How do you avoid crab pots that you can't see?
MY 'Rule of thumb' on the Ches. etc when night sailing: try to stay in water that is deeper than 20 ft., stay away from the 'mouths' of big creeks; stay away from shoals and shallow banks in 'the middle'.
If you sail the Chesapeake, the crab pots are usually in the same cluster of places, year after year after year; ditto with the eel pots in late winter and early spring, just different 'usual' places. Memorize where they are and avoid those places, ... or else.
For 'thick concentrations', I use 'night vision' ... but that soon becomes a PITA, and is used only to enter the creeks that are essentially 'blocked' with pots. Its illegal for 'commercials' to set pots inside the mouths of creeks in MD ... sail there if possible if you have 'the room'. Magothy R. is fairly pot free once you 'get in'.
Use the engine only as absolutely needed ... you have a SAIL
BOAT. Learn to sail in the 'super-light and flukey'.
Mechanically, make sure that a pot line/warp cannot get caught between the top of the rudder and the hull ... a Stainless 'whisker rod' sticking down from the hull and just in front of the top of the rudder and which blocks the line from 'jamming or pinching' in that area is 'real helpful'. A FOLDING prop is the least likely to snag a line.
If you do snag a warp, immediately try to 'back-down' --- back the sails and sail the boat in reverse as your 'first' attempt at freedom.
Make sure you have onboard a razor sharp 'hooked knife' mounted on a telescoping looooong pole, to cut the line if all else fails. Try to retie the cut line ends if possible.
Lastly, If you have a boat with a wing-keel, stay at the dock.
At night you'll have almost the entire bay all to yourself, less 'stink-pot chop', more stable winds ... even at near "0"kts. On the upper bay if 'ships' disturb you, simply stay out of the channels - The Brewerton and Tolchester channels, etc.; simply stay north or west of these or in the shallow triangle just north of the bay bridges (where the crab pots are). Do talk to the 'commercials' if a problem develops or threatens, as they really arent used to seeing sailboats at night on the Ches. - channel 13, not 16 VHF. If that doesnt work shine a BIG light on your sails, as you scamper out of their way while blowing 5 long (five to ten second) blasts on your LOUD horn.
See ya out there some night.