New mooring / riser on existing grid

[mjcp]

I have many questions! It's my 1st time arranging my own mooring (yes, the local association and an experienced diver are involved) so be gentle pls!



I've had the nod to place a new riser and mooring onto an existing grid / trot ground tackle.

Charted depth in the area is 2-5 m (TBC in the actual area when I get out there to measure later this month) and tidal range MHWS c. 5.5m. Its fairly sheltered, I've not seen more than a 1m of fetch, (but its Scotland, so could be bigger on occasions ... eek!)

Boat is ~5000kg, 33 foot with a bow roller for the mooring tackle to go over. (1m above the water line)

So questions:

What size riser chain? Length and weight.

Is the theory for swing mooring tackle based on a catenary similar to anchoring or is there an alternative theory? I assume swing room is a consideration?

Is the riser height tidal range + % or is there a more scientific formula? 7-8m has been suggested (probably assuming ~3m MLWS)


I'd also like to document the max weight on the buoy to dissuade overweight visitors who will almost certainly sneak on while I'm away. What riser chain size etc would safely support say, a max 10T "guest" ?

And then what chain (chain preferred, "just in case") weight for the buoy to boat?



M

 

[NormanS]

Check with the local association. They will have actual knowledge, while we can only guesstimate.

 

[mjcp]

Check with the local association. They will have actual knowledge, while we can only guesstimate.

"the mooring association and an experienced diver are involved"


Already in touch! Its more trying to understand the theory etc. I understand chain in terms of anchors, but have not located much info for moorings.

M

 

[William_H]

The biggest worry with moorings especially the chain is wear. So you need the biggest chain you can find to last longest. Of course your buoy has to be able to support the weight. This means that actual strength of the chain is way more than needed. Look out for old ship[ anchor chain etc and use biggest shackles you can fit.
The theory of catenary is not really applicable as you will have weight of the base grid and of course no concerns re anchor pull angle. So length should be enough to allow some chain to lie on the bottom giving some cushion effect to the jerk loads. But of course not so long as to give too large swing radius. ol'will

 

[ylop]

"the mooring association and an experienced diver are involved"


Already in touch! Its more trying to understand the theory etc. I understand chain in terms of anchors, but have not located much info for moorings.

M

Slightly different set ups seem to be used in different areas. Whether that’s based on science or experience or just well it worked before I’m not sure. My diver is a specialist mooring contractor so I accept his word as he’s maintained all the other mooring locally and produces a bit of paper alongside his invoice so I can keep the insurer happy!