FOR GREA T BRITAIN AND IRELAND. 85 



OVERLAPPING POSITIONS OF PIER-HEADS. 



This, from a nautical point of view, is a great convenience 

 and advantage, as it allows boats or vessels much facility 

 of ingress and egress in foul winds. A boat or vessel can 

 take her departure from the lee of a pier-head overlapping 

 its fellow to a certain extent, as shown in the diagrams, and 

 weather the lee pier-head without difficulty in working out 

 of the harbour, and when working into the harbour, can 

 then stand along the outer face wall of the inner of the 

 two, and fetch inside, according to her position. The writer 

 has seen so much difficulty and damage result from the 

 position of the piers vis-a-vis that, wherever the exposure 

 is not too great, he would confidently recommend one pier 

 to be placed in advance of the other. 



PIERS En Avance AND PIERS Vis-a-Vis. 



Piers en avance^ or overlapping, are found excellent in 

 bays, or where islands exist as natural breakwaters to a 

 long fetch, in fact wherever there is a certain amount of 

 natural protection. In such positions these covering piers 

 receive the impact of the waves from th'e point of greatest 

 exposure, and shoot off the chief portion of their violence 

 towards the shore of the bay, or free space to leeward. 



The question, however, naturally arises in what length of 

 drift or fetch a covering-pier, i.e., en avance, ceases to be use- 

 ful, beyond which it may be positively prejudicial, owing to 

 the amount of undulation it will throw into the interior of 

 the harbour, during a gale of wind blowing on its inside face. 



From observations made by the writer, he concludes 

 that about two-and-a-half miles is the longest fetch to 

 be allowed in most cases, where such drift would fall on 



