[Gustav Schiebert]

Low draft ships are certainly harder to hit for the reasons you mentioned there, but not impossible.

I don't know how the game calculates wave height, but when I'm recording sea state for my war diary, one way is to watch your Pappenberg in the control room (the 25m depth guage). Since on the surface your depth is about 6m, observe the maximum depth you drop to. The difference between the two (ie, you running between the average surface depth and the trough of the wave), is half the max wave height. Hang on:

Wave height = (max depth - 6) x 2

That does me fine. Alternatively, you can use real-world Beaufort Scale charts, which give a good indication of windspeed and wave heights. But not swell.

As for depth settings:

You're right for surface runners. But given that in the roughest seas (in SH world) have 8-10m waves, in order to guarantee that an impact torpedo will be, say, 2m below the surface, you'd have to set it for 12m. That would obviously eliminate the majority of low-draft ships.

I usually set torpedoes to magnetic, and set them to strike 1m above the keel. That way, if they run too high, they will still detonate (albeit less effectively), or it will run too deep, pass under the keel, and get you a perfect magnetic detonation and break its back.

Basically, magnetic eels are less dependent on striking a specific portion of the hull compared to impact. They can go anywhere and still be detonated in close proximity to the hull.

Of course, this has to be set against the realism settings - with torpedo failures on, in the early war you can fail with 75% of eels in 1940. Hope this helps!