662 proceedings of section h. 



Curves and Widths of Navigable Channels in Kivers and Canals. 



Recently I had occasion to pay some attention to the question of 

 'CuiTes and widths of navigable channels, in connection Y\-ith a paper 

 •on the Port of Brisbane, which I read before the Queensland Institute 

 •of Engineers on the 25th June last. 



As the subject is one of more than local importance, the follow- 

 ing extracts from the paper may be of interest: — 



" From an independent investigation I have made, I am satisfied 

 that the law of curvature of rivers and canals that would permit of 

 vessels of any given dimensions passing each other safely in opposite 

 ■directions on such curveS; and in cuttings of ordinary width — 270 ft. 

 to 500 ft. — may be stated as follows : — 



Let the lengih of the vessel, regarded as a chord of the required 

 inner curve, be called A, then the versed sine at centre of chord 

 should equal the cube root of A. 



From these simple elements the required curve can be readily 

 •determined as follows — 



Let B equal half the chord, that is, half tlie length of the ves^sel. 

 Let C equal the versed sine, equal, to the cube root of A. 

 Let R equal the radius of the required curve. 



B^ 



Then —- +C = 2R = diameter of required cui-ve. 

 C ' 



The width of deep Avater channels suitable for vessels of any given 

 [length is governed by the clearance that may be considered necessary 

 between two vessels of the same dimensions that are required to pass 

 each other in opposite directions on curved portions of the river or 

 ■canal. By the term " clearance "' I mean the distance from centre to 

 ■centre of the ships, as measured along the tangent of ship A's course 

 at the moment when ship B is crossing that tangent. (Vide Diagrams 

 Nos. 1, 2, and 3.) The clearance sliould never be less than twice the 

 length of the ship, and preferably should, I think, be somewhat 

 longer, extending to a maxijnum of, say, two and one-half (2h) times 

 the length of the ship. The table of widths of channel suitable for 

 vessels of from 200 ft. to 1,000 ft. in length, given below, is based 

 upon a tangential clearance of two and a-half times the length of the 

 ship. 



Where the cost of a channel corresponding in widtli with llie 

 tangential clearance of 2 '5 times the length of the ship would be 

 excessive, I am of opinion that a clearance of 2'1 times the maximum 

 length of vessels using, or likely to use, the watenvay would give 

 •economical and fairly satisfactory results. 



Assuming that the maximum length of steamships will be 

 1,000 ft., then the width of channel corresponding with my formula 

 for curvature and with the tangential clearance of 2,100 ft., (2'1 times 

 1,000) would be 350 ft., or 22 ft. wider than the width (100 metres) 

 now being provided at the Suez Canal. The width of channels may 

 he computed by the following formula : — 



Let A equal tlie length of the vessel. 



Let B equal the number of times that A is contained in the 

 clearance allowed. 



