DayTank » Page 2 of 5

maintaining a really clean system. The Lehman engines, however, return only a very small amount of fuel to the tanks. I don’t know the exact amount, but recall hearing something like less than a quart an hour. Thus, there is little hope of cleaning out the dregs of the fuel tanks even if they are run to empty. Imagine what that means for older boats like Francesca.

All this uncertainty and unreliability was too much to live with and I set about to design a system that cleaned up these issues; a tall order indeed. The primary player in the fix was the inclusion of a day tank mounted on the aft deck such that it would gravity feed a secondary fuel filter and the engines. Gravity fed, there would be no potential for air leaks. Additionally, an engine fuel pump failure would be inconsequential and probably even unnoticed. The mechanical fuel pumps can even be removed and the engine ports blanked off.

The next change was to plumb the two Racor filters such that the primary (10?) filter cleaned the fuel ahead of the day tank and the secondary (2?) filter ahead of the engines. The two engine mounted filters were then removed and gleefully buried-, deep. Removal of these filters also improves the engine room crawl way clearances. The overall system was plumbed such that there is no need to purge air when changing either of the fuel filters. The secondary Racor was plumbed with a vacuum gauge to warn of loading. Note that care must be taken to route the fuel line from the secondary Racor below the filter housing and without loopy air traps. This precaution is necessary to avoid the need to purge the line after a filter change.

An electric fuel pump pulls fuel through the primary filter and pumps it to the day tank continuously. The pump is activated when the engine control power is turned on. The day tank is maintained full and excess fuel is returned to the tanks. Thus, the fuel is continuously circulated through the primary filter and back to the tanks. The rate of circulation for our system is about 15 gallons per hour (with 3 gallons per hour to the engines). With a second switch, just to activate the fuel pump, the system can be operated as a fuel polisher. This feature can be especially useful for vessels that spend a lot of time at the dock. A float switch is mounted at a high level in the day tank to provide indications that the primary fuel filter is loading up and not providing sufficient fuel flow to maintain the tank full. Even when this occurs, the 12-gallon day tank provides at least four hours (more like 10 or more hours because filters don’t suddenly stop up altogether) of engine runtime without changing the primary filter. This feature is wonderfully useful because you have many options of when and where to change the primary filter.

Yikes-, I hear the nay-sayers already (wailing-gnashing of teeth-pulling hair). Well, I wouldn’t recommend this system if it had not been proven completely. Three years and 8000 nm of cruising, including a Caribbean circumnavigation, almost any sea condition one can imagine