Talkin' 'Bout a Buoy
Some of those ships can weigh thousands of tonnes. The large cruise ships catch the wind, acting like a huge sail, putting a huge strain on the buoys holding them. We thought it was a big enough question to go find the answer.
So we went to chat to assistant harbour master Nick Clarance to find out how the buoys up and down the river Dart are secured so the boats stay where they are supposed to!
‘The large buoys in the centre of the river are Admiralty Class moorings and are similar to the ones used in Plymouth Sound to moor the Naval ships there,’ he told us. ‘People might notice that when a large vessel is coming in, one of them might just disappear creating the right size berth for the new ship.
‘We will have a meeting with the mooring team and moorings supervisor Mathew Stephens and discuss what size of berth a particular vessel needs and then he and his team will get to work.
‘The basic setup is that all the large buoys are connected by ‘rising lines’ to a network of heavy chains on the riverbed. These fan out from a central line creating an incredibly strong and secure base for the rising lines – which attach to the large buoys - to link to. The holding power of these chains is just immense and means we can safely moor very large vessels in the harbour.
‘When we remove one of the large buoys to create the correct length berth for the ship coming in, the floating buoy you see on the surface will be lifted out by our river crane, Hercules. Then a pennant, or small piece of chain, will be attached to the rising line and this will then be placed on the river bed fanning out from the main line of chains, and Matt will use GPS to mark its position, so when the large ship leaves, we can easily find the chain, bring it back to the surface and then reattach the large buoy.
‘It’s a major operation, but one our mooring gang is more than used to now! Matt’s knowledge of the river and the mooring system is immense and he and his team do an amazing job.’
The network of chains on the river bed are regularly inspected by divers to make sure that they are in the best possible condition and maintenance is carried out whenever it is needed.
‘The weight of that network of chains is simply phenomenal,’ said Nick. ‘We carry out maintenance using divers because the crane you would need to bring it to the surface is massive! It is why it is such a safe mooring system.’
There are more than 1,600 moorings on the river Dart and the Dart Harbour maintenance team check every single one during the winter, making sure that mussels and seaweed do not weigh them down. They also replace any corroded chains or weak rope.
The harbour’s other moorings use simpler and less weighty solutions than the admiralty ones in the centre of the river; there are the pontoons, secured by large pilings into the river bed; swinging moorings using 1-2 tonne concrete blocks on the river bed to which chains are attached and to which the buoys are secured; the trot moorings created by using lengths of chain or large blocks along the river bed with two buoys for each boat to be secured fore and aft and finally running moorings which are again created using blocks with line connecting them to the river bank, which boats can then tie up to.
Depending on the size of the buoy, chain or rope can be used to secure it. The choice depends on the weight the buoy can carry - if too heavy a chain is linked to it, it could then sink, rather ruining its usefulness.
‘We have a strict agreement not to increase the number of moorings on the river with the Duchy of Cornwall who own the river bed,’ said Nick. ‘It’s an important part of Dart Harbour policy. However, with 1,600 to check and perform maintenance every year, I think we have more than enough to be going on with!’
First Published August 2011 By The Dart