T&T: Offshore with a single screw

[Nosy 34]

Big fuel tanks accumulate dirt and are not easy to clean. Here's one  
solution:

Our (1961) boat was built with a 120-liter "service tank" in the  
engine room. All diesel consumers draw from this tank. The line  
coming from the main (3,300 liter) tank in the bow pumps through a  
series of filters before entering the service tank. All fuel from the  
service tank then goes into a Racor 500, then into a manifold, then  
each engine has its own filter series.

As had been pointed out, if you polish the fuel and return it to the  
main tank, you're cleaning the fuel, not the tank. But if you store  
polished fuel in a service tank (which is smaller and easier to  
clean), you have better chances of keeping dirt out of your engine.

The drawback is, of course, that you have to constantly monitor the  
fuel in the service tank to make sure you don't run dry. In our case,  
the service tank contains enough fuel to run 10-11 hours (which  
covers most of our trips), but we refill it at the halfway mark  
nevertheless. A bonus is that the graduated sight gauge on the  
service tank makes it easy for us to monitor our fuel consumption by  
the hour. We clean the service tank once or twice a year, and haven't  
ever found much dirt.

One important point made by an engineer who surveyed our boat is that  
the service tank must NOT be located so high as to put too much of a  
pressure head on the fuel injection pumps. This can lead to leaking  
at weak points of the fuel circuit while the engine is shut down  
(it's a 48-year-old engine), which could be inconvenient or even  
disastrous.

Rafael