What Causes Moisture Buildup on Sailboats?
Moisture buildup in the cabin of a sailboat is more than just a nuisance. It's the main cause of structural damage on many boats, and it can utterly destroy the liveability of your sailboat cabin faster than you'd expect. But what causes moisture buildup on sailing vessels?
The most obvious cause of moisture buildup on boats is a leaky deck or hatch. Counterintuitively, it's not usually the hull of the boat that leaks. Rainwater is the primary culprit, and a very large volume of it can accumulate inside your boat.
The problem is compounded by poor ventilation. A fiberglass boat is a lot like a plastic bag, and water can't evaporate and escape nearly as easily as it can get in. It's also important to note that vents themselves can also be a source of leaks.
What does Moisture Buildup Do?
Moisture buildup has nasty effects on virtually every structural and technical system inside a boat. It can also pose a serious health threat over time. This is especially true in hot and humid climates such as Florida or Hawaii.
Structural Damage
Fiberglass sailboats have a layer of shaped material between the layers of glass. Often, this is organic material such as plywood or particleboard. If moisture builds up between these lasers, it can compromise the integrity of the fiberglass. This can cause the deck to sag, and it will eventually ruin the boat.
Cosmetic Damage
Moisture can cause wood to warp, which will lead to issues such as doors that won't close or peeling veneer. These cosmetic issues are usually relatively easy to repair if the underlying structure remains intact.
The one exception, though, is upholstery, as it can be very costly to replace stained and water-damaged cloth, leather, and foam.
Electrical Damage
Moisture is an obvious threat to the electrical systems aboard a sailboat. Water causes everything from contact corrosion to short-circuits, which can be dangerous and a real pain to repair. If you begin having electrical problems after it rains, moisture is the most likely culprit.
Mold and Mildew
Moll is an extremely common problem on fiberglass sailboats. It grows in dark, damp places with poor ventilation. In other words, the cabin of a sailboat is the perfect breeding ground for mold.
Many kinds of mold are harmless, but toxic mold also grows on sailboats. Mold of any kind is difficult to remove, and it can cause long-term damage to your health.
Mildew, on the other hand, is mostly a nuisance and not as serious of a health threat as the toxic black mold. However, the musty smell of mildew is a warning sign that moisture is building up, and mold could soon follow.
How to Prevent Moisture Buildup
Preventing moisture buildup on a sailboat is the best way to avoid costly interior and structural repairs. The best way to prevent water from entering your boat is to visit after a rainstorm or sailing trip to check if (, and where) water is pooling up inside the cabin.
If you have a leak, look for the source. Portlights, hatches, vents, deck plates, and light fixtures are common sources of difficult-to-find leaks. Once you identify the source of the leak, fix it promptly and ensure the vessel has adequate ventilation to dry the water.
If a leak leaves your upholstery soaked, take it out to dry and promptly clean the surrounding area to prevent mold or mildew from proliferating.
If humidity is the problem, you may want to consider adding active ventilation to prevent musty air from becoming stagnant. Even a small amount of active ventilation can prevent or reduce mold in humid environments.
Active Ventilation vs. Passive Ventilation
The difference between active and passive ventilation is important to consider when equipping your boat to deal with moisture buildup.
Active ventilation uses a powered fan or blower to artificially induce a draft inside of the boat. Many sailboats utilize solar-powered deck vents as a low-maintenance and self-powered form of active ventilation.
Passive ventilation simply refers to deck cowls, open windows, or any other ventilation system that doesn't utilize a fan. All sailboats should have at least one form of ventilation that's open all the time.
Active ventilation is better for reducing moisture, as it pulls a much greater volume of air through the cabin almost all the time. Solar vent fans are an excellent choice for this. However, the ideal combination of vents includes both active and passive vents.
Dehumidifiers
Dehumidifiers have long been used as part of the HVAC system on larger commercial vessels and yachts. In humid climates, even sailboats larger than 30-feet in length could benefit from a dehumidifier.
This is especially true for liveaboard sailboats, as the addition of a dehumidification system can make the cabin much more comfortable. A typical home dehumidifier will work, but it's not the best solution.
This is because home dehumidifiers are bulky, and their water containers often don't seal completely. The last thing you want is for a passing boat wake to topple your dehumidifier and spill the water right back into the boat.
A marine dehumidifier is a better option, and there are many options available for larger family sailboats. Dehumidifier units are also available for small boats, and they typically run on 12-volt DC current. These smaller units are self-contained and portable, allowing you to run them periodically when you're not aboard.
Dehumidifiers are an excellent option for sailors who don't use their boats often, as they're an inexpensive way to keep your boat safe and dry. For long-term use, consider installing a permanent dehumidifier as an integral part of your ventilation system. These units don't have drainage tanks, as they drain excess water directly out of the side of the boat.
Tips for Repairing Moisture Damage
Moisture will always be a problem that sailboat owners have to deal with. As a result, there's a good chance that you'll have to deal with moisture damage at some point in your sailing career.
When dealing with suspected moisture damage, it's important to determine the actual extent of the damage. If you notice a peeling cabin board, don't just replace the veneer. Make sure that the wood below hasn't begun to rot, and make sure that surrounding areas are free of mold. The same applies to upholstery, as cloth can trap moisture for long periods of time and dramatically accelerate wood rot below it.
If electrical systems are involved, hire an electrician to get an accurate picture of the extent of the damage. In many cases, simple wiring can be saved, but any circuit board-used electronics are usually toast.
It's important to use extreme caution with electrical systems, especially any system that uses 120-volt AC power. DC systems are a bit less hazardous, as they typically use much lower voltages and amperages, which reduces the risk of a dangerous shock.
Upholstery can usually be cleaned after sustaining moisture damage. If the smell of mold or mildew remains after a thorough cleaning, you may have to replace the foam inside the covers. When mold is involved, you may be best off replacing the non-washable materials regardless.
Always wear gloves and a respirator when dealing with mold. A standard painter's mask probably isn't sufficient, as industry professionals recommend a full respirator with filters designed to capture mold spores. For the best protection, use a respirator with P100 filters, such as those certified by the EPA for lead paint, asbestos, and mold.
