Cored Hulls

Take Pasco with a very large grain of salt. Very knowledgable, but a bit alarmist and fussy. Someone new to boating could read his web page and never buy a boat, as none would ever be good enough.

Yes, C-Dory's are balsa cored in the bottom of the hull, and some deck areas and cabin tops. There have been few problems with the core because of the small production runs, quality workmanship and materials, and the lack of through hulls in the boat.
 
Cored hulls are widely mis-understood, and have been maligned because some manufactures do not built the boats properly. If the core is added to give stiffness, and adequate amounts of glass inside and outside of the core are present, a cored hull is in many ways superior to a non cored hull.

Yes, many of us have read Pascoe--and I recommend that everyone who buys a boat read his various articles and books. He is correct. He is the the business of finding defects in boats which people want to buy. Now lets look at the amount of glass, the forces and the construction of a large Sea Ray with a Balas Core, and a C Dory. The C Dory is very light. The large Sea Ray boats were 40 to 55 feet and were built in the years 1995 thru 2002. This was also a time peroid when Sea Ray was experimenting with decreasing amounts of glass, using different techniques, using chopper gun construction and various resins. As Matt noted, there are multiple thru hulls, which are not properly isolated (the hull should have either had solid glass structure where the thru hull was, or the hull core should have been routed out, and then epoxy filler put around the hole, to seal the core.

If you read the Pascoe articles carefully, you will note that he tells you that some builders do use Balsa properly, and actuallly have ABS or LLoyds certification.

I was sailing on a large vessel which was entirely balsa cored, and we hit a submerged container. Most single hull fiberglass boats would have sunk. This boat had the outer glass (over 3/8") damaged, and the core intented, with some delamination of the inner glass--(over 1/4" thick)--the boat did not take on any water, and sailed another several hundred miles to a place where it couold be hauled and repaired.

As you gain experience in the boating world, by asking questions, personal observations and reading good forums, like C brats, they you will be able to discern what is valid and what is not. Also hopefully you will learn which is good boat construction and what is not.
 
Last year I read a book on boat construction: "Fiberglass Boats", by John Roberts. I started a blog on it: C-Dory Fibreglass The gentleman knew more that I had imagined, and a very important point was about hull cores. The claim by Mr. Roberts was that end-grained balsa cored hull offer some significant advantages over structural foam, or synthetics. One advantage quoted is that since end grain is used, water doesn't wick as with some other coring.

Also I found some pictures showing the construction of Journey On: C-Dory Hull Construction

I remain convinced that a C-Dory is well built, (though not perfect.) And, good Heavens, I've tested that.

Boris
 
When I first took possession of my C-Dory back in October 1990, I was sold on cored hulls. Last year, I paid $1,900 to have the core in the starboard transom corner repaired. The dealership had said "Don't worry, the balsa is on end grain." You better worry because a large section under the starboard fuel tank was turned to mush. Could barely identify it as balsa.

Now, since I had the new 4-stroke 90 hp Yamaha put on my boat, I have two stress cracks on either side of the motor (in the pan forward of the motor). Now, I'm more concerned that I could have more structural problems either in balsa or transom wood.

Be very careful putting screws in that stuff. The sealant can dryup and shrink and balsa will soak up the water like a sponge.

Bill
 
My balsa transom rotted and I'm going to rebuild a new one with a core of epoxy laminations I'll build myself. It's my opinion that balsa as a core is kinda like a nuclear power plant; as long as there's no problem all is fine; but a little leak can turn into a big problem in a hurry.

There are certainly ways to reduce and nearly eliminate the potential for water to penetrate the core at thru-hulls and fasteners, and those methods should be used whether it's balsa or Honduras mahogany. But, I still can't see using a species whose primary attribute in a boat core is being lightweight. In Bruce Hoadley's book, Understanding Wood, Table 6-1: Comparitive Decay Resistance of Heartwood of Various Species lists Balsa in the Slightly Resistant or Non-Resistant category. Seems to me that if weight is of concern that one of the foam core products would be well worth the increased cost to protect the overall investment in ones boat.

That's my two-cents...

Tom
 
Any cored hull should be treated the same--properly sealed. The rot in transoms is a common problem in many boats. For example the Grady White has a reputation with rot in the transom. The cause of the transom problems is also in-adequate sealing. In the Grady, as in many other boats, the hull to deck joint is on top of the transom, and only a single layer of mat or even just a plastic cap "seals" the core. If the hull to deck was properly sealed, and any holes in the transom were sealed, there would be no problem. The problem is NOT the core material, it is the method of construction. If you want to replace a transom, you can laminate wood with epoxy, but still all holes have to be sealed. Coosa board is another material which is good for transom building. Also "Seacast" resin can be poured into a transom void, after the wood has been removed.

Balsa has some specific characteristics which make it a better core material for some applications. It is stiffer than many foams, for the weight. It adheres to the laminate better, due to absorption of resin in the open cells of the wood. It has better compressive properties. Expensive is not a major issue in the use of Balsa vs other coring materials. Unless you are going to cold mold viniers, balsa is one of the few woods used in cores (Some bulkheads and flat pannels use high quality ply was a core, just because it is easier in construction.)

For a bottom under fuel tanks to have turned to mush, it must have been wet for some time, and there most likely was water standing in the boat. Of course the culpret is the screws for the tank hold down--which were not proberly sealed (meaning that the core was not removed, undercut and then refilled with epoxy filler, a new hole, and sealant.

Also if there are cracks along the sides of the splash pan, it is very posible that there is not enough glass in that area (see the repairs done to Frequent Sea--and the lack of glass in that area of the 2003 C Dory 25).
 
I'm not aware of any thru hull fixtures that are installed correctly into the core from the factory from any brand of boat. Every single thing that goes into the core must be removed and properly sealed to prevent water damage. I would take look at your raw water intake. The raw water intake for the Tomcats are installed through solid glass fortunately but many other items are improperly drilled into core. This includes the bilge pumps, all around light base, rigging wires through the transom, etc., etc. I suspect the same applies for the stanchions, cleats, etc.

In the case of the largest rigging wires/hoses for Napoleon the dealer installed some kind of hard plastic sleeve. I could not remove it (without major surgery) so I opted to carefully seal around it with Lifecaulk and 4200. The bilge pumps and all around light are on my winter project list. I probably will not prioritize the stanchions until/unless I see evidence of trouble. Everything I installed (radar, wires, bow cleats, etc.) I overdrilled, undercut, filled with epoxy paste - etc.

To prevent the opportunity for water entry I avoid thru-hull items at all costs. I opted for an In-hull (shoot thru) transducer for example.
 
I just finished going through my new to me 16 angler doing the same thing, and I had done a fair portion on my 22 before I sold it. I think with these boats it's a wise decision on anything going into the wood core or transom to overdrill,undercut and backfill. It's not that much time or cost/work. Now my boat is 20 years old and never had this done previously, a few of the holes were wide open in the cockpit, but even then the moisture really was minimal in most places, the worst went about 2-1/2 - 3 inches across. All the rest were not at all or a 1/4 inch if it wasn't sealed properly.... But the boat probably was covered a fair portion of the time and not moored. Plus it's made me more familar with both the boat its construction, and minor fiberglass/epoxy/ work.

Sark
 
I recall there being an article written, by Dr. Bob perhaps, and posted here some time ago with details on how to do the hole re-drill job being mentioned in this thread. Could someone please look that up and post the link? Now would be a good time to bring that procedure to light again. Thanks.
 
Socrateur":2osftzh6 said:
I recall there being an article written, by Dr. Bob perhaps, and posted here some time ago with details on how to do the hole re-drill job being mentioned in this thread. Could someone please look that up and post the link? Now would be a good time to bring that procedure to light again. Thanks.
Click to expand...

Dr. Bob was kind enough to write this for my website.

http://www.commercialcaptains.com/marine_articles

Choose the first link on the page.


While on the topic, I don't yet know if my arms will be long enough to do the work I want to do with the bilge pumps on Napoleon. I suspect that is the most vulnerable area on our boats though since you will always have some standing water down there.
 
matt_unique":2q3bxxqp said:
Socrateur":2q3bxxqp said:
While on the topic, I don't yet know if my arms will be long enough to do the work I want to do with the bilge pumps on Napoleon. I suspect that is the most vulnerable area on our boats though since you will always have some standing water down there.
Click to expand...
Click to expand...

Matt- I don't know if this approach will work on your TomCat 255 or not, but I've got two bilge pumps on my Sea Ray, one of which is totally inaccessible without pulling one of the V-6 motors. My plan (if that pump or the float switch serving it ever quits, is to mount a new one on a weighted HDPET plastic board and slide it back into place with all the connecting hoses and electrical connections attached so I won't have to deal with the original one. Maybe you could do something similar, though it might have to be secured more tightly with a strut or two that could be removable.

Unfortunately, my mechanic had the starboard engine out about a year ago to replace a gymbal bearing connecting the motor to the Mercruiser outdrive, and I should have thought to just replace that pump, switch, and all connections at the time, but ......

Joe. :teeth :thup
 
Thanks for the suggestion Joe.

I can *just* access my pumps and actually replaced one last year. My concern is whether I can get down far enough to remove the housing, overdrill/undercut/fill with epoxy paste/etc. I'm concerned about water damage with the existing pump housings screwed into the cored floor.
 
I did the same thing that Joe recommended on my Cal 46. The bilge sump was about 4 feet straight down, (behind the lead in the keel and under the transmission. I screwed the pump into a 3/4" teak board, and screwed lead weights to the board, and put a 1/8" line on it so I could pull it back up, without pulling on the cord or discharge hose. 1/4" high density poly prop (cutting board from WalMart) would work will with the pump bolted thru the board--same for the lead in the Tom Cat.
 
I'll post a few of the photos I made in explaining the technique. This is a suppliment to the link which Capt. Matt posted, and I suggest that you read that also.

fillets_and_filler_024.sized.jpg
The hole is drilled or cut with a hole saw (or may already exist). The edges are routed out, with a Dremel tool, or short bent piece of coat hanger, or allen wrench chuckedd in a drill. I keep several of the Dremel tools, since they are so handy for all sorts of things.


fillets_and_filler_027.sized.jpg
This shows the hole being sanded smooth with a small drum sander

fillets_and_filler_028.sized.jpg

Now the hole has been filled with epoxy, and smoothed at the diameter of the thru hull or deck fitting.


This a an oversized hole drilled in the deck, which will then be filled with epoxy filler paste. The paste is mixed with epoxy resin, 50% Cabosil (fumed silica) and 50% high density filler. The sides of this hole are also undercut to give strength to the repair and prevent it from pulling thru the deck.

fillets_and_filler_032.sized.jpg

Dremel tool with cutter bit (about 1/4" diameter inserted into the hole to cut out core.

fillets_and_filler_040.sized.jpg

Popsicle stick cut in half to push epoxy paste into the hole under cut edges.

fillets_and_filler_043.sized.jpg

Final hole filled, and ready to have a new pilot hole drilled in the epoxy filler, so a new screw can be attatched. The core is completely sealed, and there is far more strength for the screw to hold, than the thin fiberglass laminate.

Disclosure: No C Dories were destroyed or harmed in making these photos. This is a deck section out of a 27 year old Peterson Sailboat which we cut up for some of our ultrasonic bond tester studies. We found no moisture in the Balsa cored deck of this boat, despite almost 3 decades of heavy use. The C Dory deck and hull laminate is thicker and better build that this boat's deck.
 
I guess I have the same question as a previous owner. I have a 2007 22' C-Dory with the factory installed thru hull wash down system. Is the general consensus we should remove the strainer and piping, redrill and undercut the hole, epoxy and reinstall everything back or did C-Dory create a fiberglass hole that makes this unnecessary? The reason I ask as I’m not sure what I’m going to break trying to get all this hardware out and I don’t want do this unless it’s a known problem. If so, has anyone removed the wash down and got any tips in getting the hardware out? Also if C-Dory messed up the wash down, does everyone redo the transom drain plug with the same procedures?

Thanks Jim
 
Here is my opinion...I have worked on boats for 40+ years...any older boat that had balsa core...Its a organic substance folks..another wood.Its only going to last so long before it starts to fall apart and turn to dust...Great stuff Below a waterline???Obviously not...So all you old c dory owners can think about that...
 
flyinbob2001":1e0qsn2n said:
Here is my opinion...I have worked on boats for 40+ years...any older boat that had balsa core...Its a organic substance folks..another wood.Its only going to last so long before it starts to fall apart and turn to dust...Great stuff Below a waterline???Obviously not...So all you old c dory owners can think about that...
Click to expand...

There must be some good reasons why many companies still use balsa rather than foam (or whatever other choice there is) as a core. Any opinions?

Jake
 
flyinbob2001":1tohqspa said:
Here is my opinion...I have worked on boats for 40+ years...any older boat that had balsa core...Its a organic substance folks..another wood.Its only going to last so long before it starts to fall apart and turn to dust...Great stuff Below a waterline???Obviously not...So all you old c dory owners can think about that...
Click to expand...

Your profile shows a 1981 19' C Dory Angler. Did you recently buy this boat? Saw where you were interested in a 22 a month or so ago.

I have never seen a 1981 Angler--but there are some 18' 8" Toland anglers listed in the membership. Most of the 22's of that era had a plywood core--but it is possible that your boat does have a balsa core.

My father's boat was built in 1936--that makes it 80 years old. A very good surveyor happened to survey this boat 2 years ago--and remarked to me what exceptional condition it was in. (He did not know the boat had belonged to my father, and I had lost track of the boat.)

We saw some folks who dug up a boat built in the mid to late 1800's, and was in the mud in the River Gambia. She was Trunnel fastened. They did a few repairs and sailed her across the Atlantic, when she was over 100 years old!

I can give you lots of examples--and including the deck which that demo ago was done on, which is old. That specific deck came from a 1964 boat--which was doing well until Hurricane Ivan broke the hull--and I had the privilege of cutting her up, to do some destructive testing on.

I have been working on wooden boats for over 70 years...and contend that properly built, & cared for, balsa is a very good core material. It has good shear and compressive strength as well as adhesion. It depends on the application as to the best core material. David Gerr has some excellent comments on Balsa core material in his book "The Elements of Boat Strength".

So what is your point? Do you own a C Dory, and if so, what is the core material?

If a new C Dory owner, Welcome aboard. Come join the group in Apalachicola in Oct--and let us see your boat.
 
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