The outboard needs cooling water as well as a load on the prop. A OB owner
or mechanic can't properly test or adjust an outboard without running it in
water.

Those clamp on muffs will provide cooling water but leave a hell of a mess
around the test stand. The smaller or dingy outboards don't receive the
muffs very well..

It is also strongly recommended after operation in salt water to flush the
system and stop corrosion.

I keep a plastic barrel at home to run my dingy outboard between uses.

Steve
s/v Good Intentions