The only problems I’ve encountered were when operating on fresh water. Not a great ground or a counterpoise. I have done some lake sailing but used a dipole strung from the mast. On a lake with an aluminum canoe you would just have to depend on the canoe for a ground, not the water. A short experiment on the kitchen counter with a plastic mixing bowl full of water, two table knives, an ohm meter and a little salt is informative. Fresh water isn’t a very good conductor.

On salt water it takes less of a ground than you might think to run a vertical. Just hooking up to a metal rudder post is often enough. The main lesson I’ve taken for my experience is to NOT expend a great deal of energy in making an installation until you test it. Just put something reasonable together and when you come up with an arrangement that works, then go back and make it solid. A remote autotuner works best. Having a radiating feed line inside the boat is poor for sending and receiving.

Commercial marine SSB verticals are about 20 feet long or so and that seems to be a good compromise. I find them laying about in corners of boat yards. They have been removed for various reasons often because of surface deterioration due to sunlight. I talk them out of one for free or not much, sand and paint it and then mount it to a rail of the boat with hose clamps. The conductive wire is internal to the fiberglass tube so you are free to do as you please when mounting.

As for danger to the rig from water when kayaking, you’d be surprised how well you can work the controls of a rig through a plastic bag.

Mike