Comfort Ratio and CSF: calculate them and inspect their blind spots

Continue with the fictional 6,000 kg boat: LOA 10.5 m, LWL 9 m and beam 3.2 m. Comfort Ratio is an empirical index associated with Ted Brewer.

Capsize Screening Formula, or CSF, combines beam and displacement. Both can be reconstructed from specification fields.

This lesson also examines what their inputs omit. Correct arithmetic can still answer the wrong question about life at sea.

No plotted curve represents observed vessel motion or a measured capsize response.

After conversion use 13,227.74 lb, LWL 29.5276 ft, LOA 34.4488 ft and beam 10.4987 ft. The weighted length is approximately 31.0039 ft.

Multiply it by 0.65 and beam to the power 1.333, then divide mass by that denominator: approximately 28.57. We retain the customary 1.333 exponent used in the comparator.

Exact four-thirds or another convention changes the number slightly. This empirical index is not acceleration, roll period or a comfort percentage.

Its numerical convention must accompany the value.

The cube root of 13,227.74/64 is approximately 5.9125 ft. Divide 10.4987 ft beam by it to obtain CSF ≈1.776.

There is no vertical centre of gravity, flooding opening or stability curve in the formula. A value below a historical threshold is consequently not an offshore certificate.

Applying it to a multihull or substantially different geometry without establishing its scope also produces a misleading comparison. “Screening” describes a limited index rather than an actual capsize test of the boat.

Experienced motion also depends on hull shape, mass distribution, sea state and the encounter between speed, heading and waves. The same boat can feel different on two days while a static catalogue index remains unchanged.

An owner’s account can illuminate particular conditions, provided it remains identified as experience. Neither the account nor the index replaces technical assessment of the individual boat.

Avoid converting a tendency into a promise that every person will be comfortable in every sea.

Use the values to organise questions between boats of similar size and design intent. Then inspect input condition, architecture and evidence relevant to intended use.

Do not add Comfort Ratio and CSF into a safety score: different origins and directions do not gain validation through addition. An editorial comparison should explain its criteria and preserve limitations instead of calling the boat with a pleasing number “safer”.

Ask which missing property could reverse the apparent conclusion.