Condensation is one of the biggest problems while the boat is ashore. All sailing boats get some salt water down below during the course of the season, and salt is hydroscopic: it attracts water. So unless you rinse away all the salt, the interior will stay damp, and by the spring will be covered in black mould spots.
It's not too difficult to get rid of this, washing down with a proprietary mould remover, but far better to stop it happening in the first place, and save the effort! This requires removing as much water as you can to start with.
Skin fittings
For frost protection, it is essential to drain all fresh water pipes, pumps, calorifiers and watertanks (and don't forget the cockpit shower if you have one). Otherwise there is the danger of a burst pipe or worse.
Flush lots of fresh water through the heads, and the holding tank, if you have one. Open the sea cocks so that everything drains when the boat is lifted out. Some people recommend disconnecting the hoses from the skin fittings to let them breathe, but this should come with a health warning: they must be reconnected before the boat is relaunched.
Whether leaving pipes disconnected or not, now is the time to grease and service the seacocks, to prevent them seizing up over the winter.
Bilge water
And it is no good getting rid of every drop of fresh water if you forget about the bilge. One problem with many modern designs is that the bilge is relatively flat, and so almost impossible to empty, even with a bucket and sponge, never mind the bilge pump.
So at laying up time it is a good idea to lift the floor boards and get into those corners where water seems to get trapped, no matter how many limber holes are provided. A thorough clean, to get rid of all the salt will pay huge dividends. Not only will the boat stay drier, she will also smell far fresher come the spring.
Ventilation helps to prevent condensation and therefore damp, but you have to balance the benefit of letting the boat breathe with the danger of letting in rain water.
Dehumidifier
If you have access to shore power, it's kind to the boat to leave a dehumidifier running.
The internal reservoirs fitted to most dehumidifiers don't hold enough to keep the machine going for more than a few days, requiring regular visits to the boat to empty them
If it can be arranged so that the machine drains directly into the sink, so that water collected runs straight outboard, this problem is solved. Make sure though that the dehumidifier is secured in position, as they are heavy and a fall from such a height could do serious damage.
Alternatively, choose a dehumidifier than can be adapted to drain into a larger, closed container.
Leaving cabin and locker doors open will enable the benefits of ventilation and/or the dehumidifier to reach all parts of the boat. Taking doors and floorboards home for varnishing would be even better…..
One word of warning. Don't expect a dehumidifier to miraculously restore anything that is saturated with salt water. We know of a racing boat where the crew weren't too fussy about flinging wet spinnakers down below, or sitting around in soaking oilies, where the bunk cushions were effectively destroyed by the dehumidifier.
Once all the water was taken away, sharp salt crystals remained, which cut the foam to ribbons, making the cushions flat and hard. The moral of this story is that before anything exposed to salt water can be dried properly, it first has to be rinsed!
