As far as I could make out, the spate of fires caused by dehumidifiers last year was due to them not having the filters changed or cleaned.... but dont quote me on that.
I left ours on in Lagos for weeks, but invariably came back to find it off due to the marina supply tripping and being turned back on.
Wish I hadnt bought one with an electronic switch!
As said, its OK as long as its in good nick. However, you dont want to dry out the boat too much, especially if there is lots of teak or whatever in the cabin. One suggestion is to put a timer on the mains socket and run it for say one hour a day - keeps the electrickery bill down too.
Otherwise, just leave it on a low setting.
I stand mine over the galley sink so it drains, but put a mug or bowl under the drain pipe which in turn overflows into the sink. That way, I could tell if there had been any water collected from one week to the next.
Not really - the air circulation alone, when you are at the boat, is a good thing. In one day, you could bring down the humidity quite quickly, then as soon as you open up the cabin it would go back up again prior to you going home.
As others have said a time clock is the best solution. Run the dehumidifier every day in daylight hours (when the temperature is highest and the dehumidifier most effective) for a week, then progressively drop it back so its on for just a few hours every other day as the boat dries out.
For the first few weeks its a good idea to open all the lockers, lift the boards and put the cushions on their sides - then also have a fan on the timer as well so that the air inside the boat gets really moved around and all the nooks and crannies get dry.
Dont forget to seal all the vents and hatch otherwise you will be trying to dry the marina
Dehumifiers are remarkably effective and inexpensive to run if you follow this strategy and if you sleep on board during the winter its nice that the bedding feels dry and warms quickly
We leave ours on all the time in winter on a medium setting; never had any problems & everything is nice & dry & it warms the boat a bit too. Also leave a couple of fans on to circulate the air - all vents sealed up etc..