The Simplest Way For Preventing Boat Mold & Mildew

What is exactly is mold and mildew on a boat, and what are the best steps for preventing them on your boat

Mold, mildew and the unmistakable smell they cause are a major problem on boats. Even if you think you’re on top of preventing boat mold and mildew, chances are its winning. Unless you take some steps to stop it. One tell tale sign you have a mold and mildew problem onboard is smelling that distinct “boat smell”. For those of you who haven’t, its a musty, damp smell. People associate the smell with older boats and it doesn’t have to be a thing anymore.

The best defense to tackling a mold and mildew issue on a boat is a good offense! Going on offense against mold and mildew requires several steps. Performing some steps on a regular schedule allow you to stay on top of mold and mildew.

Steps Involved:

  1. Remove mold and mildew on your boat
  2. Keep water out
  3. Ventilate your boat
  4. Preventing boat mold and mildew from returning


Step 1: Remove mold and mildew on your boat

Mold and mildew can live for years on a surface. If we don’t get rid of it at the source then we’ll never be able to have a clean smelling boat again. Le-Sigh… Before we rid our boats of mold we need to understand what it is and where it tends to grow.

What exactly is mold?

The technical definition: “mold (or mould) is a term used to refer to fungi that grow in the form of multicellular thread-like structures called hyphae.” Mold comes in many colors; grayish white, white or gray green fuzz that grows from warm, dark and damp environments. What you see on the surface is mildew while the mold digs deeper down into the surface its on.

Mold and mildew love to grow in damp, dimly lit, warm environments, cue your boat. The list of places which don’t fit these criteria is shorter than the areas on your boat that do. The reason we see so much mold on boats is because of the nature of fiberglass. When two extremes exists like an outside temperature of 40°, cabin temp of 70° and there is dew on the boat. You have a high probability of mold forming.

Some typical places to check for mold include:


•Anchor Lockers


•Deck Storage Lockers

•Rope Lockers

•Bait Wells

•Air Conditioning & Chiller Systems


•Black Water & Fresh Water Systems

•Electrical Panels

•Wood Surfaces

Cleaning mold and mildew on your boat

Now that we have a better understanding what mold is and where to look for it, its time to clean the mold. The two best homemade approaches to rid mold infected areas are a bleach or vinegar solution. If you walk into your local marine store and look at the mold and mildew products they are all bleach based. So why not craft our own mixture for a lot less money.

Start very diluted and work your way up till you feel comfortable. You can start with 10% bleach and increase the ratio as needed. Its better than being too aggressive from the start.

Bleach is the perfect remedy for cleaning hard nonporous surfaces. It will remove stains, kill growth and work on unfinished woods as well. A word of caution do not mix bleach with other cleaners, the results can be harmful to you.

Vinegar is not quite as strong as bleach but serves its purpose in some more sensitive areas. Its less toxic and will still kill mold. I would recommend starting with a 3:2 ratio vinegar to water. If for some reason you need some extra strength give it a whirl. Like any cleaner, less is more. Don’t start too strong and not be able to work back, you can always work up. Put it in a spray bottle and spray the affected area and let it work for 5-10minutes.

** A word of caution always test these solutions in a small non-conspicuous area first to make sure it will not discolor or cause unwarranted harm to the surface.**

On exterior fiberglass a little soap and water will do the trick to clean the mold off of your boat.


Step 2: Keep Water Out

Easier said than done right? It is a boat after all and she sits in the water. In the grand scheme of things it’s much easier to prevent mold than it is to stop it. With that said lets keep mold away from the start. Its as simple as one water leak onboard your boat for mold to grow and spread.

The first thing we are going to want to do is find and seal any leaks. The first place you should look are portholes and hatches. Mold loves to target these areas and are the primary spots you’ll find a leak on a boat. Next, look at your deck hatches, cleats, stanchion bases and windlasses. Make sure they are sealed well with a quality product such as 3M 4200 or 5200 to provide a waterproof seal. The last thing you want is water going through the deck and rotting your boats core. Repairing a rotten core is an expensive fix.

The last place you should check on a routine basis is your boats scuppers. Leaves and debris clog them and can flood the deck into the cabin, just what mold needs to grow and thrive.  Be careful in regions where snow and freezing water occur. They can clog the scuppers causing the water to flood into the cabin. Worst part is you won’t realize this until you open you boat up in the spring.

After eliminating any possible water intrusions, we need to circulate the air in the boat. Doing so will help to further help prevent mold and mildew from brewing onboard.


how to get rid of mold on a boat

Step 3: Ventilate Your Boat

Breath baby! Stale air onboard your boat is the reason why mold grows over the course of the winter on boats. Mold thrives in a closed boat, add moisture and its the perfect ingredients for mold and mildew. This is why its always a good idea to leave your boat on dehumidify to keep circulating fresh air on the boat. Thus, in turn helping to keep mold at bay on the boat.

An easy solution is to install vents. Two good vent ideas are cowl style ventilators and solar vents. The cowl style is a waterproof vent that forces outside air into the cabin to help match the temp inside. The latter is placed on hatches and will run on both solar power and electric to help move air around inside your boat.

Replacing the air inside your boat with outside air helps reduce mold and mildew from forming inside your boat. A rule of thumb for replacing air inside your boat is to do it every hour. Keep some hatches/lockers open to allow air to circulate as well.

Mooring covers and shrink wrap don’t allow the boat to breath and promote the growth of mold and mildew on boats. Im not a proponent of shrink wrap for this reason alone. Shrink wrap causes more mold in my boats up north than anything else. A greenhouse effect caused from much warmer temperatures under the wrap vs. outside. Bring home any bedding, linens, towels, clothing, and anything that can attract mold in the winter this way they don’t get ruined.


Step 4: Preventing Boat Mold and Mildew From Returning

We’re so close to a mold free boat I can smell it. A few more little additions and were there! If its winter time, DampRid containers are excellent at keeping moisture at bay. Be sure to check on them from time to time and replace if needed.

Besides, DampRid, our Ocean Air – Air Purifier Containers help pull mold and odor contaminants from the air. Ocean Air not only has a great smell but neutralizes odors, mold and mildew. This simple natural solution cleans the air onboard your boat. Helping prevent mold and mildew once you have rid the boat of it.

Its easy, place a container in an inconspicuous spot and let Ocean Air do all the leg work. The containers work through natural air flow activating the gel and letting it go to work for you and your boat.

Great places to use them include storage lockers, rope lockers, bait lockers, bilges, lazarettes, galleys, staterooms and any other areas you feel necessary.

Our containers start off with a pleasant citrus scent. As they remove all the harmful contaminants in the air. The smell begins to dissipate leaving you with nothing but the crisp ocean air.

Ocean Air tea tree gel for a mold getting rid of mold on a boat

Moving Forward

Now armed with the best practices to preventing boat mold and mildew and what to do if your boat is already suffering from mold, go out there and tackle them. The key to keeping mold away from your boat is staying up on the practices mentioned in this chapter. No one method alone will work by itself to prevent and rid your boat of mold and mildew. The second you ease up will be the second mold shows up.

Remember, after you’ve rid your boat of mold and mildew:

  • keep the boat dry
  • keep fresh air circulating throughout the boat
  • place down an Ocean Air Container to keep the harmful mold spores away

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