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What it is
Provisioning a boat means working out how much food and drinking water the crew needs for the whole trip, plus a safety margin, before you leave the dock. It sounds simple, but small daily amounts multiply fast: a crew of four on a seven-day passage needs nearly 100 litres of drinking water alone, and that weight and volume have to fit in tanks and lockers that are already full of gear.
Good provisioning is also about morale. Running short of water forces rationing, and running short of food turns a pleasant passage into a miserable one. Planning the totals first lets you shop once, stow sensibly, and know on day one whether the trip is feasible with the tankage you have.
How to use it
Enter the number of people on board, the days at sea, the drinking water each person needs per day, and the food each person needs per day in kilograms. Three litres of water and about 0.8 kilograms of food per person per day are reasonable starting points for moderate climates, but raise water in heat and raise food for a hard-working crew.
Press Calculate and you get drinking water, a 20 percent reserve, total water to carry, total food, and the number of meals to plan. Compare total water with your tank capacity and jerrycan space before you commit to the passage length.
Worked example
Four people sailing for seven days, at 3 litres of water and 0.8 kilograms of food each per day, need 84 litres of drinking water and 22.4 kilograms of food. Add the 20 percent reserve and total water rises to about 101 litres, and the crew must plan 84 meals. If the boat carries only 80 litres of tankage, the trip as planned does not fit: either add jerrycans, fit a watermaker, or shorten the leg.
That single check is the point of the tool. It turns a vague feeling that you have enough into a number you can compare with the boat.
How to read your result
Drinking water is the headline number, but the reserve is not optional padding: tanks leak, jerrycans spill, and passages run long. Food weight is a planning total, not a shopping list, so split it into breakfasts, lunches, dinners, and snacks, and remember that canned and fresh food weigh more than dried food for the same calories.
Meals to plan counts three meals per person per day. Snacks, tea, and coffee are extra, and so is the water used to cook and wash.
Common mistakes
The classic mistake is counting only drinking water and forgetting cooking, washing, and emergencies, which can add litres per day. Another is planning food by weight alone without checking calories, so the crew eats light but hungry. A third is ignoring that a passage may run two or three days longer than planned when the wind dies.
Limits
This is an estimator, not a diet plan. Real needs vary with heat, workload, age, and health, and it does not cover fuel, gas, medical supplies, or spare parts. It also assumes the water you carry stays drinkable: check tank cleanliness and carry a backup way to make or treat water on longer trips.
Questions people ask
How much water does a person really need at sea?
About 2 to 3 litres a day for drinking in mild conditions, more in heat or with hard work. Cooking and washing add more, so most cruisers plan 4 to 6 litres per person per day all-in.
Should I count the reserve as drinkable?
Yes, but treat it as untouchable until you need it. The moment you start using the reserve, start planning your next refill or a shorter leg.
Does canned food change the food weight?
Yes. Canned and fresh food carry water weight, so the same calories weigh more than dried food. If you provision mostly with cans, raise the food weight per person per day.
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