474 TRANSACTIONS OF SECTION G. 



12°, he showed by calculation that the corresponding maximum wave-slope must 

 have been 5 o- 09. For 20° maximum inclination the wave-slope was 10°"3. Both 

 these cases were for periods of ship and wave of 16 and 13 seconds respectively. 

 For similar periods of 16 and 146 seconds the wave-slope to produce 20° maximum 

 before uniform rolling is only 7°. These figures give some idea of the effect of the 

 wave-slope on the maximum inclination. It is to be remembered that these are the 

 maximum angles obtained by Mr. Froude ; but if we take Colonel Russo's maximum 

 angles, which in some cases are double those obtained by Mr. Froude, it is easy to see 

 that large wave-slopes may produce very large angles of roll. 



Summarising, we see that : — 



(1) With wave-slopes of 3° - 6 the angles of maximum roll obtained in the Revenge 

 with bilge-keels may be taken at 22°. 



(2) This roll takes place when synchronism exists between the wave and the ship, 

 when the wave is 910 feet long and 18i feet high and has a wave-slope of 3°'6. 



(3) Waves exist which are of this length, but which may have a height of 50 feet, 

 and possibly more, and a wave-slope of 10°. 



(4) In such steeper waves we should expect to get much larger angles of roll. 



• (5) Each ship has peculiarities of rolling due to its form as well as to its lading 

 and bilge-keels, &c. 



(6) These peculiarities and the effect they have upon rolling, and the effect different 

 waves will have upon the rolling of the ship, can best be studied experimentally. 



It was my intention when you appointed me as your President to have placed before 

 you the results of an experimental study made on lines somewhat similar to those 

 carried out by Colonel Russo, but extended to a wide range of types of ship, waves, and 

 resistance. 



The machine for carrying out these experiments is practically complete, but having 

 met with an accident at the end of April last which incapacitated me for some time I 

 was prevented from being able to do anything to this subject since then. I am, there- 

 fore, obliged to ask you to be content with the general resume of the subject which 

 has been given. 



I tbink enough has been said to show what a field of investigation is open to the 

 experimenter. The little that has been done and published by Colonel Russo is only 

 for three battleships of about the same size. For the great bulk of the ocean way- 

 farers nothing has been done. If it is possible to determine the kind of rolling which 

 is likely to take place under stated conditions it seems to be desirable to do so. 



In all that has been said it will be seen that it is possible to determine experimentally 

 the kind of rolling which will take place in a ship which is snug and seaworthy. But 

 it'is also possible to study the effect of loose water in a ship under the same set of 

 conditions as to waves, lading, and form of ship. This part of the subject has not 

 received any experimental treatment except in a very limited number of full-sized 

 ships. It is quite conceivable that some conditions of loose water associated with 

 some conditions of sea may produce large angles of inclination. 



The subject has been treated as one in which it is probable that the kind of waves 

 met with at sea will be uniform in size and period. That this is not so is a fact with 

 which we are all more or less familiar. The effect of a uniform system of waves is 

 rapidly to induce a condition of uniform rolling. But any deviation from uniformity 

 of sea immediately introduces non-uniformity of rolling, and generally greater 

 extreme angles of roll. Any experimental study of the action of waves upon a ship 

 must include a variation in the character of the waves. The field of investigation is 

 thereby widened and the search for large angles of inclination made more laborious. 

 But the work is of a kind which can be done by many people, and can be done fairly 

 rapidly, so that there seems to be no insuperable objection to doing it. The details 

 of the apparatus need not be described, but the study of the objects attained may 

 be of interest. 



(1) Wave-motion is simulated by the revolution about parallel axes of two parallel 

 cranks of different lengths. The fine joining the ends of the arms of the cranks is 

 always in the line of the normal to the wave-surface, and a fine perpendicular to it is 

 therefore parallel to the wave-surface. 



(2) From the form of the ship are determined curves which are the shape of rollers 

 which roll on a straight line parallel to the wave- surface. The form of these rollers 

 is such that the model of the ship in rolling maintains the position in relation to the 

 wave- surface (a) which cuts off constant volume of displacement at any angle of inclina- 



