US3468280A

US3468280A - Ramp for lst

Info

Publication number: US3468280A
Application number: US670811A
Authority: US
Inventors: Ira E Williams
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1967-09-26
Filing date: 1967-09-26
Publication date: 1969-09-23
Anticipated expiration: 1986-09-23

Description

Sept. 23, 1969 u. E. WILLIAMS 3,468,230

RAMP FOR LST Filed Sept. 26, 1957 3 Sheets-Sheet l ATTORNEYS I. E. WILLIAMS RAMP Fon LsT Sept. 23, 1969 5 Sheets-Sheet Filed Sept. 26

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C41. ATTORNEYS United States Patent O M' 3,468,280 RAMP FOR LST Ira E. Williams, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Filed Sept. 26, 1967, Ser. No. 670,811 Int. Cl. B63b 27/14 U.S. Cl. 114-72 6 Claims ABSTRACT F THE DISCLOSURE Background of the invention This invention relates to an extensible ramp and operating mechanism therefor, on shipboard, to provide a self contained means for rapidly loading and unloading a shallow draft vessel in pla-ces where conventional harbor installations and facilities do not exist.

Prior to this invention the amphibious forces sought a Landing Ship Tank (LST) with speed commensurate with that of other modern amphibious ships. All past efforts to design such a ship have been frustrated because of the incompatability of the fine ship form required for high speed and the ramp size and location required lfor debarking vehicles when the ship is beached or married to a causeway. It is necessary, therefore, to provide a ramp system and having a configuration and location which would not compromise the tine ship form required to meet speed requirements. All of the ramps used for this purpose in the past have numerous shortcomings which greatly limit their usefulness. In most conventional ramp ships, the ramp is hinged at one end similar to a drawbridge, so that the length of the ramp is limited to the distance between decks at the bow. The ship form at the bow of existing LSTs permits provision of an approximately 17 X 34 foot opening and a 19 x 37 foot ramp for debarking vehicles when the ship is beached or is married to a causeway. The inboard end of the conventional ramp is hinged at approximately frame No. 8, 6 feet below the third deck. When the conventional ramp is raised or stowed, it forms a watertight cover for the bow opening. Spoon shaped bow doors are provided to close the cut required in the shell of the conventional ship. The limitation of a ship of this form is that it cannot meet the speed requirement. A major disadvantage of debarking vehicles at the third deck through the bow, assuming that the ship has a proper hull form to meet the speed requirement, is the fact that the prior art simple bow ramp and handling system cannot be maintained or continued. This is primarily due to the fact that the hinged point of the ramp must be moved aft in a ship until the ship is wide enough to accomodate the required ramp width. This occurs at about frame No. 32 or about 40 feet aft on existing LSTs. The required ramp length will then be so great and the bows so large that developing a suitable handling system would not be practical in terms of the required tradeoffs, such as reducing vehicle stowage area and compromising the ships structural integrity under slamming loads.

In ramp vehicle vessels heretofore produced, the ramp was limited to one exact size and type by its function as a fixed element in the vessel structure. This invention introduces a ra-mp which is not, in itself, an integral part of the ships construction and therefore, can be stowed on the deck of the vessel. By using a ramp which is not 3,468,280 Patented Sept. 23, 1969 a structural part of the vessel, ay wide variety as to design type and manner of application is possible.

Summary The general purpose of this invention is to provide a ramp system for a ship whose speed matches that of other convoy ships. Combat vehicles are stowed on the third and main decks and are olf-loaded over the bow on a light weight aluminum bow ramp directly to a beach or onto a pontoon causeway to the beach. When extended, the ramp is connected to the ship at the main deck by a pivot post. The outboard end rests on a beach or a pontoon causeway for olf-loading vehicles from the ramp directly to beaches. The ramp is capable of rotation about horizontal and vertical axes for flexibility of operation. When stowed, the ramp rests on the main deck forward `between guide and support tracks attached to the main deck and to the inboard sides of two lixed derrick arms protruding over the bow. The ramp is handled between the operating and stowing positions by a cable or an endless chain system. Remote controls for the ramp handling system are operated by one man from the top of either derrick arm.

The major advantage provided by the instant invention is that it permits a ship hull form capable of meeting the high speed requirement. The instant invention eliminates the need for any rigid contact between the bow of the LST and the causeway. The LSTs independence from the causeway enables it to achieve a maneuverability not obtainable vwith prior art methods.

An object of the present invention is to provide a novel ramp construction which will eliminate the difliculties and shortcomings mentioned above and which will have flexibility of use beyond that of the conventional ramp.

Another object is to provide means for handling a ramp of long length which may be extended from the ship to the short or into relatively shallow water adjacent to the shore.

Another object is to provide a novel construction and mechanism for extending and retracting a ramp.

A still further object is to provide expendient loading and unloading equipment for a ship while retaining the fine form required for speed.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following description of the preferred embodiment of the invention as illustrated in the accompanying sheets of drawings, in which:

Brief description of the drawings FIG. l is a longitudinal sectional view of the bow portion of a ship embodying the present invention;

FIG. 2 is a detail of the bow ramp handling system; and

FIG. 3 is a sectional view taken on the line 3-3 of FIG. 2.

FIG. l, which illustrates a preferred embodiment of the invention, shows a one piece essentially rigid ramp 11 both in its extended and partially retracted positions. The top surface 11a of the ramp 11 is preferably covered with a nonskid bar type grating to improve the traction of wheeled vehicles during wet conditions. The after end 11b of the ramp 11 is shaped and a recess 12 is provided in the main deck 13 to enable the inboard end 11b of the ramp 11, in its operating position, to be essentially flush with the main deck 13. The ramp 11 and the recess 12 for the ramp 11 are also shaped so that the forward end of ramp 11 can rest 6 feet below a 2% beach slope without being supported as a cantilever beam in the vertical plane.

In one embodiment, a cable system, not shown, is powered by three Winches, one each for hoisting, out-haul,

and in-haul of the ramp. Pairs of cables for out-hauling, hoisting, and in-hauling the ramp were attached to each side of the ramp 11. Each pair was led over fairlead sheaves around slack cable ram tensioning devices onto Winches located on the second deck.

Description of the preferred embodiment In the preferred embodiment shown in FIGS. 1 and 2, a bow ramp handling system with chain drive for ramp extension, retraction, seating and unseating is used. In this preferred embodiment, which requires a minimum of controls and components, an endless chain drive 14 is used instead of the aforementioned three Winches for moving the ramp 11. On each side of the ramp the endless chain 14 is passed through a chain guide 17 over a drive sprocket 15a and an idler sprocket 15b. A shuttle 18 forming a link in endless chain 14 is essentially a U-shaped metal clamp which performs a function of connecting the chain to a lower ramp roller 16 located at the aft end of the ramp 11.

Port and starboard derrick arms 21 mounted on the bow of the ship are extended sufficiently forwardly and upwardly of the bow to provide the hoisting and out-haul cables with supports so that the ramp can be extended completely and so that the forces required to handle the ramp are minimal.

The ramp 11 in its completely extended position, can be seen in FIG. 1. Each hoisting whip 22 is supported by a pulley located at the forward end of the derrick arm and fitted with a sheave 22a which in turn supports a sling 23. The ends of the sling 23 are attached fore and aft of the center of gravity of the ramp 11 so that ramp extension can continue without dropping the ramp due to motion of the hoisting sheave 22a when the upper ramp support and guide rollers 27 are no longer supported by upper and lower guide and support tracks 24 extending longitudinally on both sides of the ship. The length of the hoisting sling 23, the two block of the hoisting whip sheave 22a and the attachment point of the hoisting sling 23 to the ramp 11 have been selected so that a smooth transition of the load of the ramp from the ramp support and guide rollers 27 to the hoisting system can be made during either out-haul or in-haul of the ramp 11. The inboard end 11b of the ramp 11 carries the aft lower ramp rollers 16 and a socket 31 located in the control portion of the underside thereof. The lower and upper guide and support tracks 24 for the ramp 11 are designated 26a and 26h respectively and, taken together as a unit are essentially E-shaped intransverse cross section. The ramp 11 has an approximately 19 degree bend near its after end so that when the long portion of the ramp 11 is horizontal, the ramp rollers are positioned so that the pair of aft lower ramp rollers 16, which are located aft of the bend, run in the bottom channels 26a of the guide and support tracks 24 and the pairs of support and guide rollers 27 along the ramp forward of the bend run in the upper channels 2611 of the guide and support tracks 24.

The path or track traveled by roller 16 is designated as 19 and terminates in a vertical track 19a for guiding the socket 31 of ramp 11 downward onto a pivot post 25 which is mounted on the ships centerline. The lower end of the vertical track 19a terminates sufficiently above the bottom of the main deck recess 12 so that the ramp 11 in the seated position is free torotate, that is, rollers 16 are free to move up and down to a limited extent and to move freely with rotation of the ramp. The upper part of the guide and support track 24 terminates at the forward vertical face of the derrick arms 21.

In addition to the ramp support and guide rollers 27 being rotatably attached to each side of the ramp 11, vertical axis guide rollers 28 are fixed to the derrick arms 21 in suiiiicient number and at required spacing to prevent contact between the aft lower ramp rollers 16 and the guide and support tracks 24 during ramp extension and 4 retraction, and to assist in guiding the ramp 11 onto the pivot post 25 during ramp seating.

To supplement the fixed vertical guide rollers 28, guide rollers 29 are installed outboard of the derrick arms 21 port and starboard to assist in guiding the ramp 11 onto the pivot post 25 during ramp seating, and are made retractable so that the ramp 11 is free to rotate to either side of center line when lowered. Although the ramp may rest on pivot post 25, the bottom of portion 11b thereof may act as a bearing rocker bar resting on a ships structure surface to act as primary gravity support of the ramps aft end.

To facilitate jettisoning of the ramp 11 in an emergency, the pivot post 25 has been made retractable and provision made for safely disconnecting all hoisting equipment from the ramp.

A pivot post socket 31 is provided in the after end of the ramp 11 for engagement with the pivot post 25.

Description of the operation The normal sequence of ramp operation consists generally of extending ramp 11 to its fully extended position, lowering the outboard end approximately eleven degrees, seating the ramp, and fully lowering it onto a beach or a causeway. To ensure that the ramp is resting on a beach or a causeway with suiiicient slack cable paid out to allow for relative motion between ship and beach or ship and causeway a limit switch is installed to activate a light to indicate to the ramp operator when to stop the winch.

The ramp 11 is shown in broken lines in FIG. 1 as only partially retracted, the ramp being retractable under control of chain 14 and roller 16 to a position completely within the landing ship aft of the stem. The retract sequence of ramp operation consists generally of centering the ramp, raising the ramp to the intermediate position, unseating it and raising it to the two-block position, and retracting the ramp 11 to the stowage position.

Outriggers 32, shown in a vertical position, are lowered to a horizontal position with line 35 extending to the forward end of the ramp 11 in its extended position to prevent transverse motion.

The ramp 11, at the outboard end, is fitted with a hinged foot 33 to compensate for the variance of beach slopes and of causeway height around the world as ship and sea conditions change. The hinged section is made up of three independent sections so that the forward end of the ramp will always be in contact with the beach or causeway although the ship may roll relative to the causeway, thus reducing the chances of casualty to the vehicle attempting to negotiate the ramp 11 at the same instance that relative roll is experienced.

The two outriggers 32 are provided with means for raising and lowering them between their stowed and operating positions. The ends of the outriggers 32 are iitted with swivel snatch blocks 34 to fairlead lines 35 from their attachment near the outboard ends of the ramp 11, port and starboard, to the snaking winch gypsy on the port side (not shown), and to the mooring capstan starboard (not shown). This vanging system is capable of centering the ramp 11 by rotating the ramp 11 and holding the ramp 11 against either the port or starboard guide rollers 29 until the opposite side of the guide rollers 29 have been fully extended. The vangs are relaxed when both sets of positive guide rollers 29 are fully extended so as not to interfere with ramp handling.

All electrically operated components of the bow ramp system are locally controlled. In addition, two identical lamp remote control stations, not shown, are located on top of the derrick arms 21, one port and one starboard. Each control station consists of controls for in-hauling and out-hauling the ramp 11, hoisting and seating the ramp, and controlling the retractable guide rollers. The controls are of the three positioned lever type with spring return to the mid (stop) position. The forward and backward lever position are marked and electrically connected The advantages of the invention are manifest. The present invention provides a novel ramp construction of unusual length which may be extended from the ship to facilitate loading and unloading the ship while retaining the fine form required for high speed.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as only a preferred embodiment thereof has been disclosed.

What is claimed is: 1. A ramp system for retracting and extending a ramp from the bow of a ship having faired lines extending from a pointed bow, the ship having doors mounted on the upper portion of the bow above the waterline enabling passage of the ramp, the system comprising:

an essentially rigid ramp oriented longitudinally of the ship and having a stowed position entirely within the ships plan outline, said ramp having a central opening in the underside of the aft end thereof;

a pair of overhead derrick arms extending beyond the bow for a distance approximately half the length of the rarnp;

drive means located on the ship and connected to an engaging element at the aft portion of the ramp for 3 moving the ramp longitudinally of the ship to a fully extended position and to its stowed position;

exible support means attached at one end to :a forward position of the derrick arms and at the other end to said ramp for supporting said ramp against gravity when in positions substantially extending from its stowed position;

an upstanding post pivotally attached to the ship near its forward end for engaging said aft opening of the ramp when fully extended, thereby enabling rotation 45 of the ramp in planes essentially lateral and longitudinal with the ship, and guide means for guiding said ramp to a position engaging said upstanding post.

`2. The ramp system according to claim 1 wherein said upstanding post comprises retractable members thereby enabling immediate detachment of the ramp therefrom.

3. The ramp system according to claim 1 wherein the aft portion of the rigid ramp is canted downward from the remainder of the ramp thereby enabling the ramp when extended to be canted downward so that its extended end rests on a level below that of the stowed position of the ramp, and so that its aft canted portion is substantially level with and resting on a structural portion of the ship.

4. The ramp system according to claim 1 wherein said drive means comprises chain drive means having an elenient attached to the engaging element of the aft portion of`the ramp, said engaging element extending laterally from the ramp and rotatable about a transverse axis of the ship.

' 5. The system according to claim 4 wherein said guide means is oriented longitudinally of the ship, said guide means having at its forward end a downwardly extending portion opening out into the location of the upstanding post, whereby the aft portion opening of the ramp when extended is guidedly brought downward into locking engagement with the post.

6. The ramp system according to claim 5 including laterally extensible outriggers carrying exible support means attached to the forward end of the ramp for further controlling transverse motion of said end.

References Cited UNITED STATES PATENTS 502,568 8/ 1893 Kuckartz 1472 2,568,330 9/1951 Flippin 14--71 XR 3,386,405 6/ 1968 Knight et al. 114--72 FOREIGN PATENTS 101,703 4/ 1963 Norway.

JACOB L. NACKENOFF, Primary Examiner U.S. Cl. X.R.