Page 127 - Practical Design Ships and Floating Structures

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5.1 Motion Paratnetem

a WIG model test with different motion parameters include V, Y 1 , has been conducted. According to
the result of calculation, ‘I- (Maximum impact overload coefficient) increases rapidly along with
increasing v, and the relationship of them is almost in proportion to v.2. In fact, if yo =const, the
amount of v. varies with the vertical velocity component directly (v,= V. tg Y ,I, that is to say impact
overload is proportional with vertical velocity square and this is just agree with the result of wedge
impact theory. The rl - also rises rapidly along with the increasing Y ,. When V, is fixed, the change of
Y , actually means the change of vertical impact velocity, if Y ,is small enough, as Y, increases, rl-
will rise a little bit, when Y ,increases not too large. But ‘I- will rise withy ,obviously wheny ,is large.
The rlmm rises a little bit along with 1 when yo is fixed, so the influence of 1 is rather small than
that of Y,.
5.2 Effect of Hull’s Main Parameters
The important hull parameters are deadrise B and beam-loading coefficient cb. If B increase, rl will
decrease, this phenomenon will be more evident with small B . Small cb doesn’t affect impact load
evidently according to the result of calculation, Only when cb gets to a larger value, impact overload
begins to decrease. Critical value of cb which ‘I- begins to decrease notably is about 4.0. If there is
Cb =18, the qmax decreases about 50%, so cb >18 is an ideal situation, in this case, 9- can decrease
more than 50%.
6 PRIMARY STUDY OF HYDRO-SKI

How to reduce impact load in waves is one of the most important problems which should be solved for
large WIG in service. Besides theoretical prediction and influence rule research, hydro-ski is a kind of
efficient method to reduce impact load. Theoretical and experimental research for plate-ski which has
been used by Russia on its large WIG, or for strut-type-ski shows that hydro-ski is efficient for WIG to
reduce impact load in waves.
6.1 Zrnpact Load with Plate-ski

Model test about impact load with changing attachment of both plate-ski and strut-type-ski have been
carried out and the results show that ski can reduce impact load efficiently like what we have imagined.

6.2 Planing Resistance during Takeog with Plate-ski
Model test on resistance of ski has been carried out to study the effect of plate-ski on planing resistance,
the result shows:
is
(1) Influence of plate-ski on planing resistance at low speed (V~CZ~S) not evident.
(2) At relatively high speed (Vm>2m/s) 1iWdrag ratio will increase and this will be more evident under
the condition of rather small trim angle ( 1 ). In general, the sum of 1 and o which is the angle of ski
installed is favorable at about 10 degrees.
(3) Ski which is installed near CG can make lift center moved slightly on planing surface when the trim
angle changes, this is good for longitudinal stability during takeoff.

7 CONCLUSION AND RECOMMENDATION
(1) Theorical method proposed in this paper for predicting impact load in waves has been proved by
model test to have enough precision for engineering application.
(2) Hull parameters’ selection is one of efficient ways to reduce impact load of WIG.
(3) Controlling motion parameters reasonably can also reduce impact load.