"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).