The effects of Salt water and humidity?

Discussion in 'Boat Design' started by chrisyk, Feb 25, 2013.

  1. chrisyk
    Joined: Dec 2012
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    chrisyk Junior Member

    I am investigating the potential of natural ventilation on marine platforms. With some success I have been able to tabulate the effectiveness of a range of passive design technologies however, often they require large apertures which permit good air flow but carry the following risks:

    1. Safety/security
    2. Infiltration of water and debris
    3. Infestation of animals and insects
    4. Infiltration of humid air and salt water

    1 - 3 have a range of different solutions all of which will effect the air flow rate to some degree but can be configured suitably.

    However, I want to ask this forum how they might tackle the issue of salt water and humidity? Is this even a big concern? What are the effects of salt water on the interior? What are the signs of salt water infiltration?


  2. Stumble
    Joined: Oct 2008
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    Stumble Senior Member


    Salt laden air is one of the worst contributors to corrosion on a boat. The problem is that small salt crystals will land on surfaces and because they are hydrophilic will pull water out of the air. This creases a super high concentration brine that forms the basis for crevice and pitting corrosion.

    The best ways to limit this damage are to switch to different materials (aluminium, stainless, titanium) all with different resistance, cost and weight implications. Add a coating (paint, epoxys, enamels, ect) that have large lifetime and service costs. Or to be ble to easily and frequently wash the area with fresh water (expensive and labor intensive).

    The humid air itself I don't think of as a problem, except for its effects on living confort. So application specific issues more than general issues.
  3. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    My engine room blower has now run more than 15,000 hours. I dont know its Flow rate, but it is substantial... 250mm intake. I have no corrosion at all in the machine room. My steel tools are free of corrosion. The engine room air is pulled thru a standard HVAC filter. Filter is changed every 250 hrs . Air intake is thru a standard dorade style drained box located in the steering cockpit.


    Engine room and galley air is vented thru the cabin sides via drained vent boxes.


    I dont believe sea air is a problem on a sailing yacht. The yacht is now 20 years old. I see no signs of salt deterioration or humidity on the interior. 300,000 miles.

    Air conditioning and its condensation on ductwork is a problem...not natural ventilation.
  4. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    This is not a trivial subject and your questions would take a tome to answer properly but in a nutshell :

    Salt ‘mist’ is the culprit so the higher the intake the better and if you expect a lot of water particles to be in the air then a low velocity baffle arrangement with a filter is a good idea.

    The critical relative humidity of NaCl is 74%. Below this any deposited salt particles don’t absorb airborne moisture. Above 74% they may not either providing ‘t’ is above the evaporation point.

    Any marine structure should be designed and protected to cope with surface deposition of salt particles and condensation. Surfaces are coated or materials are sufficiently inert to cope with surface deposits of NaCl. So really that's not your concern.
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Living in a bay that is open to the prevailing NE winds I see the effects of airborne seawater numerous times each year, from reduced visibility in a sea breeze to thick salt crusts on all objects near the shore. The inevitable rain following a storm washes the salt from where it was deposited, so it winds up in unexpected places like the bottom of cars and other metal structures. In fact most signs of corrosion are not on the exposed parts but under them.

    The good thing is that airborne droplets are quite heavy; they cannot stay airborne when there is a sharp change of direction, so a simple deflector plate in front of a vent will stop the salt from entering the interior.
  6. tunnels

    tunnels Previous Member

    when salt water gets on any thing it will never dry out !! simple !! put a little table salt on a spoon and leave it sitting ou of the sun for a day then feel the salt its damp its drawn the moisture out of the air ! its never stops its a wonder of the natural world we live in !!
    To dry you must wipe and clean with fresh water and get rid of the salt !!
    It boats are shut up and have very little to no air movement they smell terrible after a while ! everything feels clammy and cold !! creepy sort of!!
  7. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Oh I don't know, salt isn't too bad, we'd be dead without it ! People even sit in salt-filled rooms as a health measure, supposedly to kill respiratory bugs.
  8. tunnels

    tunnels Previous Member

    Eat raw onions that gets rid of bugs and unwanted people !!! :confused:

    Finely chopped raw onion
    Finely chopped tomatoe
    Finely chopped whole garlic
    1/4 cup of sushi rice wine vinegar
    cover for 3 hours in the fridge
    Uncover and pour the juice into a glass then get a spoon and eat all thats in the bowl and then fdrink down the glass of juice !! :p
    Its yummy !!
    The sushi vinigar is the hard one to find and its not the same if you dont use it !!:D:p

  9. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I'd stay upwind of you Tunnels, 1 whole garlic is a lot, does it make a good paint stripper ?
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