I was a fan of helmsman spar urethane.
Me too. Still am, despite it’s tenancy to drip and sag if not tipped out.
I am leery of water-based stuff in boat work. Minwax Helmsman Spar Urethane sports the “oily rags spontaneous combustion” warnings, so I guess it is not water based.
I have had success with Helmsman Spar Urethane on thwarts, yokes, seat frames and other brightwork. Not my preferred choice for a canoe hull exterior, but I have used it to top coat, after an initial epoxy coat, two very old (very thirsty) glass & nylon hulls, rolling on and tipping out the urethane after wet sanding, and it has held up fine.
In 2008 I set up a varnish/urethane/oil exposure test on some raw (sanded) wood and let it run for 55 months:
http://myccr.com/phpbbforum/viewtopic.php?f=49&t=40923
Available everywhere Minwax Helmsman was at the top, at least left untouched and unmaintained outside in the weather.
Practical Sailor later replicated that test with better materials and less sole-inspector subjectivity:
https://www.practical-sailor.com/iss...d_10576-1.html
I appreciated this part of the Practical Sailor review:
“One hardware store varnish has surprisingly held its own over the long haul: Minwax Helmsman Spar Urethane. At half the cost of the recommended one-part varnishes, Minwax slacked in the color retention department, but it has proven its multi-season durability”