J/30 Class Association

Hull cracks at waterline

Posted By: cnc123

Hull cracks at waterline - 04/11/18 10:53 PM

I am a new owner of a 1981 J30 that has a few hull cracks toward the starboard quarter right at the waterline (picture is attached). I am planning to launch soon and keep the boat wet all season, so I'm wondering how concerned should I be about the cracks? Can I just seal it myself with a tube of 3M 5200, or is this the sign of something much more involved? I'm planning to get it looked at by someone at the yard, but wanted to get any advice someone might have with a similar repair. Thanks in advance!
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Posted By: Coastie

Re: Hull cracks at waterline - 04/12/18 03:07 AM

It is always hard to be certain from a picture, but what it looks like to me is the remnant of a tape line from either painting the upper hull or the bottom paint. If it were a crack I wouldn't expect it to be so straight and in almost a perfect line with the waterline. What is more concerning long term are the blisters below the waterline.

Just out of curiosity has this boat been in fresh or saltwater primarily?
Posted By: cnc123

Re: Hull cracks at waterline - 04/12/18 08:31 PM

Thanks Dave. The boat has spent most of its life in the Chesapeake, mostly in the mesohaline zone (mid level brackish) which has up to 18 ppt salinity. I have someone coming out to see it tomorrow and will let you know what the verdict is. I took a closer look at it and it looks like there was some caulking from a prior owner that was starting to rot out. The layer of clear epoxy (about 1/8" thick) which looks like the original epoxy is brittle and falling out in some spots. So I cleaned out some of the older caulking and uploaded 3 new pictures. It is localized to one small spot on the hull and follows right along the midline from the bottom hull to the upper hull.

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Posted By: Coastie

Re: Hull cracks at waterline - 04/12/18 11:45 PM

I suspect you have a bigger problem here than just the crack which is serious. The opening will have allowed water to infiltrate the balsa core. You really need to get ahold of a moisture meter to understand the extent of the problem throughout the hull. The blisters alone tell me you likely have wet balsa below the waterline and that is unfortunately somewhat common in these boats.

This is all repairable, if you know how to mix a drink, if you did paper mache' in kindergarten and you can occasionally read some directions you can do this work yourself. If you have to pay for the work to be done that will be a tough one to sort out. You will need a few tools and some serious elbow grease. The guys on this site have been supervising me pretty successfully on a similar big project.

Your first tool to buy is the moisture meter. You need it for this boat and every other boat you might ever want to buy.



Posted By: Chris623

Re: Hull cracks at waterline - 04/13/18 02:29 AM

That's an odd one. My guess is that someone improperly did some invasive investigation of the core or someone improperly did a repair. What was wrong in either case is that when they put it back together, they did not grind out a 12:1 scarf on each side of the cut. Assuming that the outer skin is 1/8" there, that would mean that they should have ground out 12/8" (1.5") of a ramp on either side of the cut and laid in cloth and biax with different widths until the ground out area was filled. Without that treatment, any flex or stress that is applied to the hull would have cracked there at the weakest link.

As Dave said, the repair is fairly straightforward. I also agree that the $145 for an Electrophysics EP-33 or similar meter is a good investment, but as any good surveyor would tell you, there is more to it than that. Wet core isn't good and will lead to future problems if not addressed, however, the more important information to glean would be if the core is no longer holding the inner and outer skins at a fixed distance. This would be because either the core has turned to mush or the skins have delaminated from the core, which would likely be the result of a very wet core and numerous freeze thaw cycles. The tool to use here is a small ball peen hammer to listen for a good sharp report in the response to light tapping or a bad dull sound.

Good luck,

-Chris
Posted By: cnc123

Re: Hull cracks at waterline - 04/16/18 07:55 PM

Thanks everyone for the comments, both on the thread and through PM. I bought an 8oz ball pein hammer and got a bad dull thump all around the area in the photos with the cut marks. I also bought a cheap MMD7NP Moisture Meter because that is the only meter that was available in any store around here. Realizing that moisture readings are very susceptible to the method, I tried all four mode settings on the meter and they all defined roughly the same exact moisture area right around the markings. The area is about 18 inches horizontal by 6 inches vertical.

The source of the water wasn't hard to find: the bilge had a lot of rainwater which probably came in from the mast which was never dismantled prior to two years of being laid up (pic attached). The starboard aft quarter corner of the bilge has the lowest run off drain (given the current storage angle) which perhaps is supposed to run aft but if so, the channel is clogged forcing the water to run off to the starboard quarter aft storage compartment where it pooled up and eventually soaked through into the core (pic attached). As the temp froze and thawed over the past two years, the wet core eventually expanded and broke through the gelcoat in the exact location of a prior repair from what I would imagine was exactly the same problem.

That's the situation, now its time to get it fixed so that I can be out on the water instead of pacing the yard!

I've found some decent links to help guide a self-repair:

http://epoxyworks.com/index.php/common-errors-in-fiberglass-repair/

http://epoxyworks.com/index.php/replacing-damaged-balsa-core/


Here are my questions/concerns:

1) The repair quote I got over the phone was $500 per sq foot. I'd imagine the cutout area here will be around 3 sq feet, so a guesstimate is about $1500 which seems low given the costs I've seen by browsing the web. I'm leaning towards doing the repair myself though since it seems a small enough area. The boat is outside in a yard that is 100+ miles from my house, so I have to do this work in a yard without power and with the tools I can fit in my car.

2) Perhaps it is fortunate that the water found a quick way out and does not seem to have caused more damage. Which makes me wonder if I do a 100% job on this repair, where will the water go the next time this happens? Perhaps if I clean out all of the bilge drainage channels, I won't have to worry about it. But since this is the 2nd time this has happened in the boat's lifetime, I don't want to create more of a problem than I am fixing.

3) It doesn't seem like it is worth it to dry out the core using a vacuum and/or heat application. The outer shell has been compromised, so the core is most likely contaminated and rotted, and will have to be replaced. It is hard to imagine there is any structural integrity left in the balsa considering the sound of the tapping report which sounds similar to tapping mud.

That's really it. If anyone else has any advice, comments or links to help me on my way, it is greatly appreciated. Thanks to Chris for recommending Don Casey's book which has a good description of the recoring process.


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Posted By: Coastie

Re: Hull cracks at waterline - 04/17/18 03:49 AM

I agree that trying to dry this core would be a waste of time. While I have had OK results in some areas with heat and high vacuum the results are uneven. On my boat I have found it is just easier to peel the outer skin off and then evaluate whether or not the core can just be air dried or needs replacement. Often the replacement is very localized. But like today I just peeled the area under the galley sink drain and I think all of that core, from the through hull to the solid part of the center of the hull is going to end up being replaced.

To do your repair it is hard to imagine how get through it without some electricity. Renting a generator may be needed. There are lots of ways to cut the skin, but my preferred method is to use the 4" grinder with a thin metal cut off blade. I cut a pattern roughly 4" x 4" over the area I am working. Then you can use a flat pry bar and a hammer to peel the squares of skin off. If the sections are too large you really struggle to get the skin off. Once the skin is off in the area you are working you still have to get through the polyester resin layer. If the core is mush then maybe it will be as simple as scraping it away. My method is to again use the small grinder this time with some 36 grit paper is your friend. This is the hard part and you will need a respirator and long sleeves, hood or a Tyvek suit because the glass fibers are nasty. Once you are down to the end grain balsa a simple sharp chisel will let you slice and dice the old core up and shear it away from the inner skin. This is easy but tedious work. The inner skin is pretty thin and can lose its shape if you open up too large an area, but you also have to get the work done, so you make a choice and if you lose the shape you will just have to do more fairing at the end.

You have to clean the inner skin up too. If you are limited on tools then it is back to the grinder but use maybe 80 or 100 grit to get the remaining balsa and fillers off the inner skin. You have to be crazy careful with this inner skin or you will go right through it. I like to use a small pneumatic right angle grinder for this work with a 2" disc, but that will not likely be available to you, unless you also have a compressor. But you have to clean this inner skin up so the thickened epoxy can fully bond to it.

So once you have the old core gone in the area that you are working you next get to figure out how work against gravity. If you have a shop vac you can use it as the anti gravity tool. In this video below you can see how I use plastic and painters tape to seal the work area and then a simple sink drain as the vacuum port.

Rebuild

What I have found to be helpful is to use both Colloidal Silica and Micro fibers to thicken the epoxy in a rough ratio of 2 to 1. The reason I do this is that the micro fibers make for a much tackier mix so you can press your core into it and it will stay put for a while. In areas where I don't need the extra tack I just use the CS as the thickener. Once you have the core in place put your plastic over the work area tape it in place and tape your shop vac to the port (sink drain) and let it run. One thing you will have to decide is which hardener to use, fast or slow. For core work I normally use slow so the thickened epoxy has lots of time to move around and extrude to wherever it wants to go. But if it is not overly warm where you are working the fast would probably be fine and it would give your vac a break after a couple of hours running.

Then it is on to the replacing the skin.

I also suspect that the quote you got was very conservative. You really don't know what is going on until you get the skin off. And Chris is a great resource for this kind of stuff, he got me started and through a ton of this work.

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Posted By: cnc123

Re: Hull cracks at waterline - 05/25/18 04:32 AM

I finally got some time to open up the outer layer and see the core. It was pretty wet and rotted around the scar mark from the prior repair - see the first picture. I scraped away all of the delaminated core, mostly by hand since it was so loose. Then I let it dry a few days to see if any of the wet but non-rotted core was salvageable. After a few days I removed any remaining core that had no structural integrity left even after being dried out. I then sanded it down to the inner skin, exposed about 2 inches of further core just to get a good bonding surface. I ground out a 12:1 scarf as best I could with a battery operated grinder. My current state is shown in picture 2, its not perfect but it might be as good as I can get it. The repair area is 35" wide, by 17" high, but in an odd teardrop shape. As you can see, there are two pieces of foam on the two ends of the repair area, both from previous work done on the boat before I owned it.

I've been looking locally for some foam for the patch, anything like Divinycell, Core-cell, Airex, Klegecell and even Coosa board. I can't find any of the foams available, but I did find a seller of Coosa board which looks way to stiff for me to shape to the hull. I don't want to use balsa because I haven't done an extensive enough repair to be convinced that water will not find its way back to this particular area.

I visited West Marine and talked to a staff member about where I could find foam core material and he mentioned that I could potentially just epoxy/glass the entire area and skip the core altogether. His recommendation was to first mix some 105 and 404 to get the desired consistency (which is a wild guess for me), then break apart some fiberglass matting with my hands and mix that in, and once that is all done, add in the 206 hardener. Use that mixture for the entire repair area, and when I'm ready to fare it out, use the 410 silica.

The drawbacks of skipping the core I can think of are (1) it will be harder for me to follow the curve of the hull with an even thickness of patch work, (2) I have to spend more money on epoxy, and (3) the repaired area will have a different amount of flexibility than the rest of the hull.

The benefits are that (1) I don't need to buy core, (2) I don't have to worry about shearing, (3) epoxy and glass is probably stronger than a glass/foam/glass sandwich, and (4) water penetration is no longer an issue.

All of the West System manuals show core replaced with core, regardless of how large or small the repair area is. But many new boats seem to be all glass below the waterline.

So I'm stuck trying to figure out which route to take. Anyone have some advice? Thank you!

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Posted By: Coastie

Re: Hull cracks at waterline - 05/25/18 05:37 AM

You definitely want to put core back in, solid epoxy would be very hard to do and pretty expensive. Balsa is fine if that is what is readily available. I think one of your good east coast sources is Jamestown Distributor, so you can check them for prices. I have used Fiberglast because they had the selection of the kind of materials I was looking for and lots of information to go along with that material and they have 3/4" end grain balsa core.

Looking at your image I think you want to try and sand the inner skin some more, if you haven't already. Remember the bond strength is only as good as the material it is trying to bond to and that applies to the outer skin too. You will be wanting some of the low density filler too so you can fill gaps between core sections and square bits. I found it easier to cut out squares to fit the core. Just take some blocks of core, trace around it and then chisel the old stuff out until the new core fits in place.

You are on the right track and making headway. Feel free to text me directly if you have questions 503-369-5218 I really don't mind stopping sanding over my head to answer questions and commiserate.
Posted By: cnc123

Re: Hull cracks at waterline - 05/27/18 03:07 AM

As always, thanks for the great advice on this! I'll definitely take your advice on further sanding the inner skin. I forgot to mention that I'm probably not going to be able to vacuum bag any of the patch, just given the remoteness of the yard and the distance to a power source. Should that affect the decision on which type of core at all? If I go with balsa, can I rely upon natural forces to pull the resin into the end grain balsa and form a strong bond?
Posted By: Coastie

Re: Hull cracks at waterline - 05/27/18 03:38 PM

I think what I would do is to use blend of Colloidal Silica (CS) and the Micro FIbers at the rate of 2 parts CS to the Micro Fibers and use a fast hardener. You want to make a mix that is about the consistency of mayonnaise. This makes a tacky enough blend that when you press your core into it by hand it should stay put. If you organize your blocks well enough and the entire assembly fits in place tightly it won't sag. When you press the blocks of core into place maintain some pressure for a short bit to make epoxy extrude. Once your core is in place and the epoxy has cured you will get to sand that core some before putting your layers of glass back on. Once you have the core fair you will use the low density filler and trowel it over the core to fill everything including any remaining gaps in the core. Then more sanding...........
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