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Old 08-10-2019, 10:47   #1
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Laying Up for Winter - Humidity

Hey guys,

I am laying up for winter in Croatia this winter for the first time.

Previously we have always been onboard and in warmer climates.

The boat will be in the water and connected to shore power. She will be left alone for 3-4 months.

What would people recommend in terms of steps to prevent humidity buildup? Obviously considering a dehumidifier but would, if possible, like to avoid the expense if it isnít necessary. Thoughts?
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Old 08-10-2019, 11:07   #2

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Re: Laying Up for Winter - Humidity

oops never mind
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Old 08-10-2019, 11:29   #3
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Re: Laying Up for Winter - Humidity

Weather on line suggests the winter climate is similar to the southern UK, is that likely to be true?

If so, then we stay in the water all winter. The only thing we do is to ensure the boat is well ventilated so humidity doesn't build up. We don't heat the boat. So whilst it is cold on board, we don't have a problem with humidity building up. On our first boat I tried to seal it up, it was a disaster and in 5 weeks we had mould. So lots of ventilation for us rather than risk electric widgets like green house heaters being disconnected.

Lift cushions, open lockers and doors and allow the air to flow around the boat. Scrub and dry bilges, remove all food to deter furry friends. Perhaps bleach and then empty the water tank. Top up diesel fuel tank. Ditch any petrol, it won't last. Sails off, dried and folded up. Rubber snubbers on mooring lines etc. Disconnect gas cylinders to be safe.

Solar panel for the batteries?

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Old 08-10-2019, 12:09   #4
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Re: Laying Up for Winter - Humidity

Ask around, because it really does depend on the local climate. For example, most of the year ventilation works well here (Chesapeake Bay). But in the spring, when the water is cold but the air is warm and humid, it can really sweat, and more ventilation only brings more water. It also depends on the boat design. My last boat ventilation was pretty good, but my new boat really needs a dehumidifier in the spring.

Some will say "ventilation only." With exceptions, they don't keep their boat in the water through the winter and don't know about early spring. It is all about the difference between air and water temperature, and whether it is humid.

Remember this is "either or." If you use a dehumidifier, you must close all openings. The dehumidifier can actually be very small.
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Old 08-10-2019, 14:41   #5
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Re: Laying Up for Winter - Humidity

I use a dehumidifier on my 36' catamaran and swear by it. I have one small unit that keeps the entire boat below 30% humidity and only runs a fraction of the time, we're talking a few bucks a month in power. One thing to keep in mind is that the intake to the dehumidifier will freeze over if it gets cold (because that's how it works, cooling the air below the dewpoint, which if below freezing causes the water pulled out of the air to instantly freeze). Mine has a freeze cycle but I still have to go down once every couple weeks because it doesn't work well on the intake section and eventually it completely ices over. So I'd read up on reviews and try to find one that has a good thaw cycle if you're not going to be able to visit the boat.
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Old 09-10-2019, 12:57   #6
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Re: Laying Up for Winter - Humidity

We have laid up our boat at Milna, Brac just off Split for 5 winters afloat now from end October to early April, without problems. The winter humidity is quite low, and in fact the Bora is the most efficient dehumidifier, often down below 30-40% humidity.
We dry the boat out as well as possible, sponge out bilge and fully air all bedding, cushions, clothes. Stand up cushions, clothes and bedding in zippy plastic bags. Leave lockers, doors and fridge open. No showers or other moisturising activities on last but one day. We book into an apartment last night to prevent sleeping and cooking condensation. We fill our water tanks ( but would empty them if on the hard) and we do not ventilate the boat over winter as we have no method to do so without rain intrusion. So far so good.

The big difference with say the UK is that the average humidity in coastal Croatia is much lower. The Yugo brings the highest humidity but even then the humidity is lower than a UK spell of SW weather. Rain comes in fewer short and very heavy chunks and many days in the winter are dry and sunny but cold. The sea water rarely goes below 13-14C.
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Old 09-10-2019, 14:32   #7
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Re: Laying Up for Winter - Humidity

Knee above give some of the standard sayings like opening up the interior of the boat for ventilation tetra. If you have power always go with a dehumidifier. Pay the extra money and get a very low temperature model. Also get a ozone generator for make one. They can be made from an old neon sign Transformer , stainless thot scrubber and small fan in a piece of PVC pipe. If you do not have power the only thing you can do is try to put a solar panel where the snow will fall off by lubricating the surface with silicone for cooking oil spray. Be sure to verify this will not destroy the surface material.
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Old 10-10-2019, 08:08   #8
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Re: Laying Up for Winter - Humidity

I would like to have as mentioned lots of ventilation but would add 2 or 3 Stor-Dry units. they have about a 60 watt element and very small fan that moves air. I have had great luck with them in the Vancouver BC area.
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Old 10-10-2019, 08:55   #9
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Re: Laying Up for Winter - Humidity

A small ($50) dehumidifier with a drain tube rigged to go into the gray water overboard works wonders. We close up, not ventilate, and run that sucker any time the boat is idle, like right now. No moldy books, no moldy matresses, nothing.
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Old 10-10-2019, 09:13   #10
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Re: Laying Up for Winter - Humidity

We wintered on the hard in Muskegon, Michigan (Great Lakes) for many years. We had a winter cover over the entire boat with bow and stern partly open to vent. As temperature starts to drop, condensing water rained down the inside. We finally propped all hatches about 50 mm open as long as they were away from leaks in the cover or blowing snow. We installed the summer hatch boards in the main companion way. (Screens). We remove all cushions, sails, soft material stuff to a warm dry place. We lift several floor boards to vent the bilge.
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Old 10-10-2019, 09:14   #11
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Re: Laying Up for Winter - Humidity

We stored our Leopard 39 in Deale Maryland this year for 3 months from May until the end of July. Closed boat tightly, no ventilation (otherwise there would have been water intrusion with rain plus HEAVY condesation from the water/air temperature difference as noted in other posts). We have a de-humidifier mode on our built in Air Conds which is extremely helpful. I talked to other boat owners in the marina who had excellent results with store bought dehumidifiers. Main issue with stand alone dehumidifiers is emptying the water they collect. Small expense in comparison to mold and mildew remediation without them. As noted by other posters, clean, dry bilges, all fabrics aired out and bagged including cushions. Closet, cabin and head doors locked open, fridge/freezer defrosted, dried out and left open, same with ice maker. Close all sun shade blinds, put on hatch covers, whatever you have to do to keep interior of boat from getting super hot while sitting in the cold water. Fill water tank, put in small amount of bleach. Pump holding tanks, rinse with fresh water, pump out then fill with fresh water and add Exterminodor (holding tank treatment). Fill diesel fuel tanks and add Biocide (AJX fuel additive can't be beat. PRICEY!! but works miracles). I've had no problem with storing petrol for 90 days and longer provided it is Ethanol free and has the proscribed amount of petrol treatment added (I've had great results with Sea Foam additive). Lastly we put one large bucket of Damp-Rid in each cabin and in the salon plus we hang one Damp-Rid bag in each of the hanging lockers where our PFD's and foul weather gear are stored. The hanging bags get filled up in about 30 days, the buckets lasted the full 90 days in our environment. Thankfully we had zero problems with mold or mildew. The above procedures were used to keep the boat mold free for the 7 years it lived in a marina in Florida according to the original owner. It takes about a good day to prep the boat to this detail but it is well worth it IMO.
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