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TRANSIT CLEARANCES FOR U. S. NAVAL VESSELS GENERAL DISCUSSION Aircraft Carriers The transiting of aircraft carriers is the most complicated problem of this nature confronting The Panama Canal. Overhanging flight decks, galleries and gun sponsons on some of these ships in combination with recent protective works at the locks impose limits upon the ship's draft and require special conditions of lake and tide levels to insure adequate vertical clearances. These overhangs also present the hazard of contact with surface installations at the locks, including control houses, emergency dams, lamp posts and towing locomotives. The sides of these ships below the flight decks have numerous platforms, booms and other appurtenances of relatively frail construction which are subject to damage and present a hazard to the lock gates in passing, being difficult to fender in an adequate manner. Special features of the design require that certain of these vessels be towed off-center of the lock chamber, introducing unbalanced lateral forces of indeterminate magnitude which complicate the problem of control. The Chief Pilot is located in such a position that he cannot see the locomotives or the lock walls and he must rely on relayed information and must in turn relay his directives.Breadth of beam at or near the water line is at present a factor in the case of the Saratoga only, which must be handled much like a battleship. However, in most cases the net horizontal clearances at the level of the main batteries are so small that some contact with the lock walls must be expected during transit. The towing locomotives under individual manual operation cannot exert positive control over the lateral movement within such narrow limits, and it is very difficult to judge the ship's position with the required degree of accuracy. The most critical point of the transit is generally the south end of Pedro Miguel Locks, where the lock entrance, control house and greatest height of lock wall above the water occur in combination. These ships are hazardous at almost all points in the locks, however, and extraordinary vigilance must be employed at all times to keep them under a fair degree of controls. Experience indicates that the use of slow speeds, not to exceed one mile per hour, during lockages will contribute to better control and help to reduce the extent of damage from contact. The improvement of chock and bitt installations in the stern of some of these ships will enable better control by the towing locomotives and will allow the locomotives to be placed in safer positions. Damage can be reduced measurably by adequate stripping and fendering of the ship prior to transit. Detailed discussion of these matters will be found under the headings of the individual vessels.
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Battleships The problem of transiting the larger battleships is considerably less involved than in the case of aircraft carriers. There are no overhanging projections to introduce the complications of limitations on draft, water and tide levels; position in the lock chamber; and danger of contact with surface installations. In seaworthy condition these ships can transit at all normal lake and tide levels with almost equal facility. The principal difficulties are caused by the extreme breadth of these ships at or near the water line, which approaches the clear width of the lock chamber. Horizontal clearances are so small that the towing locomotives do not have complete control over lateral movement. Consequently these ships will inevitably rub against the lock walls at intervals during transit. Damage resulting from this contact will vary with the individual ship. The most critical points of the lockage are the entrance and departure, when the ship passes the knuckle of the wing wall, and much of the damage will probably be sustained at these points. The use of slow speed, not to exceed one mile per hour, will help to avoid or to reduce the extent of damage. The installation of adequate chocks and bitts in the exact stern of some of these ships will improve the control exerted by towing locomotives.
(49954)
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Limiting Conditions for Transit There is no absolute limitation on draft; however, there would be an advantage in limiting the draft to 33 feet, fresh water. At 33 foot draft the height above the water line to the bottom of gun sponsons at flight deck level is about 33 feet. These sponsons would be below the tops of the lock walls at Pedro Miguel and Gatun, however, at Miraflores Locks, until protective construction at miter gates has been completed, the lock wall height there could be limited to 32 feet, thereby providing vertical clearance for the sponsons. Clearances (a) Approach Walls: No serious damage should result from landing the ship at the approach wall. There are no vulnerable projections other than small fittings which could strike the wall. The locomotives on the towing track of the approach wall are not in danger of being fouled by critical projections on the ship as it approaches or departs. (b) Lock Chamber: With the ship centered in the chamber the nominal horizontal clearance at the 40mm. and 20mm. gun sponsons is 1.5 feet. These sponsons occur frequently along both sides of the ship. There are many vulnerable projecting items on the sides of these ships; all bolted, hinged, or portable items should be stowed if practical, otherwise they are subject to damage. These items include Franklin life buoys, life rafts, motor launches, ladders and fittings, boat booms, antennae masts and fittings, and life nets. On some of these ships there are horizontal drains which project from the outermost points of the gun sponsons at flight deck level. These are subject to almost certain destruction from contact with the lock walls, and they present a haeard to handrails and other vulnerable parts of the lock gates. (c) Control House: Interference will be encountered between the yardarm, starboard, and the Control House roof, if the ship transits any lock with its starboard side to the center wall, unless the yardarm is taken in or cut back. The distance that the arm must be taken in varies with the individual ship and with the draft. In any case it should be stowed in such position that it could not foul the roof even if the ship should rub the center wall. The minimum distance from face of lock wall to Control House eave is 3'-4". - 2 —
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(d) Emergency Dam: The projecting gun sponsons at the flight deck level have a vertical clearance of 9 feet, based on a lake level of (FIX)-/87 and a draft of 31 feet. There is no danger of these projections striking the dam under such conditions; however, there is some danger at very low water levels and deep drafts, the critical clearance being 3 feet horizontally under the worst condition and with the ship centered in the lock chamber. At Miraflores clearances are 9 feet greater horizontally and therefore not critical. Much equipment is carried on the sides of the ships under the gun sponsons mentioned in the above paragraph, the most notable of which are life boats, life rafts, life nets, and antennae masts. Available plans are not complete in detail regarding these items; thus exact clearances cannot be given. On the vessels of this type which have transited a clearance of about 5 feet horizontally has been noted between these items and the emergency dams at Pedro Miguel and Gatun.(e) Locomotives: On the attached sketch all locomotives are shown forward or aft of the ship. When the ship is at low level in the locks at Miraflores, it would be possible for the gun sponsons at flight deck level to override the walls and foul amidships locomotives if used. The sponsons could also foul these locomotives on the inclines at any lock. For these reasons locomotives should stay forward or aft of the ship, as shown on the sketch, whenever practicable. An additional advantage of these positions is that under certain conditions forward and aft locomotives are visible to the pilots when those amidships would not be. (f) General: On many of these vessels it has been noted that certain appurtenances have been added which are not shown on plans and not common to other similar ships that have transited previously. An inspection of the ship should be made prior to start of transit to ascertain the vulnerability of such items and the possible danger to fixtures at the locks. Desirable Conditions for Transit
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SOURCE:
Transcribed by RESEARCHER @ LARGE. Formatting & Comments Copyright R@L.
