SOME EXPERIMENTS ON PROPELLER POSITION AND PROPULSIVE 
EFFICIENCY. 
By Rear Apmira D. W. Taytor (C. C.), U. S. N., Honorary VicE-PRESIDENT. 
[Read at the thirtieth general meeting of the Society of Naval Architects and Marine Engineers, held in 
New York, November 8 and 9, 1922.] 
After publication of results of years of Model Basin experimentation, the naval archi- 
tect and marine engineer can now determine in advance with reasonable accuracy, for nor- 
mal forms, the effective horse-power of a ship, and the dimensions and proportions of a pro- 
peller which would propel the ship with high efficiency if it were Froude’s phantom ship, 
which has the resistance of the actual ship but is assumed not to disturb the water. 
But we have to deal with actual ships, and the reactions between ship and propeller are 
very complicated phenomena. The wake of the ship of course affects the action of the pro- 
peller, and the suction of the propeller adds to the resistance of the ship. The thrust deduc- 
tion is always positive, 7. e., the thrust is greater than the resistance of the ship without 
the propeller. Nearly always, however, the wake is also positive, which tends to increase the 
efficiency of propulsion. We generally and conveniently characterize the net results of the op- 
posing factors as hull efficiency. If this is unity, the power required to propel the actual 
ship is the same as if it were Froude’s phantom ship, while a hull efficiency greater than unity 
means that we can get along with less power and vice versa. 
A brief enumeration of the factors affecting hull efficiency indicates the difficulties of 
dealing with it accurately. Considering the hull, it is affected by dimension and shape, but 
more particularly by the fullness and shape of the after body. A “V” stern, for instance, 
will show a somewhat different wake from a “U” stern, and the thrust deductions upon it 
will not be quite the same. 
Considering the propeller alone, the hull efficiency must be somewhat dependent upon 
its dimensions and proportions, blade area, blade thickness, shape of blade, etc. 
Considering the combination of ship and propellers, the hull efficiency must be affected 
by the number and locations of the propellers. For a single-screw ship, the propeller position 
may be varied vertically and longitudinally. For vessels of two or more screws, locations 
may be varied transversely for side screws. 
For high-speed ships the hull efficiency must be affected by speed. 
Probably of the many factors involved, those of location are most in need of systematic 
investigation because in many practical cases there is some choice of location and we would 
like to know whether we can gain anything by making a proper choice, and also whether we 
could gain by so shaping our designs as to permit a favorable location without counterbal- 
ancing loss in other respects. 
The experiments which are the subject of this paper, recently made at the U. S. Model 
Basin, deal with the question of location for a single-screw low-speed vessel. They were 
initiated while I was chief constructor, and my successor, Chief Constructor Beuret, has 
kindly permitted their publication. The lines of the model used are shown in Fig. 1, Plate 
