All About Engines

The Oil Engine 247 chapter on Engines for Ships, that the plan is far more satisfactory than a complicated valve gear. Secondly, the Diesel engine has a good range of speed when it has once started; the best way to start it is to get up speed on compressed air. But in a narrow or crowded waterway a ship can only be manoeuvred safely with engines that are fully under control and capable of speeds which fall to the barest perceptible movement. Nevertheless, the marine Diesel engine is grow- ing in favour, and is being installed especially on oil tank steamers, both because it is safer and be- cause the vessel trades only between ports where oil fuel can be readily obtained. Attempts are being made to overcome the difficulty of reversal by using the engine to drive a dynamo, and using the electric current thus produced to drive a motor. The motor can then be reversed by altering the direction of the current. This arrangement also allows the speed to be varied, and permits of that delicate manoeuvring which is necessary in narrow or crowded waters. But the greatest marine success has been in sub- marines. In these vessels space is restricted to the last limit, as will be seen from the illustration of the engine room of the Holland submarine, Fig. 139, Plate 24. Ten years ago these vessels were 10 feet in diameter at the largest section, or little more. To-day they are over 20. As the size increases, however, so also does the power required to drive them. More- over, the surface speed has increased in the same time