Encyclopedia of Environmental Science and Engineering, Volume I and II

668

MARINE SPILLAGE—SOURCES AND HAZARDS

INTRODUCTION

Scope

Pollution of navigable waterways resulting from operation

of commercial and naval vessels may be a consequence of

normal service or from casualties such as collisions and

groundings. Propulsion system fuel oil and liquid cargoes

may be involved in any case and will be considered in this

chapter. Waste disposal from shipping is of comparatively

small magnitude compared to waterway pollution from

shoreside sources and will not be considered. Emphasis will

be on description of the pollution problem and on means for

prevention. The subject of spill collection and disposal is

considered elsewhere in this text.

Problem Definition

Normal operations A decade ago, the primary source of pol-

lution of the world’s waterways was the intentional discharge

of oily ballast water during routine operations. At that time,

for virtually all seagoing operations ballast water was taken

aboard for a portion of the voyage in order to obtain sufficient

draft and trim for propeller immersion, adequate steering abil-

ity, acceptable conditions of seaworthiness; and to satisfy man-

dated operational and regulatory requirements for intact and

damaged stability. If assigned ballast tank capacity was inad-

equate to meet these requirements, it was the general practice

to ballast empty fuel oil tanks, or empty liquid cargo tanks in

the case of tank vessels. This procedure resulted in the neces-

sity for pumping overboard large quantities of contaminated

ballast water before taking on fuel oil or liquid cargoes. These

procedures have been largely outlawed by international agree-

ments developed by the International Maritime Organization

(IMO) of the United Nations, and enforced by the national

regulatory agencies of the member countries.

Casualties Spills resulting from casualties generally

receive more attention in the world press than incidents

involving operational discharges. Spills may occur from

operational mishaps in the pumping of fuel oil bunkers and

liquid cargoes. Incidents of spills that occur from collisions

and groundings are accompanied by associated dangers to

personnel and the environment and are likely to involve the

largest quantities of pollutant discharged in a single incident.

The magnitude of such spills is clearly far greater in the case

of a loaded tank vessel than the grounding and rupture of the

double bottom fuel tanks of a dry cargo vessel.

SHIP CLASSIFICATION AND DESCRIPTION

The arrangements and general characteristics of the various

merchant ship types are well described in such standard texts

as Reference (1) and in the technical literature, including the

comprehensive discussion in Reference (2) covering U.S.

shipbuilding during the 1936
1976 period. Accordingly,

the following discussion will be restricted to characteristics

pertinent to the pollution problem, for example, arrangement

of tank spaces.

The following standard abbreviations have been used

throughout for convenience:

DWT  deadweight  total displacement 
 light weight

 cargo  consumables

mld.  molded

fbd.  freeboard

B.P.  between perpendiculars

Break Bulk Vessels

The greatest variety of seagoing vessels are in this category

which includes the ordinary general cargo vessels carrying

a great variety of dry products in raw material as well as

finished and packaged form. An outline sketch of the cross-

section through a typical cargo hold, showing hatchway,

tween decks and fuel oil or ballast spaces, is shown in

Figure 1. Fuel oil is commonly carried in the double bot-

toms, as indicated, but may also be carried in deep tanks,

particularly outboard of shafting and in the vicinity of the

machinery spaces. Except for settling and daily service

tanks, all bunker spaces are normally piped for fuel oil

or ballast. The availability of cubic capacity for tankage

assigned only to ballast service is limited in such vessels

and frequent use of fuel tanks for ballasting is likely in most

operations.

Unitized Cargo Carriers

Ships in this category are usually designed for the exclu-

sive transport of standard containers or wheeled trailer vans,

and, to a lesser extent as hybrid carriers to handle container,

wheeled vehicles and general break-bulk cargo. In the case

of container ships, as illustrated in the typical hold section,

Figure 2. the cellular nature of the cargo stowage requires

some “squaring off” of the hold spaces, with the result that

considerable wing space is available for ballast tanks. As a

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