but I have never heard of anyone simply replacing an inboard with a
normal engine such as from a
go-kart or Volkswagon

Ringmaster wrote:
Why that complicated? I'd like to know why manufactures haven't
switched to installing B&S or Kohler lawn tractor engines in boats.

Probably because they can't get marine safety approval.

Just think when it blows up it could be replaced for $400-$600 instead
of the $6,000 that Yanmar wants.

And it could blow up your whole boat with it.


It would be possible to stick a lawn mower engine in a boat,
but it would have to be in a vapor tight enclosure which
would make it a PITA. Efficiency would be terrible.

A 2cyl lawn tractor engine has as
much HP as a Yanmar. What's the problem?


Torque & RPM mismatch. A propellor in the water wants to
turn slow with lots of grunt. Jetskis sole this problem by
convertin hi RPMs and low torque into a pressurized column
of water, which is released as velocity.... energy into the
water equals boat moving forward. Works well for a
lightweight high speed craft.

Two big problems for marine installations are fuel vapor,
which is what blows up so many gas powered inboard boats,
and cooling. Scandinavian boats have (or used to have) air
cooling and it worked great two ways, nice warm cabin and
efficient engine cooling. But in a warmer climate, the cabin
will become a sweatbox and the engine will run too hot.

If you had a small cheap engine that could be water cooled
and had fuel injection, I'd say that would be a good
candidate for dropping into a boat. Be prepared for a LOT of
work though; and do youor homework! Unless you've got the
right prop & tranny combination, the end result will not
propel the boat well enough to feel worth the labor.

DSK