Page 119 - Practical Design Ships and Floating Structures

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It shows that the difference of resistance performance between tunneled combined with twin-stem and
tunneled stem is small at same Fn.
TABLE 2
PROPULSION FACTOR OF TWO AFTERBODY IN DEEP WATER

Wake fraction (0

TABLE 3
PROPULSION FACTOR OF TWO AFTERBODY IN SHALLOW WATER (H/T=l.5)

In order to compare their performance of speed further, a synthetical index noted k is introduced which is
defined as:
K=PD/( A x V )
Where PD - delivered power at propeller in kW.
A - displacement in ton.
V - speed of ship in Km/hr
From the above expression we can see that the more smaller value of k is, the more higher performance
of speed is. By calculation according to test results, the curves k-Fn are given in figures. By comparing
tunneled combined with twin-stem to tunneled stern , we can see that the synthetical index of speed
performance (k) of the former is smaller than one of the latter. The new hull form of tunneled combined
with twin-stern is one of high performance hull form in shallow and strong current indeed.