The water tanks on my 1990 caliber 38 share a common deck
fill. They are plumbed to a manifold that let's the user decide which tank to draw from. Removing one tank from that system wouldn't be hard.
The tank top schedule of holes for the fuel tank differs from a water tank. Guess you would have to drill or plug
as need. I believe the newer LRC's fuel tanks are plumbed in a fashion that allows user choice or pump over from one to the other as in a fuel polishing system.
All of that said, why would you do this? Didn't you buy this boat to go sailing?
1) My boat, with a Yanmar
4JHBE, shows SOG of 5.5 - 6 knots at 2000 rpm
. She consumes about .4 gals per hour at that speed. Meaning I can run the engine
for 112 hours, or 610 nm.
2) Unless you are going to own this boat forever after, don't do this. I should think that to do so would seriously adversely affect the resale value of the boat.