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The Pros & Cons of Permanently Dry-Docking Historic Vessels

Captain S.T. Waite, M.N.I.
Master, Cutty Sark


In recent years more and more historic vessels are being considered for preservation, and one of the factors to be considered when planning a proiect is whether or not the vessel is to remain afloat as, in the case of H.M.S. Warrior (Click here for Illustration 1), or to be permanently dry-docked, as with H. M.S. Victory and Cutty Sark. These are not, however, the only options. Two other options have been used:

1) to sit the vessel in a hole in the ground and infill around her.

Two examples of this method can be seen in Japan, the Meiji Maru (Click here for Illustration 2) built in 1874 as a Royal Yacht and the pre-Dreadnought battleship Mikasa, (Click here for Illustration 3) built in 1900. While another example is the Caishot Spit Light Vessel in England (Click here for Illustration 4).

2)to locate her in a permanent dock that may be used as either a wet dock or a dry-dock, as in the case of R.R.S. Discovery in Scotland (Click here for Illustration 5, Click here for Illustration 6).

Ships are designed to withstand the crushing force of water outside, and are not very well suited to remaining out of the water for prolonged periods unless very well supported. This illustration (Click here for Illustration 7) shows what can happen to a vessel that is not is not adequately shored.

When Cutty Sark (Click here for Illustration 8) was permanently dry-docked in 1954 there was only one other example of a major historic vessel already preserved in the United Kingdom, HMS Victory ((Click here for Illustration 9), to which the Cutty Sark Preservation Society could look for inspiration. Unfortunately, the minutes of the Technical Committee of the Society are no longer in existence, but one has to assume that having decided to preserve the ship at Greenwich and to open her to the public as a visitor attraction, the following points were considered when deciding whether to leave her afloat or to permanently dry-dock her:

1) Ease of access
2) Evacuation in event of fire, and accessibility for emergency services
3) Need for periodic dry-docking, resulting in loss of revenue
4) Risks when under tow
5) Risk of damage from the wash of passing vessels, and the risk of collision
6) The cost of maintaining moorings
7) The possible loss of display area in the lower hold caused by the amount of ballast required
8) The extra cost of maintenance, being afloat
9) The ability to display the underwater body, and show off the ship's fine lines. In the event, it was decided to dry-dock her, it being felt that her composite construction, with sharp rise of floors, would allow her to remain out of the water for an indefinite period without the hull losing shape. It was also believed that very light bilge and breast shores would suffice to support the hull and yet allow the ship's lines to be appreciated (Click here for Illustration 10), and that with her unique construction of iron, teak and elm, and being permanently out of the water, there would never be a need for major repairs to the hull in general, nor to the keel in particular. With this in mind, the ship was docked down on a continuous concrete plinth. Experience has shown that the assumptions made in 1954 on the inherent strength of the hull were incorrect, the extent of the wastage of the ironwork, as shown in this illustration, not being appreciated. By the 1970's it was realised that the ship was losing shape and an additional 31 intermediate frames (Click here for Illustration 11) had to be fitted to maintain the shape of the hull. These run from frame 25 to frame 105, that is from abeam of the mizzen to abeam of the fore mast and rise from the keelplate to the bilge stringer. Extra shores had also to be placed to support the counter and in 1991 additional shores had to be fitted to support the bilges and the keel, because the latter was beginning to crush due to electro-chemical degradation of the timber. It has become apparent that the ship needs a massive amount of restoration, and she is likely to continue to need it in the future. Being unable to remove keel blocks makes working on the keel extremely difficult.

With H.M.S. Victory it was known that the hull was fragile when she was docked in 1922, and massive bilge stools were built to support the hull (Click here for Illustration 12), but thought had been given to the possibility for the need of keel repairs in the future, and although she is docked down on a continuous concrete plinth, wooden keel blocks were provided.

The S.S. Great Britain (Click here for Illustration 13) has the advantage of being dry-docked in the dock in which she was built in 1843, using traditional methods with wooden shores (Click here for Illustration 14). A more sympathetic arrangement than the tubular steel shores used on Cutty Sark.

In the case of H.M.S. Warrior it was decided to keep the vessel afloat in Portsmouth Harbour. This is obviously the most sympathetic way of displaying a ship, provided that she has the strength to remain afloat, which obviously the Great Britain had not, having broken her back while abandoned in the Falklands.

When deciding on what course of action to take, I believe that a ship should be kept afloat as long as is possible, but she must be placed in a safe berth, and the future costs of dry-docking, towage, insurance etc. should be taken into account. However, with the decline of shipbuilding and shiprepair in the Western World one has to consider the possibility that there might be no suitable dry-docks nearby in the future, and a long and expensive tow may be required.

Permanently dry-docking a ship removes the problem of future availability of dry-docks, but this only works well if the dry-dock looks like and is fitted out like a dock that is contemporary with the ship, and it is imperative that the ship is provided with suitable workshop accommodation nearby. Unfortunately, Cutty Sark was provided with nothing and restoration is being carried out from a temporary pound alongside the ship, with 40 ft containers being used as rigging lofts and metal working shops. The wood working shop is a quarter of a mile away!

To build the ship into the surrounding land is, I believe, the worst possible option. Not only is the surrounding totally out of keeping, but how does one determine what is happening to the "under water body". In the case of Mikasa I believe that the Japanese authorities had no option but to treat the vessel in this way, because part of the surrender agreement after WWII stated that Japan could not operate battleships, and the alternative would have been to scrap her. I am not aware of the reasons for preserving Meiji Maru in this way. The Caishot Spit Light Vessel is not open to the public, and appears to be preserved just as a piece of street decoration.

The best choice of berthing arrangement is the wet/dry dock such as that used for Discovery in Dundee and HM.S. Gannet in Chatham (Click here for Illustration 15). The dock in Dundee was specially constructed, was expensive, and unfortunately does not look like a traditional dock, but serves its purpose well, allowing the vessel to remain open to the public while docked down for underwater restoration. Here again, for various reasons, adequate workshop facilities were not provided.

Gannet has the advantage of being in one of the historic dry-docks of the decommissioned Royal Naval Dockyard, but even so there were costs involved in converting the dock to its present use. The caisson had to be modified to take the water pressure of the dock being full, when the tide in the river was out, because it was not designed to operate like this. other factors to be considered if keeping a vessel afloat are:

1) The salinity of the dock water. An iron or steel vessel is better off in freshwater, while the reverse is true for a wooden vessel.
 
2) Construction of the vessel. Wooden merchantmen pose a particular problem in that if they are afloat with the minimum of ballast, in order to make the hold accessible to visitors, there is a very strong possibility that they will hog badly. This illustration (Click here for Illustration 16) shows the 103ft wooden tops'l schooner Kathleen & May being prepared for a 600 mile tow from London to Gloucester, for restoration. For 10 years she had been in a special wet/dry dock in London floating in fresh water. No workshop facilities had been provided, and when work had to be carried out the surrounding businesses were concerned about the noise levels likely to be created, hence the move to Gloucester.


Prior to the tow all underwater seams were battened, and these battens clearly show how the keel has hogged and the bilges have dropped (Click here for Illustration 17). The vessel had a 15" hog in a keel length of 90ft!

To conclude, I believe that ships should be kept afloat when ever possible, depending on the following factors:

1) Strength of the hull
2) Construction of the hull
3) Salinity of water
4) Ability to carry sufficient ballast for stability and to prevent the hull hogging
5) Accessibility for visitors and emergency services
6) Present and future availability of dry-docks or slipways


However, whether kept afloat, docked down or in a wet/dry dock, day to day maintenance and repair will have to be carried out and workshop space must be made available.

Illustrations of: Mikasa & Meiji Maru by kind permission of The World Ship Trust
R.R.S. Discovery by kind permission of Dundee Industrial Heritage
s.s. Great Britain by kind permission of S.S. Great Britain Trust

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Version 1.02, 7 July 1997