[Crannogman]

You may find a useful alternative to crash diving is to cruise with decks awash. You can find other threads on how to do this; basically, it involves changing your boat's "radar depth" to about 9 meters. At this depth, you can run on diesels and go to the bridge, but most of the hull is below the surface; your speed is limited to submerged speeds (maxing out near 12 knots), but you can fully submerge in half the time and present a much smaller profile for enemies to spot. "Decks awash" is probably the best way to travel long distances during daylight