POSITION OF ENTRANCES. 



ii 



of 8 feet ; involving extra cost of excavations over the whole 

 area of the basin, and also extra depth of walls and foundations, to 

 be compared with the cost of gates and gate machinery (Fig. 6). 



In the first case, the times of entering and leaving the dock 

 would be restricted to about eight hours in the twenty -four; 

 whilst in the second case, ships could leave and enter at any 

 time and state of the tide. This would form one of the strongest 

 points in favour of a tidal dock, provided the depth over the sill 

 be maintained throughout the channel to deep water. 



Position of Entrances. There appears to be some difference 

 of opinion as to the most advantageous position for a dock 

 entrance with regard to the stream. With a down-stream 



1 



Jl'ater Iwel tn.'\ hours before .& 

 t-tuo hours after High ll'attr 



_U 



Fia 6. 



position, the effect of the current upon a vessel making the 

 entrance on a flood tide would be that, as soon as the head of 

 the vessel came within the shelter of the lower pier, the current 

 would cease to act upon the fore part of the ship, whilst the stern, 

 unless checked, would be slewed round and against the upper pier. 

 The reverse of this would be the case with a vessel leaving on 

 the flood tide ; the head of the vessel, as soon as the influence of 

 the current is felt being, unless checked, slewed up-stream. A 

 vessel leaving a down-stream entrance on a down-stream course 

 with an ebb tide, would do so under favourable conditions, but 

 would find more difficulty if an up-stream course has to be taken. 

 With the entrance heading up-stream, the effect of the 



