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ae As to these ships Mr. Rigg refers to, I happen to be the designer of the ships, one of them he calls the Mars class. It is not the Mars class, it is the Everett - Malden- Melrose class, the pioneer of the present colliers in this country. I fixed these proportions and can say something about them. In fix- ing these proportions I aimed to shorten the ship. If I were designing the ship today, I would shorten it much more, If it is of interest enough to put in this discussion--I have not the data with me --I will prepare a table giving one of the last competitive designs in a cargo boat that has been brought out in this country. That design was contempor- aneous with 'the Mars class Mr. Rigg refers to. .A number of large ship- 'builders went into that competition. The owners gave complete specifications as to what they desired in the ship, but left out everything in the way of di- They said: We want a ves- sel to carry so many hundred tons dead- weight on a certain draught, the ship to go to certain speed. Everything else mensions. was blank. The beam was stated as so and so, and they gave their reason for that. The design that won out was 25 ft. shorter than the longest one, and - I can also tell Mr. Rigg that the firm with which he is connected were just about 15: ft. longer than the winning- out one. That all comes back to this :-- That in a cargo boat the prismatic coefficient does not amount to anything, because we all of us would make the boat a box amidships if it were possible. You have got to have so much dead flat length when you come to the end, what can you do? You probably have one-sixteenth of the length that must be fined. A hundred designs could not vary much in the general arrangement, and we come back to the engineering again. If one boat does better than the other, it is due, in all probability, to a better design of the propelling end of the vessel. We can appreciate that, whether we are experts of the propel- ling end or not. In my opinion, to give -examples of freight boats, and to bring in the prismatic coefficient, is tommyrot. It may be all right in the case of a battleship. Let me show you where 7% cones in in . the. case of. a battleship. I do not think I am giving away any state secrets in mentioning -the Rivadavia and Moreno. A certain firm took those boats. The speed-length- ratio jumped up at the last minute. They wanted more speed. D. W. Taylor saw where they could get it, by putting 3 ft. on the beam of the boat. When he put in his prismatic coefficient, he fined off the end of the boats, and if these boats are a success, it is due to D, WY Taylor. Thomas M. Cornbrooks:--In con- nection with the example on page 3, re- garding Mars class, I desire to make a correction in the statement made by Mr. Rigg. I note Mr. Rigg gives the THE MARINE REVIEW credit for the performance of this vessel to the experimental model basin, while Mr. Simpson claims the credit for him- self; neither statement is correct. In the first place, the keel of this vessel was laid in October, 1908, the model was tried in the basin in March, 1909; con- sequently the trial had no influence on the lines. The Mars Class Mr. Simpson states that the Mars class is a copy of the Everett. While the outboard appearance of these vessels is similar to the Everett, I cannot see how the appearance would affect the economy. The lines for these vessels were designed by the company with which I am connected and the credit for the performance belongs to them. It is evident that Mr. Rigg is a great believer in the experimental model basin, and it is to be regretted that he did not secure more reliable data in regard to some:of the examples which he pre- sents. On page 6, Mr. Rigg speaks of a Sound steamer, which has recently been designed, and makes a very broad state- ment in reference to I. H. P. and sav- ing in coal bills. I would like to ask Mr. Rigg whether his conclusions are based on model experiment or on. theory. The difference in I. H. P. shown is 500. Figuring from Mr. Taylor's curves the E. H. P. for each vessel works out as follows: ; SoA (Py. 831 837. Frictional. 666 654 Residuary, 1,497 $49) TotalE Py 5: at 50 per cent eff. equals 'A"--2,994 "and "B --2,982 |. H.. P.; or. a differetce of 12 1. Ee PR: Constructor Taylor says in regard to "The Influence of Midship Section Shape Upon the Resistance of Ships": . "The shape,of the midship section has \a comparatively minor influence upon the speed, and that the midship section coefficient may range from 0.85 to 1, with very little effect on speed, and may be made as low as 0.70 with- out a material increase in resistance. "Also increased beam means increased disturbance of at least a portion of the water which a ship passes." In view of the foregoing, it is dif- ficult to see where Mr. Rigg secures a saving of 18 per cent in the coal bill. E. H. Rigg:--Possibly I have giv- en the tank too much, credit, and I am glad to be corrected. Referring to Mr. Simpson's remarks, I think if he will study my examples Nos. 2 and 3, he will find that to shorten the ship is what I did. The prismatic coefficient was only discussed in the case of a very fine Sound steamer, not in connection with a cargo steamer by any means. The whole point in exam- ples Nos. 2 and 3 was to show the January, 1913 economy to be gained by a certain amount of shortening. There was no question of prismatic coefficient in those examples. The prismatic coefficient came in on the last example. Twin-Screw Power Yacht J. Murray Watts, naval architect, of Philadelphia, has designed for a west- ern yachtsman a twin-screw motor yacht 100 ft) 'over' all, 85° ft. water line, 15 ft. beam, propelled by two 150-H.P; motors. .The motors are of the semi-Diesel type burning distillate. Owing to the heavy construction of the steel hull and the weight of the engines, no extreme speed is expected, but at 350 R. BP. M. the motors: will drive her at an average of 14 miles. In. general appearance: the boat shows the fast Vidette type with two stacks and a small conning tower for- ward used as a pilot house when cold weather makes the steering position: on the bridge uncomfortable. Head room is obtained in this conning tower by means of a sunken well which comes just over the four poster bed in the owner's stateroom below. This stateroom is a feature of the design, being of unusually large size, 12% ft. long by nearly 14 ft. wide. There is a toilet room adjoining the stateroom and plenty of room for lockers, sofa, bureau and wardrobes. The guests' quarters on this boat are aft and consist of a large double stateroom with the bathroom adjoin- ing. The dining saloon is a room 12 ft. by 14 ft. communicating with the bath room on one side and the gal- ley on the other. A Franklin stove, set off by a handsome mantlepiece will keep these quarters warm in -win- ter cruising. The engine room is amidships about iZuit. long by 15 ft, beam, and: in at are installed the fuel tanks, the lubri- cating oil tanks, the auxiliary lighting and pumping machinery and a large work bench, The crew's quarters are favored and consist of a state room and _ private dressing and toilet room for the of- ficers. Aft of this comes the fore- castle for the crew with accommoda- tions for four men and a_ separate toilet. The finish in the crew's quarters and engine room and galley will be in white paint; a special form of ground cork being used on the steel bulk- heads, and frames and side plating. The owner's quarters and guests' quar- ters will be finished in mahogany ex- cept the bathrooms which will be in tile and white enamel. The conning tower which will be used as a smoking room will be finished in teak, as will be the rest of the deck houses. also