use any "rule of thumb" you can find, BUT theoretical hp per gallon fuel burned
per hour is about:

water cooled 4 cycle diesel, 24 hp
water cooled 4 cycle gas, 20 hp
aircooled 4 cycle, or water cooled 2 cycle gas, 16 hp
aircooled 2 cycle gas, 12 hp

that's the theory, the practise is about 2/3rd that.

close enough for gummit werk. all assuming engines in decent working
condition, worn-out junkers not included.



Using the "rule of thumb" of 0.055 gallons/hp/hour, that works out to 7.2 HP.

To maintain 5 knots, a 40 footer is going at a SL ratio of 0.83, which means
about 2200 pounds per HP. If the boat displaces 18,000 pounds, that's a
little
over 8 hp.

However, if the boat is motorsailing, the fuel consumption will go down
considerably.

To double check, a Yanmar 4JH4, nominally rated at 54 HP, will deliver 8 HP
at
1750 RPM. using 0.5 gal/hour. The smaller 3YM30 would run at 2300 rpm and
be
more efficient, using .45 gal/hour.



"JAXAshby" wrote in message
...
0.4 gallons of diesel fuel used per hours equals of about 6.4 hp. but
who's
counting.

(TAWill s/v Lucky Strike)
Date: 9/7/2004 11:16 PM Eastern Daylight Time
Message-id:

Jere Lull answers this question quite well from a cruising sailor's
viewpoint. My experience in offshore cruising sailboats 37 to 42 feet
in length yields fuel consumption of about 0.4 gallons per hour at
cruise. This comes from consistent engine use when our speed under
sail drops below 3.5 or 4 knots - firing up the engine is always the
call of the man on watch - our goal is to make good about 135 NM or
more each 24 hour period underway. I have a hard and fast rule to not
leave on a voyage unless we have 200 hours of fuel onboard, or, as is
the case with the boats I normally take offshore, about 80 gallons of
fuel. This pencils out to about 900 to 1000 NM under power, with some
leeway for daily battery and frig plate charges while under sail
alone. This fuel quantity has worked quite well while on voyages of
30 days nominal length, yet we've come in on fumes once or twice,
having to wait for wind during the last week out to make it into port
with enough fuel remaining to negotiate the harbor and docks.

T A Will