Fuel Usage

A good long trip is a great time to evaluate fuel consumption and capacities.

With 200 gallons of diesel aboard, there is a tendency to think it will last forever.  Of course it doesn’t, as we’ve already proven.  We also now know that actually putting 200 gallons into the tanks is not such a good idea, and have revised our capacity down slightly.  

With the rough graduations we put on the fuel gauges during our last fill we’re now at least able to monitor the decline with some confidence.  And with the empirically determined generator burn rate (0.4 gal/hr), and the new engine hour meters, we can extrapolate our propulsion burn rate (0.6 gal/hr).  This is useful for various planning exercises.  For example, we can now estimate with some confidence that with a full load of fuel we could either motor 1,600 nm on one engine OR run the generator daily for 320 days.

Propane is our second most important fuel since we use it for cooking.  We were very uncertain when considering a switch to propane because we didn’t know how much we’d use.  With all the cooking, bread baking, and tea & coffee drinking we do, the concern was that we couldn’t reasonably carry enough propane and would be constantly in search of more.  Those concerns were unnecessary as it turns out.  Our 10-month average shows that we get 30 days out of a 20# bottle.  We carry three bottles dedicated for the galley, so we have about 3 months of fuel there.  Our last bottle is projected to run out in 10 days (yes, I have a spreadsheet for that), but we have another 30 pounds for the grill.  The grill has seen very little use on this trip due to lack of fish and cows.

It is very nice not to have to worry about getting propane.  It isn’t available everywhere in the world, and in some cases the bottles have to be sent off to be filled.  George Town is supplied by a truck that comes once a week and queries about when/where are almost a daily occurrence on the morning radio net.  Apparently the truck broke down this week which is causing some anxiety in the harbor.  I’d like to add a fourth bottle for the galley and build a rack to store them more securely and efficiently.

We also carry a fair amount of gasoline.  Our dinghy motors, little Honda generator, and hookah dive compressor all have gas engines.  Gas is harder to store (and more dangerous), so we try to strike a balance between having enough without having too much.  We have four 5 gallon jugs and try to have at least two full at any time.  The dinghy has a 12-gallon tank and we feed it 5 gallons at a time to make it easy to mix in the oil.  

We don’t really have a good way to store gas, but I’m not sure that there is a good way.  I prefer to store the full jugs on the deck to prevent the possibility of fumes inside the boat, but then they are subject to temperature and pressure variations which can’t be good for them.  A hot fuel tank can build an enormous amount of pressure.  Maybe some type of cover would help.  I suppose I could also vent the tanks, but then I’d be concerned about the fuel absorbing moisture.

I count the dive tanks among the fuels.  We have two and they live on deck also, although probably shouldn’t for the same temperature/pressure concerns.  I didn’t put them in a locker thinking they might be a safety risk there too.  We carry the tanks in addition to the hookah simply because we have them.  I can throw a hose on a tank and be in the water in minutes, while the hookah requires more setup and cleanup.  Tanks are also much quieter than the hookah.  But tanks have a very finite capacity, which makes the hookah way more practical overall.  I suspect we’ll continue carrying the tanks (because we have them and do find them useful), but need to evaluate how they’re stored.