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.
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.
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.
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.
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!
- 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.