Page 539 - Practical Design Ships and Floating Structures

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sinkages and the numerical calculations by Jiang (2000) using an approximation based on the extended
shallow-water theory. For the geometry configuration of the VBD towing tank the agreement is
equally remarkable for both sinkage estimations. However, since the numerical estimation can be
applied for general shallow water cases, the combination of the proposed prediction method with the
well-established shallow-water approximation could be a new method for the resistance prediction of
ships in shallow water.

on measured sinkage

VJkmlh]
Figure 7: Comparison of the predicted ship-resistance using measured and empirically estimated
sinkage

150
120
- 90
E
2 60

30
0
0 2 4 6 8 10 12 14 16 18 20 22
VJkWhl
Figure 8: Comparison of the predicted ship-resistance using measured and calculated sinkage
5 PROPULSION PERFORMANCE

Since the propulsion tests can be conducted by means of the so-called English method, in principle the
self-propulsion point at any considered propeller loading can be found. For a ship in shallow water, the
ship self-propulsion point should correspond a towing force defined by
) = (‘FOEM - ‘FOES - ‘A ) ,% PM ‘M ‘&
‘
M
FDE ( (7)

where CA is an empirical model-ship correction allowance.
The delivered propeller-power at the ship self-propulsion point defined above is plotted in Fig. 9
versus the effective speed for the water depth h/T=4.0, 2.6 and 2.0. For this subject container ship, the
delivered power at the same effective speed is slightly higher in deeper water. This means the
propulsion features could not be assumed as a unit function of the effective speed. However, if the
delivered propller-power at the ship self-propulsion point is plotted now versus the blockage speed
defined by equation (2), as shown in Fig. 10, it can be found that the delivered power at propeller can
be considered as a unit function of the blockage speed and independent of the water depth. If this
would be true, it would lead to a new hypothesis for the propulsion performance:
The delivered power at propeller at the ship self-propulsion point corresponding to the effective speed
could be considered as a unitfinction of the blockage speed and independent of the water depth.