Free Surface Effects tn Hull Propeller Interaction 
and the thrust deduction fraction 
= + Ss 
t om ats R,) ip Lik 
fa 
J 
2 
=)1) =, 4S /OD>) (ees Cep)/ Kay 
(20) 
Now read from the open water characteristics (Fig.8) the advance 
coefficients J_, at thrust identity (K_ = K,. ) and J_ at torque 
identity (K. = K = . Calculate ry from Hie aero (07)? £~and 
read the eae eilien oan water efficiencies nov , 70Q » 70M from 
Bagads ahs Do. 55 Sh sil respectively . Calculate effective wake 
se hes £5 Q M 
fractions 
ell Gace 
“Tr Jo/ Sey 
ae is Io/ Tey 
UM cece ies (21) 
hull efficiencies 
ee ak ee 9 
MQ = (1+t) / Uw) 
tum = O-B/ C-wyy) (22) 
and relative rotative efficiencies 
"ep = Dor tar 
Vota I/9Q "HO 
Tam = "p/"om "HM (23) 
This completes the analysis. 
The result of one such evaluation , out of fourteen actually 
carried out , is reproduced in Fig. 24 . Since this is generally typical 
of all others , the following remarks are relevant . First , the thrust 
deduction fraction and relative rotative efficiency are relatively insen- 
sitive to changes in loading. Second, the equivalent open water efficiency 
decreases with increasing loading (decreasing J_,) as expected . Third 
the effective wake fraction , and consequently the hull efficiency de - 
crease with increasing loading . This is in contradiction to the 
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