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* July, 1909 trolled by a double threaded shaft which is revolved by chain connection and from the main drum shaft. The guide roll carriage supports the double threaded shaft as well as two horizontal guide stanchions, and carries a_horse- shoe-shaped nut which fits into the grooves of the double threaded shaft. This nut swivels on an extension at the toe of the horseshoe and after follow- ing along the thread leading in one di- rection. until it reaches the end, it is automatically and positively guided so that it turns and leads back in the opposite . thread. These winding devices have been fit- ted with success. to. all sized towing machines from the largest to the smallest. It is made so strong by means of diagonal stays that it will resist the breaking strain of the line during a pull athwartship. This winding device allows the omission of the stern bitts that were formerly considered necessary at the after end of the tug boat. The line may lead back from the guide rolls in any direction required without interfering in any way with this even winding on the drum. 'ihe advantage of omitting the stern bitts on tug boats is obvious, it not only decreases the weight but also allows the line to lead from a point further forward than would otherwise be the case. This is considered a strong point among tug boat men, especially when required -~ to maneuver in crowded waters. This device has made the use of the towing machine possible on tugs that were formerly considered too short to afford the necessary space abaft the house. Machines of the type shown have been fitted on tug boats less than 100 ft. long, simply by the removal of the after towing bitts and the location of the machine in their place. Some attention has been devoted to the advantages of the spring set brake. This advantage, however, is apt to be more theoretical than practical for the great fact is that very few deck hands are capable of using any discretion in their tightening on the brake wheel, they simply screw it down hard until they can get no more, so it makes no dif- ference whether there is a spring or not, it is sure to be set up so tight that there is no chance to utilize the theoretical advantages of such a spring. Another point that has been men- tioned is that the towing machines with which the writer of this paper is familiar have adopted a quick opening valve, and such a quick opening pre- vents the paying out of an excessive length of line when the vessels surge or rear. The theory as set forth in the Paper is, that the quick admission of TAE MarRINeE REVIEW steam serves to increase the pressure on the steam cushions quickly and thus check the paying out of the line. Against this theory, however, there looms up an interesting fact that the resistance of the towing machine to paying out line is not due primarily to the admission of more steam but rather to the compression of steam already in the cylinders. Many years of observation and experience with tow- ing machines shows that the original type of automatic valve gear which opens gradually as the machine pays cut, serves to check the line fully as quickly as is desirable. It is evident that the rapid ;consump- tion of steam in the towing machine occurs only when it is recovering line, for it is then an ordinary steam winch. When standing still, holding the line by the steam compression in the cyl- inders, the consumption i} only that required to make up the loss due to condensation and leakage. When pay- ing out line the leakage is naturally increased, and there may be a slight loss due to clearance volume in the cylinder. But it. -has. no chance to. .take..in steam. in large quantities. for it 15 theoretically pumping back into the boilers. The greater importance of this compressing of steam already in the cylinders as compared: with the portance of admitting more steam is proven by a practical. comparison of machines in service. The quicker open- ing valve seems to have no noticeable effect in this connection, probably be- cause at the time of greatest resist- ance the fresh steam cannot overcome the compression due to paying out. This very feature is shown and men- tioned in the article under discussion where the steam pressure in one of the paying out cards shows a_ higher pressure in the cylinder than that used in the admission pipe. This alone would seem to prove that the resistance to paying out was due mostly to the compression mentioned and not to the admission of more steam. The quick acting . automatic valve mentioned is very ingenious and clever but seems also to be open to the same remark that the Yankee made about pyramids. No doubt further light can be thrown on this by a series of cards which will bring out the element of. time; it is to be hoped that the society may soon have further data in this connec- im- tion. Mr. Penton's Written Discussion. Henry Penton.--The gist of this paper is in the proper length of haw- ser for best results in towing and this is, practically speaking, all-im- 215 portant. Every unnecessary foot of hawsen is an item of expense, in cost and in added resistance. Frequent failures of towing hawsers, generally at a point some distance from the machine or towing hook, have led to the conclusion that they are mostly -attributable to contact with channel bottoms, and this to consideration of the dip of hawser under conditions which are sufficiently well known. But information on the subject apparently does not exist, at least I have failed to find any. Mr. Kemble has gone at the subject in a thorough and= painstakine way and his investigations bear out in every respect the conclusions previ- ously drawn. He is unquestionably right in his premise that the length of wire hawser used is due partly to the length previously found advisable with manila to provide sufficient elas- ticity, and partly to the comparative © lack of this in the wire. I am confi- dent that the view so commonly held --that a long hawser makes for het- ter. stéering--is' erréneous, tor = the reason that- the pull on the barge; both as to direction and amount, is entirely independent of length of line; and "it -is the stern 6f -the slip which swings under rudder action and not her head; and this is true for all ordinary conditions under way, and so long as the barge is clear of the race of the propeller, the shorter the line the better. This refers to normal good weather. As to the pro- peller race, I do not tbelieve that it is perceptible 300 ft. astern, for. the reason that I have repeatedly towed a log from the taffrail on 50 to 60 fathoms of line without per- ceptibly affecting its reading as com- pared with towing from a boom un- der identical conditions. It is a common occurrence to see a_ ship slewing in a seaway and her log trailing in and out of her wake. Mr. Kemble suggested a constant for length of line, but I think his figure is too large and that 450 would be for all conditions. Even in bad weather, the length of line can be 'carried too far, 4s the greater the length and dip, the greater the towing resistance, the more readily the machine is ovet- hauled and the greater the labor on the machine in recovery. The indicator cards shown afe. unique and interesting. If any one has any doubt as to the amount of labor the author has spent on this ample paper, let him look up the literature on the subject and I think he will agree that Mr. Kemble has supplied