Core material replacement, corecell, pvc, UHMW?

[Dufour4800-175]

Im in the process of replacing my water clogged cockpit sole core. Im wondering what would be the best coring material I could use to replace the original plywood that would stay dry, and be very strong so it never comes soft and support my pedestal very firmly. Any opinions?

Thanks

 

[tommays]

Balsa as it is really bonds well as is very easy to work with an crazy stiff

bad balsa is just from a bad install and bad hardware mounting

 

[Ross]

Balsa is very good but not durable if it gets wet. Paulownia wood is almost as light and is much more durable. I would stay away from any of the structural foams unless you reinforce all of the fastening points to compensate for compression strength.

 

[CalebD]

I used this 1/2" honeycomb polypropylene core for the small deck re-core I recently did.
http://www.expresscomposites.com/honeycomb.html
Costs about the same as good plywood but it is not wood.
So far very happy with it.

 

[sandpiper10471]

I am a big fan of balsa. However, in the cockpit you must also deal with the torque and pressures of the pedestal. If the original is balsa, go ahead and recore with it. However, if not balsa, I would be inclined to use marine ply, particularly in the area under the wheel. You can in fact mix ply and balsa. Also depends on how contoured the surface is. Pay particular attention to potting all holes and to your bedding compound. Read Maine Sail's links.

 

[RichH]

Cored laminate structure is what's known as 'box beam' construction, where essentially all the stresses are carried by the outermost 'skins'; the only job of the core is to keep the skins at a permanent distance (plus some compression/shear strength).

That said, you can use just about 'anything' that can take the compression/sear loads and then simply layup small areas of *solid core* in the sections that will have 'holes' and which *will* leak later on.

My favorites are "Klegecell" (closed cell PVC foam) for areas that 'may' leak, and end-grain balsa + solid sections for leak prevention.

 

[Dufour4800-175]

By "solid sections" you mean some solid plastic or UHM?

 

[Ross]

Nope, fiber glass and resin.

 

[jibes138]

Go to the website for Island Packet. They claim to use a resin based material for their cores that is impervious to leaks. I'm not sure what it is and if it is proprietary to them but it might be worth a little research. It might be epoxy with an abundance of lightweight filler? Anyone out there know what IP is using?

"A unique feature of all Island Packet boats is their method of deck construction. Instead of using balsa or foam core material, Island Packet use their own "Polycore" which is a mixture of resin fillers. I have no information on how this compares in weight and strength to well documented and more traditional core materials but, again, I have yet to run across any serious delaminations or failures."

"PolyCore® is a unique syntactic foam used by Island Packet as the coring material on the deck and engineered structural grid of the yacht. Coring materials in general are used to provide panel stiffness and rigidity at a weight savings for a given structure. Like the vertical component of an “I” beam, the core bonds with the top and bottom layers to create a structure that is strong and light. Typical yacht construction uses organic materials like plywood or balsa wood to create the core (an inorganic foam is sometimes used) but each of these rely on a mechanical bond of resin or other adhesive between the core and substrate. These mechanical bonds are subject to deterioration through the differential expansion and contraction between the laminate and the coring materials (caused by temperature differences) or simply through impacts, causing the bonding to break. Ask surveyors what one of the more typical problems is on a ten-year old conventionally cored boat and they will probably say, “delaminated coring.” PolyCore®, on the other hand, is a polyester resin blended with small glass microspheres, creating foam very similar in look and feel to a heavy shaving cream. This material is sprayed onto the substrate, where it creates secondary molecular bonding with the polyester resin used in the laminate. And because these two materials expand and contract at the same rate, differential coefficients of expansion are avoided, eliminating a major source of delamination. PolyCore® is the only material that carries with it a ten year warranty against degradation or delamination."

 

[RichH]

By "solid sections" you mean some solid plastic or UHM?

Solid FRG, either 'filled' FRG resin. An example of a 'high strength filler' for epoxy resin:
http://shop.sailboatowners.com/prod.php?13592 or http://shop.sailboatowners.com/prod.php?13579

..... or a solid layup of cloth + resin in that specific area where any 'holes' will be.

 

[25yearslater]

I can tell you getting balsa into every irregularity of the envelope is quite tricky. With the area needed for the taper to bond the new skin being the area you will have to tuck it under with some degree of accuracy. It's very time consuming marking and cutting to get a full filling of that area. The micro balloon and resin approach that jibes and Rich are suggesting is more expensive but offers full filling to preclude any voids. You will have to spread the mix carefully to keep it smooth which isn't all that difficult. The small area of a cockpit is an ideal candidate for this type of technique.

 

[Dufour4800-175]

Indeed I think I would prefer to fill gaps with epoxy/filler than taper my new core to the exact shape of the remaining structure. I think this guy method seemed adequate http://www.raggedsails.com/repairing-wet-deck-core-of-the-cockpit-floor/ but I also like the idea of solid glass. What do you think about using 2 different materials as coring material? Any problem with thermal expansion?

 

[Jumpstart]

My sole was done professionally. Solid glass in center area is 1-1/4" thick. Remaining core is 3/4" marine ply and 3/4" balsa. It came out great and pedestal is solid as a rock with absolutely no deflection when I lean on it. No worries about future wet core either.

 

[25yearslater]

I know from my own adventure that it is not uncommon to have different core material. Oday used plywood at the bow and balsa everywhere else in their deck laminate. One thing I noticed in the thread you posted is the author didn't taper the edges of his cuts for the new laminate. He created a butt joint which is extremely weak. After this season I am pleased with my results. I used balsa for my project and haven't been bashful about pushing my boat hard with no ill effects. The method of surrounding any deck penetration Rich is refering to is the method I also used. Remove the core material around any hole and fill with a thickened mix. Redrill after and the core is encapsulated preventing water from migrating into it. I also set up an isolation grid where each square foot had a 1/8 inch gap left for filled epoxy. If I loose one section the rest are isolated from wicking up anymore water. I am also a huge fan of biaxial cloth. This is 30% stronger in laminates than mat or roving. I don't want to fall on my deck as it is like concrete. Just some thoughts to consider.

 

[Dufour4800-175]

Thanks for the inputs! I like your idea of cell to contain water. I also think that solid sections is the way to go for around the holes. Id like to know how much resin/filler you guys used to give me an approximate idea. I know its probably not the same cockpit size ( mine is approx 12 squared ft) but still it will give me a rough estimate.

 

[25yearslater]

If you go with a synthetic or wood core a gallon of resin should be sufficient to wet out and bond everything. This should also be sufficient for any fairing you desire as well as the solid core areas. I used West System so the fillers were Colloidal Silica, High Density and Microlight for fairing. Here is a link to my project for some 'light' reading. http://forums.oday.sailboatowners.com/showthread.php?t=123244 As I said I haven't been bashful about pushing my boat to test the repair.

 

[Dufour4800-175]

If you go with a synthetic or wood core a gallon of resin should be sufficient to wet out and bond everything. This should also be sufficient for any fairing you desire as well as the solid core areas. I used West System so the fillers were Colloidal Silica, High Density and Microlight for fairing. Here is a link to my project for some 'light' reading. http://forums.oday.sailboatowners.com/showthread.php?t=123244 As I said I haven't been bashful about pushing my boat to test the repair.

Wow nice project!! Thanks for all the infos!! Im planning on using high density for bonding my coring material down and colloidal silicia to fill any gaps between my squares of material. Here a little pict of my nice rotten core hehe!