GB2313345A

GB2313345A - Dry docking pontoon for nuclear powered submarines

Info

Publication number: GB2313345A
Application number: GB9710563A
Authority: GB
Inventors: James Kenneth Dobson
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-05-23
Filing date: 1997-05-23
Publication date: 1997-11-26
Anticipated expiration: 2017-05-23
Also published as: GB2313345B; GB9710563D0; GB9610767D0

Abstract

A method of dry docking a marine vessel, which is preferably a nuclear powered submarine 1, comprising the steps of docking down a pontoon 3 onto the floor of a dry dock 2, filling tanks 5 in the pontoon, flooding the dry dock, docking down the nuclear powered submarine 1 onto the pontoon 3 and resting the submarine on supporting means 4, emptying the tanks 5, and reflooding the dry dock allowing the pontoon 3 to float in the dry dock facility with the submarine 1 supported above the water in a "dry" condition.

Description

Dry Docking Pontoon for Nuclear Powered Submarines This invention relates to facilities for dry docking marine vessels, and more particularly to facilities for dry docking nuclear powered submarines.

In common with virtually all forms of ships, nuclear powered submarines are dry docked to allow work to take place on underwater fittings. A dry dock facility is also used when the work includes refuelling of a nuclear powered submarine, since this enables the procedure to be carried out without the fuel elements being shipped over water, which is highly undesirable for technical reasons. In most cases, this work is undertaken in a conventional graving dock, which is a dock formed by a specially constructed hole in the ground which, when flooded, allows the submarine to be introduced over a cradle previously secured to the dock bottom. The entrance to the dock is then sealed with a watertight gate (lock gate, flap gate, caisson, etc) after which the water is pumped out, leaving the vessel resting in its cradle.

The existence of a nuclear reactor plant in nuclear submarines leads to the application of stringent requirements to demonstrate to government nuclear safety authorities that all activities involving the nuclear propulsion plant are safe. In the case of dry dock systems, it is necessary to demonstrate that the facility is able to meet demanding criteria for resistance, particularly to seismic events such as earthquakes, and to naturally occurring events such as extremes of tide, wind, rainfall, etc. and external hazards, such as collision damage. The problem is that an event or sequence of events which leads to the submarine falling out of its cradle could further lead to uncontrolled release of radioactivity. This could be brought about by the failure of the cradle itself or by the failure of the dock gate resulting in the submarine being swept off the cradle in the consequent instantaneous flooding of the dock.

To date, efforts to provide design solutions which meet the acceptable safety criteria fully have concentrated on rock anchors to hold the cradle in place, anti-rotation devices to prevent the vessel rolling on the cradle and additional forms of protection to mitigate the effects of failure of the dock gate. This work has not been entirely successful, and has been and continues to be enormously expensive in design effort.

The implementation of the emerging designs will also be extremely costly.

According to a first aspect, the present invention provides a method of dry docking a marine vessel comprising the steps of: a) docking down a pontoon on a floor of a dry dock, b) filling tanks or floats associated with the pontoon with water, c) flooding the dry dock, d) floating the marine vessel into the flooded dry dock, e) pumping the water out of the dry dock, thereby resting the marine vessel on a means for supporting the vessel associated with the pontoon, f) emptying the tanks or floats of the pontoon, g) reflooding the dry dock area allowing for the pontoon to float in the dry dock facility, with the marine vessel supported above the water in a "dry" condition.

Preferably the pontoon is a pontoon for supporting a marine vessel in a dry dock facility.

Preferably the marine vessel is a nuclear powered submarine.

Preferably the means for supporting the vessel includes a cradle.

Preferably the pontoon further includes a skirt on at least one peripheral edge thereof, the skirt bridging any gap which may exist between a wall of the dry dock facility and the pontoon.

The invention will now be described by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a side view of a submarine located on the pontoon on the floor of a dry dock; and Fig. 2 is a front view of a submarine located on the pontoon in a flooded dry dock.

Referring to Fig. 1, prior to the introduction of the nuclear powered submarine 1 into the dry dock generally shown at 2, a floating pontoon 3 of sufficient size and carrying capacity is constructed in or berthed in the dry dock 2. The pontoon 3 is then "docked down" in the same manner as a submarine would be. The submarine cradle 4 is formed on the pontoon 3 at a suitable time, either before or after the docking down operation. The tanks 5 of the pontoon 3 are then filled and the dock 2 reflooded, leaving the pontoon 3 bearing the cradle 4 on the dock bottom 6. The submarine 1 is then introduced over the cradle 4 and docked down on it in the usual way. The tanks 5 of the pontoon 3 are then emptied. The dock 2 is then refilled with water to refloat the pontoon 3, bearing the submarine 1 in its cradle 4. Thereafter, the desired work on the submarine 1 may proceed, isolated, by virtue of it being afloat, from the direct effects of a seismic event. The dry dock gate 7 is effectively redundant at this point (although probably required for security and good all round access). By maintaining equal water levels on either side, failure of the gate 7 however caused (seismic event, collision, material failure) would have no effect on the safety of the nuclear propulsion plant of the submarine 1.

Referring also to Fig. 2, due to the shape of existing dry docks, there would be a gap between the floating pontoon 3 and the dock walls 8 and 9. In the case of nuclear refuelling operations, when it is highly undesirable to move fuel elements or core over water, the water gap 10 on the route of the nuclear fuel would be filled either by positioning a further pontoon of suitable dimensions (not shown) or by fitting a skirt (not shown) to the docking pontoon 3.

If the dimensions of the pontoon 3 with respect to the entrance to the selected dry dock 2 permit, the pontoon bearing the submarine 1 could be moved from the dry dock 2 to another venue, allowing flexibility in the use of the dry dock facility.

Undocking operations would proceed using the same process in reverse.

The particular advantage of the invention is the fact that the consequences of a seismic event occurring on a docked nuclear submarine are dramatically reduced.

Further advantages of the invention and/or the ways in which the disadvantages of previously known arrangements are overcome, include: a) The consequences of events such as impact and extremes of weather (tide, rainfall, wind, etc) which might lead to dock gate failure becoming virtually negligible. Furthermore, the depth of existing dock bottoms relative to the lowest predicted tide would ensure that the pontoon and submarine remained afloat and seismically isolated at the 1 in 10000 year low tide; b) The invention would be cheaper by orders of magnitude than the approach currently being pursued to the provision of docking facilities for nuclear submarines; c) Once docked on the pontoon 3, the submarine 1 could be moved to any suitable venue, freeing the dry dock 2 for other uses; d) As the period during which the submarine 1 would be exposed to seismic, extreme weather or impact damage effects would be extremely small in relation to the whole of a normal period in a dry dock 2, it should be possible to gain safety case approval to utilise a range of dry docks, rather than one specifically and expensively purpose built.

Modifications and improvements may be made to the foregoing within the scope of the invention.

Claims

1A method of dry docking a marine vessel comprising the steps of: a) docking down a pontoon on a floor of a dry dock, b) filling tanks or floats associated with the pontoon with water,

c) flooding the dry dock, d) floating the marine vessel into the flooded dry dock, e) pumping the water out of the dry dock, thereby resting the marine vessel on a means for supporting the vessel associated with the pontoon, f) emptying the tanks or floats of the pontoon, g) reflooding the dry dock area allowing for the pontoon to float in the dry dock facility, with the marine vessel supported above the water in a "dry" condition.

2 A method of dry docking a marine vessel in accordance with Claim 1, wherein the pontoon is a pontoon for supporting a marine vessel in a dry dock facility.

3 A method of dry docking a marine vessel in accordance with Claim 1 or Claim 2 in which the marine vessel is a nuclear powered submarine.

4 A method of dry docking a marine vessel in accordance with any one of Claims 1 to 3, wherein the means for supporting the vessel includes a cradle.

5 A method of dry docking a marine vessel in accordance with any of the preceding Claims in which the pontoon further includes a skirt on at least one peripheral edge thereof, the skirt bridging any gap which may exist between a wall of the dry dock facility and the pontoon.