Screw Propeller Computer (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: GENERAL DISCUSSION OF SCREW PROPULSION. Resistance of the Ship. When a ship is towed through the water at a given speed V, it meets with the following resistance: Resistance Of the Water.?(1) Frictional, (2) Wave-making, (3) Stream-line, (4) Eddy-making, the sum of the last three being known as the " residuary resistance " and the total as the net resistance, r. Resistance of the Air.?In addition to the resistance from the water, the vessel also encounters resistance from the air on the parts of hull and upper works above the water, rigging, etc. Thrust. The thrust necessary to overcome the resistance to the forward motion of the vessel is developed, by the propeller projecting a column of water with a certain velocity in a direction opposite to that of the ship; the reaction from the stern ward momentum given to the water ?per unit of time?constituting the thrust which transmitted through the shafting to the thrust bearing, drives the vessel ahead. Rotation of the Race.?A portion of the total acceleration given to the column of water is gradually imparted to it forward of the propeller, the back of the blades exerting a suction, and in passing through the propeller it receives the final stern ward acceleration and atthe same time is given a rotary motion which is accompanied by centrifugal force causing a diminution of pressure from the center to the outer limits of the column. The effect of this rotation is to cause a larger proportion of the final sternward acceleration to be imparted to the water before passing through the propeller: it is generally accepted, however, that this effect may without material error be ignored, except with high slip and pitch ratios. Cavitation.?There is a limit, however, in the process of developing the thrust, to the amoun...