Frequent Sea, Cored decks and the fungus farm

The Nida-core is in place. All exposed balsa from the old deck has been sealed with epoxy and the area between the Nida-core and balsa is filled with epoxy. The Nida-core is laid in place with a layer of 1 1/2 oz mat, over the previous inner laminate (1 1/2 oz mat and toward the bilge is 18 oz roving one layer). Next, another layer of 1 1/2 oz mat will be laid where necessary to make the new core exactly flush with the existing deck. All of the gelcoat in the areas where we step has been ground off, and the biaxial cloth will be laid on top of that. Finally this will be faired and either regel coated or alwgripped. (which ever is easiest). It is interesting to note that there were several "impact" areas over the intact dry balsa core, where the single layer of 1 1/2 oz mat had been damaged when some object was dropped on it (Maybe a heavy fishing sinker?). With the new Biaxial cloth, the new cockpit floor will be stronger than the orgional by a factor of at leat 10 fold and resistand to any impact damage.
The last photos in the "Thataway" Album show the Nida-core in place, and the cut out for the bilge pump access, to show the structure of the Nida-core.
 
I have posted photos of the Nida-core deck glassed in place at the last of the Thataway album. We decided that 12 oz biaxial cloth is more than adequate--considering that the origional had only 1 1/2 oz mat. There is also a photo of the biaxial cloth. The fibers are bundles oriented at 45 degrees to the other set of bundles, sewn/knitted over a layer of 1 1/2 oz mat. This is laid down over the balsa and Nida-core, and saturated with resin. The Nida-core has a mat surface--also about 1 oz--so these bond well.

The next stage will be to fill and fair with a medium density filler--then decide of we are going to gel coat, with cabasol added for stiffness and try and replicate the agressive factory finish, or just roll on the Awlgrip urethane with glass beads. The latter is easier on the feet--the former will probably wear better at least initially. I like to put one layer of Awlgrip with beads, then put another layer of Awlgrip without beads to help seal the beads in place. If we use the Awlgrip, we will put an epoxy primer on first.

At this time the deck is at least 6 times stronger than it was initially and is waterproof--no more core rot. We will also fill any Nida-core edges with epoxy, although this is not essential, it is an extra precaution.
 
Hi Bob:

I live up in Michigan and don't have the available sources for the Nida Core product that you apparently have down in FL. I will be starting a similar project on an old Shamrock 20 ft. center console. I am sorry if I missed your source of materials in this posting or other similar postings, but would you please be so kind and provide a bill of materials and list their sources for this project. Thank you for your help in this regard,

Sincerely,
Rollie/C-Batical
 
I got my Nida-core at Advanced Plastics--there is a warehouse in Elberta Alabama about 5 miles from my home. I purcahsed one 4 x 7 foot sheet one inch thick for about $69, including tax. The biaxial cloth and mat can be obtained from any fiberglass supplier--as can the polyester and epoxy resins. http://www.nida-core.com/english/order_list.htm allows online ordering. You might contact Nida directly for a local source. There is a fair amount of boat building in Michigan and I am sure that thee is a local supplier near you.

I posted five new photos. The first two are the finish on the new cockpit floor. It is rolled out polyester resin/gel coat with a mohair roller. The mixture was about the consistancy of coolwhip, we did add wax to this mixture--one of the few times we do this--and we added cabasol to get the proper consistancy.

The second photo is the epoxy sealing of all hatch openings, even with the waterproof honey come.

The third photos are photos of the holes drilled to find out the extent of water intrusion in the lower transom from the screws holding the transducer mounting bracket. It appears that silicone was used as the sealant. (I don't think this was factory done). The next photo, I have cut out the 3 x 3 section of the lower transom, and removed about 1/8" of plywood, and about one inch of balsa core. The Balsa core was under a layer of glass mat (separated from the transom plywood). This is properly done. But it illustrates what happens when you get water in a core. We will remove all of the wet core, fill with epoxy and then relaminate the outer skin of the transom with epoxy. Bottom paint will be applied. There is also a photo of a piece of Starboard which I will cross hatch (for ahesion of 5200) with a dovetail bit (small Dremel tool type) and screw into the transom. The new transducers will be then screwed into the Starboard--and there is no risk of water intrusion. This is fairly easily done, if caught early enough.
 
Bob:

Thanks for the information. I had been on the Nida-Core web site but was not sure of the product or thickness you used. I will contact the corporation to find a source here in Michigan. Fiberglass and epoxy products are not a problem. Thanks again for your help.

Best regards,
 
For the deck re-lamination we used polyester resin. For the Transom, we are using epoxy, because of its greater bond strength. The deck is all in compression and there is mostly primary bonding. We did use epoxy to seal the edges of the core (although this is not really necessary, I prefer to do it
 
I'm just catching up on this thread. Has there been a response from the factory? It is totally unacceptable to have this kind of damage and poor construction practice. Who is responsible for QC at the factory for this kind of thing?

I have been researching C-Dory for my next boat purchase. This definitely changes my opinion.

--Matt
 
Apparently the factory hasn't caught on to the concept that you don't want
threads like this hanging around unresolved. But, you can also read about
plenty of problems with much larger boats, too.

Google "c-dory core problems" and see how that issue was resolved.
While those of us with older boats will need to solve the problem, we
know it is not a huge problem, either. Good factory response.

(In case google chamges, the link http://www.c-brats.com/viewtopic.php?t=1679&postdays=0&postorder=asc&start=0
comes up.)

Mike
 
In the case of the CD 25, Frequent Sea, the previous owner failed to recognize that there was a problem, even though the deck was cracked. He also didn't contact the factory until the boat was for sale, and at the urging of Forum members about the transom problem. But from what I have seen, there are a number of C Dory 25's with transom cracks into the corners of the splash well.

Perhaps a better question is should the factory have done a general recall and repaired/sealed the openings? If this had been an automobile, I suspect that there would have been a recall.

Despite the above thread done in 2005: my 2006 Tom Cat 255 still had unsealed core. So what happens at the VP level does not always trickle down to the worker level.....
 
Charlie, that is correct: any core material which is not sealed with epoxy. At times poyester is used--and is used on the transom of the C Dory 25 on the top and polyester with a layer of mat is used to seal the 3/4" pieces of plywood (2) which make up the 1 1/2" wooden core of the transom. Fiberglass with resin is often not stiff enough in a flat pannel, nor does it have the strength, so core is added to make it stronger, stiffer, or to fill a void (like engine stringers).

Epoxy has much better adhesive properties than polyester. Many of the early Taiwan boats were made with cabin sides and decks of layers of fiberglass over plywood--(vs the plywood molded into the glass). Many of these trawlers have gotten rot in the plywood core, because it was not sealed.

Another typical case is in production boat where the hull and engine stringers are wood encapsulated in polyester resin and glass cloth. Then limber holes (drain holes) are cut, but the wood is not sealed. Moisture gets into the wood (core) and then rot forms.

Balsa is semi sealed--it is actually a "hardwood" by definition. That is the cells are short, even though the wood its self is soft. As you may remember the Kon Tiki got lower and lower in the water, as the balsa logs adsorbed water. The end grain balsa theoretically should not absorb
water if each cell is sealed. Unfortuanately the polyester does not adhere well enough to the balsa, and water is adsorbed. I will be adding a piece on balsa in the transom thread as soon as I post the photos, and some new findings today--related to un-sealed core.
 
Thanks Bob. What type of the Nida-Core did you use? There are several kinds on their website. I've got a cabin top on a Columbia 26 sailboat to repair, where the mast step fitting leaked in the way of the bolts. It made the top so spongy that the guy that had it was afraid of it. It's not bad now that it's dried out but I'm going to cut the top skin off, pull out the core and replace it. There are two bulkheads under it and 4 vertical posts that'll give me lots of support. Was going to use Balsa but the Nida-Core looks better.

Charlie
 
Under a mast step I would use solid marine plywood, epoxy saturated--you can use core material around the sides if you need--but under a direct compression post--there can be too much point compression for the Nida-core, or most foams. You would have to spread out the load some way, even with a high glass content, and a heel plate. I have seen a lot of deck fitted masts which broke down core material, including plywood (especially when it got wet) (there are some exotics which are light and will work--but not worth it for this application).

We used the 8HPP Nida-core.
 
Thanks Pete, that looks nifty, I'll take a hard look at it. I like the idea of not having the bolts go all the way through the cabin top. Not quite sure how thick it is there yet, haven't cut into it. I have a 30x38 metal building to put together before I start this project! :shock:

Bob, the step isn't directly over the supports but rather in the middle of about a 2.5' X 2.5' square that has the support posts (really a part of the bulkheads of the cabin underneath) at the corners. I will probably put plywood in there though, that sounds like a smart idea!

Thanks for the info on the Nida-Core.

Charlie
 
My recollection of the Columbia 26 is that there was a laminated beam between the two bulkheads--and the area above this was plywood core.
There were 2 x 2" pieces of mahagony grooved on one side for the bulkhead, and the beam was over this. (I am thinking of the Mark I--S & S designed. If you are thinking of the Mark II, Bill Trip designed, it was relitatively similar--but I think a more substantial lamination.
 
Hi everyone,
thought I would re-activate this topic and warn everyone to check their cockpit deck plates. I knew ours were leaking when we opened the gas tank access port and found a pretty deep layer of scum. It caused our fuel level sensor to stop working. With the help of a generous fellow C-Brat we got the wires cleaned up and reconnected - problem solved! (Thanks again Tom!!)
I removed the deck plate this morning to reseal things and found the wood core all around the plate to be mush, in some spots almost two inches in. I am digging out the rotten core and will let things dry out over the winter. In the spring we will follow Bob Austin's great instructions for replacing the core and sealing the opening with epoxy.
If anyone has any additional tips let me know!
I'll post a couple of pics of my mess in the Dragonfly album.
This is a great forum. Proud to be a C-brat!
 
Thanks for the kind words, and reminders! I am going to check out that 2006 boat in Pensacola--and see if that is an issue there!

I had commented that I had assurances from the factory in 2007 that there would no longer be any leaks--that the 2007 boat would not have that problem....well--they do--and I suspect even newer ones also will. A lot depends on how the boat has been stored, and if there have been leaks, water intrusion and freeze thaw cycles.

Hopefully your core issues will only be a few inches, and you will not have to do the total rebuild. But it may be a good time to check out the fuel tank--and prevent any issues there also.

Regards,
 
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