"Sweating" steel boat

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Veteran Member
Dec 2, 2008
I finally managed to get the last of the various hatch and portlight leaks taken care of.* The way I know this is that my steel boat has started "sweating" when I am gone!*
We've purchased a dehumidifier (which works great) but I wonder if I should put it below in the staterooms and use a fan above in the salon for air circulation or if I should put the dehumidifier above in the salon area and the fan below.* Any thoughts?


M/V Antipodes
As long as the fan does a good job circulating the air it doesn't make much difference where the DH unit is.

Having used one in a 48 footer in Maryland in the Summer I can say the amount of water removed in a day is amazing so make sure the water drains into something of adequate capacity until the boat is really dried out.

I mounted mine in the saloon and used a fairly large fan down below with all the internal doors and hatches open to make sure there was not a lot of*isolated volume.
Thanks a lot!* That was exactly the feedback I was looking for.* We initially used the DH unit in Alaska this last summer and you are right about the amazing amount of water that is removed!
Was your boat unattended for periods of time with the DH unit running?
Yes, we left it unattended for a week or so at a time. It had been left on its own for an extended period and things were pretty damp, not wet but it was pretty darn humid.

We use large DH units on big ships when we lay them up and it keeps them in fabulous condition, no rust, no corrosion so we decided to DH the little boat and found it really works great. The DH is part of the boat's gear now. We got one that*allowed us to*adjust the humidity desired so we weren't trying to dry out the world, just the boat.
Thanks for the info.* We keep our boat in Mexico where it's generally fairly dry but we have had increasing problems with some recent extended absences (up to 2 months) and needed to get a better solution.

needed to get a better solution.

IF power is not readily handy , the use of an attic turbine vent , 12 or 14 inch diameter should do the job.

In the slightest breeze they will pull air from the boat , and match the inside and outside humidities.

WE have left them in place during hurricanes with no interior water intrusion.

Aluminum with sealed ball bearings , any brand.

"IF power is not readily handy ..."

Along the same line, those little canister things with (I think) calcium chloride work pretty well too. It would take a lot of them to dry out a 50 footer but if you use a DH to get the*closed up boat really dry they might maintain a low humidity if the power is lost for some period.
It may be a good idea not to close it up tight. Leave some ports open, some in the hull and some up top. If you can get air movement while you're gone that should be some help. You will have most of you condensation problems while you are on the boat. Just the act of breathing puts a lot of moisture in the air. Air circulation is your friend.
"It may be a good idea not to close it up tight."

That's a valid point if the boat is not left too long. If the point is to preserve the fittings and fixtures then a full DH is the best long or longer term solution.

Ventilation will keep things what*our senses*interpret as "fresh" which is why we open all the windows and let the sunshine in when we "open" a house.**But for preservation and protection, nothing beats hermetically sealed and dehydrated.
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