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Thread: ventilate engine pods

  1. #61

    Re: ventilate engine pods

    I had the bolts out one at a time. All good. Resealed.
    Quote Originally Posted by gazza2006au View Post
    This may be simple question but could the water be coming in thru the engine mounting holes?

    If the holes were never sealed with resin or a glue mix and the plywood around the bolt holes has assorbed water you will never get it to seal again

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  2. #62

    Re: ventilate engine pods

    Quote Originally Posted by micky flinders View Post
    The seal the previous owner employed was a mass of silicone goop.
    Once i replaced the inspection hatches and moped up the water trapped inside the Pods dried out.
    Okay, no worries. Apologies but I only flicked through the previous four pages and missed that detail.

    Assuming that (1) water was previously able to leak in to the pods and (2) soaked into the plywood, then aside from any possible rot issues, it would take time for that moisture to bleed back out of the ply. That would cause ongoing condensation issues.

    Condensation itself occurs when moisture-laden air cools below its dew point. Imagine you have a container of air that contains 10g of water vapour per cubic metre. That's what's called the absolute humidity (10g/m3).

    The capacity of air to hold water changes with temperature and barometric pressure though. Ignoring barometric pressure because it's not relevant to your issues, the relative humidity (% RH) of the 10g/m3 air in that container would be as follows for various air temperatures:

    11°C - 100% RH (the dew point for 10g/m3 absolute humidity)
    20°C - 60% RH
    30°C - 34% RH
    40°C - 20% RH

    As you can see, despite the actual physical quantity of moisture in the air remaining constant (10g/m3), the relative humidity varies with air temperature because warm air can hold a whole lot more moisture. 11°C air is saturated at 10g/m3 whereas 40°C air can hold up to 51g/m3.

    What this means is that during the day as your pod heats up in the sun, the capacity of the air inside to hold moisture increases and will wick moisture out of any damp materials (like the plywood). For convenience let's assume that absolute humidity ends up at 10g/m3 per the above figures. As the pod cools down at night, once air temperature drops to 11°C, then the air inside will be at saturation - it literally won't be able to hold any more water. As air temperature drops further, the moisture then starts to condense out of the air.

    That condensation typically occurs on surfaces because heat loss from the pod is occurring through the pod surfaces to the outside environment - ie the pod walls are the coldest place in the pod as the surrounding air chills down. Hence condensation occurs on the walls.

    So ... if you've dealt with the source of the moisture (leaking seals), dried out the pods (forced ventilation) and are confident that there's no rot, then you should pretty much be done. I'd probably just put DampRid containers in there for a while between uses to keep sucking out any remaining moisture, then see how it goes without.

    I wouldn't be keen on whacking permanent vent holes in them. Keep to the design intent.

  3. #63

    Re: ventilate engine pods

    Quote Originally Posted by micky flinders View Post
    And thanks Moephous for the Science. Helps me understand what i am trying to fix.

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    Following on from the science lesson, you can test it. Get a heat gun or a hair dryer and direct it into the pods for several minutes to drive out any moisture laden air and quickly seal the pods while still directing air to them. Check over a period of time that you feel should give you a result and if you still have the same issue then it is not condensation. Wet ply always is suspect and if water has been into the foam it will also be very suss depending on the type of foam used.

  4. #64

    Re: ventilate engine pods

    Thats a beautiful boat i reckon u should still call in the professionals

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  5. #65

    Re: ventilate engine pods

    Good idea. Will do. Will let you know how that experiment works out. I will heat gun one side and not the other to compare. Thanks.
    Quote Originally Posted by Dignity View Post
    Following on from the science lesson, you can test it. Get a heat gun or a hair dryer and direct it into the pods for several minutes to drive out any moisture laden air and quickly seal the pods while still directing air to them. Check over a period of time that you feel should give you a result and if you still have the same issue then it is not condensation. Wet ply always is suspect and if water has been into the foam it will also be very suss depending on the type of foam used.
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  6. #66

    Re: ventilate engine pods

    Quote Originally Posted by micky flinders View Post
    Good idea. Will do. Will let you know how that experiment works out. I will heat gun one side and not the other to compare. Thanks.

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    That sounds like an even better trial for an experiment.

  7. #67

    Re: ventilate engine pods

    Heat gun is a bit extreme i think resin melts or atlease softens with heat i know i have burnt resin off my metal roller a number of times

    Keep in mind the more plywood u dig out the less structure u have your really digging out the back bone to your pods the core

    Just call in a perfessional.

    He/she wont poke at your plywood and say yay or nah they will use a very expensive water meter and measure the moisture

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  8. #68

    Re: ventilate engine pods

    Quote Originally Posted by gazza2006au View Post
    Heat gun is a bit extreme i think resin melts or atlease softens with heat i know i have burnt resin off my metal roller a number of times

    Keep in mind the more plywood u dig out the less structure u have your really digging out the back bone to your pods the core

    Just call in a perfessional.

    He/she wont poke at your plywood and say yay or nah they will use a very expensive water meter and measure the moisture

    Sent from my SM-G900I using Ausfish mobile app
    Hi Gazza and Mickey
    Quality wood moisture meters can be picked up from a reputable woodworking shop, Carbatec, for less than $40. I would test ply moiture content first before ripping it out. Cheers SS.

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  9. #69

    Re: ventilate engine pods

    Sea, the professionals use units worth $700-$800 one was recommended by a shipwright on fb i think it may have been a coffs coast boat rebuilder but i have forgotten the name of the meter it cost $650

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  10. #70

    Re: ventilate engine pods

    Gazza . It would be good to have accurate moisture content of the ply.
    The boat is in Scarborough Harbour, Brisbane. I am not aware of any experts here abouts.
    I have watched a boat builder deal with wet rot. Step one: dig out the rotten timbers. Step two: rebuild.

    I am cautious about the ply strength. However, rotten timber has no strength. So as long as i only remove the soft stuff i am not making it weaker.
    Gazza's point is the rot could be hidden behind solid outer ply.
    Will a moisture meter really measure under dry outer ply?

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  11. #71

    Re: ventilate engine pods

    First of all my heat gun has a number of settings and it can be cooler than a hair dryer. Not talking about pointing it at any resin directly just in general direction, done it before without the resin even getting warm.
    Any reasonable moisture meter will measure through dry outer skin, after all they will go through 10mm of plaster. Not sure of the real cheapest but builders inspectors etc use them and the ones I've seen are sub $200.

  12. #72

    Re: ventilate engine pods

    Non-destructive moisture meters ('pinless' type) will read to depth 3/4" to 1" (19-25mm) depending on the meter. They typically use inductive/capacitive loops to measure the dielectric constant of the substrate. Water has a high dielectric constant; dry wood low.

    Mine is a Protimeter Surveymaster which retails for ~$1200. Not sure on the accuracy of the cheaper ones, but make sure they at least have an induction/capacitive scan function and not just resistance probes ('pin' type).

    Something like this (https://www.ebay.com.au/itm/4-IN-1-NON-INVASIVE-INDUCTIVE-MOISTURE-METER-318-/201117843289?_trksid=p2385738.m4383.l4275.c10) might do the job: Never used one so buy at own risk.

  13. #73

    Re: ventilate engine pods

    Will see if i can hire one. Thanks.
    Quote Originally Posted by Mopheus View Post
    Non-destructive moisture meters ('pinless' type) will read to depth 3/4" to 1" (19-25mm) depending on the meter. They typically use inductive/capacitive loops to measure the dielectric constant of the substrate. Water has a high dielectric constant; dry wood low.

    Mine is a Protimeter Surveymaster which retails for ~$1200. Not sure on the accuracy of the cheaper ones, but make sure they at least have an induction/capacitive scan function and not just resistance probes ('pin' type).

    Something like this (https://www.ebay.com.au/itm/4-IN-1-NON-INVASIVE-INDUCTIVE-MOISTURE-METER-318-/201117843289?_trksid=p2385738.m4383.l4275.c10) might do the job: Never used one so buy at own risk.
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  14. #74

    Re: ventilate engine pods

    Try get a good brand like Fluke the top end models

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  15. #75

    Re: ventilate engine pods

    Give me 2 weeks. Will report on the experiement and the moisture readings.
    Quote Originally Posted by gazza2006au View Post
    Try get a good brand like Fluke the top end models

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