For those of you who have used the fuel flow meters what do you think about
fuel efficiency?

For a planing boat, which is more efficient, motoring at 3-5 mph (no wake)
or motoring at the lowest speed that allows the boat to plane?

Is the lowest speed that allows the boat to plane the most efficicient
planing speed or is there a sweet spot somewhere between planing and WOT?

With my little knowledge, here's my 1 cent:

Bryan kirjoitti:

For those of you who have used the fuel flow meters what do you think about
fuel efficiency?

I assume that you mean to ask which speed zone is most efficient in the
terms of miles per gallon (or nm per liter).

You could take a look at boat/outboard tests - in the Internet and
magazines - as some of those list fuel consumption at various speeds.

It might be a bit difficult to generalize. What makes boating so
interesting is that you have usually many parameters to consider, and
this is no exception... For example you have different engines (and
even different engine types), propulsion types, differences between the
hulls at displacement speeds as well as planing speeds, different loads
for the boat, etc

For example, I gather that a long, narrow hull makes for good
displacement speeds but a flat, wide hull is more efficient for planing
speeds. Are we assuming that engines or propellers are not changed for
the given hull, to get better values at a certain speed?

For a planing boat, which is more efficient, motoring at 3-5 mph (no wake)
or motoring at the lowest speed that allows the boat to plane?

I understand it's a solid general rule of thumb that going at a
displacement speed is very efficient. Planing hulls are not really
designed for this, but the physics of water still favour these speeds.
I looked at some boat tests and it seemed that droning on at 4 knots or
so gave indeed the most mpg of the listed values in the test. But I
doubt this speed would be a good choice for travel in practice because:
1) for starters, it's dog slow by today's standards 2) the engines will
not like it 3) typical small planing boats with efficient design are
not too much worse off at planing speeds. If you get a boat that is
designed for planing speeds, why on earth would you want to run it
mostly at displacement speeds?

There is some theoretical confusion on when exactly your boat is going
at a "planing speed". But I think you'd need to go a few knots faster
than that to get on the plane cleanly (clear of the boat's wake?).

Is the lowest speed that allows the boat to plane the most efficicient
planing speed or is there a sweet spot somewhere between planing and WOT?

You may have noticed boats usually have a cruising speed listed. I'm
not sure how exactly that is determined (and I doubt there is a solid
common standard) but I'd think it takes into account speed, fuel
efficiency and what's best for the engine. Your sweet spot for the fuel
efficiency (when planing) would probably land somewhere between the
cruising speed and the lowest planing speed, I think...

I'll need to look at a few more tests... But it's a good question.
However you should not forget to consider this in relation to what is
best RPM in terms of engine lifespan and what are one's needs as a
boater.

Risto

On 24 Jul 2006 07:28:58 -0700, "Varis" wrote:

You may have noticed boats usually have a cruising speed listed. I'm
not sure how exactly that is determined (and I doubt there is a solid
common standard) but I'd think it takes into account speed, fuel
efficiency and what's best for the engine.

It's not written in stone, but there actually is a commonly used
standard for cruising speed. For gas engines it is usually 70% of
max RPM at wide open throttle, and for diesel engines 85%. This
assumes that the engines have been correctly propped so that max WOT
RPMs occur at the peak of the horsepower curve.

Doing a little more math yields the result that gas engines operating
at 70% of WOT are developing about 50% of their maximum horsepower,
and for diesels at 85% of WOT, about 72% of max hp. Those numbers are
useful for estimating fuel consumption at cruising speed. For
example, a 260 hp gas engine at cruising speed is developing about 130
actual hp, which in turn translates to 13 gph using the commonly
accepted estimate of 1 gph for every 10 hp. For a diesel it is about
1 gph for every 20 hp actually developed.

From what I've learned from some mechanics and my own experience, it's
the lowest speed at which the boat remains on plane AND the motor can
be trimmed so the angle of thrust is parallel, or very close to
parallel, to the surface, i.e. horizontal. If the motor's trimmed up
or down off-parallel, it's wasting energy pushing in the wrong
direction (any direction besides forward).

Sometimes surface conditions can interfere with this principle. For
example, you might have to trim the motor out (pushing the bow down)
slightly to prevent violent porpoising when the surface is rough. If
it's absolutely glass-smooth, then of course that is a different
situation.

Ron M.

"Wayne.B" wrote in message
...
On 24 Jul 2006 07:28:58 -0700, "Varis" wrote:

You may have noticed boats usually have a cruising speed listed. I'm
not sure how exactly that is determined (and I doubt there is a solid
common standard) but I'd think it takes into account speed, fuel
efficiency and what's best for the engine.

It's not written in stone, but there actually is a commonly used
standard for cruising speed. For gas engines it is usually 70% of
max RPM at wide open throttle, and for diesel engines 85%. This
assumes that the engines have been correctly propped so that max WOT
RPMs occur at the peak of the horsepower curve.

Doing a little more math yields the result that gas engines operating
at 70% of WOT are developing about 50% of their maximum horsepower,
and for diesels at 85% of WOT, about 72% of max hp. Those numbers are
useful for estimating fuel consumption at cruising speed. For
example, a 260 hp gas engine at cruising speed is developing about 130
actual hp, which in turn translates to 13 gph using the commonly
accepted estimate of 1 gph for every 10 hp. For a diesel it is about
1 gph for every 20 hp actually developed.


OK, so that theoretically gives me 9 gph at cruising speed. What does
cruising speed mean? Is it the most engine friendly speed (longevity) or is
it the most fuel efficient speed (gph)?

"Varis" wrote in message
oups.com...
With my little knowledge, here's my 1 cent:

Bryan kirjoitti:

For those of you who have used the fuel flow meters what do you think
about
fuel efficiency?

I assume that you mean to ask which speed zone is most efficient in the
terms of miles per gallon (or nm per liter).

You could take a look at boat/outboard tests - in the Internet and
magazines - as some of those list fuel consumption at various speeds.

It might be a bit difficult to generalize. What makes boating so
interesting is that you have usually many parameters to consider, and
this is no exception... For example you have different engines (and
even different engine types), propulsion types, differences between the
hulls at displacement speeds as well as planing speeds, different loads
for the boat, etc

For example, I gather that a long, narrow hull makes for good
displacement speeds but a flat, wide hull is more efficient for planing
speeds. Are we assuming that engines or propellers are not changed for
the given hull, to get better values at a certain speed?

For a planing boat, which is more efficient, motoring at 3-5 mph (no
wake)
or motoring at the lowest speed that allows the boat to plane?

I understand it's a solid general rule of thumb that going at a
displacement speed is very efficient. Planing hulls are not really
designed for this, but the physics of water still favour these speeds.
I looked at some boat tests and it seemed that droning on at 4 knots or
so gave indeed the most mpg of the listed values in the test. But I
doubt this speed would be a good choice for travel in practice because:
1) for starters, it's dog slow by today's standards 2) the engines will
not like it 3) typical small planing boats with efficient design are
not too much worse off at planing speeds. If you get a boat that is
designed for planing speeds, why on earth would you want to run it
mostly at displacement speeds?

There is some theoretical confusion on when exactly your boat is going
at a "planing speed". But I think you'd need to go a few knots faster
than that to get on the plane cleanly (clear of the boat's wake?).

Is the lowest speed that allows the boat to plane the most efficicient
planing speed or is there a sweet spot somewhere between planing and WOT?

You may have noticed boats usually have a cruising speed listed. I'm
not sure how exactly that is determined (and I doubt there is a solid
common standard) but I'd think it takes into account speed, fuel
efficiency and what's best for the engine. Your sweet spot for the fuel
efficiency (when planing) would probably land somewhere between the
cruising speed and the lowest planing speed, I think...

I'll need to look at a few more tests... But it's a good question.
However you should not forget to consider this in relation to what is
best RPM in terms of engine lifespan and what are one's needs as a
boater.

Risto

This question came to mind as I was imagining exploring a large lake (very
large in terms of shoreline to explore). I started to wonder what would
extend my limited fuel capacity: droning along (not an unpleasant option for
this purpose) at no wake speed or kicking it up a notch to planing speed
(again, not an unpleasant option).

I have no idea what the listed cruising rpm's mean! I should chase down my
manufacturer and ask.

And, yes, achieving a plane occurs a few knots above the speed at which I
can maintain a plane.

The optimal solution might be a different boat or a different engine
I wonder how big a factor the engine RPM/longevity issue is. Are you
using an outboard or an inboard? Gasoline or diesel?

One option could be to get a propeller with lower pitch. You could run
at optimum RPM but lower speed. Such a propeller might double for
trolling purposes as well, where you need lower speeds. Around here
people into trolling often get a 2nd outboard, and at least sometimes a
2nd (or 1st :-) propeller for trolling instead.

Risto

Bryan wrote:
For those of you who have used the fuel flow meters what do you think about
fuel efficiency?

For a planing boat, which is more efficient, motoring at 3-5 mph (no wake)
or motoring at the lowest speed that allows the boat to plane?


No question there, the best fuel efficiency for distance
travel is usually at (or just above) idle. But who is
willing to actually travel at that speed?


Is the lowest speed that allows the boat to plane the most efficicient
planing speed or is there a sweet spot somewhere between planing and WOT?



It is possible to make some generalizations, but most people
reject them because they really prefer to believe otherwise.

1- For a given hull & load, as speed increases, fuel
consumption increases exponentially.

2- For very light & very flat hulls (ie hulls that are easy
to lift and generate a lot of lift), the fuel penalty for
planing is not as severe... for some extreme examples, the
particular boat might actually get better mpg while planing,
but this is quite rare Only for very light, very fast boats
can achieve this.

The corollary to #2 is (of course) that heavy deep-vee
hulls, loaded hulls, "semi-planing" hulls, etc etc, are
going to get very poor fuel efficiency. But fuel has been so
cheap, who cares?

Fair Skies- Doug King

"DSK" wrote in message
. ..
Bryan wrote:
For those of you who have used the fuel flow meters what do you think
about fuel efficiency?

For a planing boat, which is more efficient, motoring at 3-5 mph (no
wake) or motoring at the lowest speed that allows the boat to plane?


No question there, the best fuel efficiency for distance travel is usually
at (or just above) idle. But who is willing to actually travel at that
speed?


Is the lowest speed that allows the boat to plane the most efficicient
planing speed or is there a sweet spot somewhere between planing and WOT?


It is possible to make some generalizations, but most people reject them
because they really prefer to believe otherwise.

1- For a given hull & load, as speed increases, fuel consumption increases
exponentially.

2- For very light & very flat hulls (ie hulls that are easy to lift and
generate a lot of lift), the fuel penalty for planing is not as severe...
for some extreme examples, the particular boat might actually get better
mpg while planing, but this is quite rare Only for very light, very fast
boats can achieve this.

The corollary to #2 is (of course) that heavy deep-vee hulls, loaded
hulls, "semi-planing" hulls, etc etc, are going to get very poor fuel
efficiency. But fuel has been so cheap, who cares?

Fair Skies- Doug King

All true except in special cases. My old boat with a 2 cycle 110HP outboard
got lousy mpg at idle. My new boat is better at idle but I haven't tested
it at idle speed. It's a 350 Chevy on a light planing hull ( will plane at
18mph). My "feeling" is that best speed is 22 mph properly trimmed. I
guess I'm getting something like 2.5 mpg. It is overpropped, will do 50+
at 80% throttle ( bought it this way). Down side is that a 2 foot chop is
hard on the kidneys. It's a simi -V- hull but is extremely light. It was
one of those Wellcraft "92" composite designs (no wood) with a couple of
layers of fiberglass on either side of foam. My brother has a plane
designed this way (Velocity design, it will do 190mph with 9G positive and
7G negative). The difference is a couple of more layers of glass in the
boats design.

The most comfotable ride is when you have 8 people in the boat (it's a 23
foot bowrider).