RE: 1982 Californian 34 LRC Fuel tanks: HOW BIG??
Actually, if you figure out the square area, which is about 20 square feet, and convert that to volume you should get about 150 gallons for a tank of those dimensions. 24x78x22. LxWxD then multiply by 7.47=gallons. If by 17 and 10 you mean knots, this could also be calculated but is a little more complicated. A quick way to test is to run the boat on full tanks for an hour at varing RPM's for an hour each and see. Run an hour at say 2000 RPM's and fill her up. The amount of fuel needed to fill it back up is the amount used. A flow meter is a great tool too. If in doubt, try to make waypoints that leave you at least 15% fuel left at the end of the run. Load, current, wind and many other variables will change your fuel consumption too. Every boat is a little different. Hopefully someone with a similiar boat will have a better estimate for you. Have a great trip and sail safe.
