I have finally replaced the jib sheet blocks. All blocks on the jib sheet arrangement were undersized originally and led to far too much friction. But they are expensive, so I have only replaced them gradually. I could have just used a thinner jib sheet, but with no winches, a thicker sheet is easier on the hands. The original blocks were also swivel blocks, as they were attached to the sliding cars, and that just leads to them twisting the now doubled sheet. I had jammed them with cable ties, but that just increased the friction more. So I finally have these two new ones, and now everything runs smoothly. I bought a dyneema soft shackle at the Southampton Boat Show and will use that to link the sheets to the jib's clew.