It will be instructive to get more details, but five people in a 13.5 foot open kayak?? - looks a lot like overloading. Personally, I wouldn't put one person in an open kayak, unless they were wearing a wetsuit with a hood.

I am a firm believer in real kayaks, as opposed to the toy-like open kayaks.

When you are in water as cold as lake Superior, life preservers function as body retrieval devices. I believe those waters are about as warm as they get right now. I have vivid memories of scuba diving off Isle Royale in June - water temps 34 degrees.