Page 21 - Ship Construction.DJ Eyres 6Ed

Ch02-H8070.fm Page 10 Wednesday, October 18, 2006 6:51 AM

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Ship Dimensions, Form, Size or Category

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The hull form of a ship may be defined by a number of dimensions and
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
terms which are often referred to during and after building the vessel. An
explanation of the principal terms is given below:

After Perpendicular (AP): A perpendicular drawn to the waterline at the point
where the aft side of the rudder post meets the summer load line. Where no
rudder post is fitted it is taken as the centre line of the rudder stock.
Forward Perpendicular (FP): A perpendicular drawn to the waterline at the
point where the foreside of the stem meets the summer load line.
Length Between Perpendiculars (LBP): The length between the forward and aft
perpendiculars measured along the summer load line.
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Amidships: A point midway between the after and forward perpendiculars.
Length Overall (LOA): Length of vessel taken over all extremities.
Lloyds Length: Used for obtaining scantlings if the vessel is classed with
Lloyds Register. It is the same as length between perpendiculars except that
it must not be less than 96 per cent and need not be more than 97 per cent of
the extreme length on the summer load line. If the ship has an unusual stem
or stern arrangement the length is given special consideration.
Register Length is the length of ship measured from the fore-side of the
head of the stem to the aft side of the head of the stern post or, in the case
of a ship not having a stern post, to the fore-side of the rudder stock. If the
ship does not have a stern post or a rudder stock, the after terminal is taken
to the aftermost part of the transom or stern of the ship. This length is the
official length in the register of ships maintained by the flag state and
appears on official documents relating to ownership and other matters
concerning the business of the ship. Another important length measure-
ment is what might be referred to as the IMO Length. This length is found
in various international conventions such as the Load Line, Tonnage, SOLAS
and MARPOL conventions and determines the application of requirements
of those conventions to a ship. It is defined as 96 per cent of the total length
on a waterline at 85 per cent of the least moulded depth measured from the
top of keel, or the length from the fore-side of stem to the axis of rudder
stock on that waterline, if that is greater. In ships designed with a rake of keel
the waterline on which this length is measured is taken parallel to the design
waterline.