Oceans of knowledge
Hawser SPM Tower system
The single point mooring tower with a hawser system includes a large-diameter polypropylene line between the single point mooring buoy and the vessel. This system requires no modifications to the vessel hull structures and can use the standard mooring strong points at the bow of the vessel.
The highly flexible hawser system is suitable for vessels of different sizes and displacements, and for short duration mooring as well as for semi-permanent mooring. In the case of semi-permanent mooring, redundancy in the hawser system is provided by dual lines. To avoid buoy-kissing between the vessel and the tower, thrust astern is required, either by the vessel or by tug assistance. This is especially urgent when the environmental conditions suddenly change in direction or when these are very mild allowing the vessel to drift towards the tower.
Typically the hawser line length varies from 40 to 100 metres, depending on the local environmental conditions. On the vessel side, the hawser includes a chafe chain arrangement to protect it against excessive damage from contact with the vessel bow. On the tower side, the hawser is connected to a load pin by means of special shackles. The load pin measures the load in the hawser during the mooring. This enables the operators to record load history and the remaining lifetime of the hawser in order to ensure its timely replacement.
The hawser mooring system can also be combined with a fluid transfer system that enables connection of (subsea) pipelines to the midship manifold of a conventional tanker. The fluid path between the tower and the tanker is realised by means of an aerial hose to the bow of a tanker with a bow loading station or by means of one or more floating hoses to the tanker standard midship manifold. To protect the hoses, they are provided with a single or double acting marine break-away coupling. Aerial hoses are especially valuable when the tower is located in ice-covered waters in the Arctic or when the hose requires aerial applications as needed for the transfer of cryogenic fluids.