I would dought it Asbestos is usually grey in colour or slightly green blue.
and to use it in a boat as a sealer it would be masticated.
Now masticated asbestos is a pretty good fire wall sealer around air cond ducts, but think that's about it not much use in a marine enviroment.
Any way spray over it with enamel spray paint if you think it's suspect and flaky, that will seal it of again.