Sorry about the long post, I need to explain this as I am not sure the best way to do it.
I have a 12.6mtr Catamaran with a Manson Supreme Anchor. This has attached 50mts of chain which is sufficient for normal use. There is a permanently rigged rope bridle attached to strong points attached to the hull end of the forward crossbeam which is attached to the chain with a snap shackle. In very strong winds (as the snap shackle is a weak point obviously) I use a short length of chain with two shackles as a backup. Even if this where to fail the main chain stop in the anchor would hold the chain, albeit without the bridle whilst I sorted it out.
To the end of the chain is attached a further 100mts of Octoplait for use in either deep water, or if I need a lot more scope as I am reluctant to put any more weight forward (we are in 'cruising' form so already a 'tad' heavy). I also have another short length of rope attaced to the attachment point in the anchor locker, again with a snap shackle to stop me accidentally using the anchor line, all I do is to back up the chain a little and release it if I want to go onto the warp. The Bitter end of the warp is also attached to the strong point in the anchor locker.
When I go onto the octoplait I need however to rig the bridle. I have a number of options, I am really not sure the best way to do it.
1. Form a 'figure of eight' in the octoplait and shackle the eye that is formed onto the existing bridle.
2. Take one side of the line to a forward cleat (these are not as strong as the main bridle attachment as they are aluminium, welded to the forward cross beam and use a second line with a rolling hitch back to the other cleat.
3. Attach two additional lines, both with rolling hitches back to the two forward cleats
4. Use two additional lines with eyes spliced in them back to the main bridle attachment points with rolling hitches onto the octoplait
5. Use a jammer of some description on the octoplait and shackle that to the existing bridle.
Clearly, option one is the simplest, I am not sure though how much damage that will do to the octoplait as clearly this will pull very tight both on the knot and onto the shackle.
There must be another way?