Hi Chris,
Your point about the 4-strokes developing power (or torque) at lower
rpm's
than 2-strokes is correct, but I'm not sure that leaves the gear ratio's
out
of the picture entirely. First of all, why would Yamaha and Mercury go
to higher
gear ratio's on their 'high thrust' engines, if it would be simpler to
just change
the propellor pitch to achieve the same result? Secondly, I would be a
little
nervous about experimenting with a propellor's pitch to match it
optimally to
the engine. The bottom line is will a 4-stroke engine with a low gear
ratio
and a compensating pitch propellor run as well as a 4-stroke with a
higher
gear ratio engine with it's appropriate propellor (I don't think so).
Actually,
both the higher gear ratio and the propellor can each contribute to the
higher
thrust. However, given a choice, I would go with the higher gear ratio
which
would allow me to get even more thrust by decreasing the propellor
pitch. With
the lower gear ratio engines, I can only lower the pitch of the
propellor which
has obvious limits as to how much this can be done.

Sherwin Dubren

Chris Edmonson wrote:

All good points being made here. If the wieght maximum you have in mind is
clear to you then go with a smaller four stroke. I have found it difficult
to move much more than fifty or sixty pounds of bulky motor around so would
tend to go with a smaller motor than a lot of folks might choose. The other
thing is that the four strokes make power at a lower RPM so may be best on
fuel economy over the long run. The gear ratio is perhaps not as large an
issue as it was when almost all of the motors were two strokes that needed
the higher RPM's to get you going. The propeller's pitch can give you some
of the pushing power that the old gear ratio change would give. If you
don't have enough umph move down a couple of inches in pitch and gain power
earlier in the curve. The four strokes definitely handle this change very
well.

Best;
Chris

"Bruce" wrote in message
...
I need to buy an outboard for my San Juan 21 and not quite sure about how
big to go. I would like a 4 stroke and I am thinking that about 5 HP
would
be a good size. Any comments about the different brands would be
appreciated.
Also, do I really need a "long shaft" motor. With the motor mount
currently
on the boat, it seems to me that any motor would easily bury the prop.

Regards,
Bruce