L/B
Length / beam ratio
Length / beam (L/B) is simply length divided by beam. Higher L/B means a slenderer plan form. FairHelm judgment: modern production cruisers run beamier than older Scandic long-keelers; that helps form stability and volume, and changes motion and marina fees.
Formula
L/B = Length / Beam (use LOA/Beam or LWL/Beam, but state which)
Same length units for both terms (metres or feet).
History
L/B is older than most brochure ratios: ship and yacht designers always tracked plan-form slenderness. Consumer yacht sites revived it as a quick 'beamy vs narrow' label next to CSF.
Rule of thumb
State LOA/beam versus LWL/beam. Older narrow cruisers often show higher L/B; modern wide-stern cruisers sit lower. Compare within the same decade and design brief.
Limits
Ignores rocker, hard chines, and cabin trunk. A slender boat can still be tender. Beam max versus waterline beam differ. L/B alone does not predict CSF without displacement.
Boat examples
- Hallberg-Rassy 36
Classic proportions: often less beam-extreme than recent charter-oriented hulls of similar LOA.
- Linjett 40
Use published max beam; cockpit and stern geometry matter more than the ratio for marina berthing.
- Beneteau First 31.7
Sportier beam package: pair L/B with CSF and ballast notes when judging stiffness claims.
FAQ
- Should I use LOA or LWL?
- Either can work if you label it. LWL/beam tracks immersed plan form better; LOA/beam is what most listings allow.
- Does lower L/B mean more comfort?
- Not directly. Beam helps form stability and volume; comfort ratio and displacement tell more about motion.
- How does L/B relate to marina cost?
- Some harbours price by LOA, others by area or beam. A beamier boat can hit berth limits even when LOA fits.