Adding Some Ventilation Inside The Boat

If there is any one thing that people object to on a boat the most, it is unwanted smells. And as a boat gets older, it develops smells from all kinds of sources. There are volumes of information out there on holding tank and head odors so we did not plan to address them with this minor modification. After almost 20 years of living aboard, we have found that certain areas of the boat can develop odors from trapped moisture and condensation in any climate and any season. A bigger problem that can surface is mold and mildew, which can generate odors and also cause health problems in some individuals. We learned all of these lessons the hard way, and the solutions were actually quite simple.

The secret to keeping a boat odor and mold and mildew free is ventilation, ventilation and, of course, ventilation. Fans, air-conditioning and heating systems all help in the ventilation department. Other things like leaving hatches or ports open, even a crack, make a big difference, and fans and solar vents make huge improvements. But none of this will help much if there are compartments all over the boat that have no way to exchange air, and allow air to flow in and out. These enclosed compartments are further insulated by cushions and mattresses, not to mention latches that keep the access closed tight. Almost all boat builders want the interior surfaces to look as smooth and unbroken as possible, but once again, this contributes to the problem.

In our current boat, and the previous one that we cruised and lived aboard for 17 years, we took some time to open up all of the interior space to air circulation. Using a hole saw, we drilled ventilation holes inside the cabinets and lockers so the air can flow from one end of the boat to another. We use 12 volt computer fans strategically placed to assist the circulation process, since they are extremely quiet, use very little power and will run continuously for long periods of time. We also use a dehumidifier that runs all year long when we are plugged into the dockside power. It is incredible how much moisture it pulls out of the air, no matter what season and no matter whether we are running the air-conditioner or the heater.

The weekend was set aside to work on the circulation issues and make some improvements. The forward v-berth was a particularly problematic area. It seemed to always be damp, and since the anchor locker was forward of it and the shower just aft of it, this was a moist environment. The dehumidifier sits in this cabin and blows the treated, dry air up into the main salon from where it sits. But we knew we needed to get the area under the v-berth circulating air and with 5 inch cushions on top, this was only going to be accomplished by cutting vents in the side. The two berths in the aft cabin are the same with the added problem of water tanks under each berth. We store lots of items, including clothing, under these berths so it needs to be dry and odor free.

In the past, we have used a variety of vent grills. Our previous boat had an all teak interior just as this one does. So naturally we use teak grills for that finished look. But aside from the fact that these teak grills are way too expensive, in my opinion, need to be varnished and the slats are easily broken if something heavy inside the locker falls against them. We have had this happen on more than one occasion.We have used stainless steel grills and they work fine, but just don't look right to us. With the areas we wanted to cover done in a dark teak, we were concerned that anything white would stand out too much. So our options were black or brown, and square or round. The brown grills we could find were either too flimsy or designed to have an air-conditioning duct attached, and stuck out too far in the back. We found a nice, sturdy, black, round grill and ordered 6 of them to do the surfaces we wanted to vent.

The installation part was very simple. We used the appropriate size hole saw to drill through in the location we wanted the vent. We measured carefully to be sure it was centered where we wanted it, and took care that there was nothing behind the spot that could be damaged by the hole saw. When a hole saw is used on teak plywood, it is best to start the hole on one side and before it goes all the way through, finish drilling from the other side. This keeps the wood from splintering as the saw passes through the opposite side. Before we attached the grills, we took the time to sand the teak around the area the vent would be placed and put a coat of varnish on the wood. This way, once we start re-varnishing the interior, these areas will be done and we won't have to remove the grills again for a long time.


  1. I am not clear on where you mounted the muffin fans. Are they mounted directly behind the new grills, on the backside of the cabinetwork?

    Also, did you arrange your fans so as to have them all blowing in a circular pattern through all areas of the boat?

  2. Doryman, The fans are not mounted at the grills, but inside the cabinets strategically placed to allow the most circulation in the individual cabinet. also move air into other cabinets if possible and not interfere with or get caught up in items stored in the lockers. So we have to do some study and planning for each situation before we install one. In some cases it won't work and in others it makes a big difference. The idea is to keep as much air moving as possible and the direction is not that important. If possible they should blow in opposite directions to really stir things up. Chuck

  3. Chuck, would you supply the sources and names for the vents, fans and de-humidifier?
    Thanks, holiday

  4. Holiday, The fans were purchased at Home Depot, much cheaper than West Marine. You can find them for around $35 to $38 on line if you do a Google search, The dehumidifier we found at but again other sources are available. The vents can be found at jms online marine supply. Chuck

  5. Nice boat! What kind of dehumidifier did you get? I have been using a real hermetic compressor model the size of a small ice chest, and I'd like to find a smaller unit that works. I have a couple of the heater element-types, but they do not separate water, they just try to keep it from condensing. I also use the salt crystal-types in enclosed spaces, and they are expensive to recharge. I need to bore some more holes, too.

  6. Ours is a pretty good size but it does a fantastic job. We do move it from cabin to cabin to keep everything dry and it is incredible how much moisture it pulls out of the air. The tray can be emptied manually, which is what we do, or you can attach a drain hose to it. I think we purchased it from and it is a Soleus Air CFM-40 E 40-Pint Dehumidifier with Humidistat. Chuck


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