Are there any safety concerns connecting two ropes (40 and 50 m) with 2 double fisherman knots and then installing an anchor with 2 carabiners connecting the anchor to the rope for top-roping?
Let's say the ropes have more or less the same diameter (8.9 and 9.2 mm)
Strength wise I think this would be fine. However, be sure the belayer (and the knot) is on longer strand so the knot doesn’t hit the belay device before the climber gets to the top of the pitch. Be very careful if you decide to rap down from the anchor. Much easier to misjudge and rap off the end with two unequal length strands. Probably not an issue since you’re top roping but be aware.
