How to calculate max boat size for a mooring ?

[gerbil]

I have managed to get a swing mooring down in a bay in Dorset and wondered if there is any simple formula for confirming what maximum weight of boat the ground tackle etc could take ?

It is in around 12/14ft of water and apparently consists of 2 x 150kg steel weights, 20 metres of chain that has 45mm thick links (from the Poole Chain ferry I believe) going back & forth between the weights, 5 metres of the same chain as 'swing chain' then 6 metres of 50mm 3 core mooring rope going up to the buoy and pick up bouy etc.

Is the holding capacity based on just adding up the weight of all the 'bits on the bottom' or are there more complex relationships to factor in ? Is it not just the weight of the boat that then has to be compared to the holding capacity or is it the length / height / windage etc too ?

Many thanks !

 

[AndieMac]

Do moorings have to comply with a local authority standard, or just lay what you think is a fair thing?

Are the weights flat discs, like train wheels, that are well embedded into a muddy sand sea bottom,

or higher profiled weights (old engine blocks) on a hard, shell encrusted sea bottom that may be prone to rolling and moving in adverse conditions?

I would imagine like anchoring, there are various factors other than just the weight of the ground tackle to think of.

 

[Poignard]

This information from the Bradney Chains website might help:

http://www.bradneychain.com/_pdf/Mooring-and-Anchoring-Leaflet.pdf

 

[gerbil]

Thanks for the replies - the Bradley Chain leaflet was interesting in that it would suggest that the chain totals around 450kg plus the 2 x 150kg weights (on a sandy bottom) - not sure what they look like - I'll have to wait until I am down again and see if I can see on a clear day).

Unfortunately it only says that 32mm chain is suitable for 60-70ft boats but doesn't suggest how much of it roughly would be needed.

I am sure it is more than enough for my boat but I was just curious as to how I could calc a reasonable maximum in case someone with a bigger boat wanted to moor up overnight on it etc.

 

[AndieMac]

If you are not familiar with the ground gear, maybe a mooring service contractor to haul the mooring up, water blast clean and check the swivels, chain links for wear and corrosion.