43 



When the pier-heads are disposed so as to form a funnel mouth con- 

 tracting inwards, such as the entrance to Whitehaven Inner Harbour, 

 they tend to produce increased agitation within ; because, as the waves 

 roll in between the outer shoulders of the jjiers, instead of being allowed 

 to jjass on freely to spread and exhaust themselves gradually, they are 

 contracted and increased in height, or in other words a heaping-iip of 

 energy takes place between the piers, which is forced through the con- 

 tracted passage by the following waves, thus producing a chopping and 

 agitated sea inside. 



In the disposition of the quays and jetties in a harbour on an ex- 

 posed coast, sufficient space should be allowed for the evolutions of vessels 

 driven in whilst under sail. Facilities for railway traffic are frequently 

 important elements of consideration ; and where sheds or warehouses are 

 required for the protection of perishable articles, the width of the quays 

 must be regulated accordingly. 



In constructing the quays, it is usual to take advantage of the 

 increased stability afforded with a sloping or battering frontage, but in 

 tidal harbours, where vessels frequently lie abreast, it is manifest that the 

 batter must be very limited, otherwise a vessel in the inside berth might 

 get nipped during the fall of the tide between a deeper-laden vessel and 

 the face of the structure. 



The expansion of traffic at a tidal harbour is frequently met by con- 

 structing open-piled timber jetties, which, though not so lasting as stone 

 structures, are less costly, and possess the advantage of affording addi- 

 tional quay space without encroaching to any prejudical extent upon the 

 water area or tidal volume of the harbour. Cheap structures of this 

 class readily meet the demands of increased traffic, and encourage its 

 development to such an extent that it becomes absolutely necessary to 

 have dock accommodation in which vessels can lie loaded and discharged, 

 or moved about at all states of the tide. It is indispensable 



to the commercial prosperity of a seaport to jjossess dock accom- 

 modation in which vessels can float at all times, so as to avoid 

 the risk of taking the ground when deeply laden, particularly after the 



