How long should boat bottom paint dry before launching?
I've just put two coats of antifouling on my 28-foot yacht, and the yard has offered me a launch slot tomorrow morning. The afternoons have been mild but the nights are cold. How can I tell whether the paint will be ready?
Answer
Many conventional boat antifoulings need roughly 8 to 24 hours after the final coat before launching in mild conditions, but follow the minimum immersion time specified for your exact paint. Check the tin or technical data sheet: touch-dry paint can still be too soft to immerse, and some products also have a maximum time allowed ashore.
Check the immersion time
Find the full product name on the tin, including any suffix or formulation. International Micron, Hempel's self-polishing ranges, Jotun and Seajet products have different drying schedules. Even paints from the same manufacturer can differ substantially.
Use the instructions for your particular product and market version. Look for three separate figures:
- Touch dry: the surface no longer feels wet. This does not mean it is ready for launching.
- Overcoating interval: how long to wait before applying another coat, sometimes with both a minimum and a maximum.
- Time before immersion: the minimum wait before the hull goes into the water, plus any maximum launch window.
Start the launch countdown when you finish the final coat. If you finish at 16:00 and the specified minimum is 16 hours at the applicable temperature, the earliest launch is 08:00 the following day, provided conditions stay within the stated limits.
Cold nights and thick coats
Temperature means the hull and its surroundings, not just the warmest afternoon air reading. A hull that has spent the night in a cold yard can stay cold after the sun comes out, particularly around the keel.
For conventional antifouling, allow overnight to a full day in mild weather when planning the job. In colder conditions, some products need 24 to 48 hours or longer; others must not be applied below their stated minimum temperature. These planning ranges do not replace the manufacturer's temperature chart.
- Cold weather: use the drying interval for the lower relevant temperature. A few warm afternoon hours may not be enough.
- Heavy application: thick roller ridges and runs can retain solvent beneath a dry surface.
- Sheltered spaces: poor ventilation can slow solvent evaporation, even when the surface feels dry.
- Dew or rain: inspect for streaking, lifting or other damage and follow the product's instructions before proceeding.