So you may be wondering why I suspected insufficient tension during beaming as the cause of my problems?
My first clue was as I was weaving the header. Now it is not uncommon that, as you weave the first few picks, slack will develop and the warp will need to be tightened. However, it usually happens once or maybe twice, not repeatedly, and not as the fell is advanced further into the length of the beamed warp. (This observation is based on the slippage happening in spite of the brake itself holding firm.)
This is what was happening on the last couple of warps.
The other thing I observed was that as I advanced the fell, even after a few meters/yards had been woven, the fell line got wavy. To me this indicated that as the warp slipped forward, it had done so unevenly. This is another indication that the warp had too much slack as it rolled on (too little tension during beaming).
My solution was to add two cups of water to each of the jugs I use for weight. Two cups doesn't sound like very much additional weight, but I noticed the increased pull/drag as I wound the warp onto the beam!
I'm pleased to say that I had no issues at all with this red towel warp. Cased solved!
Currently Reading Just One Evil Act by Elizabeth George