Machinery for large tankers 1

The lecture is concerned with machinery for large tankers both at sea and under consideration for the future. The range is up to 130,000 tons d.w. and the speeds up to 18 knots. The choice of machinery is considered, but virtually no reference is made to nuclear propulsion. Comparisons are made between the steam turbine, the heavy-oil engine, the gas turbine and the free-piston engine, and some advantages and disadvantages are brought out.

Regarding the steam turbine, the choice of pressures and temperatures are considered. Moisture content of the steam in the last stages of the l.-p. turbine is shown with special reference to the erosion which takes place on the edges of the last few rows of blades. The higher K values, now being permitted by Lloyd’s to be used for gearing, are mentioned, and also the use of excess pressure oil. The fitting of five-bladed as against four-bladed propellers for such aft end installations is discussed and findings given from the results of two ships with similar machinery.

With reference to heavy-oil engines the amount of steam made available by the exhaust gases is considered, and it is pointed out that, with engines running on reduced ratings, this amount is often considerably less than that expected by shipowners.

Cargo handling facilities for forms of propulsion other than turbines points to the possible use of small low-pressure water-tube boilers in conjunction with a steam/steam generator for oil heating.

A curve is shown giving comparative machinery installation costs of steam and heavy-oil engines for the tankers considered. This is made up from a number of ships now at sea but is extrapolated for larger installations. A further curve is given showing relative weights of turbine machinery.

A summary gives the present findings with respect to machinery for large tankers, but points out how the situation might rapidly change.