Today was the day I finally put my vacuum setup to work on MaJic Carpet. It took a bit of setup work to put all the little puzzle pieces together but I wanted to let all of you know that science is a good thing. I've known for sometime now that I could warm the hull pretty dramatically with a two burner Mr. Heater that I have. It is an infrared propane type burner. Today with ambient temperatures at about 55° I was easily able to get the surface hull temp to 200° and in fact even turned the heater down some. With the exterior at this temp the interior surface readings were about 80° so I was getting substantial amounts of heat into a very soggy part of my hull.

Within about 15 minutes of turning the vacuum pump on I was seeing moisture condensing in the vacuum line leading to my water collector. As I had suspected in the area I was working, I was only able to draw about 17 inches of Hg. and the pump is capable of doing nearly 25 inches of Hg. So the atmosphere is moving through this balsa, probably through the glass itself and the various small leaks in my setup. But as it moves it is picking up the moisture and taking away from the core.

I have no idea how long it would take to fully dry an area at this point. But the ramifications of this working are pretty substantial. In the case of my boat I had always planned on re-skinning the entire hull, but the fairing process will be much, much easier if I can leave the existing skin in place and do an appropriate repair for the saw kerfs and then cover the entire hull with new glass. As far as I can tell my balsa is also still pink, so when it is dried it should have the strength characteristics needed to maintain a very stiff hull.

I'm uploading a short video now that should be available in the next hour or so.

Vacuum Drying Balsa Core

I plan to run the setup all day tomorrow and and then will peel everything back and test the area with my moisture meter. I can take readings without peeling everything back, but I think to see what change has happened accurately I need get to the bare hull. If the readings tomorrow evening are still very high when reading through the plastic and breather cloth I may wait another day. In either case I will report results tomorrow evening.

Ok this is not a fast process, but it is working. I have run the heat and vacuum in this section for about 12 hours now. I just pulled the plastic and breather cloth off and have some good results, but this area isn't quite finished yet because some of the numbers are still too high. I suspect they will start coming down faster now that most of the test area has come down. What we also saw was that the areas above the direct test area were coming down too, albeit more slowly. There is a lot of wet area on this boat and as one molecule moves over and gets pulled out, there are several more to take its place. Checks inside the hull also showed small signs of improvement, but since the test area is directly below the ice box I can't get a reading there. So we will continue this project. I think I will enlarge the vacuum area when I start it back up in the morning with more kerf cuts to the rear of the current test area. I also need to work on condensing the moisture faster so that it does not go past my collector and start messing with my pump setup. It may be that I have to add some copper cooling coils or something to get all of the moisture to condense before it gets to the collector. Some percentage now is going past my T collector and is heading toward my vacuum reserve tanks and the pressure switch. So a couple of more tweaks to this setup are needed.

I will provide another update in a few days when we can see and report some more results. I wish this was going faster, but at least now it is going in the right direction.

This process definitely works, but it isn't fast. At this point in time after 2-1/2 days of pulling vacuum while heating I may have removed about 8 to 10 oz. of water from the area I have been working on. I'm on my 2nd setup for this area and basically the difference was that I enlarged the area I am actively pulling vacuum on. This 2nd setup has struggled to maintain 15 inches of Hg. and is often slightly less than that. What I do know is that the vacuum extends well beyond the immediate area under the plastic. The area that I had cut out the balsa core last fall is about 4' from the vacuum line. I started wondering if that open area was degrading my sealed area, so I battered up some new foam core and started pressing it into place and then started battering the transition edge between the new core and the existing hull. I was prepared to deal with the epoxy wanting to sag out, but instead it kept getting sucked into the cracks. I was finally able to batter over the entire area and I think that did make a difference in the amount of vacuum I was pulling. But this section still only gets to 15 inches of Hg., so there is either some leaking in my lines or more places in the hull that are helping to lose vacuum.

This morning I left the same setup in place and just lit the infra-red burners and turned the pump back on without changing anything. What is interesting is that there are areas above where I am pulling vacuum that have dried to to the desired level, but there are also areas directly under the vacuum that still seem to read high as well as areas that have acceptably dried out. So tomorrow I will pull the plastic and sealing tape off and cut a couple of new kerfs through those stubborn wet areas and then reseal and start again. I would like to stay with parallel kerfs, but I am wondering if a cross pattern might work better in terms of spreading the vacuum out better. I also will try using more breather cloth.

I have used one 7# tank of propane so far and just switched to the next tank. One part of the setup I did change was to add another 25' of coiled airline in front of my T moisture trap trying to condense more moisture out of the line before it hits the trap and that seems to be helping a lot.

So we are on our way to a dry hull, but I do have a lot of work to do before claiming total victory.

For anyone interested in pursuing this same approach here are some of the items and their approximate cost:

New vacuum pump, $350 plus about $100 for pressure switches, reservoirs etc.
Plastic film and Breather cloth, $100+
Two burner infra-rd Mr. Heater, $100
Propane, Estimated at $50
Moisture meter, $350
Infra-red thermometer, $20

Probably some other things I'm not thinking of. In my case the pump has utility well beyond drying the hull and doing glass work, so that was easy to add to the tool collection and I also had the Mr. Heater from other outdoor adventures. All of this is not inexpensive, but if I can restore the dryness of the core to normal levels and then keep it from getting soggy again the life of this hull will be dramatically extended.

Again it is important to know that the balsa in my boat has not decayed significantly, likely due to being in colder and milder climates and cooler water. Drying out molded core would be a waste of time, effort and money.

This process will be going on for some days. I will do another update with images in a few days when there is more to show for the effort.

So the process goes on. As I have said this is not fast, but it does seem to be effective. The work on my part is pretty simple. 1) Cut the kerfs in the area I want to work. 2) Clean the area that the yellow sealing tape is going to to be placed. 3) Put the tape on the hull and make sure it adheres well. 4) Get a rough measurement of the size of the patch being worked and cut film oversized, cut a very small X in the center and install the vacuum port. 5) Set up your breather system and tape it in place. 6) Take the film with the port and stretch it across just one side of your patch and then carefully pull and work the edges into the yellow seal tape. Trying very hard to avoid the film needing a "dart" which is a place where you stick an extra bit of sealing tape to take up extra film. 7) Attach the vacuum line and tighten the clamp dealing with whatever material you are using to protect the vacuum line from extended high heat. 8) Turn on the pump. 9) Light the infrared heater. Or something like all of this. Anyway it is not too difficult. 10) Stay in the area so you can check on everything once in a while and make sure your boat isn't turning into a torch.

Here us a look at a recent round working on the starboard side alongside the aft part of the keel.

Balsa Core Drying #2


Video should be up a viewable about 9:30 PM Pacific

In the three areas I have worked so far I think about 16 oz. of water have been collected. Some of the areas that have been worked did have moisture values that went back up a few days after working them, but they are still below the target level on my meter of 2. The vacuum is effecting an area larger than the patch directly under the vacuum film and the saw kerfs. I will have to watch this effect and decide how to deal with the areas further from the centerline of the hull. It may be that beside working the higher levels I will have to go back and do remediation in some of the lower or first areas I worked. I am resealing the saw kerfs in the worked areas with thickened epoxy and once everything is done I will sort out a plan to rework these saw kerfs with epoxy and glass followed by filler. Finally I will be reglassing the entire bottom of the boat, someday. LIkely going to get to take a pause while I deal with some carpal tunnel repair before getting to do some serious sanding.

Other work is progressing and I will do an update on that in the near future.

Dave,

Have you considered putting a terrycloth towel under the plastic sheet to help distribute the area you draw the vacuum? It may not make a difference since you have the kerfs and the vacuum will follow those lines.

ps - you can make your Youtube video display by clicking on this icon in the menu bar .
I edited your post to do that.

Bill what I am doing to better distribute the vacuum is using a 3/8" dowel wrapped in breather material that crosses over the kerf pattern. You are correct about the kerfs being the main conduit for the vacuum. I am also trying to get the vacuum port to be very near this dowel and breather setup. Applying the plastic film to the yellow sealer tape is one of those jobs that would be much easier with another set of hands, but in my case I'm working alone most of the time.

Maybe by the time I am done with this project you will have fully trained me on how this site works. So we have lots of time for training.

Ok, those of you following this saga I need some help from you. Today I pulled vacuum on the port side about the middle of the keel. Several things were different today. First we clearly were in a wet section of the hull. From the get go it was like sucking on a straw. I think moisture would have slowly dripped out of this section of the hull without any help. As soon as the vacuum was on there was moisture moving toward the pump even before the heat was applied. But we were also getting a much higher vacuum level than any of the other patches I have worked, in the range of 20 inches of Hg. vs. 10-12 Hg or less. I also made some minor changes to the vacuum line to keep it more open. Then I added a bucket of water to put a section of the cooling line in water before it hit the trap. So several really important changes, but the thing that is incredible is that I just pulled about 32 oz. of water out of this section in about 8 hours.

That is more water in one section than I got from the three others combined. The visual saw kerfs into the balsa don't look much different than the others I have done, nor does the apparent color of the balsa through the skin. There is evidence of either a lot of fairing in this area, or previous work, no way to really tell the difference.

My inclination is to say that this area is way beyond being dried and is in the process of turning to mush. I am OK with replacing the balsa, I just don't want to do it where it is not necessary. The advantage of maintaining the external skin for fairing is huge.

I need some operating theories before I decide to waste this outer skin and replace the core. So some suggestions would be really appreciated here. I just don't want to waste that skin if it isn't really necessary. So let me know any suggestions and ideas you might have here. I would much rather read bad suggestions than prematurely kill this skin and core. I can also go quickly test any ideas that you might have. But I do have to move through this area in the next day or so.

When i was having judicious done they were taking just over 2 Litres a day out of the dehumidifiers after a 12 hours shift and the core was fine.I think it took about a week before the numbers began to fall.

Dave,

That section near the keel is a low point and was really saturated on Rhapsody with wet laminate that needed to be ground out and built up again, along with the area in the aft section around the keel joint being saturated. See this post.

The water that is coming out of this patch and being collected is fairly clear, but there is some dark nasty stuff staining the breather material. I am working under the notion that black balsa is too far gone, is that the case? Or is there a better way to decide without exposing a bunch of it?

Right now I am inclined to continue cooking this patch for a while. But when I do pull this plastic off I may remove a small section of the skin, maybe a 4" x 4" piece to get a better idea of what is there. Or maybe drilling some 1/2" holes to see what comes out. I can imagine that it is possible to dry rotten balsa out if you work at it long enough.

The patch that I am working now is on the port side about the middle of the keel and almost under the water tank, so not quite in the false bilge area.

Thanks for the help and the inspiration:-)