Biological sewage treatment
A number of biological sewage treatment plant types are in use at sea but nearly all work on what is called the extended aeration process. Basically this consists of oxygenating by bubbling air through or by agitating the surface. By so doing a family of bacteria is propagated which thrives on the oxygen content and digests the sewage to produce an innocuous sludge. In order to exist, the bacteria need a continuing supply of oxygen from the air and sewage wastes. If plant is shut down or...
Cargo handling
The duty of a deck winch is to lift and lower a load by means of a fixed rope on a barrel, or by means of whipping the load on the warp ends, to top or luff the derricks, and to warp the ship. In fulfilling these duties it is essential that the winch should be capable of carrying out the following requirements a lift the load at suitable speeds b hold the load from running back c lower the load under control d take up the slack on the slings without undue stress e drop the load smartly on the...
Fire protection
Fire protection on ships is provided by detection and fire-fighting equipment together with structural features which are intended to contain an outbreak of fire and the employment when required of non-combustible materials to prevent its spread. An outbreak of fire requires a source of ignition, the presence of combustible material and ample oxygen. Of the three factors, oxygen is provided in large quantities in machinery spaces, accommodation, dry cargo holds and tanker pumprooms by...
Deck machinery and cargo equipment
The operation of mooring a vessel has traditionally required the attendance of a large number of deck crew fore and aft. Supervision of the moorings was also necessary to maintain correct tension through changes due to the tides and the loading or unloading of cargo. The installation of constant tension mooring winches, which maintain tension in ropes through any rise and fall, has removed the need for constant attendance and equipment is available for tying up which is designed for operation...
Oil tankers crude oil
Crude oil is delivered to refineries in large crude oil carriers which may carry more than one grade. Refinery products are transported in smaller tankers which may be used for a variety of cargoes. Before the advent of very large tankers, reciprocating pumps were commonly installed for cargo discharge and tank draining. These pumps require routine maintenance of suction and discharge valves, pistons and buckets, pump rod glands, slide valve chests and steam valves. Being positive displacement...
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pressure applied to an inserted rod from a pressure cylinder screwed to the bolt head. Stretching makes the bolt diameter small enough for insertion into the hole, after which the nut is nipped up. Release of hydraulic pressure allows the bolt to shorten, so that 1 predetermined bolt load is produced and 2 diametrical re-expansion gives a good fit of the shank in the hole. These bolts, when used in flange couplings and flange mounted propellers, have the advantage that they are easily removed...
Stabilizers and stabilizing systems
A ship at sea has six degrees of freedom, i.e. roll, heave, pitch, yaw, sway and surge Figure 10.5 . Of these, only roll can effectively be reduced in practice by fitting bilge keels, anti-rolling tanks or fin stabilizers. A combination of fins and the inherent damping of the ship, i.e. viscous damping and the action of bilge keels. In Figure 30.7 G is the centre of gravity, B is the centre of buoyancy, W is the weight or displacement of the ship, 6 the roll angle. M, the point of intersection...
The electric salinometer
Pure distilled water may be considered a non-conductor of electricity. The addition of impurities such as salts in solution increases the conductivity of the water, and this can be measured. Since the conductivity of the water is, for low concentrations, related to the impurity content, a conductivity meter can be used to monitor the salinity of the water. The instrument can be calibrated in units of conductivity micromhos or directly in salinity units older instruments in grains gall., newer...
Central cooling system
The corrosion and other problems associated with salt water circulation systems can be minimized by using it for cooling central coolers through which fresh water from a closed general cooling circuit is passed. The salt water passes through only one set of pumps, valves and filters and a short length of piping. Figure 1.10 shows a complete central cooling system in which all components are cooled by fresh water. The three sections are 1 the sea-water circuit 2 the high temperature circuit and...
Closed feed system and feed heating
To ensure trouble-free operation of water-tube boilers the feed water must be of high quality with a minimal solid content and an absence of dissolved gases. Solids are deposited on the inside surfaces of steam generating tubes, as the water boils off, and the scale so formed causes overheating and failure. Dissolved gases tend to promote corrosion. Distilled water used as boiler feed has a great affinity for gases in the atmosphere. Chemical treatment is aimed at preventing corrosion problems...