What Causes Moisture Buildup under Shrink Wrap and how to Fix It?

Moisture buildup occurs under shrink wrap when the airtight material traps warm, moist air inside the vessel. As outdoor temperatures decrease, the shrink wrap surface cools the trapped air. When the air temperature falls below its dew point, water vapor condenses into liquid droplets on the interior surfaces. This process is exacerbated by high humidity during the fall, residual moisture left inside the boat, and repeated freeze-thaw cycles. If left unmanaged, this condensation leads to mold, mildew, corrosion of metal parts, and wood rot.

To fix and prevent this issue, you must install purpose-built vents that facilitate convective airflow, allowing moisture to escape the enclosure. Key steps for managing ventilation include:

• Selecting proper vents: Passive vents are highly reliable for Canadian winters as they operate through natural convection, requiring no power.
• Strategic placement: Vents should be positioned at the highest points of the shrink wrap to let warm air escape, while lower openings intake cool air to create cross-ventilation.
• Correct quantity: General guidelines suggest one vent for boats under 20 feet, two for vessels 20 to 35 feet, and three for boats between 35 and 50 feet.
• Proper installation: Measure accurately, cut carefully, and use marine-grade sealant or high-quality tape around the base to ensure the area remains airtight and leak-proof.
• Preparation: Thoroughly dry all interior surfaces before wrapping and consider using moisture absorbers like desiccants inside the cabin.