|
|
|
|
n 7 Mar 2005 09:58:10 -0800, wrote:
Hi fellow boaters,
I'm a NEWBIE to this group, so thanks for your patience in case I don't
quite fit in yet.
Most of you are lucky not to have my problem: fuel economy - gas
where I'm boating costs $6/gallon.
So you'll understand why I'm seriously considering swapping 2
carburated engines for thrifty 300hp I/O Mercruiser Magnums. However,
their cost is high enough (x 2 engines) that I am thinking of trying to
keep the stock Alpha One outdrives hoping they won't die.
I know that the Alpha One outdrives are not nearly as solid as Bravo I
drives. Their horsepower rating is maxed at 300hp so it is cutting it
close. Would there be a way of changing their gearing and propeller
size to make sure that I get both maximum fuel economy as well as keep
the outdrives from busting from overstress?
FYI the boat has a 31 foot semi-planning hull weighing 10,000lbs with
cruising speed of 20-25 knots and max speed of 30-35 knots. I was
hoping that with 600 total horsepower on tap, that I could run the
engines at low rpms sparing the outdrives and saving on fuel, while
maintaining a 25 knot cruise speed (boat rated at 20 knot cruise/30
knot max when powered by twin 200hp engines). Let me know if I'm just
dreaming and about to make a very expensive mistake. Hopefully it isn't
necessary to replace the outdrives with used Bravo Ones, just messing
about with gearing and propellers?
Depending on what RPM range you are running, you will not see a great
deal of an improvement in fuel economy between a carbureted engine and
a fuel injected one. Even if you were to gain a whopping 1 MPG more,
at the cost of at least $7K apiece for the new engines, you would have
to put a great deal of hours on them before you break even. $14K will
buy a lot of gasoline IMHO.
YMMV
Dave
|