;o8 



NA TURE 



[JULV 25, 1907 



boats of about 1200 tons to 2000 tons displacement. This 

 standard gyroscope will be electrically driven, except in 

 cases where there is not a suflicient margin of electric 

 power available in a ship, when it would be driven by a 

 steam turbine. An apparatus for vessels of the displace- 

 ment named would be applicable to the class of Channel 

 steamers, and we may perhaps see it tried before long in 

 some of them. 



What I have said with regard to making ships steady 

 at sea has had reference only to rolling motion ; but many 

 persons consider it is not rolling that affects them so much 

 as pitching, or as the skew motion near the ends of 

 a ship that is neither rolling nor pitching, but an un- 

 pleasant combination of the two. There is also sometimes 

 a vertical or heaving oscillation when large waves are 

 passing a ship broadside on which may rise to an ampli- 

 tude of several feet when the wave-period approximates 

 to the period of her own dipping oscillations, but it is 

 probably seldom that the motion from this cause is great, 

 ritching is often the chief cause of trouble and discomfort, 

 .tnd the motion due to it may be greater and _ more 

 violent than any other, especially near the ends of the 

 ship. The pitching period is sometimes as short as four 

 seconds, so that there mav be three or four pitches to 

 one roll ; and the vertical distance moved through near 

 the ends in pitching is very much greater than at the 

 ship's side during a roll. 



.\fter all has been done in the way of making the forward 

 transverse sections of a ship such as will best resist plung- 

 ing into the .sea, and by good stowage, there still remains 

 considerable tendency to pitch in certain conditions of sea 

 which cannot be removed. The best way to avoid the ill 

 effects of pitching is to get as near as possible to the axis 

 of rotation, the position of which varies considerably 

 according to the nature and direction of the seas which 

 cause the pitching, but is, on the average, not far from 

 the centre of length. The modern large steamers which 

 have their first-class passenger accommodation upon three 

 or four decks in the middle third of a ship's length are 

 generally found to be the most easy and comfortable at 

 sea. That is no doubt largely because the greatest 

 itrtical distance moved through in pitching in the 

 passenger accommodation is only one-third of what it is 

 at the ends of the ship. It is to this concentration of 

 passenger accommodation near the middle of a ship's 

 length that we have to look chiefly for neutralising the try- 

 ing effects of pitching. 



One of the chief causes of discomfort and distress to 

 passengers on shipboard is vibration. This may be due 

 to one or more of several causes, to which much attention 

 has been given during recent years. The effect of recipro- 

 ■ eating engines in causing vibration has been investigated 

 by Dr. Schlick, Mr. Yarrow, Mr. Mallock, Prof. Dalby, 

 and others, who have demonstrated the manner in which 

 such engines operate to cause vibration, and how to reduce 

 this effect to a minimum bv suitable design, and by 

 balancing the principal working parts. There is little to 

 chrose, in a strongly built ship, between modern well- 

 balanced reciprocating engines and steam turbines as 

 regards smoothness of nmning and absence of unpleasant 

 vibration. Vibration is often due to the action of the 

 propellers, and when these have to run at very high 

 speeds, as with fast-running turbines, a certain amount of 

 vibration is sometimes unavoidable. Apart from the 

 essential conditions of trueness of propeller blades and 

 exact balance of the propellers upon their shafts when 

 turning, there is the action of the ends of the blades upon 

 the water adjacent to the stern-plating where they pass 

 nearest to it in revolving, which causes a hammering 

 effect that is sometimes very great. The vibration and 

 tremor of this plating may be quite local, and mav be 

 reaflily checked by strong bracket frames at the part 

 where it is greatest ; or it may be communicated 

 throughout the hull, and .set up sympathetic vibrations 

 in large flat areas of plating, .such as decks, straight 

 side-pkuing, bridges, &c. These difficulties can generally 

 be overcome by careful attention to the surfaces 

 that vibrate, .-ind by stiffening or supporting them at a 

 few critical points by struts or brackets. "There appears 

 no reason why ships should not now be kept free 

 NO. 1969, VOL. 76] 



from all unpleasant vibration, whether as regards the 

 working of the main engines or the action of the pro- 

 pellers. 



The tendency to increase the size of ships is strong and 

 continuous. It has long been known, and experience 

 proves that the power required to drive a ton of a ship's 

 displacement at a given speed diminishes, and the work- 

 ing expenses become less per ton all round, with increase 

 of size. 



There is a size and speed of ship that is most appropriate 

 and profitable for each line of steamers, or each trade, and 

 it varies greatly in different trades. It is the managers 

 of the various lines who know best what dimensions and 

 speed are likely to be most profitable in their respective 

 trades, and what are the maximum number of passengers 

 and quantities and descriptions of cargo likely to be forth- 

 coming. The approximate size, and the speed, of mercan- 

 tile steamers depend upon commercial and economic con- 

 siderations which the ship-designer usually has but an 

 imperfect knowledge of. His part consists in pFoducing 

 a design that will fulfil the necessary conditions of size, 

 draught of water, speed, carrying capacity, and accommo- 

 dation for passengers in the most efficient manner and at 

 the miniinum of cost. There is one point, however, which 

 is so important in considering further large increases of 

 speed in ocean liners generally that I would like to direct 

 attention to it. 



Speed is limited in passenger liners, altogether in- 

 dependently of size, by economic considerations. High 

 speed at sea is a costly luxury. It can be obtained by 

 paying for it — up to 25 knots, as we see by the latest 

 C'unard liners — but it has to be paid for by somebody. 

 The extra cost cannot be got out of cargo freight, for as 

 speed is increased the proportion of space available for 

 carrying cargo becomes reduced by the increase of boilers 

 and machinery, and therefore less cargo is carried relatively 

 to the size of the ship. This reaches an extreme limit in 

 the fastest Atlantic liners, the holds of which are as full 

 as they (;an be stowed of engines, boilers, and coals for 

 the voyage — their speeds only being limited by the impossi- 

 bility of getting more boilers in — and it is only a few odd 

 spaces which cannot be utili.sed for other purposes that 

 are available for carrying a little cargo. In these cases 

 cargo is reduced almost to a negligible quantity. 



It may be said generally, as regards any line of steamers, 

 that if speeds of more than 12 to 13 knots are desired 

 the extra expenditure involved by such increase must be 

 looked, for outside the cargo. "I'his element of earning 

 power does not bear an increase of rate of freight. There 

 are only two sources from which payment of the extra cost 

 of increased speed can come. One is from passengers 

 and the other from a mail subsidy. No inail subsidy that 

 could be proposed would pay more than a small proportion 

 of this extra cost ; the greater part of it must come from 

 passengers. What passengers have to pay for high speeds 

 at sea may be seen by the rates charged in the fastest 

 .\tlantic steamers, .\part altogether from special cabins, 

 or apartments de luxe, for which almost any prices are 

 paid, the cost of a single first-class passage to New 

 York varies from 22?. los. to. 48/. 10.5. for a run of six 

 days, in one of the fastest liners, .according to the position 

 of the cabin in the ship and the time of year, or from 

 i|d. to nearly 4J. per mile travelled. The prices have risen 

 rapidlv during recent years as speed has been increased, and 

 passengers across the Atlantic appear to be forthcoming in 

 ever-increasing numbers who are ready to pay them. If 

 that were not the case such high speeds could never have 

 been reached. No great improvement of speed is to be 

 looked for upon the other main lines of ocean traffic, unless 

 some revolutionary change is made in the mode of pro- 

 pulsion which will cut down the cost, or a sufficient nuinber 

 of passengers are found, as in the .Atlantic trade, who will 

 pay the higher rates it necessit.ites. 



I have not done anything this evening towards reducing 

 the number of the many and difficult unsolved problems 

 that trouble the mind and tax the skill and judgment of 

 the shin-designer, but if I have succeeded in conveying 

 some idea to you of their nature, and of the interdepen- 

 dence of science and engineering in all wise attempts at 

 their solution, I shall have accomplished my object. 



