No abstract

No abstract

said that quantitative data on the movement of ships at berths was rarely obtained and there was none in the case of Tema, but by all accounts the berths were remarkably quiet. There had been no case of a ship having to put to sea because of ranging.208. The contribution of the Hydraulics Research Station to this happy state of affairs was rather a modest one. There were three major factors in determining the movement of moored ships at berths, only one of which had been studied at the Hydraulics Research Station:(a) the waves in the vicinity; (b) the attenuation of waves by the harbour; (c) the response of the ship and its mooring system to waves.At the time when the harbour was designed there were virtually no wave records.None of the few records that were obtained was harmonically analysed because there were no techniques for making use of such analyses. 209. Again; at the time the Hydraulics Research Station was making its investigation, in 1955, no information on the response of typically moored ships to waves was available. One had merely mariners' views that waves around 1 ft highsome said waves around 2 ft high-were just tolerable for a ship lying alongside. The only one of the three problems that was amenable to study was the attenuation of waves by the harbour, and this was examined minutely in an undistorted model built to a scale of 1 :l 20. 210. Fig. 9 showed a typical response curve, one of a large group which together revealed the performance of the harbour. The ordinate was the maximum waveheight found wherever it occurred along one berth expressed as a ratio of the steady wave-height at sea; the diagram showed how this ratio varied with the period of the waves. The abscissa covered a range of periods from 7+ to 45 seconds. The figure showed that in the 10-S period wave band responses were very satisfactory, around 1/20. At the long end of the scale, around 45 S, the response rose to one third and there was another whole set of data relating to waves with periods extending from 40 S to 5 min, which showed responses generally in excess of unity. 21 1. One wondered whether the harbour's freedom from the very long waves in the 40-S to 5-min period band was due to the absence of such waves on this particular coastline. The speaker was inclined to think that this was not the explanation. On the contrary the waves normally reaching Tema formed a regular swell from distant storms and were precisely of the type likely to set up surf-beats.212. It could be demonstrated that very long waves, or surf-beats, were not too troublesome provided they were not accompanied by shorter period swell. One found that rather stiff ropes were desirable, giving the ship a natural period shorter than that of the surf-beats. The speaker thought that the great success of the design in excluding swell had led to quiet berths in spite of the presence of surf-beats from time to time. Unfortunately this must remain a matter of conjecture because no wave records were available.

283custody of the port organization are the loads broken down and the packages handled separately. Even that is not always necessary, however, for at isolated places the practice has already begun for dock-owned pallets to go to consignee for unloading. FUTURE TRENDSIt is true to say, of course, that the mechanized methods described are so far being fully employed only at certain pioneer berths. Nevertheless, the modern trend is now clear. For piece goods, it is unit-load handling instead of individual package handling-to effect savings in time, space, money, and arduous labour.The evolution of this method is already far enough advanced to affect not only the types of port equipment required and the layout of quays, sheds, and warehouses but also, in the general industrial world, goods-packaging, transport-vehicle design, and the pattern of factory and other premises. There is little doubt that, it will ultimately affect ship construction.In maritime countries, speed of ship discharging and loading, with care of cargo and safety of personnel, is essential t o the national economy and, although existing kinds of equipment are being improved daily, it is from the new-type appliances that the more dramatic benefits are expected. When these accrue, the recipients will not only be the port employers and the shipping companies, they will include manufacturers, shippers, receivers, haulage and lighterage contractors, many groups of work-people and, it is hoped, the consumer. The Paper, which was received on the 18th October, 1955, is accompanied by eight photographs and one drawing from which the half-tone page plates and the

(formerly Chief Engineer, Manchester Ship Canal Co.) said that the part of the investigation in which his company was vitally concerned was the Eastham channel. The Eastham channel formed the approach to the Port of Manchester and it was absolutely essential that it should be maintained at a depth sufficient to deal with the class of traffic which the port handled.108. As Mr Price had said, since 1953, a great deal of difficulty had been experienced in dealing with the Eastham channel. The rate of siltation consistently exceeded the maximum possible dredging output, and consequently the channel slowly but surely silted up.109. When the Hydraulics Research Station took on the investigation, his company asked if it would examine certain schemes for training walls to see whether that type of construction would be of any use in dealing with the extremely difficult situation. The Research Station tested various schemes. All were fairly promising, but from an engineering point of view it was felt that none of them could be recommended to the company for the simple reason that the constructional difficulties were enormous. It would have been necessary to carry out the construction in a tidal estuary where the tidal range was 30 ft, where current-velocities ran up to a rate of 4-5 knots at half ebb, and where the work could be carried out with the least possible interference to traffic. The final objection to any project of that kind was the high cost of any of the schemes. The cost was not estimated accurately. but it was quite obvious that it would run into very big figures. That was expenditure of a kind which the company was not prepared to meet having regard to the uncertainty of the results likely to be achieved.110. The second proposal that the Wallingford station made was a very attractive one indeed from the company's point of view. The Research Station suggested that the company should stop dredging altogether and allow the channel to find its own depth. They said the depth would never become less than 5 ft and, on the model, it had been demonstrated very conclusively that that was so. But Mr Milne himself, with his day-to-day experience of that small part of the Mersey, could not agree with the Research Station that that was likely to occur in practice. His own view had been, and still was, that the channel could shoal up to 5 ft, and that the 5-ft soundings would develop into 4 ft, the 4 ft into 3 ft, and so on. That had been the case in the past, and he thought it would be the case in the future.111. Although, by stopping dredging altogether and adopting a channel with a depth of 5 ft below L.B.D., the company would have saved about S600 000 a year, DISCUSSION ON YIELD AND MODEL INVESTIGATION lNTOit was decided that it would not be possible for Manchester to continue as a first class port with an entrance channel of only 5 ft, and therefore they had to consider continuing with dredging. 112. About that time there was an alteration in the pattern of siltation which enabled his company to alter their dredgin...