How to Prevent and Eliminate Mould on Your Boat

Mould can be terrible for your boat. In a best-case scenario, it’s going to look ugly, interfering with your ability to enjoy your boat on the water and lowering the resale value. In a more serious situation, mould can interfere with your boat’s functionality – and the problem just gets worse over time.

Fortunately, if you take a proactive approach, you can prevent most instances of mould on your boat and eliminate the mould that does eventually show up. 

Mould vs. Mildew

First, let’s explain the difference between mould and mildew. While similar in name and appearance, these are actually two different phenomena. Mould is a type of fungus that can easily spread on a boat. It produces an awful musty smell and if left untreated, can cause a variety of health problems, including allergic reactions and respiratory issues. Mould is distinguishable because it’s fuzzy and appears in circular patterns; it may also come in a variety of colours, such as black, brown, yellow, blue, white, and grey. Oftentimes, mould is a sign of a deep and hard-to-remove infestation.

Mildew is a different type of fungus. It looks more like dust, appearing on the surfaces of your boat. It can be black, grey, yellow, or white, and it often appears suddenly, like overnight. Fortunately, mildew is much easier to remove and results in fewer health problems. 

Mould and mildew often appear in the same conditions and can be removed in similar ways, so most of the advice in the rest of this article can be followed for both. 

Preventing Mould and Mildew

Your first line of defence is prevention. In an ideal world, you’d be able to prevent all forms of mould and mildew from appearing on your vessel. Unfortunately, this is a near impossibility, since mould and mildew thrive in damp areas. However, you can work to minimize its appearance.

  • Find and seal leaks. Check all around your boat for potential leaks. Your hatches, stanchions, ports, vents, bow rollers, windlasses, and cleats are all potential sources of water leakage. If you’re getting water in through these areas, it could easily leak into the core of your deck – which could eventually result in a major mould infestation. If you notice a leak, check for core rot and get rid of it. Then, reseal the area and reinstall the hardware in question. 
  • Use a boat cover when necessary. A good boat cover will keep out moisture and prevent new air from getting into your boat. Try to keep a cover on your boat whenever it’s not in use; it can make a huge difference. 
  • Make sure to ventilate your boat. Stagnant air is a perfect breeding ground for mould and mildew. Still air holds moisture and allows mould to develop easier. But if there’s a constantly moving flow of air, it will carry that moisture away and make it much harder for mould and mildew to thrive. Ventilation is the way to ensure the air keeps moving. You should install vents throughout your boat and ensure all areas of your boat have adequate airflow. Keep your bilge covers, cupboards, and lockers open whenever possible. 
  • Start dehumidifying. Mould and mildew need moisture to thrive, so if you deprive them of moisture, they’ll be unable to survive. The most straightforward option here is to run an electric dehumidifier when you’re occupying the boat. However, you should not leave a running dehumidifier unattended, or you could risk a fire. A better long-term option is using a chemical dehumidifier, such as calcium chloride, to absorb moisture onboard when you’re not present. 
  • Clean and eliminate mould and mildew at the first sign. Mould and mildew are fungal organisms that are capable of spreading quickly. If you notice a small spot of mould or mildew and allow it to remain unmolested, it will quickly grow and infest other areas of your boat. Try to clean it as soon as you see it to prevent it from getting out of hand.

Eliminating Mould and Mildew

So how are you supposed to eliminate mould and mildew once it has already manifested? 

  • Use a homemade mixture. For starters, you could clean the area using a mixture of your own making. You can mix together bleach, trisodium phosphate (TSP), and powdered laundry detergent with water to create a diluted mould-killing formula. Use a gallon of freshwater, a quart of bleach, 2/3 cups TSP, and 1/3 cups laundry detergent. You may also use a mixture of vinegar and water in a 1:3 ratio for a simpler, if less effective solution. 
  • Use a mildew remover. Commercial mould and mildew removal products can be used in the same way. They’re also easier to find and require less upfront manual work. They also typically come in spray bottles, which can make them easier to apply. 
  • Let it sit. After applying one of these solutions, consider letting it sit for at least a few minutes. The bigger the area and the stronger the mould seems, the longer you’ll need to let it sit. This will allow your cleaning product to fully penetrate the colony, killing it entirely. 
  • Gently scrub. Use a stiff brush to begin scrubbing the area after you’ve allowed the cleaner to sit. However, you’ll want to scrub gently to avoid damaging the area. Consider using a toothbrush for crevices and other hard-to-reach areas. 
  • Rinse afterward. After your first line of scrubbing, make sure to wash the area well. Use a basic soap and water mixture to remove the cleaner, rinse again, and dry completely. Even a single mould spore can cause new growth. 

If you follow these steps and still have a mould problem, it may be time to contact a professional. Some mould infestations are too deep to be handled individually.

Taking good care of your boat is the best way to maximize its lifespan. When it’s time to sell your boat, or look for a new one, make sure to use TheYachtMarket’s innovative buying and selling platform!

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