What Deck Machinery Has To Do — Duty, Rating and Control
The deck is the one place on a ship where machinery is asked to stand idle for weeks and then work perfectly the moment it is wanted, in salt, weather and cold.
Key Principles at a Glance 5 points
- Deck machinery is intermittent-duty machinery: it stands idle for weeks and then has to work first time, in salt, weather and cold, usually with nobody available to nurse it.
- Its four duties are anchoring, mooring, cargo handling and boat handling, and each has its own chapter in this volume.
- Drives are rated for restricted intermittent duty, from thirty minutes to one hour, and the design must assume that the first duty after a long idle period is the heaviest one.
- Totally enclosed equipment with oil bath lubrication is standard because the failure mode is not a slow loss of performance but a machine that will not start on the morning it is needed.
- Control belongs where the operator can see the load or the wire; where that is not possible, the indication is brought to him instead.
1. What the machinery is
Deck machinery is intermittent-duty machinery. Its rating, its lubrication and its protection are all built around the assumption that it stands still for most of the voyage — which is exactly why it has to be exercised and greased on a planned basis rather than left until the day it is needed. It must work first time, and there is usually nobody available to nurse it.
Deck machinery is the group of machines that works the ship's cables, ropes, cargo and boats. It divides into four duties:
- Anchoring — the windlass, the cable lifter and the cable stopper.
- Mooring — the mooring winches, the warping capstans and the rope drums carried on the windlass.
- Cargo handling — the cargo winches and derricks, the deck cranes and the hatch covers.
- Boat handling — the lifeboat davits and their winches.
Each of those is dealt with in its own chapter in this volume. What they have in common is the deck itself: an exposed, corrosive, moving platform where the machinery has to be worked by people who are also standing on that platform.
2. The duty cycle — idle, then instant
Most deck machinery is idle for much of its life while the ship is at sea. In port the cargo equipment may be in use for one or more days, but the machinery for anchoring and mooring is used for a very limited time. The duty is therefore described as restricted and intermittent, and drives are designed with a rating limited from thirty minutes to one hour.
That rating is not a licence to abuse the machine. Despite long periods of idleness, often in severe weather conditions, the machinery must operate immediately when required. Two consequences follow directly:
- Cooling vents which are open when the machinery is working must be closed for the sea passage. The machine is not running, so the vents serve no purpose, and leaving them open admits the weather.
- The design must assume that the first thing the machine does after a fortnight of idleness is its heaviest duty — letting go an anchor, or taking a strain on a mooring wire.
3. Why maintenance is the whole story
It is essential that deck machinery should require minimum maintenance. Totally enclosed equipment with oil bath lubrication for gears and bearings is now standard, and that is a direct response to the deck environment rather than a refinement.
Maintenance cannot be completely eliminated, however. Routine checking and greasing still has to be carried out, and on a planned basis — because the failure mode of deck machinery is not a slow loss of performance that announces itself, but a machine that will not start on the morning it is needed. The maintenance schedule is in Chapter 10.
4. Control — local, shipside and remote
There are many instances where remote or centralised control is of great advantage:
- Letting go anchors from the bridge, which is the case the rules are written around, because it must be possible to do it under emergency conditions.
- Shipside controllers with mooring winches, so the man working the wire can see what he is doing.
- Central control positions for the multi-winch slewing derrick system, where one man is coordinating several winches at once.
The general principle is that the control should be where the operator can see the load or the wire. Where that is not possible, the indication has to be brought to him instead — which is why remote windlass control carries a running cable speed and a length-paid-out indication.
5. What changes with the ship type
The four duties are common to all ships, but the machinery installation is not the same on all of them.
Oil tankers. The machinery on the deck is limited to that used for anchor handling and mooring, plus pumproom fans and equipment for handling the gangway and stores. Power was universally provided in the past by steam. Hydraulic equipment is now common, sometimes with air motors for gangway duties, and the availability of safe electrical equipment means that electric motor drives can be used where appropriate.
Liquefied gas carriers and product or chemical tankers. The deck machinery installation is similar to a tanker's, but the drive motor for the deepwell pumps may be an induction motor of the increased or enhanced safety type (Ex e), because those pumps are submerged in the cargo.
Dry cargo vessels. Either electric or hydraulic drives are installed for the deck machinery.
Container ships. The mooring installation is heavier and more automated than on a general cargo ship, and the hatch covers may be lifted bodily by crane rather than rolled or folded. There are now hatchcoverless container ships in service.
Geared bulk carriers. Some have overhead cranes arranged to travel on rails above the holds, which is a cargo-handling arrangement rather than a deck machinery one in the ordinary sense, but it falls to the same people to maintain.
6. How the work itself has changed
The direction of travel is the same in every duty: fewer people, doing less of the work by hand, with the machine doing the holding as well as the moving.
Mooring. The operation of mooring a vessel traditionally required the attendance of a large number of deck crew fore and aft, and 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 by as few as two men.
A large container ship may have four mooring winches on the after deck, each of the self-tensioning type with its own rope drum. Controls are duplicated and are situated at each side of the vessel, giving a clear view of the operation. Mooring ropes are paid out directly from the drums as they are hauled by the heaving lines from the quay; with the loop in place on the bollard, the capstan is set on auto-tension after slack is taken up and the ship is correctly moored. A common arrangement forward is for two similar winches plus rope drums for auto-tensioning on each windlass.
Cargo access. The introduction of steel hatch covers not only speeded up the operation of opening and closing the covers but also reduced the number of personnel required for the task. Rolling and folding covers may be operated by a pull wire or hydraulically.
Cargo handling. Cargo handling may be by winches and derricks or by cranes. The choice is discussed in Chapter 6 and Chapter 7.
7. Surveys and certification
Deck machinery and its fittings are surveyed, and the survey is one of the reasons the machinery has to be kept in a condition to be examined rather than merely to work.
Under the load line survey, anchoring and mooring equipment is to be examined as far as is practicable, and this sits alongside the examination of gasketted steel hatch covers, which are to be tested or alternatively proven tight.
Cargo lifting appliances carry their own regime. Safe working load and identifying marks must always be visible, and the file containing the certificates is examined to ensure that all are valid — a chain, ring, hook, swivel or block whose certificate has lapsed is not a lifting appliance. The intervals at which winches, cranes and their brakes are overhauled are set out in Chapter 10.
8. What follows from all this
Three things run through the rest of the volume:
- The drive has to suit the duty. Anchor and mooring work needs torque at very low speed and a positive means of holding a load; cargo work needs speed and fine control on the lowering side. That is why electric and hydraulic drives divide the work the way they do (Chapter 2 and Chapter 3).
- The brake is as important as the motor. On a windlass, a mooring winch, a crane and a lifeboat davit the brake is what makes the machine safe rather than merely useful, and it is the item most often neglected.
- Everything on deck is exposed. Enclosure, lubrication and protection are chosen for the weather, and the maintenance schedule exists because the weather always wins in the end.