just an answer- sort of…
I have only had one situation in which I have had to drop the canoe from the cradles. I was on the Horse Portage on Basswood River. A person that I will charitably refer to only as a “stooped twit” caused me to get my feet tangled in the rocks and take a tumble. I had to go with the turn of my ankle or most probably break it. Had I been fresh I might have had the strength and/or clarity of mind to prevent dropping the canoe, but I had been out all day and was weary. I focused on going with the trapped foot so as not to break the ankle and didn’t really think about the canoe until it hit the ground. I had gel-coat damage on each side, which I covered with duct tape for the rest of the season. I’ve had many stumbles of course, but this is the only time I lost control. The system uses a line that runs from the bow to stern and that you hold and use to control the pitch of the boat. This actually makes it much easier than you might think to control the boat when you loose balance.
O.K. To answer your question as directly as possible, if you go down the dynamics are different than when carrying the canoe directly on your shoulders. So the need to jettison will probably be different. If I understand your question correctly, your primary concern is whether the falling canoe night hurt you or complicate your fall.?. It could, especially if you haven’t done your homework and practiced with it. If you go sideways it will automatically go farther to that side and be well clear of you. If you go face down or fall backward I suppose it could hit you. It’s not lashed to the frame or anything like that, so it isn’t going to somehow trap you. I guess I don’t really see that it’s any more, or less, likely to facilitate an injury. I originally bought the system because of whiplash from an auto accident and couldn’t handle long portages with the canoe on my shoulders. While I don’t use it for short hops, after using it for several years now, I categorically wouldn’t willingly give it up. As I get older the Knu-Pac becomes more and more important to my ability to handle long portages.
As my wife is so fond of saying, “Canoeing is good, portaging is evil.”
just an answer- sort of…
I use a ‘big wall’ climbing pack
Usually overbuilt for dragging up big walls by climbers. Also usually have shoulder straps and a hip belt, as well as 'haul loops' as the bags are hauled up on the end of a line behind the climber, also facilitating those who travel in bear country in hanging their pack. Fill 'em w/dry bags and go. I use an old Gregory model, but a lot of climbing gear companies (Metolious, Black Diamond, A-5,etc.) make 'em as well as a few pack companies, and they come in many sizes but stick to the smaller volume ones unless you are a brute. Most are usually just a one compartment pack, often with a pocket on the top flap. Think Duluth Pack on steroids. Have used mine for years in both my solo and my tandem and the sucker carries great on portages, and I can throw, drag or simply beat the crap outa it with no worries.