Removing Water From Waterlogged Foam - Shop Vac

Discussion in 'Boat Design' started by kach22i, Aug 23, 2011.

  1. kach22i
    Joined: Feb 2005
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    kach22i Architect

    I did some debate on placing this in the Material section or the Design section, if the Mod's want to move it, go ahead.

    Removing Water From Waterlogged Foam - Shop Vac Method

    My Scat II hovercraft developed a water logged hull (2-part foam) condition after cutting some holes in the deck (+ hull) and leaving it uncovered for the better part of a winter four years ago. I posted a thread last year or the year before about the possibility that it would dry out on it's own. Much to my surprise after lifting the tail up today, it feels quite a bit lighter than what I remember two years ago, but still not as light as I remember before the cutting incident.

    Article on moisture meter usage:
    http://www.yachtsurvey.com/moisture_meters.htm

    Another moisture meter article:
    http://www.pbase.com/mainecruising/moisture_meter

    Does anyone in SE Michigan have a moisture meter? I'll come out to you, drop me a PM. I'd like to know my starting point and find the problem areas to focus on.

    Removing Water from a Boston Whaler Hull – Foam Waterlogged
    By Steve Cole
    http://infozing.com/bostonwhaler/removing-water-from-a-boston-whaler-hull-foam-waterlogged/
    [​IMG]

    The article above is for a fiberglass hull, not a ABS plastic hovercraft hull, but I'm sure adjustments can be made.

    The real question, does anyone here have experience or know someone with experience using the shop vac method?

    Does it really work?
     
  2. viking north
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    viking north VINLAND

    Thats a million dollar question. I haven't heard of anyone attempting this proceedure before but I should think it's possible however extracting it thru one 3 in. hole and mulitple intake openings with a shop vac might be a problem.(not enough air flow) If it were placed in a small room with a de humidifier using multiple openings it should work but using a vac system ? Here's what i'd try. Multiple small openings over the surface say 1 in. dia and a 6in. 2hp. dust collector attached to a 6in. hole whereby you can adjust the intake leakage to prevent the unit from air starvation, overheating and burning out. This increased much larger volume of air should draw the dampness from a much wider area and as the water is drawn out near the intake one could adjust to reduce the intake leakage to compensate and create more vacuum for those areas further away. You could actually control which areas to dry by taping over selected intake holes.Will it work ? I think it will but time is the unknown factor here. Good luck--Geo.
     
  3. masalai
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    masalai masalai

    Hi George,
    I do not know how "grabby" A-B foam is to water/moisture... My guess is that with 2 frozen winters the cellular structure would have collapsed in the expansion stage of water turning to ice and in the summer, of the ice melting (eventually?), and evaporating, growing vegetative matter, and what else?

    Maybe drying with petrol and matches may be the end solution? (after taking a mould, if the shape was worth preserving/replicating)..., or cutting in half so the foam could be removed, and an A-B foam mixture poured in again to eventually glue the two halves together again...

    To test the water retention of the foam put a sample weighted down so as to remain underwater and freeze and thaw several times in your kitchen-freezer... You may then have an idea as to the integrity of the foam innards...
     
  4. kach22i
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    kach22i Architect

    Interesting point, but a hovercraft is not a boat. The hull will never be subjected to pounding waves.

    There are controlled splash downs, called plow-in. And some of these stops can happen on land, ice, mud or water. Maybe I should be concerned.

    The articles I've read showed balsa core, the core was turned to pulp after a cycle of freeze-thaw after getting water logged.

    Foam was reported to get spongy under the fiberglass deck, something I've never had an issue with. Not that I've noticed anyway.
     
  5. PAR
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    PAR Yacht Designer/Builder

    You know, this is what makes the internet suck. I've had more then one shop vac apart and I can tell you with complete certainty, that if you use one as a suction pump, like that guy "supposedly" did, then it'll die a fairly quick, bearing screaming, smoky death. The air flowing through the vacuum is also what cools the motor, so if it's sucking a plugged load there's next to no air being sucked in (only one fan) so the plastic gets hot, deforms, the bears lose alignment, the turbine loses alignment and the whole shooting match literally melts into a smoky noisy mess.

    Lastly, if you're so uninterested in your boat, that you can afford to wait a few years as it "dip dries" it's foam (it'll never completely dry folks), then why bother killing a shop vac!
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Looks like there's a market for a vac that doesn't use air from the suction hose to cool the motor. They are probably available, I'm guessing.
     
  7. viking north
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    viking north VINLAND

    PAR is 100% correct thus as I stated in my prev. post if you allow intake leakage sufficient to keep the motor cool (if this is even possible ?) then it might just operate long enough for the experiment to produce an answer. Dust collector vacuum systems tend not to be as sensitive to overheating due to the design and the heavy motors being exposed to the cooling effects of open air. To be honest other than long term storage in a small room using a de humidifier, I think the only other option is dis assembly to remove it.
     
  8. masalai
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    masalai masalai

    Not so much the "float-ability" but the structural integrity/strength where the foam & glass are not bonded and holding things in place... "plow-in" could cause greater damage to the passengers where the structural integrity is lost because the foam has disintegrated...

    Dig the muck out or dissolve it with a suitable solvent (ascetone?) then cut the body in two parts so that some A-B foam can be poured in, then same on the other half remove excess and bond back together and tape with your usual GRP system, bog/sand (fair), bog/sand (fair), bog/sand (fair), bog/sand (fair), then go through the usual paint processes to bring it back to a use-able but slightly heavier hovercraft body...
     
  9. kach22i
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    kach22i Architect

    Thanks for the input, I saw the idea and something looked wrong. First off the suction of a shop vac depends on air being fed to a fan of some kind. If it's trying to draw air though a fairly solid foam then it cannot breath. The cooling issues aside, fan stall will be the problem and therefore I cannot imagine this working except in short spurts in a push pull fashion.

    The Dust collector vacuum systems seems to stand a much better chance of working.

    My long term plans are to replace the floor with Monopan, the exact thickness I'm still debating on.
     
  10. Stumble
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    Stumble Senior Member

    Kach,

    I am not sure a vaccume is really a good idea since it is very possible for foam to 'rot' the same way wood can when left wet. Not as badly in a hull that hasn't been used since foam rot depends on minor flexing causing hydraulic presure to build up, but the freeze thaw cycle would do the same thing.

    That being said I would think you would need to put the area under vacume, which means a real vacume pump. With the idea of bringing the boiling point down low enough that the water will vaporize. A shop vac doesn't have the power to do this, but a 1-200 dollar pump could. Take a look at the vacume infusion threads for suggestions.
     
  11. tom28571
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    tom28571 Senior Member

    Has anyone ever, ever, heard of water being successfully removed for two part foam? I haven't and doubt it can be done in any reasonable way. Some early FG Lightnings had this problem and the answer was either to cut out the interior surface and tear out the foam or pour in some solvent like gasoline and drain the residue.
     
  12. PAR
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    PAR Yacht Designer/Builder

    This is the point I attempted to make Tom, the foam will never dry out. A buddy in Arizona took the cap off his bow rider for stringer and sole repairs and still had wet foam a couple of years later, in spite of the desert conditions. I've personally never had any luck with drying foam, nor anyone I know. Cut it out and replace it.
     
  13. themanshed
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    themanshed Senior Member

    I've done vacuum bagging with a rather cheap vacuum pump from Harbor Freight. With the proper seal you pull up to 25 micron vacuum. I modified the pump to accept plastic tubing and built a "bong" type container to collect any fluids, in my case epoxy.


    Here is link to my webpage from prior request in building a vacuum system.

    http://themanshed.net/tms-20-trimaran/8-18-09-layup-and-vacuum-bagging.html

    http://themanshed.net/tms-20-trimaran/4-16-10-updated-faring-and-vacuum-information/?g2_page=2
     
  14. erik818
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    erik818 Senior Member

    A vaccum for wet vaccuming is designed with separate cooling air for the motor and does not have the overheating problem. I use them quite often for vacuming water, dirt, wet soil and unidentified stuff I don't want to touch. I've only bought cheap ones (around 50 euros) and I've only wasted one so far. I have no opinion if this is a possible way to dry the foam though.

    Erik
     

  15. rwatson
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    rwatson Senior Member

    You might be better off using the mechanical vacuum method.

    Tape a plastic bag together around and under the hull. making it as airtight as you can, with a manual valve on a piece of plastic protruding somewhere through the airtight seal.

    Leave about a foot of clearance from the hull, and put sand in the bottom.

    Now, open the valve, and raise the bottom of the bag ( sand and all as close to the hull as possible ). This will expel a lot of air.

    Now close the valve, and release the bag to hang clear. The weight of the sand should now be creating a partial vacuum.

    Repeat the process until you don't see condensation inside the bag.

    The partial vacuum is the most effective method for extracting moisture.
     
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