Nowackt and Sharma 
arbitrary choice of any one method , we carried out three complete 
analyses : one based on thrust identity (subscripts T) , one on torque 
identity (subscripts Q) , and one based on a mean (subscripts M) 
advance coefficient Ju defined as 
peewee (ay Top ore ey ye 7 (17) 
where J_. and J_ are the points of thrust and torque identity (be- 
tween the beled niftl condition and an equivalent open water condition 
of the propeller) respectively . 
Our procedure for evaluating the propulsion factors can be 
briefly outlined as follows . Fig. 23 shows the typical result of a self- 
propulsion test at one Froude number , i.e. dimensionless coefficients 
of measured thrust T , torque Q , and residuary towing force F 
as functions of propeller advance coefficient J_._ (based on hull speed) . 
Obviously , this presentation is suitable for determining the self-pro- 
pulsion points . Thus the model self-propulsion point lies at Cop = 0 
and the ship self-propulsion point at 
Spdlieul) Aenea eee) 
(18) 
if viscous resistance is estimated by the form-factor method and a 
surface roughness allowance is neglected for the sake of simplicity . 
Here Cy and C are the predetermined coefficients of friction 
at the model and ship Reynolds numbers respectively , see Equation 
(7) . For instance , the self-propulsion point of a smooth geosim 80 
times as long as the model ( and running in fresh water at a tempera- 
ture of 15° C) is found to lie at J,. = 0.733 . Leaving aside the self- 
propulsion point for the moment , at any value of J (representing a 
certain propeller loading) the propulsion factors are found as follows . 
Take from the resistance test (Fig.3) the coefficient of total resistance 
Cr at the given Froude number and obtain the propulsive efficiency” 
n (R yy W72 ™mQ,, (19) 
3 
a 
(s/D°) (Cc 
D 
p> Crp) /4™ own 
* For a truly self-propelled system the towing force F)=0, and 
then Equation (19) agrees with Equation (15). 
1862 
