Antifouling paints are designed to prevent fouling organisms like mussels, algae and other growth from attaching to the bottom of your boat. But what if your boat is trailered and not immersed in the water for any length of time? "Can you use topside paint below the waterline on a trailered boat?" is a question we are often asked.
Customer canoe build showing TotalBoat Wet Edge 1-part polyurethane topside paint in Flag Blue below the waterline
The answer is "it depends." We have had customers choose to use topside paint below the waterline on kayaks, canoes, and dinghies. If topside paint is applied over a properly primed hull (using epoxy primer), a daysailer that is in the water just for a few hours or a single day might be okay. There are people who have done this, usually waxing the finish for additional protection. However, there's not a lot of data on 'how long is too long' when it comes to topside paint immersion.
The truth is that 1-part polyurethane finishes like TotalBoat Wet Edge, Interlux Brightside, and Pettit Easypoxy are not intended for immersion greater than a few days. Even harder 2-part polyurethane finishes such as Interlux Perfection will blister. Worse, trailers with carpeted bunks or other padding can stay wet for significant amounts of time and can cause blistering even after short periods of immersion.
If aesthetics are important - and you don't want the 'dull' finish of conventional copper-based bottom paints, consider a copper-free antifouling like TotalBoat Krypton or Pettit Vivid. These paints feature brighter, more bold colors. For maximum performance and resistance to the wear of launching and retrieving, consider an epoxy finish such as Interlux VC Performance Epoxy. While it contains no biocides, it is specifically designed for trailered or rack stored boats and may be wet sanded / burnished to a fine finish.