boat trims out nicely, and it
gains about 1 knot for every 100 RPM thereafter. Anything under 3000
RPM is not really fun for very long.

Obviously these characteristics vary a great deal depending on the
length and weight of the boat, and the type of motor.. My 12 foot
inflatable for example will come up onto a nice stable plane at about
12 knots because of its light weight and short length.



My 25-footer does 60 mph at 2000 rpm. Attached to its trailer and being
towed by an SUV...

"Gould 0738" wrote in message
...
Gould,
Since you boat with a trawler I think you have forgotten what happens
when a
planning hull is no longer planning but is "muscling" it's way through
the
water. Most boats drop off of planning at 2200 rpm to 2800 rpm.
The numbers do look reasonable for a "planning hull".

Once a month I do test runs on a wide variety of different boats. A number
of
them are planing hulls. I cannot remember a boat where an increase of 500
rpm
would have brought the boat from 9mph to 25mph. As I said, I'm not in a
position to comment on that specific boat, but the numbers seem strange to
me.

Once a boat is over the bow wake and on plane, (which should be occuring
somewhere in the low to mid teens speed wise), in most cases fuel
consumption
goes up exponentially to obtain additional speed. It would be interesting
to
view a speed/fuel chart for the boat NOYB is referring to.

A boat with the operating characteristics NOYB described would be
frustrating
as hell. A difference of 500 RPM increases the speed by 2 1/2 times?
Unless you
wanted to run (and the conditions permitted) 25mph, you'd have a dickens
of a
time setting the throttle for a speed somewhere between 9mph and 25mph and
keeping the boat there. Everytime a mosquito landed on the throttle lever
you'd
pick up or lose a couple of miles an hour. :-)

Naw. You might only have to jump the engine speed to 2550 to get up on
plane...and your speed might go up 5-7 mph. Once on plane, every 100rpm
might increase your speed 2-2.5 mph until you hit 25mph.

Naw. You might only have to jump the engine speed to 2550 to get up on
plane...and your speed might go up 5-7 mph. Once on plane, every 100rpm
might increase your speed 2-2.5 mph until you hit 25mph.


Reasonable statement, but not consistent with the original example.

"Gould 0738" wrote in message
...
Naw. You might only have to jump the engine speed to 2550 to get up on
plane...and your speed might go up 5-7 mph. Once on plane, every 100rpm
might increase your speed 2-2.5 mph until you hit 25mph.


Reasonable statement, but not consistent with the original example.

You're right. See my post with the corrected numbers above.
Here they are again:
3000rpm is 16mph and 6.5mpg.
3500rpm is 25mph and 6.2mpg