Scout wrote:

It is a fuel tank, baring any esoteric definitions. He might be a seasoned
sailor, or he might be an hvac technician, who would also call "certain"
fuel filled tanks, daytanks. In the mechanical trades, they're part of an
elaborate fuel delivery system that offers a few benefits over the
conventional main tank to fuel pump relationship.

Yep. But certain folks really like elaborate & complex & difficult-to-operate
systems. And the benefits are real enough *if* you are the type who will not
take good care of the fuel unless forced to.

Disadvantages: more expensive, more bulky, greater likelihood of spillage,
more valves & lines to maintain.

Advantages: offers a check on fuel quality (note: the same checks can be done
with a regular fuel system also), allows easy priming, allows the engine to
keep running if lift pump fails.

IMHO a day tank does not make sense on a small cruising boat. Big ships draw
fuel from "service" or "ready" tanks that are the same concept, but the fuel
is measured in tons rather than gallons and all the storage tanks are certain
to have a lot of seawater sloshing around in the bottoms, so stripping it in
transfer to ready tank makes sense.

Fresh Breezes- Doug King