Cored Hulls

[mjsiega]

Are C-Dory's Balsa cored below the waterline? Has anyone read any of the articles by David Pascoe?

http://www.yachtsurvey.com/structuralissues.htm

It makes you want to start your own boat company...

-Mark

[Matt Gurnsey]

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.

[thataway]

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.

[journey on]

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

[C-Bill]

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

[tomherrick]

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

[thataway]

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).

[Don and Brenda]

Does anyone know how C-Dory factory installed the thru hulls for the wash down system? Is this something I need to keep an eye on?

[matt_unique]

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.

[Cutty Sark]

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

[Socrateur]

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.

[matt_unique]

[Sea Wolf]

[quote="matt_unique"]

[matt_unique]

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.

[thataway]

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.