"Wayne.B" wrote in message
...

On Sun, 29 Apr 2007 19:27:48 -0400, "Eisboch" wrote:

The difference is the speed at which you play. Consider the differences
in
a couple of boat examples:

Boat "A": 25' something with a 225 hp gas outboard or a 300 hp I/O setup.
Boat displaces about 5K-6K lbs. With a couple of people aboard plus
"stuff"
what is it's fuel burn at "cruise" which is probably 32-35 kts?

Boat "B": 50' something with twin, 370hp turbodiesels. Boat displaces
38k-40k lbs. With any legal number of people aboard plus all their
"stuff"
what is it's fuel burn rate at "cruise" which is 18-19 kts?

Betcha Boat "B" (which is over 7 times heavier) is burning fuel at a
comparable rate to boat "A".

If so, which boat is more efficient?

It's easy enough to balpark the numbers.

I happen to own a Boat "A", SeaRay 270 Sundeck, actually 26.5 ft, 5800
lbs dry, 320 hp I/O gas. It cruises 25 to 30 kts and burns 12 to 15
gph, averaging a little better than 2 nautical miles per gallon.

Boat "B" will typically burn 25 to 30 gph averaging about .7 nautical
miles per gallon.

So in theory Boat "A" is about 3 times as efficient ignoring weight.

Boat "B" however is 6 or 7 times heavier so on a per pound basis is
about twice as efficient as Boat "A".

It all depends what your boating objectives are.



I should have qualified the efficiency question in a better way. I was
looking at it from the weight point of view and in terms of how much fuel
was being used to move it.

Agreed with the objectives issue. My point was that bigger boats aren't
necessarily "less green" than smaller ones, depending on how both types are
used. I'll bet I use less fuel on a leisurely cruise over to Martha's
Vineyard on the Navigator than I would spending an afternoon pulling kids on
a tube or waterskiing on a boat like the Scout I recently sold.

Now, the GB is a different story altogether. I couldn't burn a quarter of a
tank in a day if I tried.

Eisboch