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Moisture underneath main queen mattress

Discussion in 'Mid-Size Boats' started by Helli M, Sep 3, 2017. Add this thread to a FAQ

  1. Helli M

    Helli M

    Joined Sep 3, 2017
    3 posts, 0 likes
    Catalina 320
    CA Victoria BC
    Hi. Re 2003 Catalina 320, we get a fair amount of dampness underneath our queen mattress after sleeping overnight. Board above water tank damp too and will attract mould if we don't air it out each morning. Does anyone have the same problem? I have mattress cover as well as bottom sheet on top of mattress. Any solutions ? Thanks :)

  2. Benny17441


    Joined May 24, 2004
    5,612 posts, 382 likes
    CC 30
    US South Florida
    It is hard to say as there are many variables but it seems there could be a condensation problem at the partitions that separate the interior of the hull and the interior of the cabin. While there is usually some water trapped in the hull stringers below the sole of the cabin an excessive accumulation could lead to increases in moisture throughout the boat extending to the stern and bow of the boat. Do you have rain leaks? Do you wash the deck frequently or take frequent showers inside the boat? It is a verified fact that using a propane heater or stove aboard induces humidity into the air. A person's breathing warms the air and adds humidity when exhaling which is significant over a period of hours. Ventilation usually reduces the problem if air flow can be directed to the problem area. It is hard to get proper ventilation when the air outside is cold and you are trying to warm the cabin to a comfortable temperature. This differences in temperature promote condensation. What can be done? Dry the boat by running a dehumidifier when at the dock, fix any leaks for either rain or plumbing, minimize the use of hot water in the cabin and create an air cross flow. Use fans to maintain air circulation (remember air does not flow around bends on its own). Basically think about all the ways humidity may be induced inside the boat and try to minimize their effect. Use fans and cross ventilation to promote air flow and try to maintain as little a temperature differential between boat compartments.

  3. jssailem


    Joined Oct 22, 2014
    7,216 posts, 2,753 likes
    CAL 35 Cruiser
    US Salem, Moored Port Everett WA
    Look at the "HyperVent Mattress Pad"
    I had a similar issue. This resolved it on my boat.

  4. ebuck97


    Joined Mar 16, 2011
    2 posts, 0 likes
    Catalina 320
    US Everett
    Hi Helli,
    I have an earlier model yr C320 and had a similar problem with that queen bed condensation issue and the "HyperVent" matt material resolved it for my boat. I have some additional extra material sections of the HyperVent that I have listed on Craigslist here in Anacortes, WA but haven't yet sold, if you are interested, please contact me via my regular email or call me as you not far away in Victoria, BC.
    Cheers, ed (425.387.0186)

  5. Don S/V ILLusion

    Don S/V ILLusion

    Joined Sep 25, 2008
    5,183 posts, 361 likes
    Alden 50
    US Sarasota, Florida
    May be impracticable on a Catalina but insulating the opposite side of the bulkhead/support should work.

  6. chuckwayne


    Joined Mar 20, 2004
    1,463 posts, 39 likes
    Hunter 356 and 216
    US Portland, ME
    the hypervent works. you can also install a froli spring system under your mattress - makes the typical mattress much more comfortable by adding a 1 5/8" plastic spring system under it, and lets in plenty of ventilation. we installed it in the aft cabin on escape, and after jealous complaints from the crew did the forward cabin too.

  7. ravenbob


    Joined Dec 21, 2017
    4 posts, 0 likes
    Jeneau 42
    US Keys
    We're liveaboards in the Chesapeake bay. The nights can get pretty cold, and like most boats, we don't have much insulation. We do have shore power though, and with shore power comes an (a drum roll please)...


    Oh glorious warm berth... After shivering in the salon (I exaggerate), we go into the aft cabin and slide into the pre-warmed bed and skoosh down into warm blissful sleep.

    Only one problem. The blanket keeps the warm air trapped against our skin. That's its job. So where does the humidity and air actually go? Down into the mattress. And, if the mattress is resting on the cold fiberglass, it condenses into water and BANG. The cabin starts smelling like a dank mildewy basement.

    We use Den-Dry. It lifts our mattress about three quarters of an inch above the fiberglass, and lets the air move freely, carrying the humidity away before it can condense, and what little does condense on the fiberglass evaporates easily, because it's not soaking into the mattress. It's sort of like hypervent, but cheaper and a bit stouter, with cross venting channels.

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