When we talk about the 'environment' on our boat, we are talking about the air. Since we will be in a marine environment, this means moist air almost all the time. Moisture is a problem on boats, which can cause humidity below deck, musty air, trapped moisture, damage to electronics, mold, and mildew. All of these are very undesirable things! What we can do to combat these is ventilate the boat well and use dehumidifiers, including Air Conditioners. Let's take a look at some of these systems, below.
Every boat comes with some amount of passive ventilation, we're talking about hatches, cowls vents, clamshell vents, louvers, grilles, ports, etc. The amount of passive ventilation are some of the features we will be comparing between the three boats on our short list. However, there are additional things which can be done to improve ventilation and dehumidify the air by using a more active ventilation system. Here are some options S/V Lynx might employ.
Solar Hatch Fans
We could add solar cell powered fans to some or all of our hatches. These fans will operate for a full 24-hours in many cases, and work as either intake or exhaust air, depending on your needs. That being said... reading up on cruising forums, it seems that more recent models of these fans don't last very well, some less than a year. However, we may give them a try and, if they fail, replace the fan inside with a simple (and inexpensive) computer fan. We would then tie that into the house battery bank. We will let the main solar array charge the batteries which power the fans. When installing a fan for ventilation, it is also important to install an exhaust fan as well, one in, and one out (for air flow).
These reversible vents can work if you have one facing forward and one aft. The idea is that the cowl captures airflow from the wind direction and any water that comes in drops down from weight and flows out the small holes in the bottom sides of the box, while a lot of the air goes down another tube, offset from the intake cowl. This way, air makes it in, but water does not.
Unfortunately, due to the configuration of a catamaran narrow side decks over the cabins, there usually aren't places that makes sense to mount these, so we probably can't use dorado boxes on S/V Lynx.
Leaving your hatch open for ventilation while at anchor is a must in many locations. However, if a squall shows up while you are sleeping or away from the boat, you can drench your cabin. A Hatch Canopy is designed to keep the rain out yet let the air flow into your open hatch. The picture (left) is of a Sailrite DIY hatch canopy. There is an instructional video online about how to make one, you can find the video here: Sailrite Video
Though A/C is not something that you will leave on all the time, it is something we plan to have on S/V Lynx, especially for hot nights in the tropics. One of reasons we plan to go with a combo hybrid system is so that we have a massive battery bank. This allows us to run the A/C units in the cabins all night long without having to turn on a motor or generator. That means we aren't making a racket for other boats in the anchorage while they are trying to sleep.
With four cabins needing A/C and assuming each of them is using 10,000 BTUs, they each burn about 13 amps (at 48v). That works out to 416 ah over eight hours. Our boat will have about 920 ah of battery power (552 ah usable), so that is possible.
In addition, A/C dehumidifies the air, so it cuts down on mildew and mold. They also act as heaters for when we are in cold climates (like above the arctic circle in Norway).
If the boat does not already come with A/C units, we have two styles to choose from...
Self Contained A/C units
In these A/C units, everything is contained in a small package. These units are installed somewhere in the cabin, often under a bunk or inside a locker. They are usually small, 8,000 to 10,000 BTU units, Since they only have to handle a small cabin size space of about 500 sq. ft., these should do the trick. The rule of thumb is you multiply the square footage by 20 to find the BTU number you need for a given space. Many smaller cats use these systems, (44' and smaller). The biggest issue is noise, these are louder in a cabin than a Split Unit (see below).
Split A/C units
These are the equivalent of central air in a house. These have two 'split' components. The condensing unit is mounted in the engine compartment, (and consists of a compressor, seawater condenser, and some electrical components). The evaporating unit is installed in the living area (and consists of an evaporate coil and a blower). These are commonly found on larger yachts, but some large cats (46' and up) do use these. Depending on how hard it is to run the copper tubbing between the two component installations, we may decide to go with the these to get a quieter system.
Since air is moist, it causes mold and mildew. No boat is going to solve this problem completely, it's more about making it less than eliminating it all together. We have already talked about Air Conditioning and Ventilation (above), but let's take a look at the options for standalone dehumidifiers.
In simple terms, compressor driven dehumidifiers are really much like air conditioners except that they don't vent hot air outside. These work well in hot climates but they do raise the temperature a couple of degrees. They also don't work well in cold climates (below around 60 degrees Fahrenheit). These pull similar amps to an A/C unit, so, in the end, this means that we may as well just run the A/C instead and save the cost, space, and weight of adding additional equipment in the way of compressor driven dehumidifiers.
These don't do well in a high humidity environment, like a boat on water. Also, when it is too cold or too hot, thermo-electric humidifiers don't absorb moisture very well, which also makes them a poor choice for places we will visit, some of which will have extreme temperatures.
These work well in cold climates, but tend to heat the air up about 10 degrees, so not great for hot locations. These don't pull a lot of amps, less than A/C, but since they don't work well in hot places, the only time they will be useful is when we are visiting cold climates (and we might get a few for those years, like when we are in the UK, Northern Europe, or Alaska, then get rid of them once we leave for warmer locations).
These are a disposable option, which means we would have to keep buying them and then disposing of them everywhere. This is not a very 'green' option, so we won't be going this route.
As you can see, dehumidifiers don't work well for a boat. Fans are a better solution so we will go over those next.
Fans are the least expensive in power to get a lot of cooling and dehumidifying on a boat.
Caframo Ultimate 747/757 fan
Compact, Powerful 12 and 24 Volt Cabin Fans
The quiet and compact Ultimate provides airflow equal to much larger fans yet draws less than an amp. The grill-free fan has a shock absorbing FingerSafe blade that makes it whisper quiet. The 747 Ultimate comes with a suction cup mount that enables the fan to be moved about the boat, it also includes a 6' cord with lighter plug. An optional clothespin-style clamp allows for additional positioning.
First Choice of Boaters All Over the World
Compact Design Fits in Tight Spaces
2 Speed, Low Power-Draw Motor
Grill-free and Whisper Quiet
Available in 12 and 24 Volts Options
Available in Direct Wire or Lighter Plug Adapter
Item Dimensions 2.5 x 5.25 x 8 inches (LxWxH)
Caframo Bora Fan
Compact & quiet 12V OR 24V fans for marine and RV use
The Bora is a favorite of both boat manufacturers and boat owners. This high-performance cabin fan offers quiet operation and impressive airflow. RV owners also appreciate its small size yet powerful air output. Made in the Canada by Caframo Limited, the Bora is backed by one-call support for any manufacturer defects up to 2 years after purchase.
Available in 12V or 24V models.
WEIGHT (LBS) 1.59
CFM ON HIGH 130
CURRENT DRAW ON LOW 0.15A (12V) 0.06A (24V)
CURRENT DRAW ON HIGH 0.27A (12V) 0.18 (24V
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