I must be missing something here. For I don't understand why a person would want to try to flare the tubing in the boat and such. With a normal hole drilled through the hull, I was able to insert the tubing quite snugly and watertightly, particularly when slathered with epoxy.

If I were to have tried to chamfer the holes I drilled in the hull, and then try to flare the tubing to match, this process would have been quite difficult and would have required a good bit more epoxy to seal up the gaps that would have inevitably existed.

Is it a concern over cutting the rope? While the tubed hole does end abruptly at the hull, it's in no way sharp enough to cut the rope. Nor is sliding of the rope through the tubed hole significant. At least for me. I did my tubed hole at 1/2", and used 1/2" rope in it because I like the feel of a wide rope when hauling. It doesn't cut into my hand like a thinner rope will. The rope just lives tied onto my bow and stern tied into a loop that just big enough for me to comfortably grasp, and just small enough to not drag in the water.