MOB

One Man Bridge Operations when a sole OOW maintains a navigational watch on the bridge without the support of additional personnel, other than a helmsman engaged in steering

With its power and speed best suited to large, fast container ships. The increase in running speed is obtained by a slight decrease in engine stroke. High thermal efficiency is maintained by an increase in mean effective pressure (M.E.P.).
Construction can be considered generally as typical for the whole range. The engine bedplate is of rigid box form, fabricated from steel plates with main bearing supports of cast steel. Welded ‘A’ frames are assembled into a frame box which contains the crankcase, the crosshead guides and also supports the wheels for the chain drive of the camshaft. A cast iron cylinder frame accommodates the scavenge space between the cylinder jacket and the diaphragm, both of which are water-cooled. Long pre-stressed tie bolts are fitted between the top of the frame and the underside of the bedplate girders.
The cylinder liner is of alloy cast iron, its upper flange lands on top of the frame and has bore cooling, it is secured by a forged steel cylinder cover which is also bore cooled and is shaped internally to accommodate most of the combustion space. Cylinder lubricating oil is injected at one level in the liner. Pistons have a chrome-molybdenum alloy steel crown with hard chrome-surfaced ring grooves in which four compressing rings are fitted. In this particular model a protective layer of Inconel is welded to part of the crown surface to prevent high temperature corrosion. The piston is oil cooled, oil being supplied by a telescopic gland to the crosshead and then through the piston rod. It is returned from the crosshead to a slotted pipe in the crankcase. A short cast iron skirt is added. The crown is bolted to the piston rod at an inner support ring.
Surface hardening reduces wear on the piston rod at the diaphragm gland. The rod is bolted at the top of a cylindrical crosshead which is of large diameter and incorporates a full-length bottom half-bearing shell. Floating guide shoes are attached at each end.
The crankshaft may be either semi-built up or of welded construction, with large journals and pins. All crankcase bearings are of white metal. Main bearings have thick shell, crankpin (bottom end) and crosshead (top end) bearing have thin-wall shells. White metal is used for the guide surfaces. The exhaust valves are operated hydraulically under oil pressure from cam-timed actuated pistons.
They have air compressed springs which allows them to be rotated by vanes. The valve spindles are usually manufactured by the hot isostatic pressure (HIP) method, a compound Nimonic and austenitic steel part construction. Valve housing is cooled at its seat and spindle guide bush but its upper duct is un-cooled to avoid low-temperature corrosion.
Fuel pumps are cam driven and timed by the plunger helix. An adjustable barrel allows variable ignition timing to maintain combustion efficiency at low speed and can be adjusted to connected at the cam roller guide which is activated by compressed air. Each pump supplies three identical fuel injectors for the corresponding unit. Injectors are un-cooled but they circulate hot fuel oil directly while their needle valves are in the closed position.
The engine operates with a constant pressure system. With un-cooled turbochargers. Two auxiliary blowers are fitted to operate at low charge air pressure or at low engine revolutions. A number of waste heat recovery and power take-off systems can be operated under running conditions.