Why use LWL and not LOA?

The classical formula uses waterline length because wave-making and immersed volume scale with LWL. LOA includes overhangs that do not carry the same immersed length at rest.

Is a high D/L always better for offshore?

Not always. Payload and motion can improve, but so can marina costs and light-air needs. Match D/L to your passage profile and crew size.

My listing only shows metric tonnes. Can I convert?

Yes: convert mass to pounds and LWL to feet, then apply the formula. Do not mix metres into the imperial expression without converting first.

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D/L

Displacement / length ratio

D/L = Displacement_lb / (0.01 * LWL_ft)^3

Displacement / length (D/L) compares immersed weight to waterline length. Higher D/L means more volume for a given LWL. FairHelm judgment: many Scandinavian cruisers sit heavier than charter production boats of the same LOA; that is often intentional for payload and motion.

Formula

D/L = Displacement_lb / (0.01 * LWL_ft)^3

Displacement in pounds. LWL in feet. Keep both imperial for the classical form.

Try your numbers

D/L

Displacement (kg)Waterline length (LWL, m)

Result

Enter positive numbers in all fields.

Ownership cost calculator Listing review (€49)

Rule of thumb

Under about 200 is often called light; 200-300 moderate; 300+ heavy for cruising monohulls. Ultra-light racers sit far below. Treat bands as conversation starters, not class rules.

Limits

Wrong LWL (using LOA) skews the cube term badly. Half-load versus light-ship displacement changes the ratio. D/L ignores beam, ballast, and sail plan. A heavy D/L boat can still be tender if ballast is low.

Boat examples

Hallberg-Rassy 36
Expect a heavier D/L than a same-LOA charter hull designed for marina berths and light crews.
Sweden Yachts 390
Swedish performance-cruiser lineage: confirm published displacement basis before ranking against HR.
Linjett 40
Coastal Scandic design: D/L helps explain payload and motion claims in owner forums.

History

D/L appears in design texts and broker sheets as a shorthand for 'heavy' versus 'light' hulls. It grew with imperial yacht measurement culture and remains quoted even when yards publish metric specs.

FAQ

Why use LWL and not LOA?: The classical formula uses waterline length because wave-making and immersed volume scale with LWL. LOA includes overhangs that do not carry the same immersed length at rest.
Is a high D/L always better for offshore?: Not always. Payload and motion can improve, but so can marina costs and light-air needs. Match D/L to your passage profile and crew size.
My listing only shows metric tonnes. Can I convert?: Yes: convert mass to pounds and LWL to feet, then apply the formula. Do not mix metres into the imperial expression without converting first.

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