Page 358 - Ship Construction.DJ Eyres 6Ed

Ch31-H8070.fm Page 347 Wednesday, October 18, 2006 7:06 AM
Load Line Rules 347
a greater degree of protection against the sea. Ships thus arranged are
granted a smaller freeboard than would be assigned to a Type ‘B’ vessel, pro-
vided they comply with the additional conditions of assignment for timber-
carrying vessels. No reduction of freeboard may be made in ships which
already have Type ‘A’ or reduced Type ‘B’ freeboards. The freeboards are
computed as described above, but have a different super-structure correc-
tion, this being modified by the use of different percentage deductions
--- ใช้เพื่อการศึกษาเท่านั้น---
given in the rules for timber freeboards. Winter timber freeboard is
obtained by adding to the summer timber freeboard 1/36th of the moulded
summer timber draft. Winter North Atlantic timber freeboard is the same
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
as for normal freeboards, and the tropical timber freeboard is obtained
by deducting from the summer timber freeboard 1/48th of the moulded
summer timber draft. The fresh water timber freeboard is determined as
for normal freeboards.

Conditions of Assignment of Freeboard

(1) The construction of the ship must be such that her general structural
strength will be sufficient for the freeboards to be assigned. The design and
ึ
construction of the ship must be such that her stability in all probable load-
ing conditions is sufficient for the freeboards assigned. Stability criteria are
given in the Convention.

(2) Superstructure End Bulkheads To be of efficient construction to the
satisfaction of the Administration. The heights of the sills of openings at the
ends of enclosed superstructures should be at least 380 mm above the deck.

(3) Hatchways closed by Portable Covers with Tarpaulins The coamings
should be of substantial construction with a height above deck of at least
600 mm on exposed freeboard and RQD and on exposed superstructure
decks within ¼ of the ship’s length from FP (Position 1) and at least
450 mm on exposed superstructure decks outside ¼ of the ship’s length
from FP (Position 2).
The width of bearing surface for the covers should be at least 65 mm.
Where covers are of wood the thickness should be at least 60 mm with a
span of not more than 1.5 m. For mild steel portable covers, the strength is
calculated with assumed loads. The assumed loads on hatchways in Position
1 may be not less than 1 tonne/sq. metre for ships 24 metres in length and
should not be less than 0.75 tonnes/sq. metre for hatchways in Position 2.
Where the ship’s length is 100 m or greater the assumed loads on hatchways
at Position 1 and Position 2 are 1.75 tonnes/sq. metre, and 1.30 tonnes/sq.
metre respectively. At intermediate lengths the loads are obtained by inter-
polation.