Problems & possible solutions:
1) They are free to use so nobody thinks twice - simple $5k 5WSU cost. Token enough but at least reflects that the ordinance isn't free. If it works I'd still play that card for a 50% chance of a 1NM gain, but a little less guilt. There should be no free lunches.
2) You can deploy them on any water - tool tip says coastal water but they can be used on any stretch of river. This needs fixing to restrict them to the sea, or as below at least restrict them in some way better.
3) You don't even need to own a province next to the target at the moment, you can literally lay them on any river or coastal region you want at anytime - firstly I would favour only coastal, but if rivers were allowed too it should be only allowed next to a friendly harbour with at least 5 or so regiments present. OR a fort. OR, even better for torpedoes only used adjacent to a Naval Engineer or Naval commander. This last one would make a huge difference I think. At least there should be some military or naval presence involved rather than firing anytime & anywhere.
4) As they trigger at the start of day one there is no escape, they are a perfect instant attack weapon - trigger after random number of 5-10 days so only really effective on fleets that are lingering. However this would be more for sea mines. If torpedoes were only adjacent to Naval Engineers/Officers then instant makes sense.
If any or all of these were implemented I really think this would fix the mine/torpedo problem. There is still a decent chance to get a 1NM result and do some damage, but not in the lazy way it is gifted to the user right now.
Next we need a bit of a tweak for those partisan raids...
