Balsa core issues on the CD 16

Sunbeam":28ehyf59 said:
Maybe I'm not quite getting what you mean.
Click to expand...

I wasn't clear. I was referring to the screws holding the wires that go to the nav light that are screwed up into the deck in the V berth. Every 8 inches there is a screw holding a zip tie. I suspect that those screws are through the fiberglass and into the core. Even though it's on the inside and protected from the weather, I still don't like the idea.

Much as I like the weld mount fittings, I was standing in the checkout line at Fred Meyers this afternoon and saw some of the first Christmas stuff on display. It was clear plastic stick-on hook gizmos for holding a string of Christmas lights. 10 for $3.99. Might have to spring for a pack and try them out for holding the tiny wire loom to the nav light.

Now I'm not sure if my hull was vacuum bagged. I finished cutting out the bad balsa and found that I had to chase down black stained kerf lines that lead off in various directions (though generally in the shape of the pop rivets holding the seat box). The area where the resin had wicked up into the balsa may have been a fluke. I'm still amazed at how firmly the polyester resin hold the balsa.

Mark
 
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:

products-at-3.jpg


They make a few other styles as well.

http://www.weldmountsystem.com/products ... reties.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).
 
:disgust 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"
 
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
 
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.
 
jimicliff":1o8f1sec said:
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"
Click to expand...

I'm going to avoid trim tabs. I've only got a few hours on the boat before it went into my shop, but I'm changing things around based on those short sea trials. First on the agenda was a fin on the motor. That helped. Second is to get weight out of the stern. I could tell from how the boat sat in the water that it was stern heavy. Whoever designed the boat probably designed for a motor weight, not a horsepower. It's boat owners who are dazzled by hp.

The designer probably also said "Do not every penetrate the balsa core with fastenings."

I have a Yamaha 50, so there's already 50# of extra weight hanging off the back (compared to a 40 hp outboard). It also had two group 24 batteries and two 6 gallon portable gas tanks right at the very back of the cockpit (another 180# in the stern). All of this weight is counterbalanced by a foam cushion in the V berth! No wonder it squats.

Not much can be done about the engine weight. I did notice that because of the stern down attitude my motor needed to be lifted. I raised it an inch yesterday when I epoxied the mounting holes in the transom. Glad I've got a chain hoist in my garage. I hope that isn't too much after I change the weight around in the boat.

The weight of the gas tanks and batteries can be easily moved. Instead of 80# of gas in the stern, I now have a 23 gallon tank (150# when full) forward of the center of buoyancy. The starter battery can be moved to the passenger seat box to get it out of the stern, close to the center of buoyancy, and help balance the boat side to side when I'm solo, which will be most of the time. The house battery could be moved to under the V berth.

Both of those could be temporary moves to see how the boat balanced. I have a lot of large gauge battery cable left over from other projects, so I'm not too worried about remote battery locations (plus, the starter cable to the engine was never trimmed, so my starter has been getting power just fine through 12 feet of wire even though the engine was 5 feet from the battery.)

Back to soggy balsa. I cut it out yesterday and ground down the edge of the fiber glass in preparation for a scarf connection with epoxy. Now I just have to wait as long as I can for the core to dry out. I'm thinking March. Pictures to follow.

Mark
 
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."
 
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"
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.
Click to expand...

If properly done the balsa core is no problem, and not an issue. Many high end boats have had balsa cores.

All most all boat companies do not seal cored structures, before putting metal fasteners into or thru them--even though they are not the bottom of the hull, and these often will develop rot--such as decks of any boat, especially if teak decks are screwed into the glass/core, any boat which has cored decks and cabin tops etc--and almost all boats have this. Look at stanchion posts, cleats, any deck fitting.

What puzzles me, is why C Dory pop riveted the seats etc of the 16 into the cored structure. They could have epoxied or used Plexus structural adhesives for less cost!

If I had a boat (C Dory 16) with this construction, I would take action on it now, before it became an issue.

On the majority of 22's, the issues have been with fuel tank hold downs--and many now have the batons, glassed in place, and the actual straps holders are easily fixed. The screws into the interior cabin floor have rarely been a problem (although they should be replace with tabbing), since most boats do not have water sitting on the interior cabin floor.

There is no issue, with putting screws into the underside of the deck, (unless you plan on submerging your boat!).
 
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
 
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/B003L1 ... ge_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
 
It looks like you are doing a great job. I agree, grinding fiberglass sucks. But at least it doesn't take that long on a small area.

I see your photos of the water pathways in the kerfed (scored) balsa. Ideally, before placing it in the boat, one "bends it over backwards" on something like a bucket (or larger thing for larger piece) and then fills all the grooves with thickened balsa. Then when you straighten it, the extra oozes out and all those pathways are filled with epoxy (though of course most of it oozes out so it's not like you are adding lots of weight/epoxy). The kerfs allow the balsa to conform, so in that way they beat "solid" core.

Great to see your progress :thup
 
Back
Top