Author Topic: A question for boat builders: Why no bungs on new foam filled boats?  (Read 129 times)

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Offline forensic

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Greetings, I cannot understand why boat builders do not use a bung to allow water incurred to drain out.
It will find a way into even the most modern boats with time: via a hatch, hairline cracks or lower and upper deck not being properly sealed.........
Also when the "cross pieces" get glassed in there should be a small canal for water to run out.
Filling with foam complicates this and i was wondering if a piece of hosepipe perforated along its sides and laid along the bottom of the keel/s wouldn't help circumvent expensive procedures down the line.
Then before the foam gets injected a length of greased steel cable gets inserted into the pipe via the bung hole.
Once the foam has finished curing the cable gets twisted out thereby allowing a clear passage along the bottom of the keel from one end to the other for water to drain out. Similar to an agricultural drain.
No more waterlogged comparments and no great expense either.

Hope this may be of some use to future builds.
 


Offline FishStyx

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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #1 on: June 30, 2020, 02:32:34 PM »
As far as most boat builders are concerned, it's a case of "what the eye doesn't see, the heart won't grieve"... It's ludicrous to expect that water will never make it's way into a hull.

For a long time now, I've been a proponent of bottles held in place with netting "bags" rather than foam. The netting bags should serve to keep the bottles together in the case of a catastrophic breach of the deck or hull. A big argument for foam is that it provides rigidity to a hull. I understand and appreciate this. But the downside of it is that foam restricts the exit of any trapped water. Further, relying on foam for structural integrity is all very well until the bond between the foam and hull/bulkhead/stringer components is broken. Granted, foam does have adhesive properties, but to rely on that for structural integrity, to my mind, is "planning to fail". Bottles allow free flow of water out of a well designed hull that has the correct limber holes in the structural elements.

If you are having a boat built, research a lot, agree with the builder beforehand on best practices and insist on inspections throughout the process. Speak to knowledgeable souls and question all but the obvious.
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Offline Rory mundy

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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #2 on: June 30, 2020, 03:17:18 PM »
because the foam in not supposed to absorb more than 1 % water if it does get a hole.  if filled properly there is no were for the water to go so a drain wont help

vidalbum

Offline forensic

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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #3 on: June 30, 2020, 07:31:40 PM »
Okay. That makes sense. Thanks

Offline Drago

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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #4 on: June 30, 2020, 09:14:44 PM »
Have to join this topic.
I would say if deck is properly sealed - you would not need to worry about foam type or if waterlogged or to have any drains  .
I am not mentioning names of boats . But I can say that our boats ( not all )  are terribly finished and also not properly designed from drawing board for deck to properly seal with hull . Wood Decking board not fiberglassed from bottom side , hatches not sealed ,  hatch drain pipes not sealed properly , transom poor glassing ( inside part ), live well poorly sealed so water splashes behind the joints ...  and I can go on and on .
Just look deep into a gunnel where meets transom . Push a goose neck mini camera and see the horrors of unfinished fiberglass with voids and pockets that sits filled with water .
1% absorption of water on PU foam is just a fact for temporary water exposure . Once you have trapped water under deck - over time foam will become fully waterlogged.
Way is to open multiple inspection points by using smaller stainless steel fittings and not those plastic rubbish once that crack and not seal properly  . I used small one 5cm diameter SS316 for near transom . Punch the hole in foam with thin wall pipe all the way to the bottom . Eject foam from pipe and see what you find . If dry you are very [size=78%]lucky . [/size]
[/size][size=78%]Then I used a large 12 cm on a deck and punched hole all the way down with 10cm thin wall pipe . Fill with silica gel and close the lid then open one day after . If your silica gel turned from dark blue to clear / you have lot of water trapped in deck wood or elsewhere . [/size]
[/size]
Way to check water logging is when itís cold weather like this . Then pull the boat from garage or a shade and place it that one full side to face sun . Leave it for 1 hr . Then start measuring surface temperature ( we all have now these digital thermometers  , I guess ) and if you have serious water logging you will pick areas (usually in lower part of hull ) where the temperature measures lot colder then rest of the hull ( obviously below deck line ) . Then you know that you have problem . Ideal job for this is with thermal camera, then you can see nicely the extent of waterlogged area.
PU foam does stick to fiberglass and it holds well until waters gets to it . When filling PU foam under deck through small openings - exceed amount of foam for 25% . Place heavy weights to support deck from foam lifting it . Lot of sand bags . Pour foam and close the holes .  Then foam will be lot denser and it will create lot nicer more solid waterproof crust and there will be also lot less voids  . That is a better way and how I would do it if I have to re foam under deck . You could also apply slow curing urethane before lowering the deck . Once foam catches to urethane , itís sealed much better.
Letís here more comments on this topic !


Offline FishStyx

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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #5 on: July 01, 2020, 07:29:48 AM »
because the foam in not supposed to absorb more than 1 % water if it does get a hole.  if filled properly there is no were for the water to go so a drain wont help


That's in theory... The reality is that over time, supposedly "closed cell" foam takes on increasing amounts of water. I've removed foam from a boat in order to get to engine bolts and it was just shy of waterlogged... I squeezed it and water literally came out of it like it was a sponge.


In a different incident, my foam filled Boston Whaler became heavy... I removed the motor and strung the boat up vertically from a gantry. Over a period of a week, I managed to drain a lot of water. I didn't measure how much, but at the time it was a great relief to me because I felt that my boat was going to be significantly lighter following the operation. but when I poked into the foam with a piece of round bar through the drain holes, more water dripped out. The boat was a huge improvement after that but the bloke who bought it from me (he basically bought only the motor... Boat was essentially free) told me toward the end of last year that it's become heavy again. Time to repeat the gantry trick. I offered to help him with it during December but we never got round to it.


The correct way would have been to remove the deck, strip the foam and opt either for sondor SPX or bottles , but for the particular boat, it would have been a drastic overcapitalisation.
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Re: A question for boat builders: Why no bungs on new foam filled boats?
« Reply #6 on: July 01, 2020, 09:44:47 AM »
There are several builders that do run drain channels under the foam. Just not many local ones. The last 3 builds we have done overseas have used preformed foam inserts custom made to fit into each compartment between stringers and bulkheads. It does not offer much in terms of structural rigidity (which is a questionable need) but is good at sound deadening.
Each insert is over dimensioned on the top by 2mm to allow it to be compressed and fit tightly.

 

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