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Keeping Your Boat Dry

Marina As the cruising season winds down, it's time to start thinking winterization. One of the biggest issues for Northwest boaters is how to keep moisture at bay during the cold winter months – especially if you are still using your boat. Mold and mildew not only can do serious damage to your upholstery, clothing and carpets – but it can also create a health hazard for people with asthma or respiratory issues. Since mold and mildew thrive in a warm and wet environment – in this Navigator we take a look at two of the main things you need to do to combat their growth: reducing the relative humidity and ensuring proper ventilation onboard.

Reducing the Relative Humidity

It's the weekend and because you miss your boat, you've decided to spend the weekend at the dock. After a great meal and an action packed movie, you're ready to hit the hay. But while lying in bed below the hatch – you suddenly feel something wet hit your forehead! Due to factors such as heating moist air, cooking with propane or even two people breathing in an enclosed environment you have increased the level of relative humidity within your boat. Relative humidity is the percentage of moisture in the air compared to how much moisture the air will hold before it turns into condensation – and when it gets too high it causes water to condense on colder surfaces….like your hatch.

There are multiple ways that you can reduce the relative humidity inside your boat – so let's review both powered options for when you are plugged in and non-powered options for when you're not.

Powered Options

Eva-Dry 2200 Electric Dehumidifier

Electric dehumidifiers are a great way to pull unwanted moisture out of the air. There are many options, but one brand we recommend is Eva-Dry – a small and quiet unit with a reservoir that collects water. It can operate safely 24/7, it automatically shuts down when full and it's small enough to be placed almost anywhere.

Products such as the DryWave Air Dryer help eliminate dampness, mildew and condensation by raising the ambient dew point, which inhibits surface condensation. They are good for keeping smaller areas (such as closets) dry and are safe to operate 24/7 with no supervision.

If you live aboard you may want to consider a much larger dehumidifier, available at most home improvement stores. These can pull an amazing amount of water out of the air – potentially too much if you're not careful. Thankfully these bigger units allow you to set the level of humidity you are comfortable with and will shut down when that level is reached – so make sure you don't set it any lower than 50% or you may overdo it – causing wood to dry out and crack.

Non-Powered Options

There are a multitude of chemical based desiccants that pull water out of the air – including products from DampRid, Dri-Z-Air, and NoDamp. While these come in different shapes and sizes, they all perform the same feat – capturing moisture and combining it with something like calcium chloride to create a non-toxic liquid solution in the bottom of the container. DampRid Super Absorbing System With options like the hanging moisture absorber for closets – you just throw the unit away when it's full, while others collect the liquid which you then disposed of down your drain. All of these options need to be monitored over the winter and refilled/replaced as needed.

An additional option is the non-powered Eva Dry products. These collect moisture by using a renewable silica gel technology that absorbs and holds the water. Over time the crystals will change from blue to pink – letting you know they've reached their full capacity. At this point you need to plug the unit into an electrical socket in a well-ventilated area to “renew” the crystals. After 12 to 15 hours the crystals will have released the absorbed moisture and the unit is ready to be used again – for up to 10 years!

Lastly – it's extremely helpful to cover windows and hatches with a protective layer – either inside, outside or both. Using hatch covers can greatly reduce the temperature differential on the hatch surface while adding a protective layer of plastic sheeting inside can create an excellent thermal barrier. Both of these options will greatly reduce condensation around your portholes and hatches when you're spending time onboard.

Ensuring Proper Ventilation

Equally important to removing the moisture from the air is making sure that you have proper ventilation. Air that can't move around becomes stagnant and provides opportunity for mold and mildew to flourish – so let's explore some options for keeping the air inside your boat moving.

Air Dryers

Caframo Stor-Dry Warm Air Circulator

Air Dryers are a great way to move air around your boat and we stock several from trusted brands.


While you can't run them 24/7 when you are not onboard, a built in cabin heater is a great option to warm the air within your boat when you are. Cabin heaters come in diesel, propane or electric models depending on how much heat you want to provide, how much power you have available (on or off the dock) and how large your boat is. We stock a multitude of popular cabin heaters from Dickinson, Heatercraft, King, Red Dot and Sig Marine.

Caframo TrueNorth Portable Heater Portable electric heaters are also an option for providing heat while plugged in at the dock. At Fisheries we offer three different options from Caframo - the TrueNorth (with or without GFCI/ALCI protection) the DeltaMAX or the Pali. The TrueNorth has a nice low profile (so it can't tip over) with an automatic thermostat to maintain a preselected temperature and an “Anti-Freeze” setting (the heater activates if the temperature drops below 38°F (3°C), if you just want to protect your boat from freezing temperatures. The Pali is an engine compartment heater - which protects your engine and/or bilge against freezing damage. The Pali also uses ceramic elements that self-limit to a predetermined temperature and cannot overheat.

While any one of these heaters is great for keeping your boat warm – heating the air isn't the whole story. You need to combine that warmth with proper ventilation (like a slightly cracked hatch or porthole) to really dry out a damp boat. Without ventilation moisture is stuck inside and while the heat will draw the moisture into the air, without anywhere to go it will soon be condensing on cooler surfaces like you hatch – putting us back to square one. With even a small amount of ventilation the warm, moisture laden air rises and vents out the opening – taking the water with it. While this will allow a little cool air into the boat, the circulation of that fresh air is what ultimately helps dry out your boat since warm air can hold more moisture than cool air. It's important to remember that cabin heaters should only be run while you are onboard and can monitor them safely.


There are many types of vents you can install – but below are two types that will keep air circulating throughout your boat year-round if properly placed.

Nicro Oval PVC Cowl Vent Cowl Vents – these vents are installed through the deck in conjunction with dorade boxes to keep water out. They are normally placed fore and aft, allowing air to move in and out of the boat. The tops of the vents can be turned in any direction so that you can position them to catch the most air no matter where the boat is located. We carry a wide selection of these vents from Nicro, Sea-Dog and Vetus Denounden.

Solar Vents – these vents are installed either through the deck or in a hatch lens and are powered by solar technology with a rechargeable battery that keeps the vent operating 24/7. It's best to install one for intake and one for exhaust for the most effective exchange of air. They can be turned off when you don't want to use them and can be completely closed up for green water shut-off when you are underway. We offer several solar vents from Nicro.

Keeping Your Boat Clean

While all of the options above will help keep mold at bay, the last important step is to remove as much mold and mildew as possible before it gets a chance to really take hold. Wiping surfaces down with a 10% bleach solution is a great way to kill mold – but it's a lot of work to reach every nook and cranny on your boat. Thankfully, there is a great all-natural product that helps you do this with no harsh chemicals – Kanberra Gel.

Kanberra Gel Kanberra Gel is an all-natural blend of pharmaceutical-grade Australian Tea Tree Oils manufactured as a gel, which when exposed to airflow allows the natural antiseptic properties of the oils to become airborne through evaporation. As the air circulates and the Tea Tree Oil lands on the source (like mold or bacteria), it begins naturally neutralizing the problem on contact while penetrating porous materials to provide long-lasting. Kanberra Gel's water based, alcohol-free airborne blend works 24/7 and is effective on a wide range of bacteria, mold, mildew and fungi – making it a great weapon in the fight against winter mold and mildew. For more information on this product, checkout this Product Spotlight.

As you can imagine, there are many factors that will determine how much moisture you need to remove from your boat – including how much time you spend onboard, how damp an area you live in and how cold the ambient temperature is. It may take a little experimentation to get it right – but if you try a combination of the ideas above you will come back to a fresh, dry and clean boat next spring.

We hope you've enjoyed this Navigator on keeping your boat dry – but if you have any additional questions, please don't hesitate to contact our product experts at (800) 426-6930.