FREEBOARD, TONNAGE, LIFE SAVING APPLIANCES, FIRE PROTECTION AND

CLASSIFICATION FREEBOARD

Freeboard is the distance from the waterline to the top of the 1 deck plating at the side 6f the freeboard deck amidghips. The freeboard dcek is the uppermost continuous deck having means of closing all openings in its weather portion.

The minimum freeboard is based on providing a volume of I reserve buayancy which may be regarded as safe, depending I upon the conditions of service of the ship. In deep sea ships, , sufficient reserve buoyancy must be provided to enable the

to rise when shipping heavy seas. Load Line Rules give a tabuIar freeboani which denends

u ; i 6 ~ y p ~ ~ f ship, the length of t ie ship and is based on a standard veszl having a block coefficient of 0.68, length t- depth of 15 and a standard sheer cusve. CorrectTons are then I made to this value for variations from the standard, together with deductions for the reserve buoyancy afforded by weathertight superstm~ct~ures on the freeboard d e b o n e further poinitownsider is the likelihood of water coming onto the fore deck. This is largely a function of the distance of the fore end of the deck from the waterline. For this reason a minimum bow height is stipulated. This value depends upon the length of the ship and the block coefficient and may be measured to the forecastle deck if the forecastle is 7% or more of the ship's length. Should the bow height be less than the minimum then either the freeboard is increased or the deck raised by increasing ) the sheer or fitting a forecastle.

Two basic types of ship are considered: Type A ship are designed to carry only liquid cargoes and hence have a high integrity of enposed deck, together with excellent subdivision of the cargo space. Because the hatches are oiltight,

I If any cargo is carried in the 'tween decks it is classed as deck cargo and added to the tonnage. Alternative tonnage I I hark must be cut in each side of the ship at a distance below the

below-the apex of the triangle, then the'reduced tonnag&may be used. If, however, the tonnage mark is submerged, then the

alteruativi tonnage is shown in Fig. 10.1; The distance W is x the moulded draught to the tonnage mark. 1

1982 Rules The 1967 and earlier Tonnage Rules influenced the design of

a- the ship and its earning capacity without influencing the design and safety of the ship.

The gross tonnage is calculated from the formula

I GIOSS tonnage (GT) =Klv V = total volume of all enclosed spaces in

the ship in m3 IG = 0.2 + 0.02 logla V

The owner may, if he wishes, have assigned to any ship reduced Gross and Net-Tonnages calculated by the method given above. This is an alternative to the normal tonnages and is wnalised by a reduction in the maximum draught. A tonnane

second deck depending upon the ratio of the tonnage length to the deuth of the second deck. If the shiu floats at a draueht at or

normal tonnages must be used. The principle behind the modified and alternative tonnages is

that reduced tonnag? were previously assigned if a tonnage hatch were fitted. This hatch seriously impaired the safety of the

. ship. Thus by omitting the hatch the ship is more seaworthybd no tonnage uenaltv is incurred. The tonnage mark suitable for

ships and introduced features which were not necessarily consistent with the safety and efficiency of the ship. In 1969 an .International Convention on Tonnage Measurement of ships was held and new Tonnage Rules were produced. These Rules fame into force in 1982 for new ships, although the 1967 Rules could still be applied to existing ships until 1994.

The principle behind the new Rules was to produce similar values t o the previous rules for gross and net tonnage using a simplified method which reflected more closely the actual siie of *.:

Thus the gross tonnage depends upon the total volume of th, hip and therefore represents the size of the ship.

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130 REEO~S ~ C O N ~ ~ C T I O N P O R M A R I N ~ S T U D E N T S

Enclosed spaw represent all those spaces which are bounded by the ship's hull, by fimed or portable partitions or bulkheads and by decks or coverings other than awnings.

Spaces excluded from measurement are those at the sides and ends of erections which cannot beclosed to the weather and are not fiited with shelves or other cargo fbents.

The net tonnage is ciaculatd from the formula

4d Net tonnage (NT' = IGVC (=) -k I4 ( N ~ + VC = total volume of cargo spaces in m3 IG = 0.2 + 0.02 logw Vc

G T + 10000 & = 1.25( loOOO ) D = moulded depth amidships in m d = moulded draught amidships in m

NI = number of passengers in cabins with not more than 8 berths

NL = number of other passengers

When a ship is designed to carry less than 13 passengers, the second term in the equation is ignored and the net tonnage is then based directly on the cargo capacity.

There are three further conditions: The term($) is not to betaken as grater than unity. The term & VC G S i s not to be taken as less &an 0.25 GT.

H e m ships wlitch carry no passengers and fit& or no ~ $ 0 win have a net tonnage of 3D% of the gross tannage. AU cargo spaqes are certaed by permanent markings CC

(cargo wmpatment). The result of these rules will be that SheIte~ D ck--Vessels

from the scene. I . carrying daal tonnage and the Tonnage Mark C'1 &sapsappear

A unified system of mMsurement will be used by all nations with no variations in tnterpwkation.

Net tonnage is used .to determine canal dues, Iight dues, some pilotage dues and some harbour dues.

Gross tonnage is used to determine manning levels, safety requirements such as f i e appliances, some pilotage and harbour due, towing charges and graving dock costs.