Balsa Core

[neilpride]

Originally Posted by clockwork orange

I think i mentioned C&C in an earlier post as one of the builders who put most of the laminate on the outside of the core and very little inside which led to core saturation from bilge water so the Mega does not surprise me, a lot of builders only gelcoat the bilge under liftouts in the sole with the rest being unsealed which combined with a thin inner skin can lead to issues.

Steve.

And i agree with this, i own a 40 C&C in the past, thin inner layer , thick outside, cored to the bones, gelcoat after gluin the inner mold i guess, and that stupid PO bilge wáter pump swicht screws make the rest ....

[clockwork orange]

Originally Posted by neilpride

And i agree with this, i own a 40 C&C in the past, thin inner layer , thick outside, cored to the bones, gelcoat after gluin the inner mold i guess, and that stupid PO bilge wáter pump swicht screws make the rest ....

Difficult to re core too, the extensive inner liners on most models make it necessary to work from the outside, and you need to rebuild the inner skin from the outside so you can bag in a new core, then of course there is all the cosmetic work associated with working from the outside. At least with most of the older J boats you can re core from the inside.

Steve.

[Moonos]

I'm currently yo looking at different ~40 foot cats for my first sail boat, and this whole balsa issue really turns me off buying a boat with a balsa core.

And it's good to know how important it is to over drill a penetration and cap with epoxy to prevent water issues. That is a new one to me, and is relevant to the vast majority of cat decks.

When I get a boat, I will do a once over on all the stanchions and and other fittings... Prevention is much easier than cure.

[Dulcesuenos]

Originally Posted by Moonos

I'm currently yo looking at different ~40 foot cats for my first sail boat, and this whole balsa issue really turns me off buying a boat with a balsa core.

And it's good to know how important it is to over drill a penetration and cap with epoxy to prevent water issues. That is a new one to me, and is relevant to the vast majority of cat decks.

When I get a boat, I will do a once over on all the stanchions and and other fittings... Prevention is much easier than cure.

Most of the current larger producers of cats, do Not have core anywhere near the stanchions, toe rails, thru hulls, hatches or deck hardware. If your talking older mod 90's then its possible regardless of core. I've seen foam wet and crumbled too. The biggest issues I've ever seen are on decks of older cats that had wood core and screws right into it.

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

[Moonos]

Originally Posted by Dulcesuenos

Most of the current larger producers of cats, do Not have core anywhere near the stanchions, toe rails, thru hulls, hatches or deck hardware. If your talking older mod 90's then its possible regardless of core. I've seen foam wet and crumbled too. The biggest issues I've ever seen are on decks of older cats that had wood core and screws right into it.

Thanks for that, there is always something new to learn about boats. A sunsail 384 is one option I'm looking at.

[clockwork orange]

Originally Posted by Panope

In the example below, the core in the middle of this span is acting in compression only.

The core near the ends of this span would also be under very high loads acting parallel to the skins as the top skin is under tremendous compression and the bottom skin is under tremendous tension. The only thing that is preventing these skins from "sliding" against each other (near the ends) is the core.

Steve

Actually the loads on most of a boats structure are quite low and the areas that are more highly loaded are dealt with independent from the skin such as transferring keel and rig loads out into the shell. This is born out by the fact that there are hundreds of thousands boats sailing around with rotten cores and yet nobody can point to a catastrophic failure because of it, even though at its worst there may be zero compressive strength left. I witnessed this fact first hand 40years ago when a well known designer in the 18 footer class rented space in my shop in Auckland to build a new boat with a welded up aluminum space frame that took all the loads of the daggerboard, rudder, huge rig, racks etc and then built the shell out of polystyrene, the white stuff, which is what, 1 or 1.5lbs density, with just a layer of boat cloth on each side, there is very little compressive, shear, peel or any other kind of strength with that stuff but all it had to do was present a shape to and keep the water out, but it still needed to have panel stiffness, which it did. It was a very graphic demonstration of where the loads are. This low overall loading on most of the hull and decks is why we only need to use 5lb density foam even though we have many more densities available to us.

Steve.

[roverhi]

You don't need to enlarge the fastening holes any larger than needed to get a tool in to route out the core around the puka. I use a dremel 199 bit to do the core routing and it barely enlarges the fastener puka if inserted on edge.. Be aware that if you do this with all the fastener pukas you may have some cosmetic issues around the holes so a deck paint might be in your future.

[Cheechako]

Originally Posted by clockwork orange

That would be much appreciated, the term encapsulated would imply that each individual block would be sealed on all side at the factory, this would be very useful for hand layups and repair work. It would be unnecessary with infusion of course as when you infuse, the blocks are totally encapsulated. All the manufacturers of balsa core that we use do offer a pre sealed core but it does not surround the blocks but rather seals the faces, the purpose being to reduce the uptake of resin into the end grain. I have been using it for years but don't need to anymore with infusion. I still use it for repair work.

Steve.

u"nnecessary with infusion of course as when you infuse, the blocks are totally encapsulated. "
So... is this reality or theory? Just asking... as I know the statements often made regarding vacuum infusion are the big savings in weight and cost and much lower use of costly resin. I've looked at samples of some of the "dry infusion" so highly touted... and I don't see how there would be enough resin to really properly infuse the balsa... or the tight spaces between the little squares...?
Anyone got pics of balsa that was fully resin infused?

[minaret]

Originally Posted by Cheechako

[B]
Anyone got pics of balsa that was fully resin infused?

I don't, and I've cut into literally hundreds of boats with balsa core. Seen lots that was almost totally encapsulated, but not quite. Seen even more that wasn't even close. But totally and completely encapsulated everywhere I have never seen in anything but small parts like hatches.

[clockwork orange]

Originally Posted by Cheechako

u"nnecessary with infusion of course as when you infuse, the blocks are totally encapsulated. "
So... is this reality or theory? Just asking... as I know the statements often made regarding vacuum infusion are the big savings in weight and cost and much lower use of costly resin. I've looked at samples of some of the "dry infusion" so highly touted... and I don't see how there would be enough resin to really properly infuse the balsa... or the tight spaces between the little squares...?
Anyone got pics of balsa that was fully resin infused?

This is not theory, it is fact, at least when i do it. To be clear, with infusion you have a great deal of control of your fiber fraction so the temptation is to go really low with the resin content which i think is a mistake, my goal is 65% fiber which is hugely better than anyone can achieve with hand layup but still allows for enough to wet everything out nicely. 70% fiber is quite doable but i think it is a little dry.When i started making parts this way i went on forums and i didn't find anyone who was using balsa, everyone was using foam, so we did our test panels and it worked great so we moved on to actual parts and it just gets better. We have done gelcoated parts and parts with no gelcoat so i do get to see both sides and to be honest i don't see how it could be better. Every single block is completely surrounded with resin with zero voids. Even though you are achieving a close to perfect laminate it may not be lighter than a good hand layup because of everything being filled but it is infinitly better. I have a lot of confidence in balsa used this way. To be honest i was a little skeptical myself as to how the resin would flow through the knife cut core as we were doing flat panels with contour core but it works very well. I do have photos but unfortunately i am a luddite and don't know how to get them off a phone and post them.

Steve.

[Nicholson58]

Originally Posted by clockwork orange

Unfortunatly what you are doing is not a good repair for several reasons, unless you are using a high elongation epoxy your microballoon mix will be quite brittle, not at all ductile like a real foam core, my guess is that since you are in Michigan you are using west epoxy which is quite low in elongation, in the region of polyester around 4% if i remember right, i don't use it because of this although G flex would be a lot better. The other problem with just drilling holes and injecting is that it is wet in there and full of composted balsa so the goo will not bond adequately to the fiberglass skins. It will feel solid but it is not a proper fix. A lot of amateurs go this route mistakenly believing that if they drill a lot of holes and let it sit for a while it will dry out in there, it does not, the only way unfortunately is to bite the bullet and cut it open and do a proper re core.
I would also disagree on balsa being a short term product, its never been a problem of the material, just incompetent builders and owners, but going forward things look good for balsa as more and more builders use vacuum infusion to build their boats and through threads like this more and more boatowners educate themselves on the correct ways to bed new hardware.

Steve.

The long explanation of the repair is:

remove the head liner. Check with moisture miter from inside. Outside measurements are often in error due to water in the non-skid etc.

Use a hole saw 3" dia to remove the inner skin in workable increments.

Dig wet balsa from the inside. Remove ALL wet balsa. Continue expanding the 3" hole pattern to expose all wet balsa.

Let the exposed area dry totally. Cut 18 to 24 oz fabmat patch to cover the entire excavated area. ALso cut cardboard and 1/8 inch crappy plywood and heavy PE sheet the same size & shape.

Scarify the remaining fiberglass. build and artist's pallet of: plywood, cardboaerd, PE sheet and fabmat ready to lift into place. Mix the resin. I use US COMPOSITE 635 THIN resin. This is an extremely slow cure epoxy engineered for wet-out of FRP and general boat building. Cure time is about 4 days at 70 F. Pot life is about 6 hours.

Pour the resin on the fabmat and spread with a brush. Make sure its saturated.

Lift the patch in place and force into compliance to the inside of the cabin using 1 x 1 wood struts. Cut the struts to length so that they can be made to bow as springs against the patch. You will need about one strut every 6 inches.

When cured, remove the plywood, cardboard & PE sheet. The resulting patch fully bonded to all of the cabin top will show nice clear 3" dia windows. Use a grinder to clean up hair & other errors.

Find the lowest and highest points in the cavity now defined by the patch and the exterior boat deck. Drill a hole in the patch at these points so that a convenient sized rubber hose can be press fitted into the holes.

Cut a SHORT hose with a V shaped notch. Press the hose into the holes to touch the bottom surface of the exterior deck. Plan that each high/low hose combo will address an area jof about 4 ft-sq.

Mix the 365 thin resin with microballoons to the thickest consistency you can pump. I use refillable caulking tubes and a caulking gun. Fill the tubes and pump the slurry into the low hose. Keep pumping until the cavity is filled and material oozes out of the high vent. This stuff will bond nicely to the inner and outer patch/deck skins. You will be able to see the advance of the slurry as you fill. It will NEVER hold a drop of water ever again. It will be stronger than any balsa of foam filler you can ever imagine. It will be low density. (the slurry is about like Kraft Marshmellow cream) The compressive strength is about 3000 psi.

Go to my photos to see the job. Nicholson58

[Is05land]

Balsa cores are great . . . but like anything, they must be built properly. I had a Santa Cruz 50, and the surveyor tapped all over the hull and could find no defects or wet spots. The boat was approx. 17 yrs old; in the water all the time. So it comes down to the builder- get references! It's easy to install balsa incorrectly, which has lead to the bad reputation of balsa.
Also, I doubt any (normal) production boat has a balsa hull. Maybe some areas in the deck. Any composite "piercing" must be done through solid glass or suitable filler, never right through the core (balsa, nomex, PVC, etc.).

[minaret]

Originally Posted by clockwork orange

This is not theory, it is fact, at least when i do it. To be clear, with infusion you have a great deal of control of your fiber fraction so the temptation is to go really low with the resin content which i think is a mistake, my goal is 65% fiber which is hugely better than anyone can achieve with hand layup but still allows for enough to wet everything out nicely. 70% fiber is quite doable but i think it is a little dry.When i started making parts this way i went on forums and i didn't find anyone who was using balsa, everyone was using foam, so we did our test panels and it worked great so we moved on to actual parts and it just gets better. We have done gelcoated parts and parts with no gelcoat so i do get to see both sides and to be honest i don't see how it could be better. Every single block is completely surrounded with resin with zero voids. Even though you are achieving a close to perfect laminate it may not be lighter than a good hand layup because of everything being filled but it is infinitly better. I have a lot of confidence in balsa used this way. To be honest i was a little skeptical myself as to how the resin would flow through the knife cut core as we were doing flat panels with contour core but it works very well. I do have photos but unfortunately i am a luddite and don't know how to get them off a phone and post them.

Steve.

I notice you mention building parts by infusion. Ever infuse the core on a large hull? Just as confident in your results on that scale? Any input on the difference in weight and brittleness infusing in VE resin as opposed to old school core bond? Ever bag core into core bond as opposed to infusing? Personally I think it a much superior method, resulting in a much lighter part which is more flexible, less brittle. Just takes lots more work. It's not the massive time/money saver infusion is, which is why I think we don't see more of it.

[Nicholson58]

Originally Posted by Dockhead

You can't make a blanket statement like "balsa is stronger, but foam is strong enough" -- it all depends on what you're trying to do. Foam might be strong enough, or maybe balsa will be tons better -- it depends. For decks, foam might be ok on smaller boats without any big spans. But for hulls, stronger is almost always better, at least for monohulls. My boat is Kevlar/fiberglass/balsa all the way to the keel, and she's as stiff as the Brooklyn Bridge, amazingly stiff, but with 200m2 of sail area and a 23 meter mast, you just can't have too much strength, and if I could make the hull even stronger, I would. Foam would absolutely not do in this particular application, although it might in certain others.

The issue is not foam/balsa strength. It is the fact that both saturate with water given the opportunity. Since the structure relies on a dry laminate, the game is lost. Especially in the North, where we get annual freeze/thaw as well as cyclic freeze all winter, these structures will be rendered mush. Open the core of a 5 to 10 year old rudder and find the core totally saturated and no longer bonded to either skin. In the case of my own rudder, most of the foam was GONE; rendered a tiny pile of moldy black krud. I learned in my fluids class that the first law is 'water leaks'. Any vulnerable structure you place permanently in water will become saturated; by osmosis if nothing else. The only recourse is to build structures that don't care.

[clockwork orange]

Originally Posted by Nicholson58

The long explanation of the repair is:

remove the head liner. Check with moisture miter from inside. Outside measurements are often in error due to water in the non-skid etc.

Use a hole saw 3" dia to remove the inner skin in workable increments.

Dig wet balsa from the inside. Remove ALL wet balsa. Continue expanding the 3" hole pattern to expose all wet balsa.

Let the exposed area dry totally. Cut 18 to 24 oz fabmat patch to cover the entire excavated area. ALso cut cardboard and 1/8 inch crappy plywood and heavy PE sheet the same size & shape.

Scarify the remaining fiberglass. build and artist's pallet of: plywood, cardboaerd, PE sheet and fabmat ready to lift into place. Mix the resin. I use US COMPOSITE 635 THIN resin. This is an extremely slow cure epoxy engineered for wet-out of FRP and general boat building. Cure time is about 4 days at 70 F. Pot life is about 6 hours.

Pour the resin on the fabmat and spread with a brush. Make sure its saturated.

Lift the patch in place and force into compliance to the inside of the cabin using 1 x 1 wood struts. Cut the struts to length so that they can be made to bow as springs against the patch. You will need about one strut every 6 inches.

When cured, remove the plywood, cardboard & PE sheet. The resulting patch fully bonded to all of the cabin top will show nice clear 3" dia windows. Use a grinder to clean up hair & other errors.

Find the lowest and highest points in the cavity now defined by the patch and the exterior boat deck. Drill a hole in the patch at these points so that a convenient sized rubber hose can be press fitted into the holes.

Cut a SHORT hose with a V shaped notch. Press the hose into the holes to touch the bottom surface of the exterior deck. Plan that each high/low hose combo will address an area jof about 4 ft-sq.

Mix the 365 thin resin with microballoons to the thickest consistency you can pump. I use refillable caulking tubes and a caulking gun. Fill the tubes and pump the slurry into the low hose. Keep pumping until the cavity is filled and material oozes out of the high vent. This stuff will bond nicely to the inner and outer patch/deck skins. You will be able to see the advance of the slurry as you fill. It will NEVER hold a drop of water ever again. It will be stronger than any balsa of foam filler you can ever imagine. It will be low density. (the slurry is about like Kraft Marshmellow cream) The compressive strength is about 3000 psi.

Go to my photos to see the job. Nicholson58

Thanks for the explanation, it seems i misunderstood what you were doing, I thought you were doing the typical boatowner repair which never works. Your repair should work just fine.

Steve.