Ships – Vessel raising and docking – Floating dry docks
Patent
1986-12-10
1988-06-14
Peters, Jr., Joseph F.
Ships
Vessel raising and docking
Floating dry docks
405 3, B63C 106
Patent
active
047504447
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a shiplifting device of the kind comprising a platform submersible in a basin and having a deck and a downwardly open lifting skirt positioned below said platform and provided with means for supplying and removing air from the lifting skirt to control the buoyancy of the platform, and comprising link arms connecting the platform with the quay or parts associated therewith, each link arm at mutually separated points being pivotally connected with the platform and the quay about a substantially horizontal axis of rotation, so that the platform maintains its horizontal orientation.
BACKGROUND ART
A ship lifting device is known from U.S. Pat. specification No. 4,381,723 comprising a deck with a downwardly open lifting skirt positioned below the platform and provided with valves for controlling the buoyancy of the deck when air is supplied and removed from the liftingskirt. The air is supplied from the bottom flowing through discharge valves located along the bottom of the basin. The deck with associated lifting skirt is pivotally connected with stationary foundations by means of a parallelogram linkage system. This shiplifting device is encumbered with the drawback that it is not possible to control sufficiently exactly the upward and downward movements of the deck.
DESCRIPTION OF THE INVENTION
It is the object of the present invention to provide a shiplifting device of the above mentioned type, in which it is possible safely and reliably to control the upward and downward movement of the platform, and in which the platform may be stopped at any time during the movement. The shiplifting device according to the invention is characterised in that the link arms form buoyancy means, the centers of buoyancy of which each moves between a first area in the immediate vicinity of a horizontal plane through the axis of rotation of the link arm in question relative to the quay, and a second area in the immediate vicinity of a vertical plane through the same axis of rotation, the center of buoyancy being in the first area when the platform is in its lowermost position (the bottom position), and in the second area, when the platform is in its uppermost position (the top position). As a result a shiplifting device is provided, which is comparatively easy to work. This is particularly due to the fact that the buoyancy, with which the link arms influence the platform, diminishes from maximum in the bottom position of the platform to minimum in the top position of the platform. The manoeuvring stability of the platform is consequently increased due to the fact that the increasing buoyancy by which the amount of air in the lifting skirt influences the platform is currently compensated for as it is being raised. As a result of this compensating effect it is made possible that the platform can only be raised by continuous supply of air and lowered by continuous discharge of air from the lifting skirt, respectively.
According to the invention the link arms on the same side of the platform may be interconnected by means of a pivotal connecting rod which together with the link arms comprises axes of rotation extending parallel to each of the axes of rotation of the link arms in relation to the platform and the quay, respectively, and being located outside a plane containing the two last-mentioned axes of rotation. Thus it is obtained in a simple manner that the platform always maintains its horizontal orientation.
According to a further embodiment of the invention the link arms may be formed as prisms with horizontal axes and cross-sections in the form of a right-angled isosceles triangle, the hypotenuse of which is substantially vertical when the platform is in its bottom position, and substantially horizontal when the platform is in its top position, and that the axes of rotation of the pivotal connection of the link arms with the quay are positioned at the sectionally rectangular corners of the link arms, and that the axes of rotation of the pivotal connection of the link arms with
REFERENCES:
patent: 3603276 (1971-09-01), DeLisle
patent: 3727415 (1973-04-01), Williams
patent: 3951087 (1976-04-01), Carson
patent: 4149469 (1979-04-01), Bigler
patent: 4381723 (1983-05-01), Furst
Avila Stehpen P.
DME Handels- Og Licensselskab Aps
Peters Jr. Joseph F.
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