I'm sure that Bluewater is recommending Rub a Dub based on a reasoning process (see the link I posted in the
first response). And the various web arguments about the bad nature of pens focused on the solvents. Notice that laundry pens have non-bleeding dyes, and are formulated NOT to deteriorate fabrics, including synthetics like nylon and polyester.
Bluewater is unlikely to recommend something that will "significantly" degrade their ropes.Even tests with regular sharpies found that unless exceptional measures were taken to stress the marked area, the rope system always broke at another weak point, typically a knot. The tester's conclusion was "big deal."
Simply getting a rope wet can reduce its strength by 15%. And even that is debated.
http://www.itrsonline.org/PapersFolder/ ... SPaper.pdf ;
http://www.sterlingrope.com/media/docum ... manual.pdfSewing another thread through the sheath will affect the properties of the rope as well. I bet that if you do strength tests on ropes marked by these other methods, you will also find the rope breaking near the altered part. And if you are not damned careful, you will catch the changed part of the rope up in a belay device, which could have a more dramatic effect on your life expectancy. If you do use the thread trick, keep it minimal, and expect to "feel" as much as see the center:
http://content.backcountry.com/images/i ... ET0193.jpgThe original 2002 UIAA tests that showed a possible 50% strength loss for ropes masked with felt tip pens, are briefly summarized in this document:
http://www.sterlingrope.com/media/docum ... manual.pdf READ THE ENTIRE ssction with the caveat by Pit Shubert, of UIAA.
Note the above documents also claims up to 70% loss of strength in a rope that is merely wet.
A less controlled test found 12% reduction for Rub-a-Dub, with rather extreme marking.
http://www.supertopo.com/climbing/threa ... id=1342794It's important to remember how the UIAA comes up with their strength reductions -- it's based on the number of falls the rope holds, vs the unaltered rope. Think about what that means in practice, if you mark the middle of a 200' rope.