This version is made from 3mm hot-pink double-braid polyester line chain-stitched around a blue 3mm Dyneema® single-braid "core".
The intent is to make a mainsheet with a slightly smaller diameter in the chain-stitch portion while still maintaining the good grip provided by the knots.
I was very surprised that after I had tied the first half-dozen knots the central line was securely bound to the double-braid. This meant that sewing the two together wasn't necessary. The whipping is just there to protect the spot where the double-braid enters the Dyneema® to make a smooth transition. If you look closely at the lower photo you can see that the diameter of the blue line gets smaller as the double-braid inside is tapered away.
I've included a section of the more typical mainsheet constructed from 3/16" double-braid for a size comparison.
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