Alternative Lifeboat Slipway Bearing Materials.

Abstract

The Royal National Lifeboat Institution has provided marine search and rescue cover along the UK and Irish coast since 1771. This is accomplished using a variety of lifeboats and lifeboat stations depending on local conditions. In regions where there is a large tidal range, or where there is no nearby natural harbour it is necessary to use an inclined slipway station to launch lifeboats. This consists of an inclined slipway, usually at a gradient of 1 in 5-6, with a large boathouse holding the lifeboat under cover at the top. The lifeboat is released from the boathouse and proceeds under its own weight along the slipway into the sea. Recovery is performed by manoeuvring the lifeboat keel onto the slipway keelway where a winch line is attached and the lifeboat hauled back into the boathouse at the top of the slipway. Advances in lifeboat technology has seen the size and mass of slipway lifeboats increase over the years culminating in the new 35+ tonne Tamar class (introduced 2005) and this has presented considerable engineering challenges to the safe and consistent operation of lifeboat slipway stations. Previous slipway launch practice had involved using a greased steel channel, along which the lifeboat keel slides, however with increasing lifeboat mass this has become unsuitable with problems of high friction along the slipway and concerns regarding the environmental impacts of the grease repeatedly being washed into the sea surrounding the base of the slipway. This research focuses on the search for suitable alternative slipway linings and lubricants culminating in the recommendation of a new jute/phenolic resin composite lining material to be used with a novel freshwater or seawater lubrication system, and with the development of techniques to reduce panel wear and to establish consistent panel monitoring and replacement criteria with the aim of reducing the environmental, material and economic costs associated with reliable lifeboat slipway operation.