Area of propeller disk x speed of ship in knots. cubed
Disk constant = --------------------------------------------------
I.H.P.

Projected      Projected area of propeller x speed of ships in knots. cubed
area         = ------------------------------------------------------
of constants                         I.H.P.

Expanded area constants may be obtained and used in the same way.]

The discussion which followed was opened by Mr. Holt.  He said that if they were to have greater speed on the Atlantic, there was one point which was not alluded to in the paper, and that was the total abolition of cargo on board the great passenger steamers.  If vessels were built solely for passenger traffic, they would be able to insure greater speed by reason of the greater slightness in build and the additional space at the command of the designer.  The existing Atlantic express steamer was far too heavy, and might, if cargo was dispensed with, be made with finer lines and more yacht-like.  He looked on the proposition to fit such vessels with longitudinal bulkheads with great fear.  If a collision took place—­such, for example, as that which sunk the Oregon—­water would get access to one side only of the ship, and it was not at all improbable that if a sea was on, she would turn right over.  At all events, very serious risk would be involved.

Mr. W.H.  White, Chief Constructor to the Admiralty, said the question of twin screw propulsion was one of special interest to himself, and had been so for many years.  In 1878 he dealt with it as fully as he then could on the basis of the Admiralty data, and he then ventured to say everything in favor of twin screws that Mr. John had said in his paper.  If greater power than that now used in such a ship as the Etruria, for example, were demanded, two screws must be used.  Good as are the results obtained with the Etruria, it was by no means certain that still better might not be had.  If she had been fitted with two screws instead of one, very great advantage would be gained by the greater submergence of the twin screws, as thus racing would be almost wholly prevented.

Mr. Calvert urged that more attention should be devoted to studying the relative values of different portions of the propeller.

The sitting was then suspended.  In the afternoon, as we have already stated, the members visited the steamship Germanic on the invitation of Messrs. Ismay, Imrie & Co., subsequently proceeding to Messrs. Cope Brothers’ tobacco works, and thence to the exhibition, where the dinner of the Institution took place in the evening.

On Friday morning no paper was read; some official business was transacted, and this being done, the discussion on Mr. John’s paper was resumed.