US2835907A - Gravity davit and shock absorber therefor - Google Patents

Description

May 27, 1958 J. P. HARKRADER GRAVITY DAVIT AND SHOCK ABSORBE THEREFOR Filed NOV. 21, 1955 5 Sheets-Sheet 1 May 27, 1958 J. P. HARKRADER GRAVITY DAVIT AND SHOCK ABSR Filed Nov. 21, 1955 BER THEREFOR 5 Sheets-Sheet 2 m. w m m JOHN P #mamans/Q May 27, 1958 J. P. HARKRADER GRAVITY DAVIT AND SHOCK ABsoRBER THEREFOR Filed Nov. 21, l1955 3 Sheets-Sheet 3 INVENTOR. Jhw P /MRKRHDER @from/EY United States Patent GRAVITY DAVIT AND SHOCK ABSORBER THEREFOR The invention relates to gravity davits of the trackway and pivot types and is applicable to single, double or any multiple part fall davits.

Gravity davits of the trackway type may include a davit carriage which is bodily moveable inboard and outboard on an inclined trackway supported on a frame fastened to the ships deck. The carriage supports a davit arm for inboard and outboard swinging movement relative to the carriage. The carriage is rolled upwardly and downwardly on the trackway and the davit arm is swung to inboard and outboard positions by the davit cable or fall which is connected to a winch. Generally, a boat is supported by a pair of such davits. Another form of trackway type davit does not include a carriage.

In gravity davits of the pivot type, the davit arm is supported directly upon a frame structure xed to the ships deck. lnboard and outboard swinging movement of the davit arm is about a fixed axis provided by the frame.

In launching boats yfrom gravity davits of the types described, a portion of the davit arm suddenly strikes with great force the adjoining solid stationary frame structure supporting the carriage or davit arm, or the davit frame, supporting the davit arm itself in the case of the pivot type davit. This high energy impact load imposes an unduly high stress upon the adjoining davit frame. In addition, the sudden shock is transmitted through the davit arm to the davit head causing an unduly severe strain to be placed upon the -fall or cable.

When the boat is hoisted inboard on a pair of davits, the davit arms suddenly disengage from their adjoining supporting structures. This rarely, if ever, occurs simultaneously. The interval between the disengagement of the davit arms from their respective adjoining supporting structures causes a change in the relative position of the ropes or cables so that inboard rotation and movement cannot be accomplished together or in phase. As a result, the equipment is subjected to excessively high torsion, and the proper functioning of the equipment may be impaired. Moreover, the initial or so-called hump load incident to initiation of inboard movement of the davits, places an excessive strain on various parts of the davit, and the davit cable in particular.

Prime objects of my invention are to dissipate or absorb the high energy impact load imparted to an adjoining davit frame by a moving `davit arm; to minimize the otherwise excessive strains and twists imparted to the equipment as the davit arm is moved either inboard or outboard; and to relieve the initial hump load, with the attendant excessive strain on the cable.

In accordance with my invention, the foregoing objects are attained by providing shock absorber means in combination with existing standard gravity type ships davits, the shock absorber means being so located with respect to the davit arm and its supporting frame structure to afford the most advantageous results.

These and other objects, advantages and results of the fr 2,835,907 Patented May 27, 1958 fi vl CC invention will be brought out by the followingdescription in conjunction with the accompanying; drawings, in which:

Fig. 1 is a side elevational view of one davit of the trackway type embodying my invention, with the boat and davit arm also being shown in outboard position as indicated by the dotted lines;

Fig. 2 is a partial front elevational view taken approximately in the direction of line 2 2 of Fig. 1;

Fig. 3 is an enlarged, partial, side elevational view showing the relationship of the davit arm, its adjoining supporting structure and an intervening shock absorber when the davit arm is in its outboard position;

Fig. 4 is a partial front elevational view taken in the direction of line 4-4 of Fig. 3;

Fig. 5 is a side elevational view of a davit of the pivot type embodying my invention, the davit arm in its outboard position being indicated in dotted lines;

Fig. 6 is a partial front elevational viewtaken in the direction of line 6 6 of Fig. 5; and

Fig. 7 is a partial side elevational view showing the relationship of the davit arm with respect to its support with an intervening shock absorber.

Figs. l to 4 illustrate a gravity davit of the trackway type, one davit, generally designated A, for supporting a boat B :being shown. As is usual the boat is suspended from two davits, but since the davits are identical in construction only one is shown and need be described. The davit includes a supporting frame structure comprising a pair of posts 10 and 12 mounted on the deck of the ship C adjacent the edge of the deck and inboard of the deck, respectively. The post 10 may comprise a pair of spaced vertically extending members 10, 10', as shown in Figs. 2 and 4. Supported by the posts 10 and 12 is a trackway 14 which extends inwardly and upwardly from the post 10. As known in the art, the trackway is formed by a pair of spaced and parallel channel bars upon which the davit carriage D is mountedfor rolling movement. The davit carriage is mounted on its inboard end on rollers 16 and on its outboard end is attached to the arm at or near the main rollers 18. Both rollers 16 and 1S run on the lower flanges of the channel bars constituting the trackway. A davit arm E is disposed between cheek plates 2t). The arm is also provided with rollers 22 that run along the upper sides of the top anges of the channel bars constituting the trackway. The davit arm normally may -be swung inwardly of and seated in the davit carriage with the rollers 22 engaging the top of the trackway, the rollers 22 acting to hold the davit arm against forward or outboard tilting.

At its upper or head end, the davit is formed with a hook 24 on which is suspended a floating sheave block 26 to which are connected chains or other lines 28 that are in turn connected to the boat B by any known type of boat-releasing gear. For hoisting the boat on the davit and for swinging the davit `arm inboard or outboard, a fall line or cable 30 is provided, one end of which is fast connected to the track frame, as indicated at 32, while the other end is connected to the drum of a winch F. The fall extends from the connection 32 around a sheave 34 (Fig. 2) `at the head end of the davit arm, thence through the sheave block 26, over a sheave 36 on the opposite side of the davit arm from the sheave 34, over a sheave 38 on the same side of the davit arm, around a sheave 40 mounted on the davit arm, over a sheave 42 on the track frame, and then to the drum of the winch F. l

In inboard position the boat is provided against lateralH movement in the davit by the usual Vgripe line 44, one

end of which is fast connected to the trackway, as .at 46 and its other end connected to the usual takeup and 3 release mechanism 48. The davit is further provided with a boat position bar 50 which is connected by a link to a rig latch hook 52 for releasing the gripe and boat position bar.

With this construction and arrangement, it will be ap' parent that by taking up the tall onto the winch, the boat may be hoisted, the davit arm may be swung into its seated position in the carriage and the carriage and arm may be pulled to its full inboard position as shown by ythe solid lines in Fig. l. On its outboard movement, the davit carriage and arm will roll by gravity down the trackway under control of the winch drum until the outboard rollers 1S engage a stop 14 at the outboard end of the trackway. Rollers 22 roll along the upper side of the trackway, down the face of the stop 14', at which time rotation of the arm is initiated in addition to its linear movement. The rotational energy is continued after the linear movement is stopped at 14. The center of gravity of the arm and the load being above the pivot axisv provided by rollers 18, causes additional force or moment tending to rotate the arm in the outward direction, 'and thus adds to the energy which must be absorbed when the rotational movement is stopped suddenly. The davit arm swings outboard to its extreme outboard position shown in Fig. 3, and by the dotted lines in Fig. l.

When the davit arm swings to its extreme outboard position, a portion of the davit arm, designated 54, below the outboard end of the trackway 14, strikes the davit frame or the supporting posts 1Q, liti with a high energy impact load. This substantial force is not only applied to the davit frame, which must be made strong enough to take this blow, but the reacting shock upon the davit arm is transmitted to the davit head, and in turn to the cable from which the boat is suspended. The result is a sudden and severe strain upon the cable.

ln accordance with my invention, yieldable shock absorbing means G is located intermediate the davit arm and the davit trame to absorb or dissipate the high energy impact load imparted by the moving davit arm to the frame when the davit arm is rotated to its extreme outboard position. Any suitable shock absorber, such as a hydraulic or pneumatic or spring unit may be used, the latter being preferred and illustrated. The shock absorber may be secured to either the davit arm or the frame. It is preferred, however, to secure the shock absorber to the stationary davit frame rather than to the movable davit arm. The shock absorber, or its working face, is located in an outboard direction with respect to the axis of rotation of the davit `arm for engagement by the davit arm when the davit arm is in its extreme outboard position. The working face of the shock absorber is located in a position with respect to the axis of rotation of the davit arm which will best serve to relieve the force exerted by the davit arm `as it is swung outboard or inboard, taking into consideration the size of the shock absorber or compression spring.

As shown in Figs. 3 and 4, a spring type shock absorber G is secured to the davit frame intermediate the posts 1t), 10. The unit comprises a face plate 56 which preferably is convexly shaped to minimize the larea of engagement when contacted by the davit arm. The face plate is resiliently supported by a coiled compression spring 58, a backing plate 60 being located at its opposite end to contain the spring.

In extreme outboard position, the davit arm no longer bears solidly on the rigid davit frame, but is allowed some restrained movement as indicated by the dotted lines in Fig. 3. The spring is of a size and degree of compressibility to be only partially compressed when subjected to peak load s'o that there is always a reserve amount of compression. In other words, the yieldable means G possesses a yielding resistance in excess ot the pressure exerted thereon through the davit arm by the peak load on the davit arm when the davit arm is at the limit of its outboard movement. The davit arm may ,4, tinus deflect o1' rotate, thereby greatly reducing or eliminating the effect of the otherwise sudden shock upon the davit arm with the resultingstrain upon the cable.

The described relationship of the shock absorber means with the davit frame and davit arm also has a number of advantageous effects when the davit arms are being rotated to inboard position. When movement of the davit arms inwardly is begun, it is practically impossible to initiate inboard rotation and movement of both davit arms simultaneously. At a result, the relative rope positions on the davits are not the same. With a shock absorber for each davit located as described, the give or deliection which it affords serves to maintain the relative rope positions on both arms. By maintaining the ropes in phase, undue strains and twists upon the equipment are eliminated.

Another important advantage gained by the described relationship of the shock absorber with respect to the frame upon which it is mounted and the davit arm movement which it serves to control is to relieve the initial or hump load which occurs when inboard movement of a davit is begun. Ordinarily, as rotation of the davit arm is begun, the solid surface contact between the davit arm and the adjoining solid, stationary frame structure is suddenly broken, thereby causing the full load to be abruptly taken by the cable or fall 30. As rotation of the davit arm inboard is continued, the load on the cable decreases rapidly until it may become less than the actual working load. The cable load, however, cannot be allowed to decrease too rapidly, for then the davit will run away, so to speak. The rotation of the davit must be sufcient, or at a rate, so that when the cable load is reduced by rotation, the load will be in such position that it may be hooked onto the hooks 24. By positioning the shock absorber to be engaged by the davit arm, as shown, contact between the davit arm and the supporting posts is not broken suddenly. Instead, the davit arm is resiliently supported so that when rotation is begun any lluctuation in load is translated into a gradual change of load upon the cable.

As inboard rotation continues from the initial peak or hump load, rotation is about the axis provided by the roller 18, which is now moving inboard on the trackway. To provide a shorter lever arm, and thereby decrease the moment of force, a bearing plate 62 is preferably positioned between the shock absorber and the outboard end of the trackway 14, that is, between the yieldable means G and the pivotal connection of the davit arm to the carriage when the davit arm is' in its outboard position. The plate is secured between the posts 10, ld', and is provided with a front bearing surface of convex conliguration to minimize the area of contact with the davit arm.

Figs. 5 to 7 inclusive illustrate the invention as applied to a gravity davit of the pivot type. A davit arm E', instead of being mounted on a carriage which in turn is moveable upon a trackway, is mounted for inboard and outboard rotation about a xed axis provided by the davit frame, generally designated H. The frame comprises a pair of spaced support members 64, 64' secured to spaced, short vertically extending outboard and inboard foundations 66 and 68, respectively, fastened to the deck C. Each support member is formed with laterally spaced inboard inclined plates 70 and 72, the latter being located on the inboard side of the frame structure. The spaced plates 7i) and 72 are rigidly connected to each other at their upper ends by a cross plate 74, and the support members 64, 64 are rigidly connected in spaced relation by the top plate 76. A shaft or axle 7S extends between the inboard plates 72 of the spaced support members 64, 64', and is located only a short dist-ance rabove the foundations. The shaft provides the axis of rotation for the davit arm E', which is pivotally connected thereto at its lower end.

This davit structure, adapted to launch or hoist a bot B', is provided with the usual cable, sheaves, winch, gripe line, boat-releasing mechanism, and further includes a torque tube 80 extending to the drum, and a floating coupling 82 at each end to allow for misaligument. A hand brake lever 84 is also provided.

For this type of gravity ships davit, a shock absorber G is mounted on the outboard side of the frame and is positioned to be engaged by the davit arm E when the davit arm is swung to extreme outboard position. The shock absorber unit shown is also of coiled compression spring type, and includes a plungerdike element $6 having a face plate 88 `adapted to be engaged by the davit arm, The relationship of davit frame, davit arm and shock absorber provides the advantages hereinbefore described with respect to the trackway type of davit.

It is believed that the advantages ot' the improved ships davits will be apparent from the foregoing detailed description. It will also be apparent that while the invention has been shown and described in its preferred form, changes may be made without departing `from the scope of the invention as sought to be dened in the following claims.

I claim:

l. A ships davit comprising a supporting frame, a davit arm pivotally mounted on said frame for inboard and outboard rotation, means for suspending a boat on the davit arm and for controlling inboard and outboard movement of the davit arm, yieldable means interposed between said frame and the davit arm when the latter approaches the limit of its outboard movement, said yieldable means possessing a yielding resistance in excess of the pressure exerted thereon through the davit arm by the peak load on the davit arm when the davit arm is at the limit of its outboard movement, thereby providing yielding restraint of such outboard movement and relief of the hump load on the davit arm at the start of the inboard movement of the davit arm, a track on said frame, a carriage mounted on said track for inboard and outboard movement and to which said davit arm is pivotally connected intermediate the ends of the davit ,6. arm, the rst-mentioned means being connected to one end portion of said davit arm at one side of said pivotal connection, and said yieldable means being interposed between said frame and the other end portion of said davit arm at the other side of said pivotal connection when the davit arm is in its outboard position.

2. A ships davit as defined in claim l with the addition of a bearing plate mounted on said frame between said yieldable means and said pivotal connection and slidably engageable by the second-mentioned end of the davit arm during inboard movement ot the davit arm from its said outboard position, thereby to decrease the moment of force on the davit arm.

3. A ships davit comprising a suporting frame, a davit arm pivotally mounted on said frame for inboard and outboard rotation, means for suspending a boat on the davit arm and for controlling inboard and outboard movement of the davit arm, yieldable means interposed between said frame and the davit arm when the latter approaches the limit of its outboard movement, said yieldable means possessing a yielding resistance in excess of the pressure exerted thereon through the davit arm by the peak load on the davit arm when the davit arm is at the limit of its outboard movement, thereby providing yielding restraint of such outboard. movement and relief of the hump load on the davit arm at the start of the inboard movement of the davit arm, said yieldable means including a compression spring mounted on said frame.

References Cited in the le of this patent UNITED STATES PATENTS 1,190,046 Tjader July 4, 1916 1,237,085 Oliver e Aug. 14, 1917 1,455,159 wright May 15, 1923 2,023,258 Young Dec. 3, 1935 2,146,015 Haseltine Feb. 7, 1939 2,411,630 Lehman et a1. Nov. 26, 1946 2,423,876 Dath July 15, 1947

Images