of the gear-cutting. The teeth are cut out of the solid metal, and it can readily be appreciated, especially in these days when most people have some experience of gears on motor-cars, that, unless the teeth are cut absolutely alike, and also most accurately and equally spaced, irregular running will ensue. The coal consumption with the marine steam turbine may be taken at 10 to 20 per cent less than the reciprocator.

Electric Drive.

The steam turbine with electric reduction gear may yet prove an alternative to the mechanical reduction gear.

Forced Draught.

On the modern cargo and passenger steamer, it is now almost invariably the case that the boilers are worked under forced draught, and as the "Howden " Hot Air Patent System of forced draught is the most popular, our remarks refer more particularly to it. A considerable saving in weight and space is effected by the installation of the forced draught arrangement over that of similar installations of equal power with natural draught. There is also the advantage that inferior classes of coal, which cannot be used with natural draught boilers, can be used to advantage with the forced draught boilers, and in cleaning fires steam can be better maintained and can be raised much quicker on the boilers. With the installation of Howden's forced draught there is the further advantage that a thorough ventilation of stokehole is obtained, as well as of the engine-room, where the fan may be placed.

Some years ago a comparison was made between two steamers of a well-known company, one fitted with natural draught and the other with Howden's forced draught. Both steamers were practically alike and engaged in the same trade, and made the same number of voyages per year. A close comparison was made of the coal used during the year's working, and a careful analysis of the results gave a saving of 13 per cent in favour of the ship fitted with the forced draught.

Similar advantages accrue when forced draught is used on oil-burning boilers,

Motor Ships.

This brings us to consider next the motor ship, with its internal combustion engine. The following table and particulars are taken from Lloyd's Register for 1922-23

Of the 1,620 motor vessels mentioned in the above table for the year ending July, 1922, 341 are of 1,000 tons and upwards, and of these 130 have tonnages ranging from 1,000 to 2,000 tons; 98 are from 2,001 to 4,000 tons; 47 from 4,001 to 6,000 tons; and 66 are above 6,000 tons.

These figures show how rapidly the motor, or Diesel engine, as it is more commonly called, is gaining in favour, which is due to several marked advantages it possesses over steam.

In the first place, the consumption is less than lb. of oil per i.h.p. hour, as compared with 1 lb. with the steam reciprocator. The oil stows, in comparison with an equal weight of coal, in round figures, as 3 to 4. The comparative costs in the United Kingdom in January, 1923, were about 80s. for oil and 25s. for coal per ton. The advantage, therefore, from the consumption point of view is about 5 to 4 in favour of oil. In some parts of the world oil is much cheaper and coal dearer than the figures given, which gives a still greater advantage to oil.

Secondly, steam boilers are dispensed with, and consequently their weight, and the necessary firemen, etc., are cut out.

Then there are several consequential savings, such as quicker bunkering, less demurrage, cruising radius increased, additional cargo capacity, less accommodation for engine-room staff, no standby losses, less cleaning ship, reduced fuelling appliances required; also perishable or special cargo can be carried in the holds adjoining the machinery with impunity, as there is no local heating, as with steam boilers.

On the other hand, there are several disadvantages. This engine only came into being within the last fifteen years, so that it is not yet confirmed that reliability is thoroughly assured. There is at present a great variety of types, among which are: Beardmore Tosi, Burmeister & Wain, Carel, Doxford, Fullager, Junkers, Krupp, Mirrlees, Nurnberg, Nobel, North British Diesel, Still (a combination of steam and Diesel), Sulzer, Werkspoor.

Some are of the two-cycle variety-that is, having one impulse every revolution, or two strokes; others are of the four-cycle variety-an impulse every two revolutions or four strokes. The latter is the more popular at present, though it seems reasonable to expect the former to attain precedence ultimately, as naturally it gives practically double power for the same weight.

The number of different types-and most of them are outstandingly different-indicates that thought is far from being crystallized as to the ultimate standard engine.

Then the first cost is considerably greater than that of the steam engine. Also and this is a very important point for the shipowner-there is not yet a ready supply of a capable personnel to handle this engine, and in the event of an accident, or repairs required abroad, the same facilities and experience are not yet available as with the steam reciprocator.

The shipowner to-day, therefore, finds himself presented with a greater variety of forms of propulsion than ever before, and has to adopt the type which best suits his requirements; and, while there seems little doubt that the Diesel engine will ultimately be the favourite, it has still a long way to go to attain the reliability of the steam engine.

Oil Fuel.

In recent years oil fuel has been increasingly used by burning it in the furnaces of steam boilers in place of coal. It has been applied more particularly to large passenger liners, giving quicker bunkering and, consequently, a quicker “turn round," and avoiding all the dirt and cleaning consequent with coal.

Some steamers are fitted so that they can burn either coal or oil, and, according to the route they are on, use whichever is cheaper.

In confirmation of the above the following is an extract from Lloyd's Register for 1922

Vessels to the number of 209, representing 1,395,929 gross tons or 55 per cent of the total tonnage of new vessels classed during the year under reviewwere fitted for burning oil fuel.

The following table shows the gross tonnage of vessels either originally fitted to burn oil fuel or subsequently converted for that purpose. The figures represent all such vessels recorded in the Society's Register, and for the sake of comparison those for the year 1914 are also included

These figures include vessels which are fitted with installations for burning oil in the furnaces of their boilers, but it does not necessarily follow that all such vessels are using oil. A number of such installations can readily be replaced on occasion by coalburning fittings when oil is unobtainable, or when its price, compared with coal, is so great as to render its use unprofitable.

Among the vessels converted during the year, under the Society's supervision, for burning oil fuel, were the Aquitania, Berengaria, and Mauritania, and several other large passenger vessels.

Speed.

The speed of vessels varies according to the power, dimensions, and form. For vessels of similar size and form it is generally accepted that the speed varies as the cube of the power. In other words, if it is desired to double the speed, the power must be increased eightfold, or, put another way, double speed means eight times the consumption of fuel.

This is one of the principal reasons why the tramp, with her comparatively moderate speed, is much more economical than the faster cargo or passenger liner. It seems also almost unnecessary