218 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



usage to which they are subjected ; the salient angle should be 

 rounded off to avoid damage to passing ships. 



The ends of the recess against which the gates abut are 

 termed the hollow quoins, and require to be made of suitable 

 form and strength to withstand the thrust of the gates. They 

 are generally constructed of massive blocks of hard stone, backed 

 up by heavy counterforts. The axes of the curved faces are 

 strictly vertical, so as to form a uniform hollow groove extend- 

 ing from the top to the level of the gate-platform on either side 

 of the passage ; the hollow faces of the bottom blocks coinciding 

 with and forming the terminals of the sill face. 



Various forms of hollow quoins have been devised. The 

 most common is that which presents on plan an outline more or 

 less similar to an ogee moulding. A modification of this form, 



FIG. 205. 



FIG. 20G. 



in use at the Liverpool Docks, is shown by Fig. 205. The 

 tightness of the joint between the heel-post and the quoin is 

 dependent upon accurate fitting and close contact between 

 the circular surfaces. This is not easy to ensure, and there is 

 always more or less leakage round the hollow quoin. 



Fig. 206 l shows a method much in favour in Holland for 

 making a water-tight joint. The hollow quoin is brought more 

 into the dock than usual, and the joint made against a narrow 

 straight face, usually about 8 inches wide, and polished from top 



1 3f.P.JC.F.,vol. Iv.p. 73. 



