> In all my reading about how much varnish to apply to a stripper
> I've only come across quantities in terms of number of coats.

The thickness of the varnish is a major factor in blocking the UV light rays. Unless you have real thin varnish, three coats should be adequate for UV protection. Put on more if you want a thicker finish for looks. If you are afraid you have not put on enough, you can always add more throughout the year, too. When the boat gets too heavy, sand off the excess, or remove the varnish with a solvent.

> What about in volume? How many quarts should I expect to lay
> down. I've come close to putting on a US quart (1 litre).

That's about right. You might get away with a pint (1/2 liter) next year, particularly if there are few scratches and dings. unless there is a great sale, though, go for the quart can. You can use the excess on your wooden paddles. If they get much abuse you may need to redo them more often than the kayak.

> How much are other people putting on?

About the same amount. Somewhere between a pint and a quart. The size of the boat is a big factor here. Bigger boats take more varnish. Larger cockpits take more varnish. Sealed areas fore and aft might get one coat of varnish, or three, or none at all.

> How often should I plan on putting on a maintenance coat of varnish?
> Yearly?

Yearly is good. Plan on either doing this at the end of the boating season, or the beginning. If you store your boats in a sunny area you can see that it will need more varnish. Lightly sand out the scratches and put on another coat or two. If the boats is mostly protected ( garage or under a tarp) you might not need to varnish it for two years. Waiting three years might be stretching things unless the boat was in storage.