On boats, especially sailboats, think it's the disuse, not the use, that shortens engine life. Diesels are 10,000 hour or more motors but most don't get anywhere near that in a boat. Condensation
from lack of use, unmaintained cooling
systems, infrequent oil changes, etc. all shorten the life.
In your case, the number of hours is quite low but way more than I put on an engine on a yearly basis. If the engine starts easily from cold, doesn't smoke more than a normal diesel
and doesn't overheat after a long run at full or lesser throttle, it's probably good for at least that many more hours. As CaptForce said, get the maintenance
records on the engine. That may tell you more. An oil analysis is another way to pick up on any impending problems though a trend analysis from several samples over a period of time is probably better.