Ventilation - Dorades and ??

Discussion in 'Boat Design' started by CatBuilder, May 20, 2012.

  1. CatBuilder

    CatBuilder Previous Member

    [​IMG]

    Can anyone describe the various types of passive ventilation systems used on boats?

    I am familiar with the dorade box and cowl, but would like to find something that doesn't affect the lines of the boat - something that is somewhat hidden from view.

    I would also like to put a fan-assist in for those times where you need ventilation, but there is no breeze.

    Any ideas? All ideas welcome.
     
  2. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    I have had good luck with solar vents. They have a small fan powered by a contained solar array. Some even have batteries so they work at night. See the first 15 pages or so at http://www.marinco.com/files/media/guides/NICRO vent manual.pdf

    But basically for passive flow you need two things, a way to get air into the boat, and a way to get air out of the boat. For a boat on a mooring it really is as easy as a dorad cowling at the bow facing forward, and one at the rear facing aft. This allows for a crossbreese to generate inside the boat, thugh ventilation amount is dependent on wind speed. More vents just increase the amount of air flow, though it is necessary to try and balance the amount of air coming in with the amount going out. In this case you want at least as much outflow surface area as inflow, to keep the boat from pressurizing which will reduce the amount of air coming in.

    Other than cowlings, opening hatches and side hatches do the same thing, but are hard to keep open when you are not on the boat.
     
  3. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    I'm assuming you will be having opening windows so are we talking about bilge areas?
    Windows are the best but when raining you need to consider in-line fan units 12V.
    with a minimum hose diameter of 3" -5"" or 6" is much better with a louver opening or clamshell typr. Lourvers do not draw your eyes to them if painted the boat color and can br directed fore or aft. Where can you create chases so the piping is not sceen? Ceiling opening hatches are great but not with rain. Where are your return air grills going to be? And your supply registers" Main unit fan can feed the hole boat with fresh cooling air--easy to do this. Very low electrical draw also.
     
  4. CatBuilder

    CatBuilder Previous Member

    Rasor: I'm really thinking of those rainy days when it's hot out and you still need air flow. This is of particular concern in the galley.

    I have taken a new approach to my systems design and will be doing everything low energy / low weight. 180 degree change from my previous posts about air conditioning.

    So... I'm trying to first, set up passive ventilation, because it's so energy efficient and where we charter, it's nearly always windy. (we do not dock the boat except at the fuel dock momentarily)

    Then, I'm looking to set up some powered ventilation as well, but that's a different thread.

    Stumble: Good points about inlet and outlet air. We are on the boat 24/7/365 unless away from the boat, at which time it is locked up tight and docked or on a mooring. The major concern is those rainy, hot days. Another concern is keeping humidity down to keep the boat fresh and mold free.
     
  5. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Assuming a monohull, and letting you run with the ideas...

    Ideally I would have air flow from the front to the back, with the exception that heads should have a solar fan exiting the boat no matter where they are. Not just for smell, but also because of the humidity they typically have.

    This would mean either a solar vent or a dorade coming down into every room forward of the mast, then louvered doors so even when closed they vent. The salon typically wouldn't need anything since the companion way is likely to be open anyway. Then exit points in all rooms aft of the salon. These do need to be balanced though, so 4 dorades in means four out. Four Solaris in means four out, ect...

    I have never seen a boat this well done, but it's kind of the ideal I have always thought about. But then when we were in the islands we just opened the hatches, and if it was raining turned on the AC since there was typically no breeze during rain storms.
     
  6. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    I do not know of a passive system to remove humidity but there are systems that require power that will work and require low power needs. Without seeing your plans I cannot really assist you in passive design BUT it can be done. THERE IS NOW BEING USED a system that when running kills mold, destroys pollin, bacteria, and purifies the air 99%. Consider adding that to your heat and AC system. About $ 450.00. Will help anyway I can. Stan
     
  7. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Fly a tarp and open the hatches. Those little commercial Windscoop sails work just fine as well but you have to tack everything every six hours if you anchor in a river. You can make individual canvas covers for two-way opening hatches that work well also if you're not flying a tarp. All of which may be okay for a cruising couple who can choose their travel plans but none of it makes any sense at all for a charter cat. Put four to six little a/c s on it and have fun.
     
  8. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    You could build the dorade concept for water entrapment into the boat. Disguised as a "style line" all the way across the front of the cabin at the bottom (or top if your going to have a brow) and drain the water out the bottom of the bridge deck. You will have to create a way to close it off from the inside, but that should present no problem.

    A 2" tall vent 10' wide would net you almost 2 sq ft of ventilation.

    Steve
     
  9. CatBuilder

    CatBuilder Previous Member

    I think this is the answer, Steve. Great idea! I will have a brow and I can use that brow to keep water out of a very thin vent. Brilliant.

    And now that you mention it, there are a few spots to stick very low profile, custom made dorades vents (wide and short).
     
  10. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    "I would also like to put a fan-assist in for those times where you need ventilation, but there is no breeze.

    Any ideas? All ideas welcome."

    Our setup is to use large 6 inch diameter pipe for the thru deck stand pipe.

    The Dorade box could be wave swept off the deck , the heavy GRP stand pipe should remain.

    WE used plastic screw in deck plates , top and bottom on the stand pipe , to maintain water tight , and in winter as double seal during the heating season.

    The plastic deck plates are easy to carve holes in so we bought a bunch.

    With 12V computer fans the air flow is great and electric cost is low, BUT they unlike most DC motors can not be reversed , so an inny and an outy are required. Hot glue gun for assembly.

    Use a 24V computer motor and the air flow is much lower , perfect over a bunk.

    FF
     
  11. CatBuilder

    CatBuilder Previous Member

    Was thinking... On a catamaran with a hard top over the aft cockpit, couldn't you have all dorades/vents blowing into the boat in every stateroom, then just leave the aft door (or an aft deckhouse window) open as an exit?
     
  12. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Better yet, feed air off the hardtop down the support tubes. Can sometimes run a vent up and out the mast that will self draw quite well in sunny weather. Requires a bit of planning regarding the arrangement of junk in the mast. It's scarry how much water can come in a masthead. Better if you have external halyards for this because you loose a lot of draw at the halyard exits.

    The only downside to the hardtop roof source that I can think of is if guests were smoking in the cockpit.
     
  13. CatBuilder

    CatBuilder Previous Member

    Phil, what do you mean when you are talking about a "support tube?" Not sure which part you are referring to.

    Ah, the smoking one is easy! There is no smoking permitted aboard our charters! :)
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Lots of 4" Nicro vents. Put them everywhere.
    [​IMG]
    They're not as good as Dorades or open ports, but move enough air to keep the boat fresh and if you have enough (they're not cheap) you can probably get a level of comfort out of them. If you have an A/C'd boat, this is what you want.
     

  15. Angélique
    Joined: Feb 2009
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    Angélique aka Angel (only by name)

    Cat, you called these an "Excellent invention" - are they still in the race . . ? ?

    Good luck !
    Angel
     
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