Encyclopedia of Environmental Science and Engineering, Volume I and II

670 MARINE SPILLAGE—SOURCES AND HAZARDS

result such vessels are able to operate with clean ballast only

and no ballasting of fuel tankage is normally required.

Roll-on/roll-off or trailer ships are similarly “squared

off” internally and, in addition, may have extensive deep

tank spaces available below the lowest vehicle deck. As with

the container ships, tankage is likely to be available in suf-

ficient quantity to permit full clean ballast operations.

Dry Bulk Carriers

Dry bulk carriers are engaged primarily in the transport of

such commodities as coal, grain and ores. Two general con-

figurations exist, as shown in Figure 3. For light weight,

high cubic cargoes, such as coal and grains, the hold con-

figuration is such that water ballast capacity, in the amount

of 35 per cent to 40 per cent of cargo deadweight, is avail-

able for clean ballast service, as shown in Figure 3a and 3b.

Fuel oil bunkers are generally confined to deep tanks within

the machinery spaces or to portions of the wing and double

bottom tanks adjacent to the machinery spaces. Clean ballast

operation is generally feasible.

Vessels designed specifically for heavier cargoes such as

ores are generally arranged with comparatively small cargo

holds and large surrounding tank spaces as shown in Figure 3c.

Clean ballast operation is readily accomplished under all loading

conditions.

Liquid Bulk Tank Vessels

The modern tank vessel has evolved from the standard 16,000

deadweight ton (DWT) “T2” tanker of World War II to

modern tank vessels exceeding 500,000 DWT capacity. The

transport of liquid cargoes, predominantly petroleum crudes

and refined petroleum products is the single largest category

of waterborne commerce and represents the greatest potential

pollution hazard with respect to normal operations as well

as casualties. Accordingly, characteristics of vessels in the

liquid bulk trades will be considered in somewhat greater

detail than other ship types.

Petroleum Crude and Products Carriers With the exception

of the steam turbo-electric main propulsion machinery and

electric drive cargo pumps, the World War II T2 tanker is,

in general arrangement, a parent of the tanker designs devel-

oped during the early post-war years. Typical characteristics

of these vessels include:

1) Cargo section divided by a pair of longitudinal

bulkheads into port, center and starboard tanks.

2) Relatively short cargo tanks independent of ship

size.

3) Poop, bridge and forecastle superstructures with

navigating bridge located amidships.

4) Forward and after fuel bunkers.

5) Forward and after pump rooms.

6) Relatively long, single screw, main propulsion

machinery, with separate boiler and engine rooms.

From the late 1950s until the present, tanker design evolved

through the following changes, all directly related to reduced

cost of construction and operation:

1) Increase in size to over 500,000 DWT capacity,

with corresponding increases in dimensions and

operating drafts.

MAIN DECK

INNER BOTTOM

BALLAST BALLAST

FUEL OIL OR BALLAST FUEL OIL OR BALLAST

FIGURE 2 Outline midship section through container hold, typical container ship.

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