arrow T represents the torque which must act on the propeller shaft. This torque is exerted upon the propeller shaft by the bearings as indicated by the arrows FF' in the top view, Fig. 20. The high speed and great weight of the rotating parts of a steam turbine represent a very great spin-momentum (arrows S and S' in Fig. 19
very long) so that the increment of spin-momentum ΔS which corresponds to a given angular movement of the ship is very considerable, and the torque T is great. Therefore the forces FF' in Fig. 20 may be very great. These forces are transmitted to the bearings of the propeller shaft through the hull of the vessel from the middle and forward parts of the vessel, and therefore excessive stresses may be brought into existence in the hull. It is supposed that the loss of the
British torpedo boat Viper several years ago in a rough sea was due to this action.
Figs. 21 and 22 represent the details of the gyrostatic action of a high-speed steam engine, such as is used for driving dynamos on board ship, the shaft of the engine being athwartship. In Fig. 21 the ship is represented as rolling in the direction of the curved dotted arrow, and T in the vector diagram represents the torque which must act upon the engine shaft. The details of this torque action are shown in Fig.