A slipway, or boat slip, is a ramp on the shore of a river or estuary that is used for the building or reparing of ships or boats.

Simple Slipways

In its simplest form, a slipway is a plain ramp, typically made of concrete in modern construction, extending to well below the level of the water. Normally there is a flat paved area on the landward end.

When used for boats or small ships (i.e. ships of no more than about 300 tons), the vessel is moved on a wheeled carriage, which is run down the ramp until the vessel can float on or off the carriage. Such slipways are used for repair as well as for putting newly built vessels in the water.

Large Ship Use

For larger ships, slipways are only used in construction of the vessel.

Normally they are arranged perpendicular to the shore line (or as nearly so as the water and maximum length of vessel allows) and the ship is built with its stern facing the water. The slipway then takes the form of a plateway with the two plates nearly horizontal. They are actually arranged in the form of a very flat 'V' to give stability to the vessel being worked upon. The plateways extend to well below the water level taking into account tidal variations. The vessel is built upon a wooden frame that is constructed as the ship extends up from the keel.

The process of transferring the vessel to the water is known as launching and is normally a ceremonial and celebratory occasion. It is the point where the vessel is formally named. At this point the hull is complete and the propellors and associated shafting are in place, but typically the engines have not been fitted and the superstructure has not been built.

On launching, the vessel slides backwards down the slipway on the frame until it floats by itself.

Some slipways are built so that the vessel is side on to the water and is launched sideways. This is done where the limitations of the water channel would not allow lengthwise launching, but occupies a much greater length of shore. The Great Eastern built by Brunel was built this way as were many Landing Craft during WWII. This method requires many more plate runs to support the weight of the ship.

In both cases heavy chains are attached to the ship and the drag effect is used to slow the vessel once afloat until tugboats can move the hull to a jetty for fitting out .

The practice of building on a slipway is dying out with the very large vessels introduced from about 1970. Part of the reason is the space requirement for slowing and manouvering the vessel immediately it has left the slipway, but the sheer size of the vessel causes design problems, since the hull is basically supported only at its end points during the launch process and this imposes stresses not met during normal operation.