Throwing a bag from a boat is always a risky endeavor, especially if you haven't carefully considered what is likely to happen when the full force of a swimmer is applied. If someone is on shore to grab your boat, you might be just as well to hand them the bag and let them make the throw.
The exception might be when someone is stuck in a hole. They aren't moving downstream, so if you can get a rope to them and keep from having them pull you in with them, that might be a reasonable thing to do. If I were unwilling to join them in the hole, I probably wouldn't throw them a line from my kayak.
Class II and Class III whitewater is a great place to learn and practice. There are many rapids that produce swimmers at reliable locations, so finding a spot to practice is a good idea.
I don't care for 1/4 inch line at all, especially the kits with 40 feet of 1/4 inch polypro. Yeah, it's a small bag, but it is very short for many situations and it's hard to grip for the rescuer and the swimmer. The 3/8" and 5/16" are much better and 60 to 75 feet is much more practical. I have a bag with 100 feet of 3/8" nylon/poly, but I can only throw it about 75 feet. I carry it in remote rivers where a long, strong (3200 lbf) rope may be needed. It isn't as stretchy as polypro, it's cheaper than Dyneema/Spectra and it has a great grip. I think Sterling calls it Grabline.
I have also seen the 7/16" throw ropes. to me, they are just too big for a small kayak -- the 5/16 to 3/8" seems to be plenty sufficient and strong for throw lines and simple haul lines.
Dock & Launch Systems
Rescue / Throw Bags
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