I agree with Warren...90+ %.
Diesels generally have three problems: fuel
, and fuel
in the tank of your new boat may or may not be OK, depending on it's quality when purchased, additives used or not used, moisture levels, and what's come before (i.e., how dirty the tank has become over the years).
The safest approach is to dump the old fuel and CLEAN YOUR TANK. There are several ways to do this, either by direct access if there's an inspection plate easy to get to, or by using a professional filtering system which draws fuel from the bottom of the tank, filters it, and puts it back at pressure into the tank, with a wand used to clean the walls of the tank.
You really need to be neurotic, if not psychotic, about clean fuel if you want your diesel to perform reliably in all conditions. I can't tell you how many boats I've seen, know of personally, or have read about which have diesels that work just fine -- for years sometimes -- UNTIL they get into some rough water. The rough water shakes loose all the crap from the tank sides and bottom, it gets sucked into the filters, and....the engine stops!
So, to be on the safe side, do what you can to ensure that both the fuel and the tank are as clean as you can make them. And, of course, change the filters and the engine oil while you're at it!