The seasonal lay-up of the Manannan has been identified as a contributing factor to increased sediment build-up in Douglas Harbour.
The build up, along with extremely low tide, led to Manxman running aground in Douglas Harbour.
In Tynwald Infrastructure Minister Dr Michelle Haywood explained that the vessel’s absence during winter months has reduced the scouring effect it provides, leading to heightened sedimentation issues.
The Manannan, which operates from spring to autumn, helps manage sediment levels by disturbing the seabed with its thrusters during regular sailings.
Dr Haywood said: “It’s a well-known feature in nautical terms that the movement of vessels creates disturbance of the sediment. The Manannan operating last summer likely reduced sedimentation in the area that caused the recent problem in the harbour.”
Dredging
The debate also addressed ongoing maintenance dredging efforts, carried out by the harbours work boa.
While maintenance dredging has been effective in some areas, the harbour has not seen a successful capital dredge in over 20 years due to financial constraints and the risk of destabilising the piers.
Tynwald also heard that the DoI has never adhered to the Sea Services Agreement is has with the Steam Packet on harbour depths, but also raised doubts about how and why they were even included.
Dr Haywood noted: “The depths specified in the sea services agreement have never been achieved in Douglas Harbour in the entire records we have.
“We are unsure where those depths were written into the agreement or if they were based on any knowledge of the harbour’s profile.”
The Manannan’s return to service this summer is expected to aid in sediment management.
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