98 EXPERIMENTS ON THE FROUDE. 
Froude from the towing tests can be accepted, the determination of thrust- 
deduction has a similar degree of positiveness. The large value of this 
factor and the correspondingly small value of the hull efficiency for the 
1-inch and 3-inch settings, both of which may be considered to be normal 
are notable. The thrust deduction for the Manning is certainly less than 
for the Froude and probably much less because the power required for the 
Manning is relatively less and consequently the propeller race is relatively 
less. If it can be admitted that the thrust-deduction is proportional to the 
square of the velocity of the race then the reason for the exaggeration of 
thrust-deduction for a model is at once evident. 
The setting of the propeller 6 inches astern of the stern-post corresponds 
to 30 inches astern in the Manning which would be impossible with the 
arrangement of the screw-aperture and the rudder-post of that ship. But 
for a new design such a setting would be possible and would appear to 
be an advantage of 12 per cent. as shown by a comparison of the shaft 
horse-powers. 
COMPARISON WITH THE MANNING. 
One of the most interesting and important results of our investigations 
is the comparison with the progressive speed trials of the Manning reported 
by the writer to this Society.* A consideration of the conditions of those 
trials and a study of the results by the writer and by others justifies the 
claim that they are reliable to the degree of precision properly attributable 
to such work where the power is determined by aid of the steam-engine 
indicator. ‘The indicators used were of the old enclosed spring type, piped 
by three-way cocks to both ends of the cylinders; the power may be under- 
estimated with such an arrangement but the writer does not wish to venture 
an estimate. 
In his original report the writer gave an analysis of the trials by the 
method proposed by Naval Constructor Taylor, estimating the wake of the 
ship and the efficiency of the propeller by aid of Froude’s theory of the 
propeller. The tests of the actual propeller used on the Froude enables us 
to estimate the wake and thrust-deduction for that boat as has already been 
shown, and also to assigna probable efficiency to the propeller of the Manning. 
With this additional information a new analysis of the trials of the Manning 
is offered as a basis for comparison with the Froude. 
In this analysis the fundamental data, namely, the revolutions per 
minute, and the indicated horse-power for speed in integral knots per hour, 
* Transactions, vol. 7. 
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