UV Resistant AND Waterproof

I'm sure this is an old question because I did a search and was overwhelmed by the list of results. It's easier to ask again than it is to read a multitude of multi-page threads.

I want to leave my rudder mounted on the transom all summer. While tied to the dock, the top 1/4 of the rudder is exposed to sunlight. While under way, the entire length is submerged. Is there ONE coating that offers both UV protection AND is waterproof?

Gelcoat must meet that requirement. Is there an epoxy additive that makes it suitable for above and below waterline applications? The other requirement is that it has to be easy to apply.

 

White paint?

 

I haven't been able to find a paint that is suitable for below the waterline. Can a bottom paint be used ABOVE the waterline? Or will it deteriorate in the sunlight? Can I paint the whole rudder with VC17?

 

Waterproof is easy, antifouling is not. What is more important to you? There are good reasons to have different paint formulations for different conditions.

 

He doesn't need antifouling if it's on a lake..

 

No? You should see the weed and Zebra Mussels on the bottom of our committee boat... Unfortunately being a drinking water reservoir we aren't allowed antifouling.

 

Most members of the forum already know this but worth mentioning in case a few don't.

"Bottom paint", also known as antifouling paint, is used on the bottom of a boat to keep weeds, barnacles, etc from growing on the bottom, not because of any special "waterproof" properties. If a boat is not kept in the water there is no need to use bottom paint.

There are several types of antifouling paint available. Some older types should be launched soon after painting and kept wet to be effective. But other types do not require staying wet and can be used on areas usually above the water.

 

David, are you saying that bottom paint can resist UV? That could work for me. No, I'm not concerned about anti-fouling. Maybe, I could apply VC17 and not bother to add the powdered copper, if that was a solution.

However, bottom paints don't seem to last more than a season or 2. The gelcoat on my 40-year old boat is still in good shape (between the scratches and scrapes and gouges and rub marks).

Is there not a paintable substance that can spend it's life above and below the watermark without peeling and flaking?

 

I have never heard of any concerns about bottom paint being susceptible to UV.

A good "topsides" paint properly applied should last below the waterline provided fouling is not a concern. If fouling is a concern use bottom paint on the rudder applied in accordance with the manufacturer's instructions. Do you use bottom paint on the hull?

Where did "add copper powder" come from?

 

Anti fouling formulations typically aren't waterproof (by a long shot) nor particularly UV resistant. In fact, most anti fouling paints don't last long above the waterline, quickly losing color and effectiveness as an anti foul coating.

The only thing that performs both roles fairly well are truck bed liner coatings, these most commonly are polyurethane or polyurea coatings, last longer in UV, though the polyurethanes tend to chalk up in a few years and are about as waterproof as you can get with less than 100% solids coatings.

I disagree in that continuously submerged topcoat paints eventually will lift. The surface tension and binders are different enough between topside and anti foul formulations, that a typical topside paint can't be trusted for more then a week, in continuous immersion situations. There are mitigating factors, such as a stable substrate (inert materials, epoxy encapsulation, etc.). The LPU's can be trusted longer on stable substrates, but if the rudder is wood and some movement is likely, no LPU will help and an alkyd might be a better choice with it's more favorable modulus of elongation properties, but then you'll still have an anti fouling issue.

In the end, what you'll have is a painted out of water portion and some form of anti fouling on the immersed sections. Depending on your location, intended and frequency of use, will help determine which type of anti fouling will perform best for you.

 

In northern Ontario mussels and weed? In Hudson Bay yes but in fresh water..

 

Hey guys, excellent discussion. Thanks for the help.

The rudder is wood, but encapsulated in epoxy and glass. In the absence of any other solution, I intend to roller and brush white gelcoat onto the rudder. I will then spend a bunch of time sanding and polishing the gelcoat to a reasonable finish.

Will a waxed gelcoat adhere to the glasswork or will it "release" and fall off in the same way that it pops out of a female mold?

 

yep Anti fouling is required in fresh water most permanently afloat boats on the Norfolk Broads are anti fouled. they make a special variety for the job.

http://www.hempelyacht.com/en-GB/products/hempels-broads-76111

 

Putting gelcoat on an epoxy/wood construction is distinctly peculiar, and gelcoat adhesion to epoxy can be very problematic. There are some distinctly odd statements and advice on this thread too.

I think you should contact the technical support for a coatings manufacturer and discuss your need with them: the advice will be more reliable.

However in your place I think I'd work out a way to keep the rudder blade out of the water and use ordinary topcoat. Any growth on rudder blades is going to have an adverse effect on handling.

 

Zebra mussels were accidentally introduced into the Great Lakes circa 1988, and have since spread to other inland waters.