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Landfall-Learning > Mathematics > Provisioning


Provisioning describes the water, food and fuel needs of a vessel and crew at sea. While Landfall could say at sea indefinitely, her crew and passage-making are limited by the amount of supplies we can carry. "Provisions" are the water, food and fuel that we need to carry with us. To purchase provisions with the currency required in other countries, we need to perform currency conversions, to figure out what an item costs in US dollars. After reading the information, try your hand at the exercises!


Our first concern is always to have an adequate supply of fresh water. Landfall's freshwater tank holds 50 gallons. There is a fitting on the deck that allows us to fill the tank with a hose from a spigot on the dock. When we are away from the dock, the only sources of freshwater are the water we leave the dock with, the rainwater that falls onto the boat, and the water that we make from seawater. While sailing in the middle of the ocean, you might think that water is the last of our concerns, but because salt water is not drinkable, this can be a real problem.

To fill our water tank when we are at sea, there are two fittings on the deck that allow us to funnel rainwater into the tank. In the tropical rainy season we can depend on catching rainwater fairly regularly. In the dry season (about 4-5 months each year), rainwater is simply not available. Some countries that we will visit do not have clean drinking water, and some islands we will visit do not have any water sources at all. So where can we get our fresh water? To solve the important issue of having adequate supplies of fresh water, we have installed a "watermaker".

The watermaker is a machine that takes in salt water from the ocean, removes the salt, and leaves us with pure, fresh water that is then pumped into our water tank. The salt and impurities are removed by means of a process called "reverse osmosis". In the reverse osmosis process, salt water is mechanically forced through a special membrane, or filter, which is porous enough to allow pure fresh water to pass through (although very slowly), but the salt and dirt molecules are too large to pass through. The salt and impurities are trapped on the membrane and must be periodically cleaned off. Because of the hot weather in the tropics, each member of the crew must drink two to four gallons of fresh water each day or we will become dehydrated and get sick. Additionally, we need fresh water for cooking, bathing and rinsing dishes. With a watermaker, we can go farther and stay away from land longer in the dry season without constantly worrying about our water supply, and we also don't have to worry about the purity of the water that goes into our tank.


As we travel, we often may be weeks away from a grocery store. Landfall's refrigerator is very small, and the freezer is tiny. So, most of the food we carry onboard must have a long shelf life and need no refrigeration. Dried and canned foods make up the bulk of our "ship's stores," or onboard food supply. Rice and dried beans are tasty and will last a very long time without spoiling. On the down side, these staples require lots of water to clean and prepare. Also, they take a relatively long time to cook, and so use a lot of the propane which fuels our stove and oven.

We have also learned some tricks to keep fresh foods longer without spoiling. By rotating unrefrigerated eggs once a day, for instance, they will keep much longer. We also keep long-life milk that requires no refrigeration until opened. Other staples like canned cheese and canned butter, as well as whole canned chickens, help make tasty meals without needing to be refrigerated.

Sometimes the seas are simply too rough to cook a regular meal. In rough seas, the pans will fly off of the stovetop!This could be very dangerous. So we also carry prepackaged meals that can be purchased at camping stores and military surplus outlets. While these prepackaged meals might not look as inviting as a home cooked dinner, after a couple of days without being able to cook, they really hit the spot.

Fresh fruits and vegetables are replenished whenever we can find them. Fortunately, these items are usually available in most places we plan to visit. Often, however, the native fruits and vegetables are foreign to us, and we have to ask for preparation and cooking instructions as we buy them. While this can be confusing at times, it does give us the opportunity to try new local specialties.

Lastly, we do take advantage of the bounty of the ocean. Where the water is clean, fishing and diving for lobster and shellfish provide us with tasty meals.


While it might seem that fuel would be a minor concern on a sailboat, we actually need to carry four different types of fuel on board:

  • diesel for the boat's engine
  • propane for the stove
  • gasoline for the dinghy boat's outboard engine
  • lamp oil (purified kerosene) for the lamps

Landfall has two separate diesel fuel tanks, each holding 75 gallons. These tanks are located one on each side of the boat, to stay balanced. While we would always prefer to sail rather than use the engine, when we find ourselves in tight quarters, like a marina, the boat is much easier to handle under power rather than sail. Also, it is very hard to back the boat up without use of the engine. Also, there are times when there is no wind, or we would like to go directly into the direction of the wind. Lastly, sometimes we need to run the engine to charge the batteries.

Our stove and oven use propane, or liquefied petroleum gas (LPG). Propane burns cleanly, is relatively inexpensive, and is readily available almost anywhere in the world. The drawback to propane is that it is heavier than air, so the tank must be stored in a place that will allow it to drain outside the boat in case of a leak.

The dinghy's outboard engine is a 9.9 horsepower gasoline engine. While we can row the dinghy or even attach a special sail rig to propel it, there is nothing like an outboard engine when you just need speed. Gasoline is highly flammable and very volatile, so we must take special care in how we store and transport the gasoline.

Lastly, we have two alcohol lamps that we use when we don't want to turn on an electric light. Not only are these lamps a good backup in the event of an electrical failure, but they are just plain old pretty to use. Their soft glow provides a very nice light for a quiet dinner at a remote anchorage, or to tell sea stories by.

Currency Conversions

Each country we visit has its own form of currency. While traveling in these places, we need to convert US dollars into the local currency before we can go shopping for provisions, eat in a restaurant or ride in a taxi. In the Caribbean, where we are starting out, many places will readily accept US currency, but others will not.

When we are shopping, prices for the items we want to purchase are marked in the local currency. We need to understand the conversion rate so that we can relate the "US dollar" cost of items. For instance, in the British Virgin Islands, the currency is the British pound. So, if we were to buy a loaf of bread marked at 3 pounds, unless we understood how much that was in terms of dollars, we wouldn't know whether we thought that was a fair price or not. However, if we know that the exchange rate is $1.80 per pound, we can calculate that 3 pounds is equal to $5.40. At that price, we would probably not buy bread at that store!

To convert pounds to dollars, we simply multiply the number of pounds times the exchange rate. If we want to reverse the equation, we divide 1 by the exchange rate. Therefore, one dollar would be worth .5556 pounds. However, to add to our confusion, the exchange rates do not stay the same from day to day. But we can find the current exchange rate for any currency at the following web site ( When we do not have Internet access, we can find out the exchange rate at a local bank.


  1. If we use 20 gallons of fresh water a day, how many days can we go without refilling the tank?
    (Answer: 2.5 days)
  2. If it is the rainy season, and we catch an average of 10 gallons of rainwater each day, how long can we go before the tank runs dry?
    (Answer: 5 days)
  3. If we bring along 5 pounds of rice, and each cup of rice requires 1.5 cups of water to cook, how much of our water supply will we use cooking rice? Assume that each cup of rice weighs 4 ounces (dry measure) and that there are 8 ounces of water in 1 cup (liquid measure).
    (Answer: One pound of rice equals 16 ounces, so there are 4 cups of rice in each pound. Five pounds of rice equals 20 cups of rice. 20 cups of rice times 1.5 cups of water equals 30 cups. 30 x 8 = 240 ounces of water, or 1.875 gallons.
  4. If the engine burns gallon of fuel each hour, how many hours can we run the engine before we run out of fuel?
    (Answer: 200 hours)
  5. If the boat travels at 6 miles an hour while running the engine, how far can we go without putting the sails up before we run out of diesel fuel?
    (Answer: 1,200 miles)
  6. If we want to go 120 miles under engine power without raising the sails, how much fuel do we need?
    (Answer: 15 gallons, 120 miles/6 miles per hour = 20 hours X .75 gallons per hour).
  7. If the exchange rate for Euros (EUR) is $1.19 and the price of a loaf of bread is 1.50 euros, what is the price equal to in US dollars?
    (Answer: $1.79 = 1.5 (euros)*1.19 (exchange rate))
  8. If we arrive at an island and convert $100 into euros to go shopping, given the exchange rates above, how many euros will we receive?
    (Answer: 84.03 euros = $1/1.19*$100)
  9. When we are ready to leave the island, if we have 15 euros left over, how many US dollars will we receive when we convert the euros back?
    (Answer: $12.60 = 15 euros*.8403)
  10. For extra credit, go to the currency exchange Website ( and work these same problems with two different currencies.