Width of a ship at its widest point
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 sides 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.
[1]
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
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]
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
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]
[
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:
- For a standard 27 ft (8.2 m) yacht: the cube root of 27 is 3, 3 squared is 9 plus 1 = 10. The beam of many 27 ft monohulls is 10 ft (3.05 m).
- For a
Volvo Open 70
yacht: 70.5 to the power of 2/3 = 17 plus 1 = 18. The beam is often around 18 ft (5.5 m).
- For a 741 ft (226 m) long ship: the cube root is 9, and 9 squared is 81, plus 1. The beam will usually be around 82 ft (25 m), e.g.
Seawaymax
.
As catamarans have more than one hull, there is a different beam calculation for this kind of vessel.
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
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]
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
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]
Notes
[
edit
]
- Hayler, William B.; Keever, John M. (2003).
American Merchant Seaman's Manual
. Cornell Maritime Pr.
ISBN
0-87033-549-9
.
- Turpin, Edward A.; McEwen, William A. (1980).
Merchant Marine Officers' Handbook
(4th ed.). Centreville, MD: Cornell Maritime Press.
ISBN
0-87033-056-X
.
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Length
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Breadth
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Depth
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Height
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Volume
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Specialized
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Archaic
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Capacity
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Weight
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Stability
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Limits
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