I personally distrust spectra. Everybody tells me Dyneema and spectra are the same fibre, but I don't believe that. All who have used spectra as trap line seem to have snapped it. Also I ONLY use 500 kg line. I can get 300 kg line that is supposed to be 3 mm thick but is actually 2.5 mm thick and that one has snapped on me in varying uses as well. So be careful with cheap imitations. Get the ral thing ! It works. As far as I can tell I only use Marlow 3 mm 500 kg line.

800 lbs = 363 kg and is probably to little. Remember that the knots and such do degrade a line to about 50%-60 % of its nominal strength. And you also want about a factor of 2 as safety margin to withstand G-forces and shock loads.

If you really want Paul I can buy and send you the stuff. You'll need to transfer the money to me up front though.

What I did with my own line is buy plastic swages and stitch the line around it. Than I slide a handle on the line and use a figure 8 knot to position is. A loop on the bottom end with a fishers hitch is used to attach the adjusting jam cleat or a small block. This hitch is easy to undo and you can replace the block at any time without using any tools and it can never get undo due to vibrations. Added benefit ? You can cut the line with your sailing knife = added safety !

Ohh and another advantage is the fact that because it is so light you only need very mild tension on the bungees to keep it straight and it won't bang and rube again you mainsail.

I've been using these dyneema traplines for years and so too several befriended crews. We all swear by it. However I must say that both Phill and Kirt used some line they could get locally (spectra) and these both failed. So I think you must look for the right line. And I think the 500 kg is the one

Wouter