Hull flex and why carbon fiber was destined for failure.

I am not an engineer but I spent my twenties in the US navy on submarines. And one thing stands out in my memory. When we would go to test depth for a demonstration a sailor would often tie a cord to each side of the hull while we were on the surface. The amount of slack in the line when we were at test depth was wild. The line would go from tight to sagging at least a foot. This was on a 33 foot diameter steal hull and we were no where near 3000 meters.

Carbon fiber is not compliant enough for the task.