In the spreadsheet below I have posted the numbers for some common cruisers and one lightweight racer. If you don’t see your boat, you can also look up your own numbers online. To understand the numbers better, see the bottom of the page for the formulas from Ted Brewer.
You can also download this data as a Spreadsheet of Cruising Boats (right click and save).
note: the last boat, the Dufour, is not generally considered a cruising boat but rather a racing boat. It is included for contrast
Please credit Ted Brewer for these numbers and algorithms and much of the verbage below. His book Ted Brewer Explains Sailboat Design is well worth study.
- Ballast / Displacement is an indication of stiffness and expressed as a percentage. Stiffness has to do with how much sail the boat can carry before heeling and so has a relationship to achievable speed. In other words, people cruising are likely to reduce sail if the boat is heeling dramatically and making the voyage less comfortable. A boat that can carry more sail before heeling can be sailed faster more comfortably. (Ballast/Disp)*100
- Displacement / Length ratio allows us to compare the displacement of different sized boats as being in a “weight class”. Originally cruising hulls were expected to be 300-400 or higher, but modern design is driving these numbers lower. You still want to see over 200-250 for an offshore cruiser and some of the most respected cruisers are much higher. You must convert to imperial numbers for this to work out: (Disp/2240)/(0.01 x LWL)^3
- Sail Area / Displacement area in a nondimensional number that gives an indication of light air performance. It is calculated as Sail Area divided by Displacement in cubic feet to the 2/3 power or in spreadsheet language: SA / ((Displacement /64)^.67)
Note that displacement is divided by 64 to convert pounds of displacement to cubic feet of sea water displacement – sea water weighs 64 pounds per cubic foot.Also note that sail area is taken as the area of the main and the 100% jib. Obviously using the genoa or drifters in light air will give better performance, but this gives a way to compare boats. If you end up with a boat that is a little high or low, you will probably have to use less or more sail to get equivalent results. For example, Tolo, above has a very high SA/D meaning that she could really move in light air, but she was also easily overpowered and would have to be reefed down. Likewise our current boat Phoenix is a bit low, so we might have her next genoa cut larger than normal to compensate. On an off shore cruising boat there’s an argument that lower is better than being overpowered. For coastal cruising in the San Juans, however, it would be very nice to have a boat with a high SA/D since there is a lot of light air in the summer.
- Comfort or sea-kindliness is a Brewer-invented term to account for motion comfort. I think this is one of the most important numbers for cruising so I have sorted the table using this number – the more seakindly boats being listed first. A motion comfort number of 40 or more is quite acceptable. Note that smaller boats, having a higher beam/length ratio, have lower comfort numbers.
Displacement in pounds/(0.65*(0.7*LWL + 0.3*Length)*(Ballast^(1.33)))
- Capsize Ratio (Cap R)
- Capsize Ratio should be under 2.0 for cruising boats. Lower is better for offshore use.
- Hull Speed
- Hull speed is calculated from water line length: (1.34*(LWL^(0.5)))
Links to more performance data
- Sail Area look-up. This site has sail measurements for thousands of boats.
- Sail Area calculator. Once you get the measurements from the charts in Link 1, use this site to calculate the area. (.5*I *J) + (.5*P*E)
- Sail boat performance parameters. This site allows you to use your boat’s specs to calculate its performance. If the boat you’re interested in is not in this list, go to yachtworld.com/freestateyachts/ or other brokerage sites. Most of these sites provide full specs for the boats they’re selling. Just do a search on the boat you want data for.