Yep. Either a true marine spar varnish (that's not Helmsman) like Epifanes from your local marina or Jamestown Marine. Cheaper, and very good, would be untinted paint. This would be the oil base they use for the darker colors, normally #4. You may have to check whatever brand you buy, but it should dry clear, looking very much like varnish. Here's a link to the thread where I first read about it. The paint may not be as robust as the Epifanes, but it will be a lot cheaper.