Nelson-class freeboard and North Atlantic seakeeping

Were Nelson and Rodney mainly designs for calmer waters rather than the North Atlantic?

No; they could operate in the North Atlantic, though the G3 and N3 designs likely would have been better seakeepers.

The as-built freeboard figures answer the criticism that Nelson and Rodney were suited only to calmer waters. Their bows would take water in heavy North Atlantic conditions, but that would not make the ships unusable there. The class was workable, though it was not an ideal seakeeper. The larger G3 and N3 hull forms would probably have behaved better at sea.