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Old 19-08-2012, 14:53   #16
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Minaret - Thanks for all of the great info! It sounds simple ... kinda!

Hauling out next month - will need to first locate the source(s) of the water intrusion. The yard said that with sustained vacuuming, sometimes the source of the leak can be found by a telltale "whistling" of air - does that sound logical, or just too-good-to-be-true?
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Old 19-08-2012, 18:25   #17
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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Minaret - Thanks for all of the great info! It sounds simple ... kinda!

Hauling out next month - will need to first locate the source(s) of the water intrusion. The yard said that with sustained vacuuming, sometimes the source of the leak can be found by a telltale "whistling" of air - does that sound logical, or just too-good-to-be-true?
Oh, no, very logical. I have found leaks 20' from the area in question like this. It's surprisingly common. It's when you can't find the leak that there's a problem. Anyone who's spent time vacuum bagging will be very good at this, that's how you find pinhole leaks in a bag too. If you're doing a big 80' long bag laminate you get really good at listening for leaks. We keep our vacuum pumps in a shed outside the building and run the hose from it so we can listen carefully, all tunes go off when bagging.
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Old 20-08-2012, 10:30   #18
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

I use a "Spy Ear" listening device I got of of e-Bay for $2

Don't laugh, it works well at finding leaks in a vacuum bag!
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Old 20-08-2012, 10:39   #19
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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I use a "Spy Ear" listening device I got of of e-Bay for $2

Don't laugh, it works well at finding leaks in a vacuum bag!

Lol! I used one in the shop once and got laughed at pretty good. I own a pretty nice one made for hunters, I use it for paintball a lot. Ssshh, it's a secret...
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Old 20-08-2012, 10:42   #20
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Knotty, if you're doing infusion you should consider the 5 gal bucket resin trap. The advantage is that you can pull the lid off, flip it upside down, and smack it with a hammer to drop the resin disk, then just put the lid back on and you're ready for the next round.
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Old 20-08-2012, 11:21   #21
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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Knotty, if you're doing infusion you should consider the 5 gal bucket resin trap. The advantage is that you can pull the lid off, flip it upside down, and smack it with a hammer to drop the resin disk, then just put the lid back on and you're ready for the next round.
My trap has a screw out lid on the bottom that I've soaked with lanolin. So far I haven't gotten a drop in the trap! "Knock on Wood".
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Old 05-09-2012, 19:19   #22
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

Minaret -

Great information! Thanks! Some questions on your mentioned home-made hotvac ...

I've got my UNIQUE vacuum contraption set up with a 1/2" tube leading to a home-made manifold in each bilge - from there - 6 - 1/4" tubes. Each of the 1/4" lines goes into it's own hole thru the inner skin, but between each hole & manifold, it passes thru a pint mason jar so I can see the volume of water coming from each hole. I only fired it up for about 45 seconds today & the wettest hole produced almost a 1/4 pint, so I shut it down. Tomorrow I'm going to install a large water trap before the vacuum pump so I don't get any water into the pump from the overfilled mason jars! That will hopefully be a temporary problem, as I assume the majority of the water will be sucked out the first day or two, then I'll go back to using the mason jars to see what each hole is still producing.

I've read your description of a home-made hotvac & I have a couple of questions:

What type of electric blankets do you mean? You mentioned 2 -3 - do you double/triple them up?

Since I'm already committed to only working from the bilge & already have a set-up running, could I continue with my method, increase the number of holes, use the electric blankets but skip the bagging? I assume the bagging is only to make it easier & not have individual tubes going to each hole?

Thanks again for all of your help!

Russ
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Old 05-09-2012, 19:57   #23
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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Minaret -

Great information! Thanks! Some questions on your mentioned home-made hotvac ...

I've got my UNIQUE vacuum contraption set up with a 1/2" tube leading to a home-made manifold in each bilge - from there - 6 - 1/4" tubes. Each of the 1/4" lines goes into it's own hole thru the inner skin, but between each hole & manifold, it passes thru a pint mason jar so I can see the volume of water coming from each hole. I only fired it up for about 45 seconds today & the wettest hole produced almost a 1/4 pint, so I shut it down. Tomorrow I'm going to install a large water trap before the vacuum pump so I don't get any water into the pump from the overfilled mason jars! That will hopefully be a temporary problem, as I assume the majority of the water will be sucked out the first day or two, then I'll go back to using the mason jars to see what each hole is still producing.

I've read your description of a home-made hotvac & I have a couple of questions:

What type of electric blankets do you mean? You mentioned 2 -3 - do you double/triple them up?

Since I'm already committed to only working from the bilge & already have a set-up running, could I continue with my method, increase the number of holes, use the electric blankets but skip the bagging? I assume the bagging is only to make it easier & not have individual tubes going to each hole?

Thanks again for all of your help!

Russ
Interesting approach. So, to be clear about the science involved here. When under a vacuum, the boiling point of water (ie the point at which water becomes vapor and thus easily removable) becomes steadily lower as the vacuum increases. So by combining the two (heat and vacuum), you get an effect whereby the water in the core will begin to vaporize and turn in to steam at a fairly low temperature, in this case about 170F. So you need both to achieve the desired effect. Just running a vacuum in the panels core cavity itself without a bag is not something I've done before, mostly because it would be hard to gauge this way, I'm used to getting a good vac pull in a bag, and the blankets work as a nice bleeder material so the air and moisture have a good area to travel in. This technique is not something I have done for many years, as we have had a custom Hotvac system for a long time which does the same thing in a much more high tech fashion. I would stick to using film to bag the blankets on myself, I doubt you could acheive the desired temps in the core otherwise. The bagging process holds the blankets right on the patch you are drying too. You want to get half a dozen or so blankets, sometimes you can get lucky at Goodwill and the like. The trick is getting the bag up to a steady 170F-180F, without any hot spots. Hence the use of a laser thermometer, and maybe stacking 2-3 blankets up to get the necessary temps. With a pro Hotvac you set it up and leave it running for a couple of days at a time, no worries. With a homemade gizmo, I wouldn't leave it running overnight unsupervised, a short in a blanket due to too much moisture could burn your boat. So dry time will be longer. But you still ought to be able to completely dry a section of core in 3-4 days of run time with this method, I mean really dry. This means the more blankets and the more bags you can run at once the quicker you will dry a hull. If you only have some patches I would think you could dry it quickly by this method.
Be careful using Mason jars, if you pull a really good vacuum on them I wouldn't be surprised to see them implode. I suppose if you gauge a hole in the inner skin and pull vacuum on the core it could still work without the bag, but it would be an experiment. Here is a link to an old thread elsewhere where people were discussing some of the basics of this stuff. If you Google about you will find other people have used this method to good effect as well...


Refrigeration vacuum pump for drying out GRP - Boat Design Forums
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Old 06-09-2012, 08:13   #24
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

couldn't one also direct one or two of those kerosene fired heaters (the ones that look and sound like a jet turbine) at the bottom of the hull too? That should heat up a large area nicely, the spacing could be used to regulate the temperature. But the noise would make it difficult to pinpoint an air leak.
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Old 06-09-2012, 08:59   #25
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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couldn't one also direct one or two of those kerosene fired heaters (the ones that look and sound like a jet turbine) at the bottom of the hull too? That should heat up a large area nicely, the spacing could be used to regulate the temperature. But the noise would make it difficult to pinpoint an air leak.

Yes. But they are expensive and finicky pieces of equipment. Most tool rental places don't have them. And the big 90k BTU models you would need for this cost a grand a pop or more. Blankets work great and are often dirt cheap. Remember that at -30 atmospheres the boiling point of water is something like 60 below zero. You just have to pull a good bag and apply even heat, while reducing the risk of overheating as much as possible.
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Old 06-09-2012, 09:03   #26
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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Yes. But they are expensive and finicky pieces of equipment. Most tool rental places don't have them. And the big 90k BTU models you would need for this cost a grand a pop or more. Blankets work great and are often dirt cheap. Remember that at -30 atmospheres the boiling point of water is something like 60 below zero. You just have to pull a good bag and apply even heat, while reducing the risk of overheating as much as possible.
I had no idea they were that expensive, I grew up in western Montana surrounded by the things during winter construction........just kicked them around and took them for granted!!
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Old 06-09-2012, 09:08   #27
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Re: Vacuum Pump Requirement for Drying Out Core-Cell

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I had no idea they were that expensive, I grew up in western Montana surrounded by the things during winter construction........just kicked them around and took them for granted!!

Yeah, I spent some time in the midwest around that as well. We run three, a pair of 60k BTU and a 90k BTU. I hate maintaining them, they require constant fiddling with, although we do run them ten hours a day for most of the year. Ever since we retrofitted all of them with marine water separator/filters, they have been less hassle. I would still use blankets myself, even though I have several big heaters available. It just works, and a bleeder material is needed in the bag anyway.
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