Core rot and replacement

I

IntoTheMystic

New member
Afternoon All, longtime follower but first time poster. Same old story, old C-Dory with core rot. My bad for not getting a marine survey. LESSON LEARNED!! ALWAYS ALWAYS ALWAYS get a survey done. I am looking for input/suggestions/thoughts. I was thinking of replacing rotted balsa core with rigid foam board insulation. My thinking is, I only want to do this once. So if I use foam board instead of Balsa, there's a "near" zero percent chance of it rotting out again. I plan on laying down a layer of 1708 on the hull. Does anyone know if the fiberglass resin will bond with or will it dissolve the rigid board? Thanks in advance.
 
There is a difference between rot and wet. Balsa can rot when it gets wet, but it is still wet. Foam won't rot, but it can still get saturated with water.

Freeze thaw cycles on wet balsa or foam can cause greater damage.

FWIR, for a given thickness balsa is stronger than foam.

Either way you go, you still need to be diligent to keep water out of the core.
 
Hey Eric, I sooooo feel your pain. I would recommend, since you are in Ninilchick, that you get in touch with Eric Sloth in Homer. I'll put his contact info at the end. He is a boatbuilder and ordered the 1.5" balsa that I need to re-core my boat. It is only sold in large lots so I couldn't get it direct.

Anyway, he was a wealth of information when we spoke on the phone, though certainly not more than you'll find right here on C-Brats! The advantage is you can drive to him and I've found that the whole Kenai Pennisula has actual boat shops and places to get supplies. Ketchikan doesn't have near as many resources, which I find odd, but our local marine store is ordering all my odd (to them) supplies and not charging me any shipping! The prices are comparable to what I've seen online so no shipping will be a real savings. That is the advantage of staying local if possible. Here is his info:
Homer Marine LLC (Eric Sloth)
5075 Kachemak Dr. #11
HOMER, AK
ericsloth@gmail.com
907-435-7881

Good luck,

Jackie
 
I am looking for input/suggestions/thoughts. I was thinking of replacing rotted balsa core with rigid foam board insulation. My thinking is, I only want to do this once. So if I use foam board instead of Balsa, there's a "near" zero percent chance of it rotting out again. I plan on laying down a layer of 1708 on the hull. Does anyone know if the fiberglass resin will bond with or will it dissolve the rigid board? Thanks in advance.
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As to the question if it is compatible with polyester resin, it depends on the type of foam used in the rigid foam board. But, the hull of a C Dory is a series of curves, and thus the balsa has kerfs in the make up of the blocks of balsa. Thus it can contour to the hull. If you don't put any holes in the deck (inner bottom of the boat), there will be no wet balsa core. Balsa has better shear strength and better compressive resistance than many foams. There is a reason that balsa is used. Some of the boats have foam cores--As Ssobol says, it can get wet, and with freeze thaw cycles causes delamination. Putting in polyester resin against old polyester resin, will be a weaker bond than than originally at the factory. If you go with vinyl Ester or Epoxy the bond will be stronger, but $$$.
 
I am on my 2nd year of boating with my rebuilt 26' CD ProAngler. We will see how it stands up. It was a 21K rebuild at a boat shop in Anchorage. The transom and deck near it rotted it due to poor sealing of the bolts holding t he Armstrong bracelet on.
Eric, of you ever want to look at mine I am at 138.1 Sterling and west uphill towards the water on Tidal Knoll Rd. top pf the hill.

Jack
 
Eric,
Looks to me that you are asking about using a insulation board used in house construction called " pink board " ?

The " foam " boards that people would be refering to when used in boat construction are not the same, and cost more than 10X what "pink board" sells for.

"Pink board" has a very low compressive value.
Let others chime in.
 
Jackie: Thanks for Erics info, I work in Homer so will definitely be contacting him. And I have been following your story, keep up the good work. It will be worth it in the end, at least thats what I am telling myself.

SoBelle: I am in the process of plugging all the little holes/rub rail/teak top rail etc, so as to keep the water out. Perhaps I should have named her "Swiss cheese"

Thataway: Thanks for the expert advice. I Knew I was at right place for this project.

C-Val: I haven't made any cuts into the floor yet but 1 or 2 days after a rain, water seeps up from the floor just inside the door. appears to have had some repairs done there previously. Assuming the worst and hoping for the best. Transom seems solid/dry at least from the material that came out when I was installing transducer.

Jack: Hopefully my "rebuild" wont be near that much money- divorce for sure. I just may swing by sometime as I am just south of MM 130. You have probably seen "her" in front of my garage.

San J. :Sorry I wasn't more clear in my original post. That IS what I was referring to, "Pink Panther" type for home construction that you get at Home Depot / Lowes. The type they use for under slab, below-grade walls. I believe its called Extruded polystyrene. If its designed to go below grade I assume its fairly water proof, thus preventing it from rotting should water ever find its way into my sub-floor. And to Bobs point, I was going to make necessary relief cuts/kerfs to conform to hull curves.

Again, thanks All. Will keep you posted and pics to follow.
 
Eric, sorry you have to face this problem!! Unfortunately it is too common when penetrations into the core have not been properly sealed. There's lots of info on this site as well as on the web on repairs. Check out " Boatworks Today" for lots of proceedures when working with glass laminates.
I agree with the others about using pink board for this job. If you're lucky it may work but why take a chance using an unproven method. The $$$ saved are a small part of the total job it would be really crappy to have to do it over!!! I agree that balsa has lots to recomend it. It is good enough that It would be my first choice. Cored laminations need proper prceedures for penetrations. This takes time so most manufacturers don't do it. They feel that just sealing with caulk is good enough. Sooner or latter it leaks. Of major importance is properly sealing core penetrations in the future. This is more than just spreading goop around the head of the bolt or screw. There is lots of info on proper sealing on this website. Dr Bob (Thataway) has one of the best instructions.
I agree with his recomendation to use vinyl ester or epoxy. They both have better secondary adhesion than polyester. Repairs to the original layup use mechanical adhesion as opposed to the chemical adhesion of the original layup. I'd tend to use epoxy for the whole job even though it will be the most expensive it's just superior.
 
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