Steam-ships

by R. A. Fletcher

The floating dock is one of the most interesting of the many developments in connection with the naval and mercantile marine of the second half of the nineteenth century. Like all innovations, floating docks were received with derision.

Now they have proved their worth, but circumstances are easily conceivable in which all the marvels they have already accomplished will be far eclipsed by what they may be called upon to do. In the case of a naval battle, for instance, it may be a matter of impossibility for a crippled warship to enter a dry dock, or even to get to one; but a floating dock can be sent to meet the injured warrior and possibly save it from going to the bottom altogether.

The floating dock is a sort of raft, and the first man who ever hauled a boat from the water upon another boat or raft to repair, it started the idea of the floating dock. The first real floating dock, as the term is now understood, was probably that which was improvised in the Baltic Sea, so tradition says, by the skipper of a vessel which had sustained some damage in those waters. He bought an old hulk, removed the stern, and in its place constructed a flap gate. His vessel was then floated into the hulk, the flap gate was closed and the water pumped out. Floating docks of this type were almost the only kind known up to the beginning of the nineteenth century, and are in use to-day at some ports for small yachts, fishing-boats, and vessels of similar dimensions.

With the growing size of vessels, greater docking facilities became necessary, and, as the commerce of the world increased and ports were developed, demands arose for docking accommodation which could not always be met, owing in some cases to financial difficulties, and in others to the engineering difficulties connected with the localities. As a solution of the problem, the floating dock, as it is known to-day, was invented. In spite of the opposition with which it was greeted, the new contrivance held its own, and its merits became generally recognised.

The difficulties and the cost of constructing dry docks are very great, and the time taken in the work may run into years; one dock, indeed, is stated to have taken fifteen years to complete.

As an instance of rapidity of floating-dock construction, the Vulcan Company of Stettin required a dock 510 feet long and of 11,000 tons lifting power at short notice. The complete dock with all machinery and fittings was launched within seven and a half months, and within eight months and thirteen days of the inception of the project, the dock, after being towed across the North Sea and moored in place at its site, was sunk ready to receive its first ship. The Havana dock was delivered at Havana within eleven months after the signing of the contract for its construction; the actual time expended on it, dating from the day the first plate was laid until the complete dock was launched, was six months and a day. Both these docks are of over 10,000 tons lifting power. How long would it have taken to excavate and build graving docks capable of receiving vessels of the size that these docks can accommodate?

No dry dock can take a vessel larger than itself, and in reckoning the dimensions of a dock for receiving purposes it must be remembered that its cill is a fixture, that the width of the entrance at the cill must not be made greater than the strength of the structure will permit, and that though a dock may in other respects be able to receive a vessel it cannot do so if that vessel through any mishap should draw as much water as that at depth of cill, or if in heeling over, its bilges should be wider than the width of the dock entrance. None of these drawbacks apply to the floating dock. These immense modern structures of steel and iron can receive vessels longer than themselves, and in the case of the off-shore docks, can receive vessels wider than themselves.

Should a vessel be heavily down by the head or stern, a floating dock can be tilted to lift it, and should the vessel be heeling over, the dock itself can be inclined so that it shall receive it without difficulty. Yet another advantage is that the floating dock can be used in any kind of ordinary weather. Lying at its moorings it is head on to wind and sea. The amount of surface it opposes to the direct action of wind and sea is comparatively slight. The very massiveness of its structure reduces longitudinal and lateral motion to a minimum, especially when submerged. Even with a fairly heavy sea running, a damaged and leaking vessel can be brought upon the dock where its weight, added to that of the dock itself, makes the combined structure additionally stiff, so that the necessary repairs can be undertaken in safety as soon as the vessel is lifted, and with as much ease as if the dock and its burden were in still water. Floating docks also can be used at any state of the tide, but he would be a rash man who attempted to warp a vessel into an ordinary dry dock with the tide running past the entrance with any degree of strength.

Old Floating Dock at Rotherhithe,
circa 1800.