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January, 1910 tained in many boats which have both bow and stern rudders at a smaller angle of inclination that with boats which have stern rudders only. With this comparatively unimportant difference, the same "stunts" can be performed with either disposition of rudders. imum speed limit submerged, for which Mr. Hay refers us to the paper on "The Stability of Subma- rines,' by J: G. Johnstone, is likely to be dangerously approached. Mr. Johnstone places the speed limit for stability of motion in a British sub- marine of 310 tons submerged dis- placement, fitted with stern rudders, and a valué tot: B+ .G, ot- 1 "tt; as 22 knots. Mr. F. W. Baker's Discussion. Frederic. W.° Baker: 1° am 'sure that the author of this most interest- ing paper should be congratulated on having handled a very difficult sub- ject, in such an able manner. | say "difficult subject" because owing to the great secrecy maintained in re- gard to submarine construction no one person could expect to become familiar with all the different prin- ciples and details of construction which are incorporated in each of the several types of submarine boats. A person may become familiar with the construction and method of hand- ling a certain type of submarine boats built by the firm with which he may be associated and naturally would 'be able to expound the advan- tages of this type, but if he attempted to discuss the advantages of other types his progress would naturally have to be somewhat along the lines of what a sailor would call "dead reckoning." All this should be taken in account when criticising a paper on this sub- ject and no doubt this will in a meas- ure account for the author's apparent lack of information in regard to the "even keel' method of submergence. Submerging Planes. It is a well known fact that sub- marines both in this country and abroad have time and time again been submerged on the even keel principle by means of the submerg- ing planes sometimes called "hydro- planes." These submerging planes are generally located near the center 01 the boat and when properly fitted so as to be free from hull influence may be made to exert a downward pull on the boat when she is under- way, thus overcoming entirely or in part her reserve buoyancy when trimmed for submerging. I; d6 mot: see that the max 'TAE MaRINE REVIEW During even keel submergence the longitudinal axis of the boat has a tendency to move, more or less, out of the horizontal plane but is pre- vented by the action of the trimming rudders situated at the stern, or in some submarines, at both the bow and stern. These trimming rudders are constructed exactly as are the diving rudders in a diving submarine and -while they both operate to in- cline the longitudinal axis of the boat the trimming rudders produce the contrary effect to the diving rudders; the latter purposely incline the longitudinal axis of the boat out of the horizontal plane in order that she may dive, while the former act to hold the longitudinal axis in the horizontal plane, and thus keep the boat on even keel. Submarines constructed on the even keel principle have run submerged for long intervals of time main- taining constant depth and with prac- tically no inclination of less than one degree. These results are what one would expect from a theoretical study of the forces acting during even keel submergence and they have been dem- onstrated in practice time and time again. The Drop Keel. In regard to the drop keel, the au- thor's method proving that it is unnecessary for a single hull is very ingenious, but as very few, if any, submarines have ever been lost by collapse of the hull, due to descend- ing beyond safe depths, its sound- ness is not so apparent. It is easy to conceive that a sub- marine might be disabled in quite shallow water and suddenly sink to the bottom, in such a case the in- stantaneous release of a drop keel weighing several tons might be the means of bringing the boat to the surface and thus allowing the crew to escape. The drop keel should, therefore, in the opinion of many commend it- self for use on all submarines wheth- er of the single or double hull type, especially as its presence leads to no real disadvantage. Commander Hovgaard's Discussion. Capt. W. Hovgaard: As regards Mr. Chace's remarks, that the sub- marines are built chiefly to attack battleships, I think in a general way that that is a correct view, but that function requires for its fulfilment two distinct types of boat, which I think are Ikely gradually to develop, in place of the present style of boat. It requires one type for harbor or 23 coast defense, in the narrow sense, a boat which has a moderate radius of action, and not very great seagoing qualities, at least moderate sea going qualities, and that type we find al- ready produced, practically in use, such boats as are produced by the Electric Boat Co. and also by the European boat builders. The other type is really not yet in existence, but there is undoubted- ly a tendency to produce such a type, a. larger, more sea going type of boat, with' greater speed. We all know that the great difficulty in realizing the construction of such a type is the motive power. We have at present no motive power which will lend itself satisfactorily to driv- ing such a boat at a great radius of action, and with great sea going qual- ities and of high speéd. The com- bustion engine has its limitations, and the steam engine, where it had been tried, seems not to have given full satisfaction, although it is still pos- sible that steam in.\some form may ultimately: be adopted, but it seems certain that there is an undoubted tendency to incréasé~ the displace- ment of these boats. By increasing the displacement we should always be able to gain in seaworthiness, and also, in a certain measure, we are able to increase the speed, and when we get further along this road of increasing the displacement, in or- der to obtain to a sea-going boat, it seemes likely that we shall arrive at some.type intermediate between. the single hull type in its pure form, and the double hull type. I mean thereby a boat which has the straight structure, as most boats have now, and light superstructure, giving the sea-going qualities and besides that, a lower structure, an under structure below the strength hull, can serve as water ballast tank, which need not be so strongly con- structed as the hull proper, but I do not think it is likely that the double hull complete, if it is used now, is likely to be retained. I un- derstood that it was used in the first boat constructed by M. Laubeuf ot the French navy, in the first of the so-called submersibles. That boat, I understand, has a _ double hull all around, but proved very un- - satisfactory, in that immersion was difficult to obtain, and the water tanks were long and difficult to fill com- pletely, so that there was considerable difficulty with filling, it took a long time, and the trim was apt to be af- fected by the incomplete filling of these tanks between the two hulls. . (To Be Continued.)