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What it is
The sailing comfort ratio, from yacht designer Ted Brewer, is a single number that sums up how gently a boat moves in waves. It compares the boat’s weight with its length and beam, because a heavy boat with a long waterline and a narrow hull tends to ride waves with a slow, easy motion, while a light, wide boat reacts faster and feels livelier. The number is not a safety rating and it says nothing about build quality, stability, or how well the boat is sailed.
Comfort matters most on long passages, where days of quick, jerky motion wear a crew out and make cooking, sleeping, and watchkeeping hard. A boat that feels fine for a weekend can feel punishing after a week at sea. That is why buyers comparing two similar boats often check the ratio alongside displacement, ballast, and cockpit size before they choose.
How to use it
Enter the displacement in pounds, the length overall, the waterline length, and the beam, all in feet. You will find displacement and dimensions in the boat’s specification sheet or brochure, but check whether the displacement quoted is light, half-load, or fully loaded, because the number changes with it. Use the same load state when you compare boats, or the comparison is meaningless.
Press Calculate and read the ratio and its band. Try the same boat at light and loaded displacement to see how much provisioning, fuel, and water change the feel, and compare two or three boats you are actually considering rather than chasing one magic number.
Worked example
Take a 40-foot cruiser that displaces 20,000 pounds, with a 34-foot waterline and a 12-foot beam. The formula divides displacement by a factor built from length and beam, and gives a ratio of about 29. That sits at the top of the coastal band, close to moderate, which matches a typical family cruiser: comfortable enough for coastal passages and fair-weather crossings, but not a heavy ocean boat.
Load the same boat with 4,000 pounds of stores, water, and fuel and the ratio rises to about 35, in the moderate band. The boat has not changed, but its motion has: weight settles it. This is why a boat’s real comfort depends on how you actually load it.
How to read your result
Under 20 means a light, fast boat that is lively in waves and best for racing or fair-weather coastal sailing. From 20 to 30 is a coastal cruiser with a good balance of speed and comfort. From 30 to 40 is a moderate cruiser that settles well in a seaway and suits longer passages. Over 40 is a heavy boat: slow, but steady and comfortable in rough water.
Read the band as a tendency, not a verdict. Hull shape, ballast ratio, and rig all shape motion too, and a well-sailed moderate boat will beat a poorly handled heavy one every time.
Common mistakes
The most common mistake is mixing units, for example entering displacement in kilograms or lengths in metres, which wrecks the result. Another is using brochure displacement for one boat and loaded displacement for another. A third is treating the ratio as a seaworthiness score: a heavy boat can still be badly built, badly maintained, or badly sailed.
Limits
The formula is a rough rule from the 1970s, not a physics simulation. It ignores hull shape, freeboard, ballast placement, and wave period, so two boats with the same ratio can feel quite different. Use it to shortlist boats and to understand the trade between speed and comfort, then sail the boats, read a survey, and talk to owners before you buy.
Questions people ask
Is a higher comfort ratio always better?
No. A higher ratio usually means a slower boat that needs more wind to move and more sail area to keep up. Racers and daysailers trade comfort for speed on purpose, and for short coastal trips that trade is often right.
Does the ratio predict seasickness?
Only loosely. Gentle motion helps, but seasickness also depends on wave period, your own susceptibility, sleep, and food. A heavy boat in short, steep waves can still make a crew ill.
What if I only know metric figures?
Convert first: 1 kilogram is 2.205 pounds and 1 metre is 3.281 feet. Convert all four inputs before you enter them, and keep the same units across every boat you compare.