Is the calculator 100% accurate?

It's a solid starting point, but hull geometry varies considerably from boat to boat. The wetted surface area formula used here (Length × (Beam + Draft) × 0.85) is a reliable industry approximation for most monohull sailboats and powerboats, but it won't be perfect for every vessel. A full-keel sailboat, a catamaran, or a barge-style hull will all have different wetted surface areas. When in doubt, add 15% to your calculated amount. Running short of paint mid-project is a much bigger headache than having some left over.

Do I need both bottom paint and barrier coat primer?

While they serve different purposes, pairing antifouling paint with an epoxy primer is a powerful combo. Barrier coat is applied to the bare hull to seal and prevent osmotic blistering on fiberglass and corrosion on metal. You can even use this formula to repair existing blistering. While not always needed, such as if the hull has existing paint in good condition, applying an epoxy primer first helps protect your boat and greatly improves adhesion with compatible bottom paints.

Can I apply antifouling paint over existing paint on the hull?

Not all paints play nice with one another when it comes to compatibility. Ablative (self-polishing) paints generally cannot be applied over hard antifouling paints. Hard paints can often be applied over ablative paints, but only if the existing paint is in good condition. Solvent-based paints may lift water-based coatings. When switching product types, brands, or if you're unsure what's already on the hull, the safest approach is a full strip to bare fiberglass followed by a fresh barrier coat system. If you can't strip, test compatibility with a small patch first and let it cure for 72 hours before committing to the full hull.

Does it matter if my boat is in saltwater vs freshwater?

When comparing the two environments, saltwater creates more demanding conditions for boats. Marine growth is more aggressive, dissolved salt in the water leads to faster galvanic corrosion, and stronger currents speed up ablative release. Formulas with higher biocide loads, like TotalBoat Spartan, are often preferred in saltwater to minimize maintenance and reapplication. For freshwater boaters, you can get excellent results from lower-biocide ablative paints. If your boat moves between fresh and saltwater, consult the product data sheet or our technical team for guidance on the right formula.

How soon after applying bottom paint can I launch?

This depends on the paint type. Most antifouling paints require a minimum of 6–24 hours of dry time before launching, and may also have a maximum launch window. TotalBoat bottom paints have no max time, meaning the biocide remains active and is ready to go in the water when you are. Other brands tend to have a 30-90 day window to launch after applying. Launching too late can dramatically reduce the effectiveness of the antifouling season. If your boat will stay out for longer than the launch window allows, plan to apply a fresh coat of antifouling paint within the proper window. Always check your specific product's data sheet for the correct launch timing.