FAQ: How much fuel do you use?

Depends on our usage.  The boat carries 200 gallons of diesel.  Between what was in the tanks when I bought her a year ago and what I’ve put in, I think I’ve burned about 100 gallons to date.  In theory, each 29HP propulsion engine burns .75 gal/hr and the 12KW generator about 1.25 gal/hr.  

If we’re taking daysails or overnights from the dock, the generator doesn’t see much use since the batteries will hold us for a couple days  and we’ll recharge when we get back on shore power.  Sailing is generally faster and more enjoyable than motoring, so unless the wind is against us and/or we’re in a tight channel we try to sail whenever we can.  

If we’re on a trip the generator is the primary user since we would get to a place and then stay anchored there for awhile.  On most boats, generator usage is determined solely by power replacement needs but we’re a little different because our oven/stovetop are electric instead of the usual propane.  We have big inverters to provide AC power from the batteries, but heavy loads aren’t practical on battery power.  We try to use the more battery-friendly toaster oven, electric skillet, and electric kettle whenever we can.  If only for charging batteries we could get away with running the generator an hour every other day, but for heavy-duty cooking it runs more irregularly.  Thanksgiving required a 4-hour run.  

After the batteries are charged to 80% capacity their acceptance rate drops, thus the load on the generator drops, and it becomes very inefficient.  It runs a constant 1800RPM to produce power at 60Hz.  If we have to run it for cooking, this is a good time to use the extra capacity for something else like vacuuming the boat or running the air conditioners.  We have a dishwasher but don’t use it.  Instead we’ll be replacing that with a clothes washer/dryer that would be another good free power user.  We would probably be better off with two smaller generators sized to individual appliances instead of the one big one.  Someday we’ll get solar panels that should reduce our need for bulk charging.

I had previously estimated that we could live for a year in conservation-mode on 200 gallons in our current configuration.  That may not be accurate because based on my understanding of our usage I really can’t account for the 100g of usage cited above.  We have propulsion problems and it may be that those engines are wasting fuel.