WO2004022421A1

WO2004022421A1 - A cradle for lifting and launching a small watercraft on an exposed marine landing site

Info

Publication number: WO2004022421A1
Application number: PCT/NO2003/000309
Authority: WO
Inventors: Gunnar STAVØSTRAND
Original assignee: West Innovation
Priority date: 2002-09-05
Filing date: 2003-09-05
Publication date: 2004-03-18
Also published as: AU2003261037A1; NO20024228D0; NO317543B1

Abstract

A watercraft lift with a landing cradle (10) for landing and launching a small watercraft (40) on a generally rigid fish cage or wharf/pier (30). The watercraft lift comprises at least one davit arm (20) pivotable in the vertical plane, comprising at least one set of an overlying and an underlying parallel enlongate davit arm joint (21a, 21b), in which the davit arm joints (21a, 21b) are supported in bearings at their inner ends in an inner, upper horizontal axle bearing (31a) and an inner lower horizontal axle bearing (31b), respectively, on a generally vertical beam (36) attached to the hull of the fish cage (30), and in which the davit arm joints (21a, 21b) are supported in bearings at their outer ends in an outer, upper horizontal axle bearing (14a) and an outer lower, horizontal axle bearing (14b), respectively, on the landing cradle (10). The landing cradle (10) may have buoyancy properties. Further, the watercraft lift comprises a control device (65) for a motorized elevator device (60) arranged for elevating and lowering the landing cradle (10) between an outstreched position under the sea surface for landing/launching of the small watercraft (40) at or above the deck (34) of the fish cage (30), and so that the landing cradle (10) retains the boat in a generally upright position between the sea and deck level; and in which the elevator device (60) is arranged to be released so that the landing cradle (10) with the small watercraft (40) can heave in a free position in the sea before elevation.

Description

A CRADLE FOR LIFTING AND LAUNCHING A SMALL WATERCRAFT ON AN EXPOSED MARINE LANDING SITE

Introduction This invention relates to a watercraft lift for safe and secure landing and launching of small watercraft at large on generally rigid fish cage structures or wharf/piers.

Background of the invention Fish cages constructed by two or more parallel floating pipes connected by cross members, walkway and guardrail in an annular flexible floating structure, are floating low in the water. Such fish cages are generally easy to land against with small service boats or work boats, and are commonly used in protected waters. For use in more exposed waters there are also large fish cage platforms with rigid steel buoyancy structures. These platforms are sometimes located in sea areas in which landing of a small watercraft at times can be very difficult and dangerous because of strong wind and the tall waves action. In such conditions, attempts to land against the platforms can lead to collision or very rough landing that can cause damage to the boat the crew, subsequently injuries and drowning. Injuries and damage to the crew may also easily occur when shifting equipment and crew from the watercraft to the platform and back onboard. In conditions with strong wind and large seas necessary maintenance and change of shifts might be difficult or impossible.

Ordinary watercraft lift systems by stationary cranes and hoists by wires and winches, elevates the boat slowly and requires deck space. Moreover, To maneuver a watercraft safely under a crane-hook in heavy seas, fastening a hook or strapping is demanding, and will normally require personnel onboard the platform to operate the crane/lift, except when evacuating. When lowering the watercraft suspended in wires, uncontrolled swinging and swaying is likely to occur. Prior art

US 3.753.355 (Knoch) describes a dry-dock for lifting a boat out of water, with a subsurface support, a cradle for cradling the boat, and a plurality of legs pivotally connecting the cradle to the subsurface support in a manner which permits movement of the cradle between a Iowered position in which the cradle is located below the surface ofthe water a distance sufficient to permeit the boat to float thereover, and a raised position in which th cradle is clear of the water. A winch is proviced for effecting movement of the cradle between its Iowered and raised position. US 4.678.366 (Williamson) relates to a boat lift for with a vertical H-beam driven into the floor of a body of water adjacent a pier. A shaft housing surrounds the H-beam and slides up and down it on rollers mounted within the channels defined between the opposed flanges and web or base of the H-beam. A fork liftlike boat support is mounted to the shaft housing for vertical movement therewith to raise and lower a boat to and from the water. Forces are transferred from the shaft housing to the H-beam by the rollers engaging the web surfaces and the inner flange surfaces. A hoist, supported by the pier and the top ofthe H-beam, raises and lowers the shaft housing and boat support therewith.

In US 5.245.940 (Rockwood) a load lifting device for small watecraft is described. The load lifting device has a vertical post with a lower post portion extending downwardly in the water from the top ofthe dock and rigidly mounted thereto and having an upwardly extending rectilinear extension. A vertically movable cradle is cantilevered off the post with a winch at the top of the extension connected to the cradle for raising and lowering it. The upwardly extending extension of the post is rotatably mounted to the lower post portion so that when the cradle is moved vertically to a position carried by the extension it meay revolve with such extension to swing a watercraft carried by the cradle over the dock or the water as desired. A lock is provided for preventing the post and extension from rotating during transistion ofthe cradle between the two parts. US 5.908.264 (Hey) concerns a watercraft lift having raised and lowered positions. The lift includes a substantially rectangular base with longitudinal side beams and forward, rear and intermediate transverse beams connected to the longitudinal beams. Forward booms 12 are pivotally connected to the base at a location near the front transverse beam. Rear booms 14 are pivotably connected at a location close to the intermediate transverse beam 32. A watercraft support platform 24 is pivotably connected to the forward and rear booms. Raising and lowering of the lift of the present invention are, according to US 5.908.264, accomplished by an actuation assembly. In preferred embodiments, the actuation assembly includes two dual-directional high pressure hydraulic cylinders pivotally connected between the intermediate transverse beam and the rear booms. During use, the actuator assembly rotates the booms upward and for- ward about their pivotable connection to the base, further raising the watercraft support platform and the watercraft to an over-center position.

The above lifts are all located on or mounted on the ground in shallow waters, and they involve that the watercraft is supported by suppports or platforms. These supports do not float freely with the water when not in opera- tion, even if a watercraft itself may float freely over support or platform before lifting.

In some of these documents, the frame protrudes and may be dangerous for a small watercraft in in rough waves (Knoch,Hey). In other documents (Williamson, Rockwood), supporting beams or platforms are arranged at the dock front in such a way that boats approaching these will have to maneuver very close to the dock, and thus make them unsuitable for use in rough waves.

In other words, there is a requirement for a watercraft lift which enables use in swells and rough weather, that performs in a safe and dependable way when landing or launching a small watercraft or service boat from a generally rigid cage platform or wharf acted upon by waves.

Short summary of the invention

The above object of the invention is solved by means of the apparatus according to the invention which is a watercraft lift with a landing cradle for landing or launching of a small watercraft on a generally rigid fish cage or wharf/pier. The watercraft lift includes at least one davit arm pivotable in the vertical plane, comprising at least one set of an overlying and an underlying parallel enlongate davit arm joint, in which the davit arm joints are supported in bearings at their inner ends in an inner, upper horizontal axle bearing and an inner lower horizontal axle bearing, respectively, on a generally vertical beam attached to the hull of the fish cage, and in which the davit arm joints are supported in bearings at their outer ends in an outer, upper horizontal axle bearing and an outer lower, horizontal axle bearing, respectively, on the landing cradle, the landing cradle having buoyancy properties. The watercraft lift further includes a control device for a motorized elevator device arranged for elevating and lowering the landing cradle between an extended position under the sea surface for landing/launching of the small watercraft at or above the deck (34) of the fish cage, and so that the landing cradle retains the boat in a generally upright position between the sea and deck level; and in which the elevator device is arranged to be released so that the landing cradle with the small watercraft can heave in a free position in the sea before elevation. The invention further relates to a method of landing of a small watercraft on a generally rigid fish cage or wharf/pier acted upon by waves, by use of a watercraft lift according to the invention with a landing cradle, wherein the method following steps: keeping said landing cradle free floating in free vertical movement with the waves, wherein said landing cradle is held at a distance from said fish cage by at least one davit arm being pivotable in the vertical plane, including at least one set of an overlying and an underlying elongate davit arm joint, driving said small watercraft into said landing cradle, waiting to said landing cradle and said small watercraft are elevated by a presumed high wave and locking said landing cradle from being Iowered from this position; starting a fast elevation of said landing cradle with said small watercraft by means of an energy accumulator until the landing cradle is free from potentially higher successive waves; and - continuing elevation of said landing cradle with said small watercraft until said small watercraft reaches a desired position at the deck ofthe fish cage. The invention further includes a method for launching a small watercraft on a generally rigid fish cage or wharf/pier acted upon by waves, by use of a watercraft lift with a landing cradle, comprising the following steps: lowering said landing cradle with said small watercraft until said small watercraft reaches a desired floating position in the water, - releasing said motorized elevator device so as to keep said landing cradle freely floating in free heave movement in the waves and held at a distance form said fish cage (30), driving said small watercraft out of said landing cradle.

Further inventive features are described in the accompanying dependent claims.

Description of the drawings

The invention is illustrated in attached drawings, which are meant only to illustrate the invention, and should not be considered to limit the scope ofthe invention.

Figure 1 shows an end view of a small watercraft alongside a large fish cage platform, where the watercraft is kept in a raised position above the sea by one emodiment of the invention comprising a watercraft lift with a landing cradle supported by a parallel joint on a davit arm attached to the platform. The figure also shows an alternative embodiment ofthe attachment for the parallel arms where they are pivotally supported by a plate welded to the base ofthe landing cradle. Figure 2 shows a plane view of the fish cage platform with the watercraft lift arranged on the leeward side of the platform side with a small watercraft approaching. Figure 3 shows a plane view of the fish cage platform with the watercraft lift arranged on the leeward side ofthe fish cage platform, in which the small watercraft has been maneuvered into the cradle. Figure 4 is an end view of the landing cradle along the leeward side of the fish cage platform, showing the small watercraft having entered the landing cradle, the landing cradle being arranged in a generally parallel position at a distance from the platform by means of the parallel arms. Figure 5 shows, in the same end view as in the previous figure, the landing cradle with the watercraft at the moment when a pressure accumulator release accumulated pressure when the cradle is at the top of the wave and then quickly lifting the landing cradle with the watercraft to an presumed safe level above potentially higher subsequent waves. Figure 6 shows the cradle with the small watercraft elevated to a higher level after the energy accumulator has lifted the cradle with the watercraft to the presumed safe level, the hydraulic pump, supplying pressure to a hydraulic piston, allowing the hydraulic piston to run more slowly and longer, elevates the watercraft lift further. Figure 7 shows the small watercraft raised to a level above the platform deck, arranged so that work crew safely can enter the fish cage platform, bringing equipments and small cargo from the small watercraft. Figure 8 shows the same plane view as figures 2 and 3, the fish cage platform with the boatlift being arranged at the leeward side of platform, wherein the small watercraft now has been elevated to a top position close to the platform deck, where work crew can enter the platform in a safe and simple way. The invention will now be described in more detail.

Description of preferred embodiments

For a more detailed description of the watercraft lift according to the invention, reference is made to fig. 1. The boatlift is here shown with a landing cradle (10) for landing and launching of a small watercraft (40) on a generally rigid fish cage platform (30). A davit arm (20) being pivotable in the vertical plane is arranged in connection to the cradle (10) comprising at least one set of upper and one set of lower parallel longitude davit arm member (21a,21b).

Davit arm members (21a,21b) are supported at their respective inner ends by an upper horizontal axle bearing (31a) and an inner lower horizontal axle bearing (31b), preferably on a generally vertical beam (36) attached to the frame of the fish cage platform (30). At their respective outer ends the davit arm members (21a, 21b) are supported by an outer, upper horizontal axel bearing (14a) and an outer lower horizontal axel bearing (14b) on the cradle (10).

The cradle (10) has buoyancy properties, possibly by functioning as a buoyancy element itself. However, a preferable solution is that the cradle (10) has buoyancy elements attached (16). The cradle (10) has buoyancy, possibly by structurally built in buoyancy properties. However, a preferable solution is that the cradle (10) has elements of buoyancy attached (16). The cradle (10) can include at least two set of outside and inside forks (10a, 10b). For a more evenly distribution ofthe forces acting between the forks (10a, 10b) and the hull (41) of the small watercraft (40), the forks (10a, 10b) can be provided with fenders (15a, 15b). In yet another embodiment oft he invention, the shape of landing cradle (10) may generally correspond to the shape of the hull (41 ) of the small watercraft (40), wherein the forks are connected by horizontally running surrounding pipe-frames. Below the pipe-frames there is attached at least one plate (12') welded in place as a curved, longitudinal beam structure connecting the forks. Such a welded plate (12') works as attachment for a davit arm (20). The pipe- frame is constructed with the required strength and stability so that further longitudinal strength, e.g, in the form of a stabilizing beam is not necessary. However, it will be apparent that it is possible to arrange the landing cradle (10), e.g., on a main beam (12) being pivotably attached in the outer, upper horizontal axle bearing (14a) and the outer, lower horizontal axle bearing (14b). However, it is clearly possible to arrange the cradle (10) on a main beam (12), being pivotably attached to the outer, upper horizontal axel bearing (14a) and the outer, lower horizontal axel bearing (14b). For supporting the small watercraft (40) in the landing cradle (10), a perforated canvas or net (13) may be arranged in the landing cradle (10), wherein the net (13) may be streched over the buoyancy elements (16). Preferably, the landing cradle has an opening in its stern end for entry of the watercraft. A different embodiment in which the cradle (10) is open in both ends for a two-directional use is also possible. The boatlift has a control device (65) for a motorized elevation device (60) being arranged for elevating and lowering the landing cradle (10) between a extended position floating at or under the sea surface for landing/ launching of the small watercraft (40) and a raised or elevated position above the sea surface for the cradle (10) with the small watercraft (40) at or above the deck (3*0 of the fish cage platform (30).

The control device (65) for the motorized elevating device (60) is advantageously arranged for remote control. A remote control transmitter (66) is then arranged for control of the control device (65) for the motorized elevating device (60), so as to make landing and launching of a small watercraft possible by remote control. Signal transmission preferably takes place by means of radio waves, but the signals may also be optical, e.g. infrared waves. Remote control transmitter (66) may be installed in the small watercraft (40), but is preferably mobile for easy operation by the crew of the small watercraft (40). Under normal condition the crew of the small watercraft start the landing and launching action ofthe watercraft lift. The landing and launching action ofthe watercraft lift can also be started and controlled by a person already at the platform or the dock (30).

The elevation device (60) is in a preferred embodiment ofthe invention arranged to release the hydraulic system, thus permitting a free floating action in which the landing cradle (10) with the small watercraft (40) is allowed to heave freely with the waves in a generally vertical direction, before elevation starts or departing from landing cradle (10). By landing or launching, the parallel arms (20) will keep the landing cradle (10) in a generally upright position through the action during elevation between the sea level and the deck level. One of the advantages with elevation device (60) releasing the hydraulic system so as to let the landing cradle float and heave freely with the waves, is that the landing cradle in a Iowered position, in particular by landing/lowering of said small watercraft (^ 0), may avoid collision with the small watercraft (HO) heaving out of phase with the landing cradle (10).

In a preferred embodiment of the invention the motorized elevating device (60) includes a hydraulic cylinder (61) with a piston (62), wherein the said cylinder (61) is connected to a hydraulic energy accumulator (63) and a pump (64). At the hydraulic cylinder (61) there is arranged an adjustable valve (67) that may be set so that the oil will flow freely in both directions and thus allow for a free float and heave movement for the cradle (10), or to function as a one-way valve only working in a lifting motion, lifting the davit arms (20), and blocking downward movement by the davit arms (20). This valve (67) will allow the piston to receive the accumulated oil from the pressure energy accumulator (63). The elevating device (60) is arranged for being releasable so as to allow the landing cradle (10) with the small watercraft (40) to heave in a free movement in the sea before landing. By landing or launching, the landing cradle (10) keeps the small watercraft (40) in a generally upright position between the sea level and the deck level. Furthermore, the elevating device (60) may be releasable so as to allow the landing cradle (10), when in a lower position, preferably by landing and launching ofthe small watercraft (40), to adjust to the waves and avoid collision with the small watercraft (40) caused by the heave movements in the sea being out of phase with the small watercraft (40).

Preferably, a sensor (68) is arranged in connection with the hydraulic cylinder (61). The sensor (68) preferably senses pressure and pressure changes in the hydraulic cylinder (61) behind the piston (62). The sensor (68) also may include a temperature sensor, sensing temperature and temperature changes in the hydraulic cylinder (61). When elevation ofthe landing cradle (10) starts, it is generally allowed to float and heave freely with the waves. The heave movements from the landing cradle (10) in the sea will be transferred to the piston (62) in the hydraulic cylinder (61), then being in a free flow condition. When the landing cradle (10) is being elevated by a wave or a swell, the pressure over the piston (62) in the hydraulic cylinder (61) increases, the hydraulic oil will flow to a reservoir, and from there be supplied via the valve (67) to the hydraulic cylinder (61) under the piston (62). After the landing cradle (10) has passed the top ofthe wave and start to fall back, the pressure under the hydraulic piston (62) in the hydraulic cylinder (61) will increase. The pressure sensor gadget (68) then sense the increase of pressure and transmit a signal to the pressure accumulator (63) to release. The valve (67) is then set so that hydraulic oil only can flow through this valve (67) one way, to lift the piston in the hydraulic cylinder (61) at the moment the pressure accumulator is released. In this way the hydraulic cylinder (62) prevents a downward movement by the davit arms (20) by restricting the hydraulic piston (20) action to elevate only. When the pressure accumulator (63) is released, the hydraulic oil will flow through the valve (67) into the hydraulic cylinder (61) below the piston (62) so that the landing cradle (10) with the small watercraft (40) is elevated to a presumed safe level above successive potentially dangerous waves. After the rapid elevation movement is executed, the hydraulic pump (64) can supply required energy to the hydraulic cylinder (61) in a slower pace, so as to continue the elevation to the desired level at the deck (34) of the fish cage platform (30).

It will be apparent to professionals skilled in the art that the motorized elevation device may be replaced with a strictly mechanical lifting system, which may include weights and pulleys, or a pneumatic system, or even an electric powered motor system.

In daily practical use there is no need for extra safety measures to retain the landing cradle (10) in position by the deck (34) ofthe fish cage (30). If specific safety measures for securing the watercraft lift in an upper position ofthe landing cradle (10) is desired or required by regulation, the deck (34) ofthe fish cage (30) can be provided with one or more safety devices (50) for locking at least one inner fork (10b) and thus the cradle (10) in its upper position close to the fish cage (30) and the platform deck (34).

Figure 2 shows a small watercraft (40) arriving at a fish cage platform (30), the fish cage (30) being secured by anchors at sea, and in which arrows indicate the prevailing direction of wind. The fish cage (30) is secured by mooring lines (70) of desired type. The watercraft lift may in principle be installed at any sides of the fish cage (30). The only practical limitation is that a small watercraft (40) does not favor wind from behind when entering the landing cradle (10), easily gaining more speed than what is desired and thus a greater risk for damage to the small watercraft (40) or landing cradle (10).

Elevating of a small watercraft (40) by means of the boatlift according to invention is shown as a series of drawings at figures 3 to 7. According to a preferred embodiment of the invention, landing of a small watercraft (40) at a in general rigid fish cage (30) in swells may be carried out by the means of a watercraft lift with a landing cradle (10). The method may advantageously be performed in the following manner: The landing cradle (10) is arranged floating in free heave movement in the waves and kept at a distance from the fish cage (30) by means of at least one davit arm (20) being pivotable in the vertical plane. Davit arm (20) includes at least one set of overlying and one underlying parallel elongate davit arm members (21a, 21b). The small watercraft is driven into the cradle (10). Normally there is no need to secure the small watercraft (40) to the cradle (10), because it is held adjacent the fendering (15a, 15b) ofthe landing cradle by friction. The small watercraft (40) can then be secured to the cradle (10) if desired.

The cradle (10) with the small watercraft (40) inside will then be heaving with the waves, awaiting a supposedly larger wave. When the cradle (10) and the small watercraft (40) are situated near the top of a larger wave, the motorized elevation system can be activated, and prevent the landing cradle (10) from being Iowered from this position. A pressure sensor (68) which relays a signal to release an energy accumulator (63). Thereafter, a rapid elevation sequence ofthe landing cradle (10) may be given by means of energy accumulator (63) until the cradle (10) is clear of potentially dangerous successive waves. The energy accumulator (63) is in a preferred embodiment a hydraulic pressure energy accumulator (63). This rapid elevation may of course be performed from any level of the cradle (10) heaving in the waves, but it may be waste of energy not to let the wave elevate the cradle (10) and the small watercraft (40) along the first piece.

When the energy accumulator is fully or partly discharged and the cradle (10) with the small watercraft (40) is elevated to a presumed safe level above the waves, the further elevation of the cradle (10) and the small watercraft (40) can continue to a desired position by the side of the fish cage (30) platform deck (34). This last part of the elevation is preferably performed by means of the hydraulic pump (64) supplying the hydraulic cylinder (61), alternatively solely by means of the energy accumulator (30).

After elevating the small watercraft to the desired position by the fish cage (30) platform deck (34), the method according to a specific embodiment ofthe invention includes the step of securing the cradle (10) in a stable and secure position by the platform deck (34) by means of a safety lock (50).

Furthermore, the small watercraft (40) should also be launched in a safe and secure manner by means of the watercraft lift. According to a preferred method, launching ofthe small watercraft (40) on a generally rigid fish cage platform (30) in waves may be carried out as follows: Ifølge en foretrukket fremgangsmate foregar sjøsetting av lettbaten (40) pa en hovedsakelig stiv merd (30) i sjøgang, ved bruk av en batheis med en slippvugge (10) slik:

The cradle (10) with the small watercraft (40) is Iowered from the elevated position until the small watercraft (40) arrives at the desired floating position. The motorized elevation device (60) is released so that the landing cradle

(10) and the small watercraft (40) float and heave freely with waves, kept at a distance from the fish cage (30).

The small watercraft (40) is maneuvered out of the cradle (10).

According to a preferred arrangement ofthe invention, before the cradle (10) is Iowered, the cradle (10) is released from a stable, desired position at the fish cage (30) platform deck (34) by means of releasing a safety lock (50) is released.

The watercraft lift may include an emergency stop mechanism and a terminate commando mechanism. This is absolutely a necessity in case the watercraft lift must be stopped, in particular in case of dangerous incidents or accidents.

The cradle (10) is normally positioned in a suitable position at the fish cage or wharf/pier (30) the platform deck (34) when not in use. By the means of the elevation device (60), the watercraft lift can be iowered before being arranged in a free floating position in the waves.

Claims

1. A watercraft lift having a landing cradle (10) for landing and launching a small watercraft (40) on a generally rigid fish cage or wharf/pier (30), wherein the watercraft lift includes: at least one davit arm (20) being pivotable in the vertical plane, including at least one set of an overlying and an underlying parallel elongate davit arm stay member (21a, 21b); a control device (65) for a motorized elevator device (60), of which the ele- vator device is arranged for lifting and lowering said landing cradle (10) with the davit arm (20,21 a,21b), between an extended position under the sea surface for landing/launching said small watercraft (40) and a raised position for said landing cradle with the small watercraft (40) at or above the deck (34) of the fish cage (30), and so that said landing cradle (10) retains said small watercraft (40) in a generally upright position between the sea and the deck level; characterized in that said watercraft lift further comprises: that said davit arm stay members (21a, 21b) are supported at their inner ends in an inner, upper horizontal axle bearing (31a) and an inner, lower horizontal axle bearing (31b), respectively, on a generally vertical beam (36) attached to the hull of the fish cage (30); that said davit arm stay members (21a, 21b) are supported at their outer ends in an outer, upper horizontal axle bearing and an outer, lower horizontal axle bearing (14b), respectively, on said landing cradle (10); that said landing cradle (10) has buoyancy properties; - that the elevator device (60) is arranged for being released so that said landing cradle (10) with said small watercraft (40) float in a free vertical movement with the sea, in which the transversal movements of said landing cradle are guided by the forced movement ofthe arms (20,21a,21b) and in which said landing cradle with said small watercraft is held at a distance from the fish cage or wharf/pier by said arms (20,21 a,21 b); that the motorized elevator device (60) comprises a hydraulic cylinder (61) with a piston (62), wherein said cylinder (61) is arranged for movement of said davit arm (20, 21a,21b) and is connected to a hydraulic pressure accumulator (63) and a pump (64); og - that a sensor (68) which is located on a the elevating pressure side of said cylinder (61) includes a pressure sensor which is arranged for sensing pressure and pressure changes by movement of said landing cradle (10) with said davit arm (20,21 a,21b), so that said sensor (68) by elevation sends a signal to said pressure accumulator (63) so as to release when the pressure in said cylinder (61 ) reaches or exceeds a value which corresponds to that said piston is on top of, or on its way down from a position which corresponds to that said piston (62) is in a position which corresponds to that said landing cradle is on top of, or on its way down from, a high wave crest.

2. The watercraft lift according to claim 1 , wherein said landing cradle (10) comprises at least two sets of outer and inner fork arms (10a, 10b).

3. The watercraft lift according to claim 1 , wherein said fork arms (10a, 10b) are provided with fenders (15a, 15b) for a more even distribution of forces between said fork arms (10a, 10b) and the hull (41) of the small watercraft (40).

4. The watercraft lift according to claim 1, wherein said landing cradle (10) essentially corresponds to the hull shape (41) of the small watercraft (40).

5. The watercraft lift according to claim 1 , wherein said landing cradle (10) is provided with buoyancy elements (16) and wherein said elevator device (60) is releasable, so that said landing cradle in a Iowered position, preferably when landing and launching said small watercraft (40), may follow the waves and avoid collision with said small watercraft (40) due to heave movements being out of phase with said small watercraft (40).

6. The watercraft lift according to claim 1 , wherein said landing cradle (10) for said small watercraft (40) comprising a main girder (12) being pivotably fixed to the outer, upper horizontal axle bearing (14a) and the outer, lower horizontal axle bearing (14b).

7. The watercraft lift according to claim 1 , wherein a net (13) is spanned by said landing cradle (10) and arranged for supporting said small watercraft (40).

8. The watercraft lift according to claim 1 , wherein the deck (34) of said fish cage is provided with at least one safety lock (50) for locking at least an inner fork arm (10b) and thus said landing cradle (10) in the upper position of said landing cradle (10) close to said deck (34).

9. The watercraft lift according to claim 1, wherein said control device (65) of said motorized elevator device is arranged for remote control.

10. The watercraft lift according to claim 9, with a remote control (66) for controlling said control device (65) for said motorized elevator device (60), preferably by means of radio waves, wherein said remote control is mounted in the small watercraft (40), for remote elevation and lowering of said watercraft lift.

11. The watercraft lift according to claim 9, with a portable remote control (66) for said motorized elevator device (60), preferably by means of radio waves, for use by the crew of said small watercraft, for remote elevation and lowering of said watercraft lift.

12. Method for landing of a small watercraft (40) on a generally rigid fish cage or wharf/pier acted upon by waves, by use of a watercraft lift with a landing cradle (10), comprising the following steps: - keeping said landing cradle (10) free floating in free vertical movement with the waves, wherein said landing cradle (10) is held at a distance from said fish cage (30) by at least one davit arm (20) being pivotable in the vertical plane, including at least one set of an overlying and an underlying elongate davit arm stay member (21a, 21b), in which the transversal movement of said landing cradle (10) is guided by the forced movement of the arms (20,21 a,21b), driving said small watercraft (40) into said landing cradle (10), - waiting to said landing cradle (10) and said small watercraft (40) are elevated by a presumed high wave and locking said landing cradle (10) from being Iowered from this position by means of a hydraulic pressure accumulator (63) in a motorized elevator device (60), which further includes a hydraulic cylinder (61) with a piston (62) which is arranged for movement of said davit arm (20, 21a,21b) and are connected to the pressure accumulator (63), and a pump (64); as a sensor (68) being arranged on the elevating pressure side ofthe cylinder (61), senses pressure and pressure changes by movement of said landing cradle (10) with said davit arm (20,21 a,21b), so that when elevating, said pressure sensor (68) sends a signal to the pressure accumulator (63) so as to release when the pressure in said cylinder (61) reaches or exceeds a value which corresponds to that said piston is on top of, or on its way down from a position which corresponds to that said piston (62) is in a position which corresponds to that said landing cradle (10) is on top of, or on its way down from, a high wave crest; starting a fast elevation of said landing cradle (10) with said small watercraft (40) by means of said motorized elevator device (60) until said landing cradle is free from potentially higher following waves; continuing said elevation of said landing cradle (10) with said small watercraft (40) by means of said pump (64) until said small watercraft (40) reaches a desired position by the deck (34) of said fish cage (30).

13. Method according to claim 12, further comprising the step of allowing a control device (65) for the motorized elevator device to guide elevation of said landing cradle (10).

14. Method according to claim 12 or 13, wherein said the crew on said small watercraft (40) remotely controls said control device (65) by means of a remote control (66).

15. Method according to claims 12-14, which after elevating said small watercraft (40) to a desired position, further comprises securing said cradle (10) in a stable desired position at the deck (34) of the fish cage by means of a safety lock (50).

16. Method for launching a small watercraft (40) on a generally rigid fish cage or wharf/pier (30) for acted upon by waves, by use of a watercraft lift with a landing cradle (10) according to claims 1-11, comprising the following steps: lowering said landing cradle (10) with said small watercraft (40) until said small watercraft (40) reaches a desired floating position in the water, - releasing said motorized elevator device (60) so as to said landing cradle (10) freely floating in free heave movement in the waves and held at a distance form said fish cage (30), driving said small watercraft (40) out of said landing cradle (10).

17. Method according to claim 16, wherein said method before said landing cradle is Iowered, further comprises to release said landing cradle (10) from said stable desired position at the deck (34) of said fish cage (30) by means of a safety lock (50).