Originally Posted by BogMonster
Yes it will. Anything that lets light through is going to allow that so you'd either need a solid roof, or a cover to go over the boat.
I don't think it will be an issue in reality. Polycarbonate sheet will absorb all the UV so you only have visible light coming through. Obviously coloured tubes absorb visible light too, but it will be pretty weak/diffuse light if any corrugated polycarbonate car ports I've seen are anything to go by.