Balsa core issues on the CD 16

Marco Flamingo · Posted: Fri Oct 02, 2015 11:22 am Post subject:

I just added some pictures in the Limpet file for those interested in balsa core problems. Sorry if it keeps others awake at night like it does me.

Mark

Sunbeam · Posted: Fri Oct 02, 2015 11:42 am Post subject:

Exactly why I went in and did mine ahead of time. Sitting at anchor wondering? I just couldn't.

(Having had the big re-core nightmare on a number of other boats where I never had the chance to own them before the damage was done.)

Off to look at the photos now, fortified with coffee...

Edited to add:

1) I want one of those barbed needles! I clearly don't have enough creepy medical tools. I mean, I thought I was doing will with just a few dental picks. Now I see I'm bush league Very Happy

2) I've noticed the uneven saturation with balsa as well. I didn't know the C-Dory's were vacuum-bagged (where they?), but even when doing things by hand this can happen. The balsa usually comes as blocks attached to a scrim. This is so it will conform to curves. What I usually do it open it up "backwards" over a 5-gallon bucket side or something similar. Picture a mango that is cut and opened up backwards ready to eat. Then I'll coat in the gaps with neat epoxy, then thicken it and fill all the gaps. Then when it's pulled back into normal shape, epoxy oozes out and the gaps are all filled.

On my 22 floorboards, this had not been done and when a structural issue (weak point) allowed water in, it just ran freely up and down the "halls" and spread the rot far and wide (these were floorboards I'd bought from another C-Dory, but they'd had minimal use).

But even with a tight job, I imagine the wood in some blocks is just inherently better or worse than that in other blocks.

3) As you mention, once water is in there it can be drawn to other areas of the boat by pounding, and also by a sort of pumping that can occur as the hull heats up and cools down in the sun. Much better if the water doesn't get in there!

You probably already know this, but on an area like your "square" cutout, take a sander or grinder and bevel back the good glass on the perimeter of the cut. Say something like 2" out. Then the new glass will get a good bond area with the old, plus it will be easier to feather out (and not make a hump). If you are re-using the old skin that you cut out (mine never come out in good enough shape to do this), then bevel the skin edges too. Kind of like how sheetrock is tapered where you tape it at the edges, if you've ever done that.

I also like to lay the largest patch in first, then the smaller ones (when putting back new glass). This seems to be counterintuitive, but is recommended by WEST System. Reasons are that the first layer gets a full bond, and also that when you sand and fair, you are only sanding material off the edges of the smaller patches. If you lay the smallest in first and then the largest layer on top (the one "complete" layer), then when you sand and fair you can be compromising the one full/best layer. Probably either way would work fine on your areas, but no reason not to do it the better way (it's no extra trouble).

These days the way I make a pattern for the new glass is to lay a reasonably "firm" layer of clear plastic over the hole (loose leaf section dividers made of translucent plastic work great), and then use a Sharpie to just trace the outlines of the patches I want to cut.

4) I hope the "tunnel" ends up being very short and easy to clean out.

I like how you are using this as a good reason to make some other improvements. Might as well make it an opportunity Thumbs Up

Marco Flamingo · Posted: Fri Oct 02, 2015 12:32 pm Post subject:

rogerbum · Posted: Fri Oct 02, 2015 12:58 pm Post subject:

Sunbeam · Posted: Fri Oct 02, 2015 1:55 pm Post subject:

I've bought them from both Fisheries Supply and Jamestown. I forget which, but one of them lists them more logically in terms of part numbers, etc.

That said, I'm not sure I'd use them for something like a nav light on deck. At least, if I'm visualizing what you mean, wouldn't you then have a Weld Mount stud flange on deck? Maybe I'm not quite getting what you mean.

I'm pretty comfortable with closing out the core with thickened epoxy, especially above the waterline. So for my deck fittings I have done one of two things:

1) Ream out core and backfill, then fasten with machine screws, nuts on the inside.

2) Ream out core and backfill, then tap the thickened epoxy from the top and thread in a machine screw.

I don't like to go back with "pointy screws" if I don't have to, but that's just my preference. It is possible to set pointy screws into green epoxy, or to cast them in place.

Marco Flamingo · Posted: Fri Oct 02, 2015 9:36 pm Post subject:

Sunbeam · Posted: Fri Oct 02, 2015 9:42 pm Post subject:

Ah okay, I see what you mean now. Well in that case, I do like the Weld Mount wire tie holders for small stuff like that (although perhaps the Xmas lights ones will work just as well). These are what I have used:

They make a few other styles as well.

http://www.weldmountsystem.com/products-fasteners-wireties.php

I'm with you on the screws in from the underside. Probably fine, but.... I prefer to have them attached some other way. So when I get a chance, I re-do them (like when I'm in there doing something else already).

jimicliff · Posted: Sun Oct 04, 2015 8:52 am Post subject:

Your project just blows me away, I've had a 16 now for 2 and half years. I don't have your core issues but I have done plenty to suite my many needs. Your pictues have shown me all the stuff I,ve been courious about.
Ideas I want to send your way are the fuel tank for one thing. When I started my boat renovation I wanted to put a fuel tank in the bow as well. I backed off because I could make a drawing, it's past my skill level. So I had a fuel tank company fabricate a 29 gal that fits behind the passanger seat on the deck. Mine is just high enough to make a great step into the boat as well as a great seat if you sit on a throwable cushion. With a Honda 50 it gives me a range of about 140 miles which has been fine for me.
I use my boat 98% of the time solo so this use of space has been fine. I have a Pelican cooler across from my fuel tank behind my seat so getting in and out of the boat is pretty easy. Hey when you want to drain your cooler I just turn it around open the drain hole and trim my bow up and turn on the bildge.
Oh it is also my opinion that the 16 needs trim tabs as well as a fin that fits on the engine. This boat cannot be trimed any other way. Its so light it bobs like a cork on the surface. When you get into chop you have to force that sharp bow down and it will cut like a knife threw the mess. I love this boat passionatly and I hope it serves your needs as well as mine still does. The 16 really is a "Swiss Knife"

san juanderer · Posted: Sun Oct 04, 2015 10:24 am Post subject: cored boats

Another sad result of a cored boat.
Reality is, water goes in much easier than it drains out.
Hard to believe that manufacturers are so careless when attaching things to a cored panel. But soon, they will not own it.
I had this experience with a boat brand that had a cored hull bottom, then I sweared off ever owning a brand that had wood below the waterline.
Had that experience.
alan

shellndanm · Posted: Sun Oct 04, 2015 11:21 am Post subject: core

I went through the same thing last year. Not sure if someone recommended it already, I would use nida core. If you are going to spend the time and money, why replace with the same material that could rot again.

I used progressive epoxy and 2 layers of bidirectional mat. I get the stress of the situation, but it will ultimately be a fun project and the boat will be better.

I just sold my c-dory and bought a Diesel flybridge. It has areas of rotten core and leaks etc. so you just can't win.

Marco Flamingo · Posted: Sun Oct 04, 2015 12:25 pm Post subject:

Sunbeam · Posted: Sun Oct 04, 2015 1:11 pm Post subject:

I don't have any problem with cored boats, because it's a good way to get stiffness without excessive weight and/or bulk (frames, etc.). And balsa is a great core material (has some properties that you still can't get in other core materials). The only problem is in construction methods that aren't ideal, and that's a problem for any material (fiberglass too).

Foam core has its own issues (which can be overcome, so I'm not saying it's bad, just that it's not a panacea). And also, even with a "non rotting" core material, I still don't want water in there, because it can still cause de-bonding problems (i.e. three separate weak layers - skin, core, skin). In some cases I worry that because foam core is "waterproof," maybe not as much care is taken to keep water out of the sandwich.

Anyway, this is just my opinion, but even as many horrible, messy, back-breaking re-core jobs as I've had to do (mostly on much older boats where I never had the chance to do any prevention), I still see many advantages to a cored boat. And hey, I bought my C-Dory and am very happy with it (however me being me, I had to go in and do some preventative work).

On the older boats (speaking of the 60's and 70's), I think one problem was that fiberglass was touted as "maintenance free!" Not like those old wooden boats you actually had to take care of. So of course people bought them and didn't do a thing for twenty years. Well, of course fiberglass is not maintenance free, and even if it were, there are still all the other things that every boat has (deck hardware, etc.).

It would certainly be nice if production boat builders took more measures to protect the core. You'd get no argument from me! On the other hand, the C-Dory construction is no worse than most any other production boat, and in some ways better. I used to be involved with builds where we DID close off the core (epoxy fill above the waterline; actual closing out with fiberglass below), but those were million dollar semi-custom boats, and a fair bit of the cost reflected the extra work and care that was taken.

Maybe there are - or will be - better ways to build than cored construction, but it does provide a stiff, very open boat (no frames in the way), which is part of what makes the 16 and its brethren such spacious, amazing boats for their size, plus light enough to trailer.

PS: Just a note to say, that I wish a production boat builder could do everything the best way, and then somehow educate the public such that they'd be buying the 50% more expensive (or whatever) boats in droves. However, I've never seen this happen in real life. Builders have their hands full just building boats, which is what they love to do. With small-run semi-custom or semi-production boats, there is a bit more leeway.

Also, as we can see on the forum, many folks with C-dorys (and other production boats) will never have a problem. They store the boat indoors or under cover, they re-bed, etc. There is lots of fun and adventure to be had using them and they are affordable for many people. And of course it is possible to do some preventative modifications, although I can understand the feeling that "one shouldn't have to."

thataway · Posted: Sun Oct 04, 2015 9:20 pm Post subject:

Thanks for posting the details and photos. I agree that the interior of the boat should have never been done with pop rivets, blindly into the cored part of the boat.

I wonder if the C Dory 16 was being vacuum bagged in 2004. My guess is not. I am quite sure that my 2003 C Dory25 was not vacuum bagged, and I doubt that my 2006 current 22 was vacuum bagged. Polyester soaks well into balsa core, and that is one of the features of balsa.

San Jaunderer states"

Marco Flamingo · Posted: Sun Oct 04, 2015 10:12 pm Post subject:

Having just torn out a section of the balsa in the hull, I now don't think that it was vacuum bagged. There was a small area where the resin had wicked up into the balsa kerfs, but there were a lot more areas where it hadn't. That presents its own problems. The little kerf lines in between the balsa cubes form moisture highways. I'll post some pictures once I get my camera and computer together, but the basic idea is that the balsa core is like a parquet wood floor that has tiny gaps between the individual pieces of wood. Once water gets in, it can go any direction winding through at 90 degree corners, just like the PacMan ghost. I found kerf lines that were water stained and really have no idea how far that water had penetrated. After a couple inches of finding no rot, I stopped, but who knows.

Mark

Marco Flamingo · Posted: Thu Oct 15, 2015 7:09 pm Post subject:

I just posted some more pictures as to how water can travel around inside of the balsa core.

I also just got some of these zip tie mounts. $5.44 for 100 and free two day shipping. Crazy. http://www.amazon.com/gp/product/B003L16ZYU?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 Easily strong enough to string any wire, including battery cable, and no screw holes. I will probably use them to cover up the screw holes once I fill the holes with epoxy. Good riddance screw penetrations.

Mark