Another thing I do is load up the boat with spare fuel filters. I get a couple of 5-micron elements for the engine and at least half a dozen 30-micron elements for the Racor filter. You might run for years along the coast on the same filter, but once you get offshore and the seas start bouncing the boat around, any crud in the bottom of the fuel tank gets shaken up, and you’ll find yourself having to change filters until your tank is clean.
Along those lines, make sure your engine is happy being run for a long period. Test it by motoring continuously for several hours. Too often engines in sailboats are used simply to leave the mooring and charge the batteries. That’s a rotten thing to do to a diesel.
Your engine manual should tell you what rpm you should achieve running in forward gear. Get clear of other boats one day, and slowly mash the throttle all the way to the limit. Leave it there for five minutes or so. You won’t hurt your engine. Check the engine temperature to make sure it stays under about 180 degrees. If it doesn’t, it’s time to give your cooling system some love. If it revs above the maximum rpm rating, you might be able to add pitch to your propeller; if it comes up short, you might have too much pitch. (Obviously, I’m simplifying, so check with your mechanic before making changes.) Your cruising rpm is 75 to 80 percent of maximum rpm. Top up your diesel tanks and run for several hours at that speed, then fill the tank again to give you an idea of your fuel consumption; this will be an important number to keep in mind when you start thinking about fuel management on passage. Bear in mind that running at 60 percent of max rpm can greatly increase your range when you have to stretch your fuel in a prolonged calm. I always leave my main up for a little extra push and to damp any rolling—unless the sail is slatting hard, which can kill your sail in short order. Bear in mind also that it is not really that hard to make 3 or 4 knots just sailing in light airs.
information reproduced with permisssion from article by Andrew Burton a very experienced delivery skipper