Re: Legless rope climbs and sore abs?
The fastest rope climbers in the world use a technique that is very ab intensive. Basically the better they get the more their body position resembles a front lever, and the 'kip' appears more like they are jumping up the side of building. I suspect this creates a much longer pull, since once the body is perpendicular to the rope, twisting and reaching adds some portion of width of the climbers chest to each pull. A longer pull means less pulls, means you can get up the rope faster.
Not sure its optimum for crossfit training, but its the technique I try to use, and as a result, rope climbing wrecks my abs more than any single crossfit movement.