Boat Data

Sailboat Ratios Explained

D/L, SA/D, ballast ratio, capsize screening, and comfort ratio are derived indicators. They help compare designs, but they are not complete judgments.

Level
working
Read time
10 min
Sources
1

Ratios Combine Several Inputs

Derived ratios are only as trustworthy as the length, displacement, ballast, and sail-area inputs used to calculate them.
Verified input
Source-backed measurements such as displacement, sail area, beam, and LWL.
Formula
A published calculation rule that Boatpedia should document with the output.
Interpretation
A cautious explanation of what the ratio may suggest, without ranking the boat.

Common Sailboat Ratios

Displacement/length ratio

A weight-to-waterline-length ratio used to compare how light or heavy a displacement sailboat is for its length.

Requires a consistent displacement basis and LWL. Load condition matters.

Sail area/displacement ratio

A power-to-weight style ratio comparing upwind sail area with displacement.

Does not capture hull shape, rig efficiency, ballast placement, or reefing behavior.

Ballast ratio

Ballast weight divided by displacement.

A high ratio is not automatically safer; ballast location and hull form matter.

Capsize screening formula

A beam-and-displacement screening calculation sometimes used as one offshore-context indicator.

It is a broad screen, not a stability certificate or replacement for design data.

Comfort ratio

A derived indicator intended to compare motion tendency between displacement cruising designs.

Modern hull shapes and loading patterns can limit simple comparisons.

Boatpedia Display Rules

FieldMeaningBoatpedia use
Input confidenceWhether the source measurements used in the formula are verified.Controls whether the ratio is shown, flagged, or held pending.
Formula noteThe calculation method used for the displayed value.Lets users compare ratios consistently across pages.
ScopeWhether the value applies to a base model, variant, rig package, or production band.Prevents a deep-keel performance variant from being flattened into the same record as a shoal-draft cruising version.
References

Sources and Method Notes

Boatpedia reference

Boatpedia reference standards

Public guidance for reading model facts, source notes, market context, and data caveats on Boatpedia.

Open source
Next reference
Boat DataBoat Measurements Explainedfoundation / 9 minLOA, LWL, beam, draft, air draft, displacement, ballast, tankage, and capacity describe different parts of a boat record.Boat DataKeel Types Explainedfoundation / 8 minKeel type affects draft, stability, leeway resistance, grounding behavior, maintenance, and where a sailboat can operate.Boat DataHow Boatpedia Verifies Boat Specificationsreference / 8 minBoatpedia treats specifications as cited facts with confidence, source type, unit normalization, and variant scope.