Page 354 - Ship Construction.DJ Eyres 6Ed

Ch31-H8070.fm Page 343 Wednesday, October 18, 2006 7:06 AM

31
Load Line Rules

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Reference to ‘rules’ in this chapter means the requirements of the Interna-
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
tional Convention on Load Lines of Ships 1966.

Freeboard Computation

Basic freeboards are given in the rules which are dependent on the length
and type of vessel.
Ships are divided into types ‘A’ and ‘B’. Type ‘A’ ships are those which
are designed to carry only liquid cargoes in bulk, and in which the cargo
tanks have only small access openings closed by watertight gasketed covers
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of steel or equivalent material. These vessels benefit from the minimum
assignable freeboard. All ships which do not come within the provisions
regarding Type ‘A’ ships are considered as Type ‘B’ ships.
As a considerable variety of ships will come within the Type ‘B’ category,
a reduction or increase from the basic table Type ‘B’ freeboard is made in
the following cases:

(a) Vessels having hatchways fitted with portable beams and covers on
exposed freeboard or raised quarter decks, and within 25 per cent of the
ship’s length from the FP on exposed superstructure decks, are to have the
basic freeboard increased.
(b) Vessels having steel weathertight covers fitted with gaskets and clamp-
ing devices, improved measures for the protection of the crew, better free-
ing arrangements, and satisfactory sub-division characteristics may obtain a
reduction in the basic freeboard given for a Type ‘B’ ship. This reduction
may be increased up to the total difference between the values for Type ‘A’
and Type ‘B’ basic freeboards. The Type ‘B’ ship, which is effectively adopt-
ing Type ‘A’ basic freeboard, is referred to as a Type ‘B-100’ and its final
calculated freeboard will be almost the same as that for a Type ‘A’ ship.
Other Type ‘B’ vessels which comply with not such severe sub-division
requirements can be assigned a basic freeboard reduced by up to 60 per
cent of the difference between ‘B’ and ‘A’ basic values.
Obtaining the maximum possible draft can be important in many Type
‘B’ vessels, and careful consideration at the initial design stage with regard