A disconnecting paddle engine is one in which the paddles may be driven separately or together. This is effected at the inner port bearing by a clutch wheel, which slides endways on the shaft and is driven by feathers seated in the shaft. This clutch wheel is operated by a lever so as to engage or disengage with the crank pin, which is fast in the outer crank.
Disconnecting paddle engines are always fitted with loose eccentrics, such engines being used for steam tugs and ferry boats, where quickness of turning and of reversing is of great importance.
The thread of a screw propeller is its length measured along the outer edge of the blade.
The angle of the thread is its angle to the axial line of the propeller shaft.
The length of the thread is the length of the outer or circumferential edge of the blade.
The area is the surface of one side of the blade.
The diameter is the distance apart of the two points on the edges that are diametrically opposite and furthest apart.
The pitch of a propeller is its degree of spirality, and is represented by the distance it would move forward if the water was a solid. It is measured by drawing a line representing the axis of the propeller shaft, and at a right angle to it a line representing in its length the circumference of the circle described by the tips of the blades; from the point of intersection of these two right angle lines a diagonal line is drawn representing the angle the blade at its outer edge stands at the propeller shaft axis. The greatest distance between the diagonal line and the line representing the propeller circumference is the pitch of the propeller.
A left handed propeller has a left hand thread or spiral, and revolves from left to right to move the ship ahead.
A right hand propeller has its blades inclined in the opposite direction, and of course revolves in the opposite direction to a left hand one.