Live aboard to sail away part 10

Substantial water and fuel storage
“We never know the worth of water till the well runs dry.” [Thomas Fuller: Gnomologia]

Fresh potable water is a necessity on any boat that will be away from shore for more than a few minutes. How much water is needed depend upon the daily consumption and the time it will take to reach a location with a fresh water supply. Daily consumption of water varies by person and environment. Drinking, cooking, and cleaning are activities that demand water. In addition, hot climates and cold climates will impact the amount of water used per person. Most boats carry water in 2 or more tanks. Multiple tanks reduce the risk that all of the water will be contaminated or spilled out in different situations.

Fuel is similar to water in that the amount needed varies by the boat size and engine, the methods for generating electricity, refrigeration, and the type of sailing the crew conducts. At a minimum a large sail boat will need fuel to get the vessel in and out of harbor, generate electricity when needed, and allow the engine to be used to keep the vessel safe when conditions require engine power rather than sail power. Fuel like water, is usually stored in 2 or more tanks to reduce the risk of contamination or loss in different situations.

There are many different estimates for the amount of water each person will use on a sail boat. The dogs and I use about 3.5 gallons of water a day in the winter and about 4 gallons a day in the summer and we are not trying to conserve water. Most estimates I've seen state a minimum of 2 gallons per person, and with extreme conservation 1 gallon per person. The next calculation is the time it will take to reach a fresh water supply. Since we are planning to sail all around the world, crossing an ocean is in our future. If we propose that the longest trip will be 2000 nautical miles (nm) and we can make 100 nm a day, then we need a water supply that will last 20 days. Then you have to add and time for days without wind and weather delays, in our case, we will add 5 days to the total for good measure.

It may be possible, depending on the sailing location and weather, to collect rain water to resupply the tanks, but that cannot be relied upon until the rain is in the tanks. Reverse Osmosis (RO) systems can be used produce fresh water from ocean water. Many of these systems will generate several gallons of water an hour at a cost of battery power off the house battery supply. Hand operated RO system can also be used to purify ocean water, but these systems generate a small amount of water for the human effort needed to operate them. As a result, hand operated RO systems are usually only found in life raft survival kits.

In total, the dogs and I will use 82 or more gallons of water on the 2000 nm trip described above. If we add a crew member, that would add 50 more gallons to the projected water consumption. When shopping for a boat, I was looking for a vessel that stored 100 gallons or more of water in 2 or more tanks. The boat I chose has 180 gallons of water stored in 4 separate tanks and this should be more than sufficient for most trips we will make. As an added bonus (or curse) the boat I chose also has a RO water maker that will produce about 14 gallons of water an hour.

The fuel capacity calculation is more complex. Most sailboats use the engine to recharge batteries or refreeze the cold plates in the refrigerator. In these cases, the engine will be run for a couple of hours each day. Alternative source of energy, like solar, wind, or water, can reduce or eliminate the need to run the engine to charge batteries and boats with electric refrigeration can eliminate the engine compressor for refrigeration. Larger sailboats may have an auxiliary generator that is used to charge batteries and power larger AC loads such as air conditioners. Auxiliary generators are typically smaller than the main boat engine and are not used to drive refrigeration compressors. If an auxiliary generator is used on your boat, calculate the fuel requirements for this separately since the fuel consumption per hour will lower than the main engine and loads driven by the generator will vary from boat to boat.

The next auxiliary use of the engine is heating water. Many sailboat have a radiator loop that runs from the engine to the domestic hot water tank and the engine heat is dissipated into this tank as well as being exchanged with sea water and blown out the exhaust pipe. I do not know of anyone that runs their engine for the sole purpose of generating hot water; however, it is a possibility. Most boats use the engine to recharge the batteries or refrigeration and in the process get hot water as an added bonus. Some boat have hydroponic heating systems that provide domestic hot water as needed. If this type of system is used on your boat, calculate the fuel requirements for heating separately as these systems vary widely in the fuel consumption, functionality, and complexity. When hot water is needed and not available from the tank, most boat will use a simple form of solar hot water heater such as a solar hot water bag. As a result, I would not count on using the engine for the sole purpose of heating water.

Beyond battery charging, refrigeration, and hot water, the only other use of the engine is to move the boat through the water. I would say that this is the primary use of the engine, however, I've been in situations where the engine was run often to charge up system than propel the boat. The engine will be used to maneuver a large boat in close quarters when docking, anchoring, or traveling in narrow channels. The engine may also be used when the vessel is becalmed and when forward progress is necessary for safety but sailing is impractical, e.g., in a storm. The sail plan of a boat and weather conditions will directly impact the how often the engine is used to propel a sailboat.

I assume that 20 gallons of fuel will be needed for safety purposes. This would be sufficient to power the boat for approximately one day. In addition, I calculate that one half gallon of fuel will be used for each anchorage and 1 gallon will be used for each port entry and exit. This may seem like a large allotment of fuel for situations where the motor may be needed for five minutes; however, if the engine is started, it should be run until it reaches normal operating temperature (I usually run my engine for 20 minutes). This helps prolong the life the engine by evaporating condensation that may have settled into the engine oil. So the base amount of fuel needed to make a trip would be near 30 gallons just for propulsion.

Next, the route of a trip may place additional demands on fuel for propulsion. For example, if your route is against the wind and current and you will have to either add time to the trip to account for tacking to an alternative route or fuel to the tanks to feed the engine as you motor headlong into the wind. A typical example of this would be traveling up the Baja coast where the winds are on the nose and the current is on the nose. If the engine will be used to propel the boat in this situation then you must calculate the boat speed, trip distance, and engine run time to estimate the amount of fuel you will need. You may be surprised at the amount of fuel it will take to power a sailboat for 600 miles at 6 kts of speed. A hundred hours of run time under load for most engines will require more than 100 gallons of fuel.

The more predictable demand for fuel will be the auxiliary uses of the engine to provide power, refrigeration and hot water. If the boat system require engine time for these purposes, you can count on either two hours each day to recharge batteries (actual time will depend upon the alternators on the engine, solar, wind, and the size of the house battery bank) or 1 hour for refrigeration. The engine will be run at half speed (about 1400 RPMs) for this purpose. A 25 day trip will use 25 to 50 hours of engine time for this purpose and that will require an additional 30 or 40 gallons of fuel capacity. Solar and wind can reduce this demand provide you have the space for these devices.

I decided that 100 gallons of fuel capacity was the minimum I would need without knowing the specifics of the boat systems. This would account for the 30 or 40 gallons of auxiliary usage, 30 gallons of emergency reserve and another 30 gallons for propulsion. The boat I chose has 170 gallon of fuel capacity in two tanks. I will elaborate the specific fuel consuming systems on my boat later.