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28 TAE Marine REVIEW Naval Architects and Marine Engineers. The seventh paper read at the an- nual meeting of the Society of Naval Architects and Marine Engineers was upon the subject "Influence of Free Water Ballast upon Ships and upon ee Docks," by naval constructor |. Roberts. per. was outlined in the author's op- The scope of the pa- ening paragraph. "The following notes have been de- vised so as to cover the theories governing the various considerations of stability of a floating dock through- out its various operations and the aim has been to limit the theoretical con- siderations to a minimum, while mak- ing it cover sufficient ground to obtain a clear understanding of the underly- ing principle and the direct applica--- tion to a given case in hand. The cal- culations of girder strength of an ex- isting floating dock have also been included, giving the results and meth- ods by. which obtained. The stability and strength of a dock concern both the designer and user and the writer has endeavored to connect the two by assembling the theories and forms variously scattered about within the science of naval architecture, the ap- plications 'being reduced to direct and brief forms. The structural details of floating docks have been sufficiently treated by various writers in current literature and in this case are suffi- ciently indicated in the accompanying plans. My object in approaching the subject in such elementary fashion is to lead up to certain applicable formu- lae, endeavoring to produce a self- contained article, To do this 1 will begin in terms of ships and loss of stability due to free water ballast and will include, in passing, a considera- tion of the latter also." DISCUSSION. Mr. Mason S. Chace: I think we should all thank Mr. Roberts heartily for putting before us this formula connected with calculations for sta- bility and strength in building these docks,, together with examples which show how these calculations can be applied, and have been applied, in the case of one dock in particular, so that if any of us have occasion to make a dock we will know how to go at it and follow the matter through in a systematic way, such as Mr. Rob- erts has put before us, starting with the fundamental formula as applied to a ship, a ship with free water ballast, and apply that to a dock. On page 15, Mr. Roberts refers to the question of the breaking of the dock at Pensacola,. but says this dock had five pontoons instead of three. He does not tell us why the dock broke, and it would be interesting to know whether there is an advantage in making the dock of three pontoons, and whether this breaking of the dock was due, to some extent, to carelessness in handling during the docking. It would be interesting if he would tell us how the method referred .to, of using fish-plates and bolts has been modified in our later docks. I had the pleasure of seeing this dock at New Orleans. There is one other question referred to on page 18, where he says that the docks were not pickled. I thought it was the custom in our naval service to pickle the shell of our vessels, and the docks would have been pickled in the same way... That has not been done, and probably because they had to remain in fresh water, and not in salt water, and consequently the pick- ling was not necessary. Prov © i. Peabody:.. [his paper is especially valuable, as being a log- ical development of the treatment of the problem which we find in all text books, but which is there never car- ried to a conclusion. It would be un- desirable or impossible to treat it in such fashion. In fact, as the last speaker intimated, one would look far before he would find so complete a statement of the problem as worked out in this paper. I wish to speak of the matter on page 5. The table there given shows that the advantage in the use of bulk- heads is that they break up compart- ments very quickly, because of the practical limit beyond which it is not profitable to go. I have never seen that stated so clearly. On page 6, in the second paragraph, Mr. Roberts gives a statement "that wh cos. 6 is greater than w x bm. sin. 6, even though the latter has an effect upon the initial stability dependent only on the free water surface and inde- pendent of its weight." I have no doubt that Mr. Roberts is quite right, because of the thorough manner in which he has treated this work, but I wish he would make it a little more evident, because this was not evi- dent to me at sight. I want also to raise the question on page 15, where he states, towards the middle of the page, "it is also customary on the part of some to con- sider that the side walls of the dock should be built with sufficient girder strength to carry the entire load," then he proceeds to say that the strength of the dock should be com- puted as one entire structure, but he has in the same paragraph spoken of the fact that they should be bolted together, and I have some question whether it would not be desirable to treat them bolted, for computation, as being incomplete, in which case the method he speaks of as being cus- tomary, might be one extreme, for which it might be desirable to make a calculation giving one of the sort which he has mentioned, The Vice. President: discussion? Mr. William T. Donnelly: I do not know that I can add anything to the data given in this paper relative to the application of the naval dock now in use by the United States navy. I would, however, call attention to some difference in the commercial dock with which «1 am familiar, Pirst,. in the matter of placing the vessel in the dock, we place the vessel exclusively in the length of the dock, when it is Any further tees than = the. .lensth . of . the qock, and it has been shown by this "paper that. it is caus- es unusual stress longitudinally. upon the middle of the dock, but that is counteracted by allowing water to re- main in the end pontoon. That would disregard the idea of the uniform pumping of the structure. Now, in all commercial practice, in handling smaller vessels, it is the practice to place the vessel at one end of the dock. We then pump the dock as a whole to maintain its longitudinal length. That automatically gives the corresponding condition of water level and condition of bottom, and has the automatic function of eliminating the strain due to the centrallizing of the weight at the center of the beams. Again, in the matter of transverse sta- bility, that is 'obtained in the commer- cial dock, not by making positive lon- gitudinal divisions, confining the wa- ter, but in making a number of com- partments, and connecting them with such a restricted water inlet that the flow of one to the other shall be less than the maximum capacity of the pump for that particular line of com- partments, there being, however, a central division along the longitudinal axis of the dock, such as to: operate any flow of water.