Page 351 - Ship Construction.DJ Eyres 6Ed

Ch30-H8070.fm Page 340 Wednesday, October 18, 2006 11:15 AM
340 Ship Construction
NET TONNAGE The net tonnage (NT) is determined by the following
formula:

(1) For passenger ships (i.e. ships carrying 13 passengers or more):

⎛ 4d ⎞ 2 ⎛ N 2⎞
NT = K V ------- + K N + ------ ⎠
⎝
3D⎠
⎝
1
c
3
2
10
--- ใช้เพื่อการศึกษาเท่านั้น---
(2) For other ships:

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
⎛ 4d ⎞ 2
NT = K V -------
⎝
3D ⎠
2
c
where
V = total volume of cargo spaces in cubic metres.
c
d = moulded draft amidships in metres (summer load line draft or deepest
subdivision load line in case of passenger ships).
D = moulded depth in metres amidships.
K =0.2 +0.02 log V c
10
2
K = 1.25 (GT + 10000)
3
10 000 ึ
N = number of passengers in cabins with not more than 8 berths.
1
N = number of other passengers.
2
N + N = total number of passengers the ship is permitted to carry.
1
2
⎛ 4d ⎞ 2
The factor ------- is not taken to be greater than unity. The term K V c
3D ⎠
⎝
2
⎛ 4d ⎞ 2
-------
⎝ 3D ⎠ is not to be taken as less than 0.25 GT; and NT is not to be taken as
less than 0.30 GT.
It will be noted that vessels with high freeboards, i.e. low draft to depth
(d/D) ratios will have low net tonnages. Squaring this ratio can result in
excessively low net tonnages hence the limiting value of 0.30 GT.
Measurement
Measurement for tonnage and issue of an International Tonnage Certifi-
cate is the responsibility of the appropriate maritime authority in the country
of registration of the ship. Most maritime authorities have authorized various
classification societies and perhaps other bodies to act on their behalf to
measure ships and issue the International Tonnage Certificate.
The volumes to be included in the calculation of gross and net tonnages
are measured, irrespective of the fitting of insulation or other linings to the
inner side shell or structural boundary plating in metal, i.e. the moulded