Wednesday, 8 May 2013

Mayflower Marina's pontoons

Mayflower Marina is unusual in that it has a hybrid mooring system for the berthing pontoons. The pontoons closest to the shore are secured on steel guides supported on frames that are bolted to the quay wall; a team of divers is currently replacing these guide frames as can be seen in the photo. The rest of the marina is secured by a complex spread of mooring chains and anchors. While initially cheaper to install than piled moorings anchors and chains require much more maintenance, which is why the great majority of marinas in the UK use piles to secure their pontoons.

No doubt the designers of Mayflower Marina would have used a piled solution if they could but the conditions here are decidedly difficult for piling. While relatively shallow close to the quay where Bonita is moored the sea bed falls steadily across the marina, at the outer pontoons there is in excess of 12m of water depth which would make for long, and therefore large, piles. Secondly the sea bed here consists of a shallow thickness of soft silt overlying limestone bedrock so piles would have to be drilled and socketed into the rock; a much more expensive operation than normal percussion pile driving.

On the positive side the natural deep water means that most of the marina should not need any maintenance dredging.