De-humidifier with external drain. Set humidistat at a comfortable level and let it get on with the job. I use a 500W Dimplex Coldwatch heater as well, with the thermostat set to frost guard.
<hr width=100% size=1>Think I'll draw some little rabbits on my head, from a distance they might be mistaken for hairs.
I can only "speak" from my own experience (boat kept afloat on S. Coast.), but I have had no problems. The heater keeps the boat at 5 deg C min and the de-hu is run on a time clock (morning and evening bursts). The boat has stayed beautifully dry and fresh, and has been comfortable and ready for use. I once tried running the de-humidifier over night whilst sleeping on board. Too noisy!!!
I now use a small electric fan heater when the boat is in use, a combination of warmth, air movement and ventilation seems to do the trick, even with four blokes on board.
<hr width=100% size=1>Think I'll draw some little rabbits on my head, from a distance they might be mistaken for hairs.
One alternative is just to ensure there's lots of ventilation. Use of dehumidifiers has only really started in the last few years, with the availability of cheap dehumidifiers. Before that, most people happily relied on ventilation.
Living aboard, and with no overboard drain but plugged into shorepower, we use a combination of
(i) dehumidifiers
(ii) an oil filled radiator (safer than electric fan)
(iii) ventilation
(iv) anti-condensation aides like ventair under the mattresses etc
(v) effective insulation
The real enemy is condensation so reduce the surfaces so if eg not aboard lift up all the cushions so air can circulate in lockers etc. Always did this on winter lay up of last boat with no dehumidifier and that worked fine.
our boatyard doesn't have much in the way of power outlets so last winter we switched from dehumidifier to leaving the hatches ajar (lewmar hatches can be locked slightly open). the result was at least as good and cost nothing!