Dealing with Damp
What to do with your boat in winter to avoid mildew, mould
and general dampness? Do you need to heat your boat, or will simple ventilation
do the trick? What about dehumidifiers - do they really work, or would a simple
bar heater do the job just as well?
Sailing Today's, Duncan Kent offers some sure-fire solutions
to keeping your boat fresh and fragrant, but without consuming megawatts of
power in the process.
VENTILATION
Good ventilation is the number one factor to alleviating
damp and its associated mould and mildew in a boat. In fact, adequate air
circulation can virtually eliminate the need for constant and expensive heaters
and dehumidifiers. I have left boats for months without any form of heating and
none have developed any serious damp problems - thanks entirely to ample
ventilation, in conjunction with giving the boat a thorough clean inside first
to remove any salt deposits, leaving all the doors and lockers open, and
lifting the sole boards.
Of course, if your boat lets in rainwater through dodgy deck
fittings or seawater through dripping stern glands etc, then you're likely to
get damp problems regardless of your most ardent attempts to banish them. Sort
out the water ingress and you're halfway there. Much of the rest can be solved
by ensuring the air inside your boat is changed constantly.
Modern boats tend to rely on opening hatches and portlights
for air, assuming that you will be on board to close them when it rains.
The key making ventilation effective is to open lockers,
doors and sole boards wherever possible and ensure any standing water, in the
bilge for instance, is first removed using a sponge or similar. If you're not
keen on leaving doors and lids open, then fit vents or drill holes in the back
or sides of locker doors and particularly under mattresses and bunk lockers,
where condensation commonly forms.
HEATERS
In addition to good ventilation it is often advisable to put
a small, thermostatically controlled, electric heater in the saloon and leave
all the interior cabin doors and lockers open. I use a small 500W oil-filled
radiator, set to around mark 2/10. In most cases this stops the interior
dropping below 5ºC during the winter; although in freezing conditions it only
just keeps it above freezing. During long periods of severe ice and snow I pop
on board and raise this to 4/10. Even a small, 200W tubular greenhouse heater
will do - they're cheap, safe and economical to run at around £0.50p/day.
Of course, if you have diesel-powered central heating, then you can set the
timer or frost-stat to come on for a couple of hours a day or when the
temperature drops below 5ºC. These systems do a good job of drying out the
boat, but they also consume quite a lot of battery power when they're running,
so unless you have a mains battery charger on constantly or a 20W+ solar panel
fitted, you will have to keep an eye out for flat batteries. They also consume
a reasonable amount of diesel, which you will probably need to refill at least
once during the winter period.
DEHUMIDIFIERS
Passive
There are plenty of cheap 'dehumidifying' devicesavailable that are simply aerated
containers of a desiccant, such as silica-gel crystals. While they do indeed
absorb a certain amount of moisture from the air (until they are saturated)
they are really only suitable for very small, sealed areas such as drawers and
boxes and are almost entirely useless for larger areas. Furthermore, when they
are saturated you need to dry them out somehow, which often means putting them
on a heat source somewhere for several hours. There are some around that have
integral heating elements, but they're not designed to be left powered up - the
element is merely a convenient way of drying the crystals out.
Active
Many boat owners believe that a 240Vac dehumidifier is the
answer to all their problems - but this is not necessarily the case. A properly
ventilated boat with a low-power heater can remain as dry and fresh as much as
one with a power-hungry dehumidifier churning away day and night.
Electric dehumidifier
types
There are two types of electric dehumidifier -
compressor-driven and rotating desiccant disk types. A compressor-based
dehumidifier operates like a fridge, drawing in air from its surroundings and
passing it over cooled coils. The coils force the moisture in the air to
condense and the resultant water droplets are collected in a reservoir or
discharged through a drainage pipe. The air is then reheated to room
temperature and blown back out into the cabin.
A desiccant dehumidifier, on the other hand, has no coils,
but instead uses a wheel filled with an absorbent desiccant to extract the
water from the air. The air is then heated and recirculated. This type work
better in very cold temperatures than the compressor-driven models as there are
no 'drips' to freeze and cause a build-up of ice. Saying that, cold air doesn't
hold water, so the air is often very dry in colder, high-pressure conditions
anyway, naturally lessening the problem. Besides, both types reheat the air
before blowing it back into the cabin, so the air temperature gradually rises
anyway.
It's worth pointing out that dehumidifiers aren't effective
if you have too much ventilation - so really it's one or the other. Ideally,
for an electric dehumidifier to run efficiently you should seal the boat up as
much as possible! If you have large vents or hatches open to the outside air
the dehumidifier will be working overtime trying to dry out the atmosphere
surrounding the boat and not the interior. This is wasteful of energy and money
and thus not very eco-friendly!
Dehumidifier tips
- When buying a dehumidifier for a boat you would be well advised to select one with a permanent drainage option, so that you don't need to keep visiting the boat to empty the internal water reservoir (my 7-litre tank fills after only a few hours use sometimes). The drainage pipe can either be put into the sink or plumbed into a sink drain permanently.
- If you do use an electric dehumidifier, do buy one with a built-in humidistat as it will switch off when a preset level of humidity (ideally around 50-percent) is reached.
- Finally, some dehumidifiers don't automatically switch back on if the mains is disconnected for any reason, so check carefully that the one you're thinking of buying will, or it could prove useless if the shore power trips out frequently.
DO YOU REALLY NEED
PERMANENT SHORE POWER?
Leaving your boat permanently connected to shore power all
winter is not ideal. Not only does it cost you money, but if left in a marina
berth it can create problems with galvanic corrosion to your underwater
metallic items such as propeller, shaft, skin fittings etc, unless you have a
galvanic isolator fitted to the shore power input circuit.
While it is tempting to leave a mains battery charger on the
whole time, ideally you should try not to use your batteries during the winter
if possible - especially if you're not planning to use the boat until the
spring. Better to top them up (if the wet type), charge them fully, and then
disconnect them from the boat's circuits altogether. Some even take them home
to keep them warm, but this is not often practical in modern boats with complex
electrics and large, heavy batteries.
Most modern batteries, particularly AGM, gel or similar dry
electrolyte batteries will hold their charge for up to six months without
attention. But if you're worried, or you have standard flooded-cell lead-acid
batteries that self-discharge over time, why not consider fitting a small solar
panel just to keep them topped up when you're not on board? A simple 10W
photovoltaic panel costing around £100 will produce enough amps during the day,
even in the winter, to keep a 100Ah lead-acid battery permanently topped up. In
this way you avoid the dangers of an electrical problem on board and possible
fire risks and you never have the worry of what might happen if your shore
power lead is disconnected, or your charger overheats.
TIPS TO BEAT THE
DAMP, MOULD AND MILDEW
- Leave interior doors, locker lids and sole boards propped open when you leave the boat.
- Remove all fresh foodstuffs and dirty/damp clothing.
- Remove all soft furnishing that can hold water.
- Install at least one 'active' vent to draw air through the boat.
- Make sure winter covers don't seal off the airflow.
- Give all surfaces a wipe over with anti-bacterial cleaner before leaving.
