Caisson tow completed

The caisson’s destination was its installation site at Ullapool where the unit will form an extension to the ferry pier for the new, larger, Ullapool to Stornoway ferry. Holyhead were approached by RJ McLeod on the basis of a strong relationship from the time of the Eigg Ferry terminal construction several years ago, and were asked to manage all the marine aspects of the job

In addition to the tow itself Holyhead’s scope included ballasting the caisson down on arrival at a temporary location on the seabed in Ullapool to allow installation of large fenders by McLeod; then returning to site for the final refloating and permanent installation of the structure where the tolerance on positioning specified by designers Wallace Stone was just 25mm for the 33m by 12.5m caisson, which has an overall depth of 17m. As well as being responsible for checking the draft and stability of the caisson, Holyhead were also appointed by RJ McLeod to project manage the operation and to liaise with third parties such as the port authorities, the marine warranty surveyor for the tow, and the MCA to obtain the loadline exemption certificate.

The main tow tug was the 55 tonnes bollard pull Afon Llifon from within Holyhead’s own fleet, assisted by the MV Orcadia of Scotmarine as the stern tug, which also assisted during the later installation phase. To minimise disruption from any potential weather problems an inshore route obtaining some protection from the islands of Islay, Mull and Skye was chosen by Holyhead, despite the considerable draft of over 9 metres.

The final positioning of the caisson on the carefully prepared submerged foundation structure had to be carried out in a 24 hour window which started following departure of the last Stornoway ferry at 1800 hrs on a Saturday night. The Holyhead and McLeod teams worked closely together to ensure that the caisson was in its final position and ballasted down by 0730 hrs on the Sunday morning of 16 June, and positioned well within the 25mm tolerance allowed. The ferry was able to berth later that day with no disruption to the service.

Holyhead Towing’s managing director Mark Meade told Maritime Journal: “It has been a real pleasure to work closely with the RJ McLeod teams at Greenock and at Ullapool, and all parties involved across the board have worked very positively together to overcome the particular risks and problems associated with such a unique and challenging project.”

By Jake Frith