L/B
Length / beam ratio
L/B = Length / Beam (LOA / Beam_max or LWL / Beam_max)
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 (LOA / Beam_max or LWL / Beam_max)
Strictly dimensionless. Both length and beam must be measured in identical units (either metres or feet). Specify clearly whether LOA or LWL is used in the numerator.
Try your numbers
L/B
Result
Enter positive numbers in all fields.
Rule of thumb
Cruising monohull benchmark bands (by LOA/Beam): Under 2.7: Extremely beamy offshore racers (Class 40, Open 60) and wide-body cruisers; blazing speeds reaching and running, but punishing slamming upwind in steep chop. 2.7 to 3.0: Modern family production cruisers (Bavaria 36, Beneteau Oceanis 38, Hanse 388, Dufour 382); maximum interior volume and dockside stability. 3.0 to 3.3: Moderate ocean cruisers (Hallberg-Rassy 36, Linjett 40, Sweden Yachts 390, Najad 390); the proven compromise between liveaboard comfort and soft seakeeping in open water. Above 3.3: Classic slender voyagers (Contessa 32, Folkboat, Rustler 36); sea-kindly wave piercing with compact salon accommodations.
Limits
Two critical buyer traps: First, comparing boats with overhangs against vertical-stem hulls using LOA. An older 10.5 m cruiser with overhangs may have an 8.0 m waterline (LWL/B around 2.5), whereas a modern plumb-bow 10.5 m yacht has a 10.1 m waterline (LWL/B around 2.9). For true hydrodynamics, always compare LWL to waterline beam. Second, marina berth pricing: across the Mediterranean and Baltic, marinas charge by total box area (LOA × Beam) or enforce steep price jumps when beam exceeds 3.50 m or 4.00 m. A 3.95 m wide cruiser often incurs 25-40% higher annual mooring fees than a 3.40 m classic of the same LOA.
Boat examples
- Hallberg-Rassy 36
Moderate ocean cruiser: L/B around 3.07 combines seaworthy wave entry with sufficient beam for a comfortable centre-cockpit walkthrough.
- Beneteau First 31.7
Fast performance cruiser: L/B around 2.97 provides good initial form stability under sail while avoiding excessive drag on upwind legs.
- Linjett 40
Modern Scandic cruiser: L/B around 3.30 maintains slender offshore lines for soft motion in Baltic chop without sacrificing modern cruising systems.
History
Length to beam is naval architecture's oldest planform proportion, tracked by master shipwrights long before rating rules existed. In the wooden and early fiberglass eras, Scandinavian double-enders and British ocean cruisers maintained L/B ratios between 3.2 and 3.6 with maximum beam at the midship station tapering smoothly into a canoe stern or narrow transom. Modern composite engineering and charter market demands pushed production cruisers down to 2.7 to 2.9, carrying maximum beam all the way aft to support twin wheels and dual aft cabins.
FAQ
- Why does a wider boat feel more tiring in rough seas?
- High form stability generates sharp roll accelerations (snappy roll). The hull snaps upright violently when meeting a wave crest, placing heavy strain on crew muscles.
- Should I compare LOA/Beam or LWL/Beam?
- LOA/Beam compares overall geometry and marina footprint. LWL/Beam is the true hydrodynamic slenderness index that governs hull resistance and wave-making.
- How does beam impact annual ownership costs?
- Many European marinas price berths by area (length × beam) or apply surcharge tiers for boats wider than 3.5 m or 4.0 m, increasing haul-out and slip fees significantly.