prodigal1 wrote:
Now that I have your attention, the question is related to outboards.
On my vintage sailboat, aux power is an outboard going out through a
well in the lazarette. Currently a steeenkin 2-stroke 15hp Johnson, I'd
like to replace it with one of those sweet Honda 9.9hp 4-strokes.
Currently the Johnson in place is a 15in shaft. Any comments positive
or negative with respect to putting in a 25in Honda?

For starters, HP rating methods have changed & if it's an older Johnson
that is less-than-new condition and rated at the flywheel, there will
not be a great difference in prop HP from the new 9.9 that is rated at
the prop.

How much have you sailed the boat in a seaway for observation, and how
much motoring might you have to do? Small sailboats equipped with
o/b's in a well or on a lowering bracket often don't place the prop low
enough for reliable motoring in swells, though some do. Depending upon
your personal attitude or need toward motoring, if it were mine I'd
have the longest shaft and live with the drag unless I knew her to keep
a shorter shaft's prop deep enough for the conditions I run into. I
also wouldn't think of swapping a 9.9 4-stroke for tender use because
it's just too damned heavy & risky to move back/forth under most
practical conditions. YMMV & I feel it primarily depends on how deeply
your particular well & stern design carries the motor, how she pitches,
and whether you may need it in unfavorable conditions, such as when you
cannot claw off a lee shore with the sails alone, or have to get the
hell home in upwind with bad things starting to happen. The strength
of the well mount may also be a side factor as a longer shaft exerts
more torque.

But torque is cheap. :-)

Frank