UV the Captain

Why all the fuss about protecting epoxy from UV?

Well, I am sure UV is more and more of an issue as you get closer to the equator. But how much of an issue is it in Alaska, at latitude N60°, in a boreal rain forest?

With my last two boat builds, and on my current build, I have decided not to protect the epoxy from UV. The finish is bright, with no top coat to protect the epoxy. I am not recommending this to anyone else, but I am going to give it a try. Worst comes to worstest, the epoxy will dull and I will sand the dull layer off and apply a UV-protectant layer. But until then, I'm going commando!

Epoxy manufacturers are pretty straight forward about the need to protect epoxy from UV.

From System Three's Epoxy Book...

System Three Epoxy Book page 18

From West Systems' User Manual...

West System User Manual page 13

But the epoxy manufacturers are selling their products world-wide, from the arctic to the equator. And their products are not used solely in stitch-and-glue wood boat building. Their products are used in fiberglass boats and aircraft where the integrity of the epoxy is far more important than in a stitch-and-glue wood boat. So, they have to be conservative in their recommendations lest some airplane falls out of the sky and the lawyers get involved.

But me? With my boat made with plywood that is orders of magnitude weaker than epoxy?

What does UV do to epoxy and how fast?

From System Three's Epoxy Book...

System Three Epoxy Book page 18

"six months of intense tropical sunlight on horizontal surfaces"

What about in Homer Alaska, latitude N60°? When I visit family in southern California, they can't stop reminding me of how pale I am. Well no shit! They get lots of UV. I get none.

So I ran some numbers. Yeh, I did the Bill Nye the Science Guy thingy...

My boat will be under a tarp on the trailer 335 days per year. Of those 335 days, 180 days will be in the woods, under snow, in the darkness of the Alaskan winter.

Of those 30 days outside of the tarp, the boat will be in Sadie Cove, a fjord so steep that, if it isn't raining or fogged-in, direct sunlight is available only about 180 hours. And that is if we have an unusually sunny summer!!! The rest of the time the sun is either behind Sadie Peak or behind Grace Ridge. I'm thinking those mountains provide a better barrier coat than 30 mils of paint.

So the BW will be exposed to direct sunlight 2% of the time.

According to System Three, the initial effects of UV are noticed after six months of tropical sunlight. The six months of sun are three months of daylight and three months of night.

Therefore, the BW, seeing direct sunlight 2% of the time, will take three months divided by 2% (3/0.02) or 150 months for the initial effects of UV. 150 months? Dude, that is like, 12½ years!!!

Then, after 12½ years, the horizontal surfaces will begin to dull. Total breakdown will take over 30 years.

I'll update this post in year 2027 and let you know if the horizontal surfaces have begun to dull.

Until then, you decide whether or not your epoxy needs to be protected from UV. You be the captain of your boat.

Update 04/25/15: A fly in the ointment!

I have been approach by a friend who is very interested in buying the completed BW. I am willing to omit UV protection from my own boat but I am not willing to omit UV protection from somebody else's boat. So, with the possibility that the boat will be sold upon completion I have changed my mind and will apply UV protection.