Ships Out of Water

April 14, 1995|By LOUIS F. LINDEN

A question raised time and again regarding the U.S.S. Constellation is, ''Why don't you just take her out of the water? Wouldn't that solve all of her problems?''

Unfortunately, no. In fact, taking the ship out of the water would aggravate some of her problems and introduce other even more difficult ones. That has been the experience of the few vessels that are presently kept out of the water, the best-known being H.M.S. Victory and the clipper ship Cutty Sark. The three primary issues regarding ships out of the water are dry rot, point loading and finances.

Dry rot is a misnomer. There's nothing dry about it. Dry rot is a category of several species of fungus. Rot spores require oxygen, fresh water and warm temperatures. All three are in abundant supply in our part of the world. Anyone who takes care of a wooden frame house is probably familiar with the problem. Dry rot destroys wood fiber and robs it of its strength, in some instances (depending on the species of rot) turning the wood fiber to mush.

Rot spores do not like salt water. It is not the water that wooden ships float in that causes them to rot, it is the infiltration of rain water and excess humidity. Salt water actually retards the growth of rot fungus. Wooden vessels rot from the top down. Removing Constellation from the water will not retard deterioration due to dry rot. Indeed, it will expose her exterior underbody to rot spores in the atmosphere and warm, moist air, increasing the possibility of new rot forming.

Dry rot can be controlled by denying the spores access to the wood, depriving them of moisture or oxygen, or reducing the temperature. None of these is practical in our temperate climate. Or one could use fungicides, but many of these are extremely toxic to humans as well as to rot spores and can't be used in areas of human habitation.

Dry rot is a significant problem in Constellation. Years of rain water infiltrating through the decks, along with less than optimal ventilation, has caused severe structural damage throughout the ship. Sodium borate will not cure the damage, but we expect it will retard the growth of rot infestations. Improved ventilation, the use of awnings to deflect rain water and improved decks will also help. But the structures has already been significantly weakened, leading us to the next issue, point loading.

Ships are, by definition, enclosed vessels supported by their own buoyancy in a fluid medium, water. The structure's weight is meant to be spread evenly over the surface of the hull. A ship taken out of the water must either be supported at a number of points on the hull -- hence the term, ''point loading'' -- or it must be set in a solid medium which conforms to the hull's shape.

The latter alternative has been used with a number of vessels, including two in Seawolf Park on Pelican Island, Galveston, Texas. A destroyer escort and a submarine, U.S.S. Seawolf, both steel ships, exist in sand berths. They were floated to their resting places, then the channel was closed and filled with sand, which supports the ships.

Both ships are near to being scrapped. The sand fill allowed water to collect around the hulls, and they have rusted to the point where Seawolf's hull has holes large enough to stick your head through. With the vessels entirely supported in sand there is no practical way to gain access for maintenance, and the cost of refloating them to get them into a dry dock is prohibitive even if temporary repairs would allow refloating. They are, for all intents and purposes, dead ships. Wooden vessels would not last even as long as steel ones.

All vessels are point loaded for short periods in dry docks, which are the only practical way to service large ships. The ship rests on blocks placed under her keel and bilges. The entire weight of the ship is borne by the small portion of the hull resting on the blocks. This is not a problem in steel- or iron-hulled ships. They are stiff and much of their strength lies in their skins.

Traditionally built wooden ships are built of thousands of pieces of wood held together with (in the case of Constellation) an estimated 150,000 fasteners. The deck and hull planking seams are caulked with cotton and oakum and seam compounds. It is inevitable that the points upon which the ship rests on her bottom planking will intersect with several of these seams and joints. Subjected to greater stress than they were intended to take, they begin to distort as the wood dries and weakens. The seams begin to open, providing exposure to rot spores and further deterioration of the timber. Ultimately, the hull will sag down around the loading points, stressing the rest of the structure.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.