Several hundred yards away??????
And THAT'S where Kerry claims Rassmun was in the water (when he turned around to get him?
Kerry and Rassmann have quite a few different versions for the events of that day. Rassmann was in the water for several minutes, and in one account, says he saw Kerry's boat returning "from around the bend." Also, there is no evidence that Kerry's boat hit a mine. PCF-3 hit a mine, and was damaged badly enough as a result that it had to be towed back to port. PCF-94, Kerry's boat, did the towing that day.
Here is a good post, in a good thread re: the many incarnations of the Bronze Star incident:
Bronze Star <-- But check the whole thread
There are other threads that cover the same subject, including one that dissects the Washington Post story (the story with the graphic, that fails to mention ZERO bullet holes, and the one hour+ time on scene).
To your narrow point about several hundred yards, the MINIMUM distance between the boats would have them immediately opposite each other in the 75 yard wide channel. I'd say a fair minimum distance is 50 yards. But the dog story is pure, unadulterated BS.