Beam (nautical)

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Graphical representation of the dimensions used to describe a ship. Dimension "b" is the beam at waterline. Ship length measurements.svg
Graphical representation of the dimensions used to describe a ship. Dimension "b" is the beam at waterline.

The beam of a ship is its width at its widest point. The maximum beam (BMAX) is the distance between planes passing through the outer sides of the ship, beam of the hull (BH) only includes permanently fixed parts of the hull, and beam at waterline (BWL) is the maximum width where the hull intersects the surface of the water. [1]

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Generally speaking, the wider the beam of a ship (or boat), the more initial stability it has, at the expense of secondary stability in the event of a capsize, where more energy is required to right the vessel from its inverted position. A ship that heels on her beam ends has her deck beams nearly vertical. [2]

Typical values

Typical length-to-beam ratios (aspect ratios) for small sailboats are from 2:1 (dinghies to trailerable sailboats around 20 ft or 6 m) to 5:1 (racing sailboats over 30 ft or 10 m).

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, [3] while a coracle has a ratio of almost 1:1 it is nearly circular.

Rule of thumb - formula

[ further explanation needed ]

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

Where LOA is Length OverAll and all lengths are in feet.

Some examples:

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:

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<span class="mw-page-title-main">Multihull</span> Ship or boat with more than one hull

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<span class="mw-page-title-main">Yacht</span> Recreational boat or ship

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<span class="mw-page-title-main">Sailboat</span> Boat propelled partly or entirely by sails

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<span class="mw-page-title-main">Draft (hull)</span> Vertical distance between the waterline and the bottom of the hull (keel)

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Ship measurements consist of a multitude of terms and definitions specifically related to ships and measuring or defining their characteristics.

<span class="mw-page-title-main">C&C 37/40</span> Sailboat class

The C&C 37/40 is a Canadian 12.05 metres (39.5 ft) LOA fibreglass monohull sailing yacht, designed in 1988 by Robert W. Ball of Cuthbertson & Cassian as a replacement for the earlier C&C 37 dating from 1981. The C&C 37/40 is a recreational keelboat of moderate displacement, intended as a cruiser/racer or oceangoing racer. The yachts have a masthead sloop rig, with a fin keel and an internally-mounted spade-type rudder. Over 110 of the 37/40 type were built before the Canadian plant closed in 1994. The design is no longer produced.

<span class="mw-page-title-main">F-31 Sport Cruiser</span> Sailboat class

The F-31 Sport Cruiser is a family of American trailerable trimaran sailboats that was designed by New Zealander Ian Farrier and first built in 1991.

The Bahia 22, also called the Bahia 23, is a French trailerable sailboat that was designed by Philippe Harlé as a pocket cruiser and first built in 1983.

References

  1. "ISO 8666:2016". International Organization for Standardization. July 2016. Retrieved 31 March 2020.
  2. "Definition of BEAM-ENDS". www.merriam-webster.com. Retrieved 2020-06-05.
  3. "Science News Online: Ivars Peterson's MathTrek (7/17/99): Row Your Boat". Archived from the original on 2011-06-29. Retrieved 2006-10-18.

Notes