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.

"Gould 0738" wrote in message
...
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.

The reason the first one didn't make sense to you is that you're forgetting
that the point of maximum drag is at the speed you're running right before
you jump on plane. At 9 mph, that boat is pushing tons of water. At 25
mph, that boat is displacing much less water.

The reason the first one didn't make sense to you is that you're forgetting
that the point of maximum drag is at the speed you're running right before
you jump on plane. At 9 mph, that boat is pushing tons of water. At 25
mph, that boat is displacing much less water.

I'm not forgetting anything. Even though I gravitate toward semi and full
displacement hulls, I have been on plane in many dozens of boats and the
numbers don't make sense.

Let's apply some logic.

If wew agree for purposes of discussion
that the boat is not on plane at 9mph, (and it most likely would not be), and
that we have only 500 rpm to "spend" to get the boat from 9 mph to 25, observe
what has to happen:

We will need to spend at least 100-200 RPM (maybe more) to climb the bow wave
and maintain a minimal plane. For purposes of discussion, let's say when we
throttle up enough to climb the bow wave we achieve 14 mph. The unspent 300 RPM
are going to take this boat from 14 mph to 25? Almost doubling the speed? No,
they are not.

The other example, a 2500 RPM difference between 6 mph and 27 mph is more
believable than a 500 rpm difference between 9 mph and 25.

I had a similar experience. My 1994 290 Searay would go about 12mph
at 2000rpm and slowly ramp up to about 16mph at 2900, then stay on plane
at 27mph and 3200 rpm.

That's not all that similar. You were using
1200 rpm to go from 12mph to 27......not 500 rpm to go from 9mph to 25.

"Gould 0738" wrote in message
...
The reason the first one didn't make sense to you is that you're
forgetting
that the point of maximum drag is at the speed you're running right
before
you jump on plane. At 9 mph, that boat is pushing tons of water. At 25
mph, that boat is displacing much less water.

I'm not forgetting anything. Even though I gravitate toward semi and full
displacement hulls, I have been on plane in many dozens of boats and the
numbers don't make sense.

Let's apply some logic.

If wew agree for purposes of discussion
that the boat is not on plane at 9mph, (and it most likely would not be),
and
that we have only 500 rpm to "spend" to get the boat from 9 mph to 25,
observe
what has to happen:

We will need to spend at least 100-200 RPM (maybe more) to climb the bow
wave
and maintain a minimal plane. For purposes of discussion, let's say when
we
throttle up enough to climb the bow wave we achieve 14 mph. The unspent
300 RPM
are going to take this boat from 14 mph to 25? Almost doubling the speed?
No,
they are not.

Chuck,
I apologize for confusing you. You're absolutely correct.

Numbers should read:
1500 rpm (approx. 6mph): 6.2mpg
2000 rpm (approx. 8mph): 4.5mpg
2500 rpm (approx. 9mph): 3.5mpg
3000 rpm (approx. 16mph): 6.5mpg
3500 rpm (approx. 25mph): 6.2mpg

From the graph, it appears that the boat comes on plane at a little bit over
2500rpm. The 500 rpm increase from 1500 to 2000 rpm gives a speed increase
of only 2mph. The 500rpm increase from 2000 to 2500 gives only a 1mph speed
increase. The 500rpm increase from 2500 to 3000 rpm gives a speed increase
of 7mph. The 500 rpm increase from 3000 to 3500 gives a speed increase of 9
mph.

As I was stating earlier, the worst efficiency is at the point right before
the boat jumps on plane...and then there's a very rapid rise in the boat
speed per 100 rpm increase after that.

As Wayne B. said earlier, the best mileage would come at 1000 rpm or less
(but the boat would be going less than 5 mph). The second best mileage
comes at an engine speed on 3000rpm...and a boat speed of 16 mph.

Chuck,
I apologize for confusing you. You're absolutely correct.

Good lord!

That statement, (to me from NOYB), is a collector's item. I think I'll take it
out and have it bronzed. :-)

The new numbers make sense.

"Gould 0738" wrote in message
...
Chuck,
I apologize for confusing you. You're absolutely correct.

Good lord!

That statement, (to me from NOYB), is a collector's item. I think I'll
take it
out and have it bronzed. :-)

I admit when I make an error...unlike someone here whose user name indicates
he has a fetish for smooching fish.



The new numbers make sense.

If my math is wrong, void this post.

Your math and example may be fine.
I'd have to put on my Kreskin hat to sit at a keyboard and pontificate about
fuel economy on boats I haven't actually observed.

NOYB's example seemed particulalry out of round.

NOYB double checked his example and discovered it contained some errors.

That would not mean that any example somewhat similar to NOYB's, (such as
yours) *must* be equally flawed, just as your experience doesn't vindicate the
original, faulty example.

"NOYB" wrote in message ...
"Gould 0738" wrote in message
...
Chuck,
I apologize for confusing you. You're absolutely correct.

Good lord!

That statement, (to me from NOYB), is a collector's item. I think I'll
take it
out and have it bronzed. :-)

I admit when I make an error...unlike someone here whose user name indicates
he has a fetish for smooching fish.



The new numbers make sense.

No, what you do is just act like the post in which you were wrong in,
just went away.

Say, did Bush take us to war over oil, or WMD's or to liberate people
that don't WANT us to liberate them, or what?