io NOTES ON DOCKS AND DOCK CONSTRUCTION. 



feet respectively, whilst there would still be ample room near 

 the entrance for turning long ships. 



The plan shown by Fig. 5, which was, it is believed, an 

 arrangement of jetties, first suggested by the late Mr. T. 

 Stevenson, M.I.C.E., would perhaps afford, in the least possible 

 area, the greatest amount of accommodation, with room to turn 

 a ship in the most convenient position, viz. near the entrance. 

 Practically, it would be almost impossible to adopt such an 

 arrangement in its entirety, unless under very exceptional 

 circumstances as to site. Even in cases where such a plan would 

 be possible, it does not follow that it would be the most suitable 

 to meet all the conditions of the trade to be accommodated. 

 The principle may, however, be applied in part with advantage 

 in many instances. 



Tidal Docks. In considering the question of Tidal Basins 

 versus Closed Basins, local conditions as to tides, and the 

 probabilities of silting up, have to be taken into consideration. 

 Where the rise and fall of tide is moderate, and the protection 

 good, open or tidal basins may be adopted with advantage. An 

 exposed entrance, admitting a swell that would cause the ships 

 alongside to work, would preclude such an arrangement. More- 

 over, vessels rising and falling with the tide when lying 

 alongside a wharf, are always subject to more or less damage 

 through grinding. Added to this, there is the inconvenience 

 caused by the constant attention required in adjusting the 

 hawsers, gangways, etc. 



When the water carries with it a large quantity of suspended 

 matter as for instance on the Humber it would be injudicious 

 to adopt tidal basins on account of the deposit of mud that 

 would take place, and the expense attending its removal. Where 

 the facilities for scouring are exceptionally good, the objections 

 from this point of view would of course be modified. 



The Comparative Cost of, and the facilities afforded by, the 

 two plans have also to be taken into consideration. For instance, 

 with a rise and fall of tide of 10 feet, a closed basin to 

 accommodate vessels of 27 feet draught, to enter and leave the 

 dock from two hours before to two hours after high tide, would 

 require a total depth of water of 32 feet, allowing a minimum 

 depth of 3 feet under the keel ; whilst in a tidal basin, the total 

 depth required would be 40 feet, to ensure the same class of 

 vessel being always afloat at low tide, or an additional depth 



