Volume Two - The Era of Optimism, Investment & Development - The gridiron and slipway of the Penarth Shipbuilding & Ship Repairing Co. . . .

At neap tides no vessel could use the gridiron, for the keel and bilge blocks would be submerged at all states of the tide. If the gridiron were, on the other hand, to be constructed at such a level as to take vessels on any tide, then the size of ship which could be accommodated would be limited to a draught of 10 ft., or less. This limits the application of gridirons and hards to a great extent, and not many gridirons remain in use. (as at publication date of 1949)

The next step was top haul the ship completely out of the water by mechanical means for the purpose of repair, and lower it down into the water again when the repair was finished. This process was effected in the first instance by means of slipways, many of which are still in use for trawlers and similar craft.

Slipways consist of inclined ways of timber or stone, running up from a sufficient depth of water to the requisite height above high water level, upon which a series of rails is fixed. On these rails suitable carriages run, to support the vessel, and are hauled up or lowered down by means of winding gear.

Slipways are either of the end-on or broadside pattern, according to whether the vessel is hauled clear of the water in the direction of its length or normal to this direction. A much more elaborate carriage is required for an end-on slipway than a broadside slipway if the vessel is required to be maintained in a level position. On the other hand, if the vessel can be hauled up in an inclined position, much longer haulage will be required.

An end-on slipway, however, requires considerably less quay space than a broadside slipway, which may be an important consideration, the end-on pattern requiring space equal to only about three times the beam of the ship to be dealt with, whereas the broadside pattern requires about 10 per cent. more than the length of the ship.

In the broadside type it is, however, possible to deal with more than one vessel on a single slip, provided that it is not required to release the vessels on the upper part of the slip before those on the lower, which would be manifestly impossible.

Both types of slipway are in use, principally for fishing vessels, and at the St. Andrew's Dock, Hull, for instance, there are four slipways of the end-on pattern.