For O/B sailboats.
A 50-80 Amp alternator on a 9-15 hp OB.

Sailors often carry a Honda EU1000-2000 to provide juice at anchor.
Though not real loud, they can be an irritation to nearby boats,
especially big boats using big watercooled internal gensets that don't
make much outside noise. Some of those owners think the Honda's
should be outlawed at anchorages. Can't say I blame them for feeling
that way.
Biggest problem with the Honda EU1000-2000's is they are air-cooled
noisy and relatively low hp, maybe 5 hp or so.
They have to spin up pretty high under load.
Another issue is they exhaust to the air.

The OB manufacturers could come up with the suggested option, but
given the marketplace and engineering considerations, they are not.
A retrofit kit might sell and be a profitable venture.
The heavy alt on the OB could be regulated to limit alt drag while
underway, perhaps automatically/manually dialed adjustment, or perhaps
detached and stowed.
So in port or when otherwise needed you have a "quiet" water-cooled
9-15 hp genset in the same package as your propulsion motor.
A mounted kicker OB doing gen duty is another possibility.
There are obvious issues with cowling size, pulleys and electrical
connections.
Perhaps with salt water intrusion.
Maybe a heavier electrical plug to the boat system while in port.
OEM O/B warranty is gone of course.
Don't know. That's why I'm leaving it in your inventive hands.
Let me know what you think. Anybody. I'm sure I'm not the first to
think about this.

--Vic