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pressure of a bight of the hawser behind it, the boat ferried itself quickly across from the Cincinnati to the Pershing in about two minutes, and the line was clear.
Captain L. H. Chandler, in the May number of the Naval INSTITUTE PROCEEDINGS, explains a towing trick learned from Chapman & Merrit, wreckers; the use of a spring on the tow-line to hold the towing vessel up against the set of wind or tide.
Within the past week I have seen a towing vessel forced to slip and run in order to save herself, when a spring from her bow to the tow-line would have held her safely in position.
Captain Chandler also quotes an experienced wrecker's axiom to the effect that beyond a certain point it is of little use to add to the strain on towing hawsers and kedges.
By very gradual increase in the strain on the towing gear a close approximation can be made to the maximum strain that it is advisable to put on the hawser. It may be advisable to break the weakest link in the gear in order to be sure. After knowing about what towing strain may be safely taken, it may be advisable to try towing at various angles with the keel of the stranded ship. The facilities for flooding, pumping, and shifting cargo should be carefully considered. They may solve the problem.
If a good diver is available it may be well to send him down to examine and report the underwater conditions.
The amateur wrecker undertaking salvage operations on an extended scale should prepare himself for many failures and disappointments; it is a job for Job, requiring infinite patience under adversity. On the other hand, it is a task where patience yields an almost sure reward.
In wrecking, the importance of the tidal rise and fall may vary greatly
In the salvage of a ship like the Doheny, with stern in deep water and ability to alter trim several feet quickly by shifting ballast, a small tidal rise may sometimes be neglected.
In salvaging the General Pershing the tide was the controlling factor. The best speed of discharging the cargo lightened the ship only about two inches a day.
The range of the tide was approximately twenty inches, which was equivalent to a lift of a thousand tons. It is well to remember that,
“There is a tide in the affairs of men,
RESILVERING SEXTANT MIRRORS By LIEUT. COMMANDER ROBERT T. YOUNG, U. S. Navy
At present when ships are making long sea voyages, frequently the navigator will find that his sextant mirrors are going bad and no spares available. He is also apt to find his sextant mirrors in such condition that although the sun can be handled, great difficulty is encountered with stars. If such is found, the mirrors can be very successfully resilvered with the facilities on board ship.
Frequently I have asked navigators and officers who have finished their navigator's cruise, if they ever resilvered their mirrors; invariably the answer was that they had tried it, but could not make it work.
The following system was used on a surveying expedition to the Sandwich Islands of which the writer was a member, and was found to be very successful; in fact, the system, we used entirely to keep the boating parties supplied with mirrors.
PREPARATORY (a) Get some tin-foil—that from the average package of cigarettes is entirely satisfactory.
(b) Obtain a small bottle of ether-alcohol from the doctorthis is used to thoroughly clean the glass.
(c) Get a few drops of mercury-should no other be available, a few drops from the artificial horizon will not be missed.
(d) Obtain some clear shellac—the gummy sediment which collects in the base of receptacle is better. If possible and near a navy yard, send the chief quartermaster over to the yard and borrow a small bottle of the substance used at the yard for that purpose.
OPERATION (a) Carefully unroll the wrapping of the cigarettes so as not to crumble the tin-foil. Cut out a piece about twice the size of that which will be required for the actual backing. Place this on a pad of paper, examine and see which side will be the better
for the backing. Your eye will quickly note which will be the better. Decide; place it on a pad and flatten by placing a piece of paper on top, and apply light pressure.
(b) Thoroughly clean the glass with ether-alcohol and absorbent cotton.
(c) Place a few drops of mercury on a clean blotter and thus remove any dirt.
(d) Place a drop of mercury on the part of the tin-foil which will not be used for actual backing. It will form like a blister. Raise the pad and enlarge blister by an inclined circular motion. Add more drops of mercury as necessary until the blister has extended over the entire tin-foil. Put the pad down on the desk. Take the sextant glass and gently slide over the mercury. Examine and see if clear of flaws. Then remove glass by sliding off and reclean. Some sediment will probably be found on the surface of the mercury. Again gently slide the glass over the mercury to the correct position, and if clear of flaws, turn up the outboard edges, place the pad in an inclined position to allow the excessive mercury to drain off and let backing set. At least twenty-four hours should be allowed.
(e) Collect the excessive mercury and put in bottle. It is essential that the part of the tin-foil where the mercury was first dropped on should not be used as the actual backing. For some reason this spot will crumble up and spoil the backing.
(f) When tin-foil has set, remove the edge and apply backing. In applying do not use a brush or anything that rubs. It will tear the tin-foil. Apply as you did the mercury to the tin-foil. Put on one drop and work it over the tin-foil by an inclined circular motion, until entirely covered. Be careful to just cover the observing edge, but thoroughly cover all the other edges. Then let backing set and dry.
It is well to practice first with a piece of glass about the size of an index glass, but watch the sharp edges. They are apt to tear the tin-foil. After a little practice you will be able to make perfectly satisfactory mirrors-so will your chief quartermaster.
Although the above will be found to be perfectly satisfactory, it is essential that the navigator should not allow his sextant to be unduly exposed, or his mirrors to get in unsatisfactory condition, but if they should and time be available, the above will be found to produce excellent results.
U. S. NAVAL INSTITUTE
The Board of Control announces the followPrize Essay ing awards in the Prize Essay Contest, 1919: Contest, 1919 First Honorable Mention to Captain Reginald
R. Belknap, U. S. Navy. Subject, “Military Character."
Second Honorable Mention to Lieut. Commander Beirne Saunders Bullard, C. C., U. S. Navy. Subject, “ Some Reflections on the Three Factors of Battleship Design."
No Prize Essay has been awarded for the year 1919.
Elementary Steam Engineering by C. M. Book Reed has been published by the Institute and is Announcements ready for sale ; for table of contents see book
list. The Institute will publish the "North Sea Barrage," a short photographic history of the U. S. Mine Planters' operations in the North Sea. The book will be ready about April 15, 1919, and sell for $3.00 per copy. The edition will be limited and the Institute will be glad to receive orders in advance.
The annual dues ($2.50) for the year 1919 are now payable.
Life, regular and associate membership, 5728. Membership