Yes, patroling on surface is much more effective means of patrol BUT in early war or when using slow divers like Narwhal, submerged patrol is warranted.Early war I do this because its historically accurate and adds a whole different level of
to the war patrol.Narwhals dive too slow to patrol on surface, only time I ever get bombed on surface is when when I have a narwhal.I prefer the yo-yo method myself but again in early war, I go with the tactics they used and can tell you that you will see a difference in your contacts and tonnage sunk once you switch.Conduct 3 patrols mostly submerged then 3 patrols yo-yo, you will see a huge difference.