mooring / riser chain shackle

[gramos]

I put my own mooring chain onto a 7 ton concrete block in the harbour I use .
the block has a huge re -bar cast into it and I fed 2x 10mm chains through it then up to a 150 kg mooring bouy which I have my mooring strops attached to .
This was done 3 years back and I want to replace the riser chain/s with a much bigger single 18mm + chain .
The trouble is it is 3.5 metres deep and I cannot stay down long enough to screw a pin into a decent size bow shackle onto the re- bar and mouse it .

So , does anyone have an idea for getting over this ?
is there a kind of big snap shackle that could be used to connect the riser chain to the re- bar that would be reliable enough ?

[Lagoon4us]

Borrow a Hookah system and do it right and sleep well with a simple bow shackle wired. You need to be confident of the connection. Lubricate the thread so its easy next year to undo.

Cheers