I have two large-diameter 3-strand lines that I use for moorings and they are just right for the weight of my boat - just stretchy enough to work well in high winds and seas.
Unfortunately, my two forward cleats are just a bit too small for these lines. I would like to splice on a section of smaller diameter, but stronger, of double braid to each end in order to make it possible to easily use my cleats.
Offhand I can't think of an easy way to do this, and of course my ABOK or Brion Toss books don't have a hint on this splice either. Perhaps I might need to find some smaller diameter 3-strand with higher breaking strength and just do a 3-strand to 3-strand splice.