We have a diesel
day tank on our current
yacht and it is an excellent addition. The day tank has a large sump with a pick up well above the bottom of the tank (this is only practical on a day tank). The fuel is filtered via a 2 micron filter before entering the day tank ensuring very clean fuel, but with no risk of starving the main engine
The day tank gravity feeds the engine
, so the engine will usually operate with a defective fuel pump, removing another failure point in the fuel system. The day tank can also be filled directly from a jerry can so in the event of severe fuel problems in the main tank enough fuel can be added to manoeuvre in port.
The fuel transfer into the day tank is generally done at anchor
when the tank is not agitated. This ensures only the cleanest possible fuel (even ignoring the fine filtration) with minimal water enters the tank.
We also have a fuel polishing system. In may ways this is the opposite of the day tank. It picks up fuel from the very bottom of the main tank, returning it back to same tank. This is generally on for several hours a day, but is run at times when the main tank is most agitated, ideally when sailing.
Day tanks are very common on trawler
fuel systems where the diesel
supply is obviously vital. No fuel = no propulsion
. Fuel systems for a sailing yacht are less mission critical, but a day tank is an easy and cheap
addition that often could be retrofitted. If you have the space and are contemplating a fuel system overhaul
it is an option worth considering.
All our filters are Racor 900 series. These have a large surface area and are easy to change. The Separ filter systems look very similar, but in the areas I have sailed the elements are less available. Given that many spares are ordered online, this is not a deal breaker, but if you do develop a case of diesel bug then multiple elements may be needed and local availability is a bonus.