Thanks for all your very helpful advice. On the basis of your comments and having now read Vyv Cox’s excellent review on anchoring c-links ( thanks to Pietro for the link) and taken on board Paul’s comments about the weight I am going to go for an extra 30m of 10mm calibrated chain which I will join up using a Crosby C-link.
Like Jason I would prefer to anchor in 5-10m of water but this was not always possible on our trip this year. Add in a 5-10m tide then 30m of chain is just not enough. Once again many thanks