The other day Dick and I did an experiment with a kayak he has been keeping in storage for the past few years. This is the Evolution#1, an 18ft long high volume fast expedition kayak constructed from plywood over a minimal internal frame. It was made by "Blazing Aspen Kayaks" in Olympia, and I think the builder has moved on to other pursuits. Although he named it Evolution#1 I'm not aware that there are any more of them and it may be a one off. It weighs 45 lbs and used to be painted red, but now is green with some areas left bright finished. Below the waterline the hull is coated with a very tough abrasion resistant black epoxy/silica/graphite mixture. It has hard chines and is concave between the chines and the keelson (like the old Anas Acuta), so it simulates the shape of a skin-on-frame hull in the water.
Dick brought the Evolution#1 to me to have a small hole in the rear bulkhead repaired (caused by forcing some gear into the aft compartment) and to test it out with some water ballast. The reason he hasn't been using it is because it feels very tender empty. If it still didn't feel stable after the ballast then he was prepared to put it up for sale on Craigslist.
Dick got seven mylar bags free from his local Starbucks. When completely filled with water each bag weighs 12 lbs. They are difficult to fill completely, even with a hose, so the total added weight was probably around 70-80 pounds. Success! They made an incredible difference in stability. It still didn't turn very well but we both felt like we could have paddled it all day.