Our Brewer 44 Andiamo carries 130 gallons of fuel, which at 1.25 gallons per hour should give us around four days of running time or a range of around 700 miles. Unfortunately, the last thing we want to do is run a tank dry at sea, or worse, while coming into a harbor, so we rarely drain a tank lower than one quarter, thus reducing our range to 500 nautical miles. However, I recently discovered a solution that solves this and other fuel issues — I installed a day tank.
A day tank is a smaller tank installed somewhere above the engine. Fuel is pumped through a filtering system into the day tank and then the engine draws fuel from the day tank through its secondary filter. Our day tank holds 12 gallons of fuel and I’ve installed a fuel gauge and fuel pump switch on the binnacle. At the beginning of each watch the helmsman simply tops off the tank, which takes approximately five minutes, and they’re good to go.
The day tank allows us to completely drain the main tanks without fear of sucking air into our engine with the subsequent hassle of bleeding the engine and it gives us an additional eight hours of running time. In addition, since the fuel is filtered through the primary filter before going into the day tank there is no danger of the engine stalling due to a clogged fuel filter. If the fuel in either of the main tanks is dirty and clogs the primary filter, you’ll know it while you’re refilling the day tank at the beginning of the watch and have plenty of time to change the filter. Since we only drain the day tank to half this gives you approximately four hours to change the filter and this can be done while the engine is running.
This means there is no advantage to installing a fuel polishing system, since the fuel in the day tank is already polished. And since you will be typically draining the main tanks to empty, you’ll know if there is any contamination. Another advantage is that since fuel is gravity fed from the tank to your lift pump (I made the mistake of thinking you could bypass the lift pump but gravity does not provide enough pressure to push fuel through the secondary fuel filter) if you develop a leak in your fuel line between the day tank and the engine it will be easy to find since its much easier to find a leak with positive pressure than negative.
I installed the day tank in West Palm Beach a couple of weeks ago and used it to cross the Gulf Stream and cruising in the Bahamas and couldn’t be happier with it.
Day tanks were apparently common in days of yore, but are rarely seen in new boats. Maybe its time for a comeback. I’ve included photos and a schematic.