CR
Comfort ratio
CR = Displacement_lb / (0.65 × ((0.7 × LWL_ft) + (0.3 × LOA_ft)) × Beam_ft^1.333)
At a boat show, two hulls of the same size. One has a higher Brewer comfort ratio, so the hand reaches for it: bigger number means softer motion, so buy that one. Brewer, who invented the ratio, immediately hedges. The same traits that raise the number usually also help the boat go faster in ordinary weather. A high number is not a verdict to buy. It is a trade: shorter waterline, narrower beam, heavier displacement, softer motion and often a slower passage. A low number is about motion character, not a ban on leaving harbour.
Formula
CR = Displacement_lb / (0.65 × ((0.7 × LWL_ft) + (0.3 × LOA_ft)) × Beam_ft^1.333)
Displacement in pounds. LWL, LOA, and beam in feet. Convert metres and kilograms first. Use maximum beam (waterline beam is rarely published). If the stern sits in the water, change 0.65 to 0.70.
Try your numbers
CR
Result
Enter positive numbers in all fields.
Rule of thumb
Working rule (not Brewer’s table): under about 20 feels livelier; 30-40 is a typical cruiser band; above about 50 reads heavier and softer. Compare only similar LOA. In Brewer’s own examples a light dayboat sits near 5, a heavy Colin Archer in the high 60s, Valiant 40 and Whitby 42 in the low-to-mid 30s.
Limits
The formula does not see spar and rigging weight, hard chines, rocker, or weight distribution. Brochure displacement errors hurt more than length fine print. Two boats with the same number can still move differently. Comfort at the dock is something else.
Boat examples
- Hallberg-Rassy 36
Reading cue: softer motion than many light production hulls - not a purchase verdict.
- Sweden Yachts 390
Lower number with lighter displacement; still verify under sail, not by CR alone.
- Linjett 40
Helps read Baltic-wave reports; still check on the water.
History
Designer Ted Brewer published comfort ratio as a practical index for amateurs. Magazines picked it up. It is empirical, not CFD. The year of the first column in the Good Old Boat reprint is unnamed: issue 32, September - October 2003 (reprint date, not invention). The invention year is still a Gap. Brewer puts two boats of the same length side by side (32 ft LOA, 26 ft LWL): 14,825 lb → 38.1; 10,250 lb → 26.3 - the same trade: heavier → higher number.
FAQ
- Can I plug in metres?
- Convert to feet and pounds first. Mixing units is the most common error.
- Does a high CR mean a slow boat?
- Often goes with heavier displacement, but speed depends on sails, shape, and SA/D - not on CR alone.
- Who is Ted Brewer?
- A yacht designer who published practical ratios for cruisers. Comfort ratio is tied to his name in popular literature.