I'm with you on this one, Slayer. I used the fleet tracker to look back at who passed close to Little Pea (the UK boat who posted the log brokesailor referenced). The situation was as Slayer guessed. A Dutch boat, Lady Ann (LA), passed close to Little Pea (LP) twice that night. Once coming from the south of LP's track heading WNW and passing ahead of her about 5 miles and then again several hours later LA approached LP on a SWerly course from north (LP's starboard side). The winds at the time were on each boats quarter and both were obviously broad reaching / running. From the wind angles it appears that LP was leeward boat and on a starboard tack, LA on port. As downwind, starboard tack boat, LP had rights!
Whether either boat waited too long to make a move is a tough call. I've found that at night it's really hard to judge distance, especially when it's a single light you're seeing. Hard to tell if the light is 2 nm or 1/2 nm away. Radar will resolve this quickly, which is why I always have it on and in standby at night. If the target is two miles away I can ponder the situation, if it's 1/2 I will need to make a decision quick.
It's also hard at night to judge a constant bearing. I've noticed during the day that what seems like a constant bearing on a boat 1-2 miles away becomes a rapidly changing bearing once they're inside a 1/4 mile. In a big sea like that LA and LP were in, it's particularly hard to judge a constant bearing because the boat's moving around so much.
When I'm in a situation like that LP found herself in, I do as Slayer recommends and start to take action early. I might not change the rig or course immediately, but I will think about getting additional crew on deck (especially if it's night and they're asleep as they will need additional time to dress and get ready). I'll also start reviewing the steps to take, which in this case would be to first roll up the genoa (assuming you have roller furling). I rig the pole-out genoa so that I can leave the pole in place while rolling up the sail. This will slow you down a bit, and permit a quick tack if the need arises. (Yea, I know, rules say the stand on boat maintains course and speed). Next, I'll make sure the preventer is ready to be let go or slacked (I rig the preventer so it can be controlled from the cockpit) in case I need to tack or gybe. Then I'd do what LP did -- try to raise them on the radio and then with lights. I should note that shining a spot light on the bridge of another ship is not allowed in the rules, but flashing it on your sails or in their general direction is certainly OK -- and if that doesn't get a reaction, well......
[The reason you shouldn't "embarass" (see Rule 36 Interntional) another boat is is could cause them to lose night vision and see nothing but spots for the next ten minutes. Not good if you're in a possible collision situation].
LP said they got a reaction from LA with the light but LA took no action. It could have been that LA was getting ready to take action, like I mentioned above, but was waiting until they got within a few hundred yards to see which way the crossing was going to happen. LP had no way of knowing whether this was happening or if LA was tracking them on radar, as they got no reply on VHF. I think that's were LA messed up -- how hard is it to get on the radio to call the boat that's "at Lat X, Long Y and just flashed a light at me"?
Finally, LP said in their log post they were concerned that backing a prevented main would break something. If your preventer might break when it suddenly goes aback, you need a stronger preventer -- because that's what it's supposed to do. Intentionally backing a prevented mainsail can be tricky in a situation like LPs because you may or may not have full control of the boat once the main's aback -- remember they had a 12-15 ft sea running at the time and 25-30 kts of wind. Backing the prevented main may put the boat across the swell, broaching with the main on the wrong side of the boat. Might be just a tad dangerous. Could produce a knock down and with the main on the wrong side of the boat, it's not good.
It may have been a better move to do a controlled gybe and then continue away from LA before gybing back.
So there you are....see how easy it is, sitting in your warm den with keyboard at hand and with a glass of wine at easy reach, to second guess a skipper who's tired, sleepy and rudely awakened by a helmsman who's allowed another boat to get within a 1/2 mile on a collision course in a 15 ft sea and 30 knots of wind?
All's well that ends well.