Peter,
I use D12 Dyneema, made by Marlow and also by other manufacturers.
http://www.marlowropes.c...cruising-racing/d12.html
When I changed to using dyneema, the sizes Marlow made were 6, 8, 10mm etc, and I used 8mm. Now they make 7mm and 9mm, however the current 7mm has the same break load as the old 8mm. At 5360kg average, this gives a safety factor of over 15 [anything over 10 is ok].
I use a "Chinese constrictor" knot to attach to the shackle onto the keel - using a splice is not so good, as the length of splice would mean it would run onto the sheave. An Anchor Bend could also be used.
At the winch end I put a clove hitch on the drum, before leading the tail of the dyneema out onto the outside of the drum and securing it in the same way that the wire is secured. Once I have it secured, I work the slack back through the clove hitch. I use about 4m of rope, so there are always a good number of turns on the drum. I try to put as much load on the line as possible when reeling onto the drum, to reduce the amount the rope will force between the wraps of the lower layers under the full load of the keel - but some of this will always happen. Dyneema is very chafe resistant so its not too much of a problem.
Hope this helps - sorry about the late reply, I've been sailing!
Dick
Dark Star P275 No 36