Linkspan

A linkspan or link-span is a type of drawbridge used mainly in the operation of moving vehicles on and off a roll-on/roll-off (RO-RO) vessel or ferry, particularly to allow for tidal changes in water level.

The aim of all this is to have the linkspan at roughly the same height above the water as that of the car deck on whichever ferry happens to be docking at the time.

To protect the linkspan from impact as the ship makes its final approach, stern fenders are positioned in front of it.

These absorb the energy of the ferry's impact, guide its stern and hold it from moving sideways when finally berthed.

When it becomes necessary to make longer linkspans to accommodate a greater tide range the train loads become proportionately higher until a critical reaction is reached.

Dover/Calais route, one of the busiest in the world, still require that vessels using these ports are configured to suit the restraints of each berth, in doing so this limits them from being used in service elsewhere.

In the early 1970s Marine Development a specialist design company patented a new type of linkspan for use with general purpose ferries.

Such a design proved particularly efficient with small ferries in exposed berths, it being able to cope with vertical movements at the end of the ship (as much as two meters) while still being able to load or discharge vehicles.

Wire pendants hanging from the vessel are the main method used but although these required the addition of two brackets on the ship this is a minor modification.

For occasional or single voyage visits, synthetic strops are provided and secured through the fairleads onto the ships’ bitts.

Initially when ships’ ramps were no more than 8m wide (double lane) there were very few vessels that could not use a berth that had the submerged tank linkspan .

Two recently (2007) were installed in the West of Scotland on a short estuarial crossing, and two more on a new route across the Spencer Gulf in Southern Australia.

This ramp hinged at the ship's threshold then accommodates any movement due to waves, swell and the passage of traffic.

This limitation means that ship's with rounded or tapered sterns and those berthing bow in are likely to hit the end of the linkspan with consequential damage.

Later developments allow for the berthing energy to be absorbed through the linkspan at the hinge but this will not protect from overriding of the ship or uplift from the bulbous bow.