382 Scientific Proceedings, Royal Dublin Society. 



every care and great outlay, is so frequent, that trial should be 

 given to a means of obtaining shelter which would suit many 

 localities, and which would be free from the risk of failure on 

 this score. The presence of the breakwater would in all proba- 

 bility increase the scour by deflecting the tidal current to the 

 bottom, while, at the same time, surface-currents would be checked. 

 These are just the conditions often so unattainable in harbour 

 construction, and yet so desirable. 



The stone breakwater once built has to remain. If a larger 

 area of shelter has to be subsequently provided, or if found to be 

 improperly placed, it is an additional difficulty in bettering the 

 conditions. The floating breakwater, on the other hand, is 

 removable, and may be experimentally placed so as to make the 

 best harbour. It can be added to at any time. Finally, if, as 

 often happens, the maritime development of the place disappoints 

 expectations, or a fishery dies out, the harbour can be removed 

 altogether and used elsewhere. 



With regard to the consideration of cost, it is necessary to take 

 into account not only first cost, but cost of maintenance, and set 

 these against the corresponding cost in the case of fixed structures. 

 The running expense of dredging would probably be absent. 

 Repairs, again, would be more easily effected, as, in fact, the break- 

 water may be removed and dry-docked. If this consists of several 

 units, these may be separately dealt with. It would be quite 

 possible to secure a very permanent surface against corrosion by 

 the sea- water by the use of concrete. I have not referred to this 

 in the foregoing remarks; but surfacing with cement concrete, 

 supported by projecting T-irons, might readily be applied to 

 interior work exposed to water, or to the wind and water zone. 



As regards prime cost, it must be borne in mind what very large 

 sums are sunk in quite small harbours around our coasts ; and, as 

 already observed, it must be set down on the side of the removable 

 breakwater that the lamentable failures so often attending the best 

 efforts of the harbour engineer would be impossible. In the case 

 of Arklow, now before the public, the proposed extension of the 

 piers seaward would very probably merely result in carrying the 

 accumulation of sand further out. There is an unlimited supply 

 of sand around the coa,st. The true solution of the Arklow 

 problem is, in my opinion, to trust to sand -pumping for pre- 



