It ain't spar, it's spar varnish!
A spar is a structural element of a sailboat's rig, like the mast or the boom. Spar Varnish is used to finish the spar and protect from weather and sun. It looks nice for a while but does not last very long. That's OK because you have a boat that cost you a lot of money to go slow and offers its rewards in being able to operate it and cover little ground without the use of fossil fuels, but it makes you look good while you do it. Kind of like a Raft. I use Minwax Spar Urethane which is a relatively cheap and widely available spar varnish, though it is technically not a varnish. It gives relatively poor results that do not last long. But it is kind of cheap and can be applied with those disposable foam brushes. High quality SPAR VARNISH (Epiphanes is the class act of the lot, FYI) lasts longer, protects the wood better and should be used with a high quality VARNISH brush which is religiously cleaned in Mineral Spirits and dried thoroughly between uses. The cost of the varnish and brush and mineral spirits is greater than the cost of Carlisle oars. So as nice as it is to use a real, genuine spar varnish and apply it with finely honed skills every 6 months or so, the crappy Minwax stuff wins out with the Working Class where I reside. I choose to buy Carlisle and Minwax and then upgrade to Cataract Oars with the money I saved in the varnish. For the most bang for the buck without regard to the aesthetics, use a Garage Floor/Porch/Deck latex paint and mix in a little fine sand like commercial playbox sand for the first coat. Apply a second coat without sand to make the sand adhere and give little love to your knees. If beauty were all that mattered, the world would be filled with Wooden Boats, regularly varnished with Epiphanes.
Don't Wanna Die Askin' for Another Chance