The Offshore Voyaging Reference Site

Four Winter Layup Tools

I don’t think any boat owner would argue with the statement:

Moisture is the enemy of boat reliability and gear longevity.

And that goes double when the boat is laid up over the winter.

The above photo shows four useful tools in the battle against damp. Starting from the left:

Davis Air-Dryr 1000

Davis call this a “dehumidifier”, which is stretching the meaning of that word to breaking point. In fact, it’s just a small enclosed heating element.

Nonetheless, we have used these for years and find they make a real difference, but without any moving parts or the need to keep the temperature above about ~7C, which is required for a real dehumidifier to work.

We have three of these on the J/109: aft cabin, salon and head. We used the same three on the McCurdy and Rhodes 56 with good results, so three seems optimal even for bigger boats.

Ceramic Heater

Great to take the edge off when working on the boat on cold days. We don’t leave it on unattended.


We run this hard for several days in the fall, before it gets cold, to really dry the boat out. Makes a big difference. The one in the photo is overkill for the J/109, but sure does get her dried out!

Wet/Dry Vacuum

After the boat is all put away and winterized, we vacuum all the water and spilled antifreeze out of the bilges so it’s dusty dry. Makes a huge difference to how dry the boat stays over the winter.

Heated Storage Not Required

Our J/109 has been in heated storage the last three winters, but only because our boatyard converted all their buildings to heated. Sure, it’s nice, but expensive.

For years before that we laid up the McCurdy and Rhodes 56 in unheated buildings here in Nova Scotia, and in Maine before that, and even so, the above four tools kept her nice and dry.

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Petter Mather Simonsen

As the my boat is laid up in an area that freezes during winter, without heating on I would add add a small air compressor to the excellent tools above.

I use that to blow all the water out of the fresh water system including the boiler and taps. For me that is an alternative to use food safe anti-freeze, which is expensive and for one-time use only.

If it sounds useful, here is my process; I pipe the airflow through a ball valve so I can control the flow and rate and then connect the ball valve outlet to the fresh water pipe that exits from the fresh water pressure pump. Then it is just a matter of opening one tap at the time (including the boiler pressure valve) and adding a bit of patience.

Eric Klem

Hi Petter and John,

Blowing out lines does work in most cases but requires quite a large air tank. A little homeowner compressor with a small tank will likely have its pressure drop too low during each blow. The actual compressor size is not a big deal if you are willing to be patient and let a huge tank charge up. I used to blow out the lines on a boat with runs in the 60′ range and found that we needed a 50 gallon tank or the pressure would drop too much.

On our boat, I carefully pitched all the lines when I replaced them so that they are all pitched down to the lowest point. At that point, there are 3 different drain valves (tanks, hot, cold) that I just pull the plugs off and open then open all taps and I am done. This obviously is not possible on all boats but on smaller ones it often is. I also used PEX A with expansion fittings and one of the reasons I like doing that is that it is pretty forgiving of freeze damage.


William Murdoch

Tell me about your dehumidifier. Ours is the cheapest 20 pint per day model from Walmart ($150 a couple of years ago). It drys the boat, circulates the air, and adds 200 or 300 Watts of heat to the boat’s interior. It’s a compressor sort rather than a semiconductor sort.

Stein Varjord

Hi William and John,

I don’t know what a “semiconductor” dehumidifier is, (autocorrect?) but we have a compressor type (12 years) and an absorption type (3 years) dehumidifiers.

Compressor types work by heating the air and then blowing it past a cold surface, so moisture condenses on that surface, like in a fridge. This theoretically works down to 7C (44F) but IRL it just starts working around 15 C (60F) and needs above 20C (70F) to be useful. When it’s warm, especially with high moisture levels, this is definitely the most efficient dehumidifiers, and usually quite cheap.

Absorption dehumidifiers have an absorptive element, like a rotating disc with a material that will draw moisture from the air passing it. The absorbing element moves past the air stream and then into a drying chamber, and then another round. These exist in some variants, but in general are a bit quieter, cost more, are less efficient than compressor types at normal indoor temperatures, but keep working quite well even when the temp drops far down. Many of them work just as well in sub freezing temperatures.

We live aboard full time in Northern Europe, so we get plenty of both cold and moisture. We use the compressor type dehumidifier only in the day time and in the fully heated living areas. The absorption dehumidifier is in the guest hull (catamaran) that is usually kept around 10C (50F) but colder when the outside goes well below freezing. It always gives the same amount of water output, 2-3 liters a day at the low setting, no matter what temperature it sits in. Ours is a Meaco DD8L, which is a simple but good version of this type. Also gives heating to the boat. Other more fancy types often blow the hot moist air outside, which isn’t that smart…

We let the Meaco run when we’re not on the boat, as it’s a fairly simple low power unit, (and our insurance policy is good…) The compressor type is only on when we’re present and awake, usually when the indoor air is extra moist, like when drying clothes. I’ll certainly not buy another compressor type dehumidifier for a boat.

PS. IN case some think this would be useful for wet sailing days, the answer is nope, for both types. That’s like running an AC unit. Too much power for any normal boat.

Dick Stevenson

Ahh Stein,
You bring back good memories. Living a board over-wintering in London, we tried a couple of de-humidifiers before getting our Meaco DD8L and never looked back. It stayed with us for years and even became part of our cruising kit. When we hit marinas where we had electricity, we would haul it out and wring out many liters of water out of the boat and be more comfortable ourselves.
We never did figure how to dry the boat underway or at anchor when we lived closed up. The Reflek’s heat made a big difference, but was not the same as de-humidifying
My best, Dick Stevenson, s/v Alchemy

Stein Varjord

Hi Dick,

We also love our Meaco. 🙂
You also bring up an interesting point about interior moisture and a burning heater, be it a Refleks oil oven, a wood burner or whatever. They make the interior dry quite efficiently. It’s not complicated, of course, but for anyone wondering:

The burner is only running when the outside air is significantly colder than the inside air. While burning, it draws air from the inside of the boat and sends it out the chimney. Cold air comes in to replace it and gets warmed up. That heating of cold outside air contains the phenomenon of “relative moisture”.

Air moisture level is measured as a percentage of maximum moisture that can be absorbed by the air. That maximum is a 100% moisture level. How much water that can be absorbed changes drastically with the air temperature. Warm air can absorb many times as much. The same volume of liquid water absorbed into the same volume of air has a given moisture percentage at a given temperature and a totally different moisture percentage at another temperature.

Say the outside air is 0C (32F), and has a moisture level of 80%, which is very moist but not unusual in the winter. If it then gets heated to 23C (73F), that same air becomes able to absorb several times as much moisture. That means its relative moisture level might be just 20%, (just a realistic guesstimate, not calculated) which is very dry, and feels dry. It draws moisture from its surroundings. The exact same amount of water is still in the air as when it was at 80% at 0C, but that’s the magic of “relative” moisture.

When it gets far below freezing, it’s actually normal to add humidity in the boat, so the wood interior doesn’t dry out too much. However, this system only works with heating that constantly draws in cold outside air and heats it. Electric or propane heating in a closed up boat doesn’t have this effect. Also, the effect isn’t very noticeable until it’s properly cold outside.

Stein Varjord

Hi John,

All the expensive “professional” dehumidifying systems, from Munthers etc, use this method. However, they typically are larger units mounted in the guts of the boat, connected to the ventilation system. As mentioned, they get rid of the moisture by ejecting warm moist air out of the boat, which means cold and perhaps moist air must come in to replace it. The Meaco doesen’t and is much cheaper.

You’re right about freezing temperatures. The integrated water container is hard plastic and can be damaged by frost. We never have frost below decks, so it’s not a problem for us, but I know of others who have wanted to use it to keep the boat dry in winter storage but haven’t thought things through, in Norway.

We normally don’t use the water container. The unit just drains via a hose into the enclosed bilge, where an automatic pump removes it. Others put it high and drain to a sink. The unit does make noticeable heat, around 300W at the speed we use it and 650W at full speed, which is plenty to keep most boat interiors frost free. However, if using the container, it’ll stop when full and then the heating is off too… Same issue if it’s set to stop at a certain moisture level. We use it at the clothes drying setting. That keeps it running until we turn it off.

Dick Stevenson

Hi John and all,
We spent years overwintering in the UK and, to live aboard, one needed de-humidifiers (living aboard and closed up, we took out a liter and a half of water a day). Many stored boats, especially those stored in the water of which there is many as the water does not freeze, left de-humidifiers on all winter.
I know of one fire among the live-aboard community and every year there was a report or two of a de-humidifier fires on a stored boat. I have an aversion to leaving the boat plugged in all winter or leaving electrical equipment working.
Alchemy has been stored outside un-attended for many winters in cool to cold and damp regions. Our most successful tool against damage, mold etc. has been ventilation. We open all cabinets and nooks to air, especially in the engine area and leave the dorades open and the boat pretty much equalizes to the outside temps and humidity. Things are certainly not dry, but nor are they wet or even close to the petri dish that some boats turn into if left closed up.
In any case, we have experienced no problems.
My best, Dick Stevenson, s/v Alchemy 

Dick Stevenson

Hi John, Interesting about no moving parts. Sounds like a nice find. Dick

John Gulliver

We have our new to us Tartan 30 sitting in our dooryard in Maine for the winter. With the old standard stuffing box (keeping it simple), water in the bilge was constant. When laying her up I disconnected the bilge pump lines at the check valves and let that trapped water drain out. This hadn’t been done previously and though no ice damage resulted, the humidity was greater than desirable. After a bit of sponge work I placed a fan just aft of the anchor chain locker and pointed it towards the bilge and let it blow for a few days. Not a drop remained.
Also, not being a fan of antifreeze in general, I used the cheapest vodka I could find to protect the fresh water system from freezing. I hate the lingering taste of antifreeze in those first couple of tanks of “potable” water. For the head, I stayed with non toxic antifreeze. I’ll find out in May if I made the right choices.

Neil McCubbin

We use antifreeze when in cold climates, since we know from bitter experience that blowing lines dry is unreliable.
We have Tees in the suction side of the fresh water pump and the engine seawater intake
We pump the two FW tanks dry, close the valves on the outlets and open the Tee to suck antifreeze into the system until it runs out of all outlets.
Similar for engine
In Spring f’lush through. Since there is no antifreeze in the tanks, taste has not been an issue.
We have even used regular automotive antifreeze in Europe where the non-toxic « plumbers » stuff was not available.

Eric Ploumis


How does a one-time, pre-layup use of a dehimifier help? The minute you turn off the unit moisture starts to build up in the enclosed spaces. And doesn’t the air-dryer require a constant source of electricity? I store my J-108 (a 109 with a centerboard) in a yard where I can stretch an extension cord for occasional power but have no constant source.

Art Nacht

I just learned about desiccant dehumidifiers a few days ago. They seem to be popular in the UK with the Meaco line widely known and popular. In the US they are hard to find. I just purchased 2 19 pint Ivation desiccant dehumidifiers on Amazon. Has great reviews from people using them down to low 30s F. Fringe benefit is that they’re low wattage heaters and keep air moving.

I’m in the water year round in Annapolis and determined to have zero moisture, mildew, boaty smell, etc. It’s relatively mild here. Condensation problems occur when you get days in the fifties F when nighttime temps still plunge and water temps are cold.

I’m 100% winterized except for main diesel. I have a West Marine heater set to 300 watts in the aft cabin with engine access hatch removed. A digital wifi thermostat controller turns the heat on at 35 F and off at 38 F. I have additional SimpliSafe temp and leak sensors onboard. Alerts go to my phone and monitoring service, $19/month.

I live a few minutes away. Probably is what makes me comfortable having stuff running unattended.

I’ll report back on my experience with the Ivation desiccant dehumidifiers. I’m going to drain those to the bilge. I got the wifi units that monitor and control from a phone app.

Art Nacht
s/v Pixie Dust
Beneteau 49

William Murdoch

There is a video of the disassembly of the Ivation 19 pint desiccant dehumidifier on this web site. It is the second video on the page.