Getting Ready to Place the Core - Questions

BALSA: Really bad news.

Nida Core, the company I bought the balsa from agrees with Andrew. Balsa needs to be bedded down into something, they said. I can't use it in a female form. They also said sheet balsa will not work because it will break/split and not hold. $(*$#!

So, now I have a lot of extra balsa. So what do I use for a core for the deck? What core is there that doesn't require me to replace sections of core everywhere that I want to bed something to the deck?

Are there stiff foams that aren't expensive like Core Cell?

 

My renicell E240 is stiff , I bought it for hardspots, stringers , and bulkheads, I dont know how it bends. My 5/8 was about $4.20 sq ft, it is # 15, maybe you can use a thinner core with stringers under it or bed the balsa on top of it. rick

 

Hmm.... 5/8", 15# foam for $4.20/sqft isn't so bad. The high density, 12lb Core Cell I ordered for the chain plate area was $6/sqft. You don' t want to know what I paid for the regular 6lb Core Cell. All I'll say is "less than Renicell."

I'll take a look into it. I know Joel from e-boats/bateu has that stuff. Possibly, I could build my deck out of a foam like Renicell that is in the proper density (5-6lb). Do you know what that's going for in price?

I'm willing to use the balsa later on the roof of the deckhouse or something if I can find a cheap (but good quality) foam to use for the decks. This means a lot more work, but I'm not sure there is much else I can do. Andrew was right. I can't leave that balsa out for months waiting to join the hull halves together.

Thanks

 

I think there is only #15 and one greater, cat no 5 or 6. Why cant you build your form out with battens and use a thinner core, bed the balsa on top of the thin core after the hulls are joined. A thicker deck wont hurt . rick

 

I think because the thinner core (standard foam, but thinner) will still compress. If I have 1" of all balsa, I'll have no compression. If I have 1" of all foam, I'll have my decks crushed by 1" if I tighten something down hard.

If I have 3/4" balsa, then 1/4" foam, the deck will still crush down by 1/4".

My thought is to use regular foam (but cheaper, like Airex or something) to do the deck and maybe use plywood to replace the foam core?

Does anyone have a good feeling for how to do this the easiest way?

 

Ed Horstman has a deck design sort of like that, (sandwich plywood deck) ply top, 4 to 6 lb foam, ply bottem.

 

I may have mis-spoke. I can't have foam at all in the sandwich where there is a compression load unless it's high density foam, which is very expensive and a PITA to put in after you have build the deck.

The object of balsa was a slightly easier hardware bedding process. Balsa stands up to compression loads without the need to replace any core. Foam, unless it's high density, doesn't.

So, with a foam deck, you replace the 5-6lb foam with 12lbs foam in spots where you have high compression loads.

I didn't feel like doing that difficult replacement.

Talking about plywood, I was referring to using plywood as a core replacement in the place of high density foam because it's cheaper. In that case I would still use foam cored, fiberglass deck, but instead of HD foam, I'd use plywood as a core replacement.

My designer said don't worry about it... it's not that much HD foam.

I'd like to find a reasonably priced foam for the deck that's 5-6lbs. I can't use that foam you picked up for the whole deck, Rick, because it's too heavy. 15lbs per cubic foot is a lot more than 5lbs per cubic foot. My deck would be 3x as heavy. It might make a good HD foam insert though. I'll check the specs to see if it lives up to my designer's criteria.

 

Just to satisfy my urge to think up ridiculous solutions - as I understand it, you cant put a bed of goo in the female mould, then lay the balsa in it, because you cant be sure you will fill all the slits.

If this simplistic scenario is correct, would it be possible to lay the balsa in the female mould (bare), glass the insides , and then after you pop the hull, fill in the slits manually, fair it all and cover with fg ?

I might have misinterpreted the problem, so apologies if I have. The conversation is of real interest to me for future projects - thanks for all the good discussion.

 

Catbuilder, if you want to use that contour balsa in the deck you can, you will have to make a "contact" mold for it using melamine faced sheet of a thickness that will conform to the camber- this would be best for downhand working- you can mold in hatch landings & loft out the cabin interface etc, also a tabbing rebate for interfaces such as cabin & hull deck etc. Regards from Jeff.

 

here is pic of a hard deck/cockpit on my old seawind 24, this is apretty quick boxy effort made of melamine sheet, autofiller, plasticne & shellac then wax & release agent incorperates 3 different core materials & acts as outboard nacelle also, if you can build it inside out you can mold it, your contour balsa is made for contact molding, there should be instructions for back wetting/priming & bedding to the outer laminate skin.

 

Well, you sort of have it. My female mold looks like this, but much bigger:



Those battens you see are the actual, designed hull size and shape. They are meant to hold foam in place. You then glass the inside of the mold and throw the half hull over in a corner while you turn more half hulls out from the mold. It sits there for quite a while (months) before you bring it back and joint it with a new half. Only at that point does the outside get glassed. This would mean the balsa would be sitting around my shop (outside in the humidity of Florida) for a long time, unprotected. That's the first problem.

Second problem is the balsa goes on a vertical part of the mold, so it would need to somehow be held up there, scrim, little individual pieces, and all... while I glass the inside.

Ok, it's midnight here... I'm up way too late. I'll post some more in the morning... zzzzzzz

 

Why don't you wrap it up in a big plastic sheet, seal the edges with tape, throw in some dessicant, apply a little vacuum, then seal the vacuum hole?

 

aha, yes , definite problems apart from the protection of the balsa outside. RX suggestion sounds quite feasible.

But you also need to support and 'offset' the balsa for at least the thickness of the outside fibreglass. I guess the solution needs to be a lot less expensive than throwing away the balsa you have bought.

I had a vision of getting some cheap 1/4" to 1/2" polystyrene or similar foam sheeting, hot gluing it to the mould framing where the balsa is supposed to be, then using strong fishing line to sew the balsa to the polystyrene sheet. Hopefully, when you pull the hull, the polystyrene would break away from the framing, and stay intact as an insulated, waterproof cover till you got around to finishing the outside of the hull.

There must be some way to save your investment ... its hard stuff to sell secondhand.

 

Hmmmm.... so a regular mold of melamine. Could work.

What do you all think is easier?

1) Use the balsa core by making a melamine mold, then seal and tape the core off with plastic bags using a dessicant

or...

2) Use foam and just deal with replacing the core where I have hardware.

Which would you pick? I am not out any money by not using the balsa because I can use it up on my deckhouse roof and hard bimini.

 

If you dont mind flat decks then vacuum bagging the block balsa on a flat melamine table is an option, plywood is another.

If you want camber you can still do your decks in balsa as intended, get sheet balsa.

I prefer foam.