How long is a piece of string? There's no real answer to this.
I have 680 liters. I spend about 90 days on board a year and 50 - 55 days at sea. I heat (in a cold climate; heating
can be needed any month of the year) and generate electricity with diesel
fuel. I don't have shore power
on my mooring
so use my diesel generator
several hours a day when I'm on board.
I have a 100hp Yanmar
which uses anything from 6 liters an hour on up, depending on the speed. However, I am in a windy place, so don't motor very much.
Despite all this on-board demand for diesel fuel, a full tank lasts me almost a year. I last filled up in July, 2012 and still have half a tank left. It is true that this particular year my boat was on the hard
with shore power
for several months undergoing a refit
. But even with shore power, I was heating
So is my tank too big? I think it's not good to turnover the fuel this slowly. I guess I could fill it only partially -- apparently all the business about condensation
in partially filled tanks is a myth.
But if I were doing tankage from scratch, and had enough space for it, here is what I would do:
1. First of all, a gravity feed DAY TANK. This is the dog's danglies for a cruising yacht, a firm guarantee against fuel problems underway. A good sight tube on it so you can see exactly what you're putting into it, or better yet, it should be altogether transparent. As the name implies, this should hold enough for a typical day's consumption
2. Working fuel tank
, about 300 liters. With sump and dip tube; fittings for ultrasonic level gauge and polishing system. This would be used for normal operation in areas where fuel is readily available. Polish the fuel regularly, and dip the sump to be sure everything is clean before filling the day tank.
tank, about 500 liters. For a transat or extended cruise with questionable availability of fuel. Normally kept empty. Sump, dip tube, etc. like the main tank. Feeds the day tank directly, not the main tank (so you can switch in case one tank gets contaminated).
All made out of quality polyethylene, like what TekTanks make.
YMMV, of course, and should be adjusted for the way you cruise and your own levels of consumption.