5.7 Magnum 350 MPI 300HP Mercruisers mated to...Alpha One outdrives ?!?
 

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?


Thanks for all your help! :-D

Rich