Snorkel
Personally I set the maximum permissible wind speed for snorkel use at 13-14 m/s, as it
appears that employment at Force 6 might have been possible, if barely. I however limit its use at Force 5-6 to the strict necessary.
While I do not know how well the game handles the matter it is a good idea to keep a close eye to depth to minimize snorkel head exposure to radar. The "è" key (at least in the keyboard I use) will bring you to snorkel depth, slightly deeper than normal periscope depth, which will reduce the amount of manual adjustment necessary. Automatic depth keeping and hovering gear was supposedly fitted to at least some of the boats.
Leros, at least as far late war operations in hot areas are concerned, is a don't go out without item. Observation periscope should be left up for realism's sake but actual usefulness is limited, both in the game and real life.