Re: Finish for white cedar floorboards
If you're set on having finish on them... as Wiz hints, NO film finish. Tedious to maintain, and can be slippy. Unless other steps are taken to ameliorate it. So I'd suggest a polymerizing oil... or an oil/varnish hybrid... and renew it OFTEN!!
For the former, I've had some small successes with Sutherland & Wells Polymerized Tung Oil. For the latter, I've used a lot of Daly's Seafin Teak Oil and love it. Both are dead simple to apply and refresh. The former dries quicker and you need to move quickly. The latter has some UV additives, which is one reason why I tend to favor it. But, unless your boat lives outside, either should serve.
David G
Harbor Woodworks
https://www.facebook.com/HarborWoodworks/
"It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)