The beam of a ship is its width at its widest point. The maximum beam (B_MAX) is the distance between planes passing through the outer extremities of the ship, beam of the hull (B_H) only includes permanently fixed parts of the hull, and beam at waterline (B_WL) is the maximum width where the hull intersects the surface of the water. Generally speaking, the wider the beam of a ship (or boat), the more

initial stability Initial stability or primary stability is the resistance of a boat to small changes in the difference between the vertical forces applied on its two sides. The study of initial stability and secondary stability are part of naval architecture as app ...

it has, at the expense of

secondary stability Secondary stability, also known as reserve stability, is a boat or ship's ability to right itself at large angles of heel (lateral tilt), as opposed to primary or initial stability, the boat's tendency to stay laterally upright when tilted to low ...

in the event of a

capsize Capsizing or keeling over occurs when a boat or ship is rolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it is upside down in the water. The act of recovering a vessel fro ...

, where more energy is required to right the vessel from its inverted position. A ship that

heels The heel is the prominence at the posterior end of the foot. It is based on the projection of one bone, the calcaneus or heel bone, behind the articulation of the bones of the lower leg. Structure To distribute the compressive forces exert ...

on her ''beam ends'' has her deck beams nearly vertical.

Typical values

Typical length-to-beam ratios ( aspect ratios) for small sailboats are from 2:1 (dinghies to trailerable sailboats around ) to 5:1 (racing sailboats over ). Large ships have widely varying beam ratios, some as large as 20:1. Rowing shells designed for flatwater racing may have length to beam ratios as high as 30:1, while a

coracle A coracle is a small, rounded, lightweight boat of the sort traditionally used in Wales, and also in parts of the West Country and in Ireland, particularly the River Boyne, and in Scotland, particularly the River Spey. The word is also used of ...

has a ratio of almost 1:1 – it is nearly circular.

Rule of thumb - formula

The beam of many monohull vessels can be calculated using the following formula: :

Beam = LOA^\frac + 1

Where LOA is Length OverAll and all lengths are in feet. Some examples: * For a standard yacht: the cube root of 27 is 3, 3 squared is 9 plus 1 = 10. The beam of many 27 ft monohulls is . * For a

Volvo Open 70 The Volvo Open 70 (sometimes referred to as a Volvo Ocean 70) is the former class of racing yachts designed for the Volvo Ocean Race. It was first used in the 2005–06 race (replacing the Volvo Ocean 60 yachts which were first used in 1993). A ...

yacht: 70.5 to the power of 2/3 = 17 plus 1 = 18. The beam is often around . * For a long ship: the cube root is 9, and 9 squared is 81, plus 1. The beam will usually be around , e.g.

Seawaymax The term Seawaymax refers to vessels which are the maximum size that can fit through the canal locks of the St. Lawrence Seaway, linking the inland Great Lakes of North America with the Atlantic Ocean. Seawaymax vessels are in length, wid ...

. As catamarans have more than one hull, there is a different beam calculation for this kind of vessel.

BOC

BOC stands for Beam On Centerline. This term in typically used in conjunction with LOA (Length overall). The ratio of LOA/BOC is used to estimate the stability of multihull vessels. The lower the ratio the greater the boat's stability. The BOC for vessels is measured as follows: For a catamaran: the perpendicular distance from the centerline of one hull to the centerline of the other hull, measured at deck level. For a trimaran: the perpendicular distance between the centerline of the main hull and the centerline of either ama, measured at deck level

Other beams

Other meanings of 'beam' in the nautical context are: *Beam – a timber similar in use to a floor joist, which runs horizontally from one side of the hull to the other athwartships. *Carlin – similar to a beam, except running in a fore and aft direction. *Beam – the direction across the vessel, perpendicular to fore-and-aft; something lying in that direction is said to be ''abeam''.

References

Notes

* * {{Ship measurements Nautical terminology Ship measurements