BY ED CALDWELL
One Boater’s Experiment With Fuel Economy
An engineer takes on a personal challenge of testing
prop and sterndrive configurations until he
finds the most efficient combination
hen spending a lot of time on
a boat these days, you can’t
help but think about fuel
economy. Things have settled
down a bit from the $5-per-
gallon prices we saw a couple of years
ago, but still, with prices hovering around
$3.50 per gallon, a few hours at 10 gallons
an hour add up fast. So, last summer I took
the time to see what I could do to improve
my fuel economy without ponying up for a
new engine or a new boat.
I chose to stick to some simple things
I could control, such as props and weight.
We have all heard lots of talk about what
different props can do for you, and what
effect weight might have on performance.
Being an engineer, I thought it sounded
like a fun experiment that might actually
help my pocketbook and do some good
My boat, a 1996 Seawolf Marine
24-footer with an 8-foot, 6-inch beam, has
a pretty conventional hull shape. The bow
entry is sharp, and has about 18 degrees
of deadrise at the transom. As aluminum
boats go, it’s a Cadillac or, I should say,
more like a Humvee, with a 1/4-inch bottom, 3/16-inch sides, and self-bailing deck.
It’s pretty much indestructible. We do a
lot of salmon fishing, and use it to get out
to our cabin in the San Juan Islands. It’s
had a lot of tough use, both from nasty
weather and from hauling supplies and
building materials out to the cabin. It’s not
uncommon to be hauling a load of lumber,
the occasional wood stove, or a generator,
so fuel economy with a load is important.
Weight-wise, it’s 4,000 pounds dry
and 4,950 pounds as tested, which includ-
ed 100 gallons of fuel and about 400
pounds of miscellaneous gear. Considering
its length, that’s pretty light. By com-
parison, a 23-foot, 6-inch Trophy is about
4,700 pounds dry. A 5.0-liter Volvo Penta
290 DP engine and drive provides power.
The 5.0 liter is a 302 Ford with a con-
ventional two-barrel carburetor — noth-
ing fancy, but very reliable and easy to
work on. The DP stands for the infamous
Volvo Penta counter-rotating “Duoprop”
outdrive. Volvo Penta claims this improves
mileage to the order of 10 to 12 percent
over the single-prop (SP) version.