174 



NATURE 



[December 21, 189^ 



THE MANCEUVRING POWERS 



OF STEAMSHIPS AND THEIR PRACTICAL 



APPLICATIONS. 



IN a recent number of the United Service Magazine, I 

 wrote an article tracing briefly the history of man- 

 oeuvring powers of steamships as ascertained and applied, 

 or as assumed and applied, or as omitted in application, 

 to the purposes of war and navigation. It was chiefly 

 addressed to the Navy as my apology for certain pub- 

 lisaed views on the causes of the loss of the Victoria, 

 but it is suggested that a resume with diagrams would 

 interest the readers of Nature. 



X 



b 



Quite in the early days of steamers it was noticed that 

 when they turned under the influence of their helms, 

 they took a wider and more regular sweep than 

 seamen were accustomed to notice in sailing-ships. 

 There was a limit to their powers ; for when a steamer 

 had put her helm " hard over,'' she had done all she could 

 to turn " sharp," and if the turn was not sharp enough to 

 avoid collision, for instance, it inevitably took place 

 unless she could check her impetus in time by reversing 

 her engines. 



When steamers began to multiply — I speak of a date 

 before 1854 — collisions with them began to multiply also, 

 and it was necessary to devise "rules of the road" for 

 their prevention, such as sailing vessels had for genera- 

 tions possessed amongst themselves. Admiral Beechey, to 

 whom the matter was confided, could not escape from 

 his knowledge of the sweep that steamers made in turning, 

 but it did not occur to him to make any investigations 

 ii>to its nature. He assumed it. Having done so, it did 

 not occur to him that the application of his assumption 

 could only be made by diagram to scale. He therefore 

 based a proposed law on the assumption that the first 

 90° of a ship's path was a circular arc, but he did not 

 specify what its radius might be in terms of the ship's 

 length. I reproduce in Fig. i the fundamental diagram 

 of the great " law of port helm " which was set out in 

 Clause 296 of the Merchant Shipping Act, 1854, and 

 was finally condemned by Parliament in August, i860. 

 The fact was that no steamer ever did, or could, turn on 

 the path represented, and that the law could not have 

 been drawn had the Admiral been aware of the real path, 

 and had he applied it by means of diagrams drawn to 

 scale. 



When the single screw began to supersede the paddle, 

 the characteristics of the turn remained, but constructive 

 difficulties increased the sweep in warships. The late 

 Admiral Sir Cooper Key, being in charge of the Steam 

 Reserve at Devonport, carried out investigations — 

 very incomplete in those days — which culminated, 

 in 1863, in a series of experiments with a gunboat, 

 directed to ascertain the relations between helm-angle, 

 area of rudder, and the length and duration in time, of 

 the path described in turning completely round. It was 

 still assumed that the path was circular from first to last, 



NO. 1260, VOL. 49] 



and the results as to helm-angle are shown in Fig. 

 2. The "diameter" of an assumed "turning circle" was. 

 the comparative space-measurement employed. The 

 result of the experiments was the introduction of the 

 "balanced rudder" into the Navy. 



Our first ironclad, the Warrior, had been more than a 

 year at sea when these experiments were made. She 

 was 3S0 feet long, much longer than any other man-of- 

 war, except her sister, the Black Prince, and the time she 

 took to turn round, as well as the space she evidently 

 covered, were tremendous. Still assuming that every 

 part of her path in turning was circular, means were 

 devised to measure its " diameter," which was found to 

 be six times her length, or 760 yards ; while, at 12 knots, 

 it took her 7m. 46s. to turn completely round. Every- 

 one was much impressed, but the smallness of the helm- 

 angle — 22°, due to want of power to move the rudder over 

 — was much less noticed than the length of the ship ; and 

 the fact bore remarkable fruit. 



Great changes of thoughi on the subject of manoeuvring 

 occurred both at home and abroad. Every where the idea 

 of the circular arc was accepted ; no means had been in- 

 vented for discovering the form of the path, and it was 

 not sufficiently plain that only the first 180° of the turn 

 was of any importance, and that knowledge of the nature 

 of the path for the first 90" was the most important of all. 

 Abroad, the idea of the circular arc was made the sub- 

 structure of vast and embracing theories. Admiral 

 Boutakov, of the Russian Navy, based a complete system 

 of tactics on the diagram reproduced in Fig. 3, which he 

 called "tangential arcs." It maybe seen that the path from 

 s to .S' does really embrace the whole question of helm- 

 manoeuvres. But no ship beginning to turn at N, and 

 turning back again, could ever, by any possibility, reach 

 w, or s'. The assumptions were entirely apart from the 

 facts. At home, we contented ourselves with ordering 

 that the time any warship took to turn half-round, and 



-«gie- 



A B = 534 feet iS° of helm. I A D = 238 feet 40° of helm'. 



A C = 318 feet 30' of helm. | A E = 216 feet 45° of helm. 



Note. — The ship is drawn on twice the scale of the rest of the diagram. 



Fig. 2. — Scale, J inch = ico feet. 



completely round, at named speeds, should be recorded, 

 and that the "diameter" of her "turning circle," 

 measured in any way that seemed suitable, should at the 

 same time be ascertained. No advance in the matter 

 could be arrived at by any single experiment of this kind,, 

 but I found in later years that a great fund of knowledge 



