"But it raised the question: What if we had been, say, two-thirds across one of the big lakes with head-on waves? In September water?"


one thing more - you need to be thinking about what you are doing - in trying conditions, you need to be alert for shifts in wind and waves and in wind intensity, and it always helps to kneel to lower your center of gravity.  You should have a "plan" in case you do go over during a rough open water crossing - know which shore is closest, and most likely, swim/tow your boat downwind - that way you aren't fighting the wind and waves, but are getting pushed toward the lee shore.  If conditions are that bad, I will try to stay close to one shore or another, but that's not always the smart thing to do.  The worst the conditions, the more important it is to maintain boat control - keep the bow pointed into the wind and waves - even if you want to get to a shore downwind, it may be best to travel backwards, keeping the bow into the wind and letting the wind blow you to the lee shore.  I don't think there is a canoe out there that can't handle big wind and waves if you know what you are doing, stay alert, react fast, and keep your cool.  If the wind is really bad, it can be hard to control a boat by yourself - you need to be communicating, especially if you need your bow paddlers help by doing a bow draw or sweep when you call for it.

Note that I keep saying "tow" - my opinion, you should always have  a painter line tied to your boat - with a line, you  or someone esle can much more easily rescue another boat, and you can always tie your boat when you are on shore - you just have to coil and tie it for portages.  I've helped tow quite a few boats on ww river trips - sometimes its other peoples boats, sometimes its self-rescuing my own boat (like that time on Nym Lake) - doing anything practical without a painter line is a whole lot harder.  With the line, you can swim a few feet, then pull your boat towards you, then swim some more - that is a lot easier than trying to hold on to your boat with one hand and swim with the other.   I wouldn't abandon my boat unless I though I'd die if I didn't - but if I ever had to on a lake, I'd be swimming downwind, cause that's where my boat would wind up, with my dry clothes and gear that I'd need to survive.

"He did well, but in high winds and rain on Agnes our nose got turned around in one of the bottlenecks and, yep, we went over."

This quote is why I am talking about boat control - my opinion, a bow paddler should know how to do a draw and sweep - could be a quick stroke on your part might have avoided that tip.  There are two people in a tandem,  it should operate as one team, paddling in synch and communicating - you swim less that way.