So what I am reading into this discussion is that I if I ever put my Stuart Mariner back into salt water, that need to sand off the 12 coats of spar varnish that I used to finish the solid mahogany rudder blade that I built and replace it with a couple coats of Epoxy?

Thankfully Iowa is along way from salt water, so I don't think it will be high on the list.

Varnish isn't for long-term below water applications. A couple of days or so it is fine. After that water will migrate into the varnish and then into the wood. Even coating the wood with epoxy will not work if you then varnish as the varnish will fail as it isn't for below waterline applications.

13 yrs ago, when I built that rudder blade, I didn't know much about boats and nothing about boat building. The boat lives on it's trailer and only sees water for a couple hours at a time. The last couple of years it only went swimming a couple times per summer. I know one of these days I will likely be charged boat abuse.

Because of the wet spring & summer, my mothers health issues and my wife's health issues and her parents health issues, the boat is still stored and will likely stay that way until next spring. So this winter I will strip down the rudder blade and refinish it with epoxy.

Here is your challenge: epoxy isn't UV stable. It must be covered. It can be covered with varnish (after FULL curing or the varnish will not set and following prep as outlined by the varnish manufacturer). But varnish can't be used for under water applications.

Best would be to epoxy and paint over the section of rudder that remains under water. You need to do some searching for a below waterline capable paint (I'm not aware of any). Best would be to epoxy and then cover with antifouling (some antifoul paints need a tie-coat to adhere to epoxy - read the paint manufacturer instructions). The above waterline section can be varnished. Barrier coat and antifoul 1-2' above the waterline to allow for water lapping when the boat sits at moorage.

Yes I know you likely want to keep that pretty bit of wood visible but below the waterline that isn't a good choice.

If you want the entire rudder to be bright it will need to be unshipped and stored below. Doing this means that you can leave the rudder as is as varnish is fine for a few days underwater.

Well, I have the Lusty Slogger out of the water once again. As I said before I am moving it to Leesburg Florida and hopefully this will be the last move for the old girl. Before I do I have some serious clean up work to do. When I pulled it out of the water I found BARNACLES growing in the bottom. Fortunately, I had no additional worm damage other than the rudder and that is easily fixed. Since I am moving it to a fresh water lake I won't have any problem with barnacles or worms. Of course I will have issues with fresh water vermin but just what I don't know yet! I did have a fair amount of algae when I had the boat in fresh water in TN so we will see. Since I did not sail it much for the past year and a half it has gotten rather seedy and now that its in my drive way I will have the opportunity to paint, stain, and varnish all the bright work plus check out all the lines, pumps and other parts that may need repair.

The old girl is 41 years old, I just hope for another 41 years (for both of us actually!!)