100 NON-ROLLING PASSENGER LINERS. 



increment as it arrives, irrespective of magnitude or direction; holding the ship 

 most satisfactorily upon an even keel, apparently without effort; demonstrating 

 how little is really required to keep a ship from rolling, or, rather, from beginning 

 to roll, if only a basically preventive method is employed. 



With the complete solution thus in hand, accomplished with a small and simple 

 equipment, it is believed that the older passive types, with their great weight, frac- 

 tional results, and uncertain operation, will become obsolete. 



The equipment that brings about this important result is so simple and unique 

 that a brief resume of its development, the principles involved, and the performance 

 of the non-rolling ship itself cannot fail to be of interest at this time. 



The possibility of producing the non-rolling ship was known to the leading 

 naval architects and investigators in England, notably the elder Froude, prior to 

 1880. A little later Sir Phillip Watts, one of the great masters of this noble art, 

 became convinced from Froude's work that, inasmuch as it takes so little to hold a 

 ship on an even keel and to prevent it from rolling, this very desirable result should 

 be accomplished. As Chief of Construction of the British Admiralty, he, with a 

 corps of engineers, at once started in to establish this great principle and to put it 

 into execution, by building "anti-rolling tanks," as they were called, into the ship's 

 structure and then filling these elongated tanks up to a certain critical point with 

 sea water. These were expected to take on periodic oscillations from the ship's 

 rolling motion, thus creating moments which would always be in opposition to the 

 rolling and tend to reduce it. These tanks were actually built into two war vessels 

 by the Admiralty, and experiments were undertaken with rather discouraging re- 

 sults, on two counts : — 



First, it was found that there were required a large tank and a large amount 

 of water, representing quite an appreciable percentage of the total displacement of 

 the ship — such a large percentage, in fact, as to be prohibitive. The other point 

 was the difficulty in maintaining proper phase relation between the natural period 

 of the ship, the period of the water in the tank, and the period of the waves of 

 the sea. More about this further on. It will suffice to say that when this phase re- 

 lation is not maintained, these tanks can easily become dangerous, tending to in- 

 crease the roll rather than to reduce it. 



Later the great English engineer. Sir John Thornycroft, undertook to accom- 

 plish the same result by a large horizontal pendulum operated hydraulically down in 

 the hold of the ship ; and the report of Sir William White — one of the Admiralty's 

 greatest naval architects — ^on the actual operation of this device in a ship at sea in 

 a storm (while Sir John I. and Sir William were dining together) makes one of the 

 notable chapters in the early history of attempts at stabilization of ships. This sta- 

 bilizer worked well at times, but it was found to have the same difficulty as the anti- 

 rolling tanks, namely, in order to secure a sufficient reduction in roll to make the 

 equipment commercial and practical, the weight of the equipment was prohibitive. 



Later, Herr Frahm of Hamburg re-invented Sir Phillip's tanks, but though he 

 made a contribution to the mathematical treatment of the subject and introduced 



