I have Minwax's Helmsman urethane finish down and after several years, it still looks good. It is an oil-based, gloss finish and really isn't all that slippery surprising enough. I suppose it has a similar result as using a varnish.
http://www.minwax.com/wood-products/cle ... r-urethane My previous boat, I used Waterlox which is a tung oil based finish that has hardeners in it, it held up very well too and it is water/chemical resistant. Probably easier to apply than the urethane.
http://www.waterlox.com/Both products can be found in hardware stores.....saving $$$ by not going marine.