Balsa VS foam core

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mahnamahna
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Location: Gosford NSW

Re: Balsa VS foam core

Post by mahnamahna » Thu Dec 19, 2013 9:44 am

The standard reason the anti balsa brigade quote for its ubiquity among kit designers, despite there being a foam option for nearly every design, yet designers (who's reputation and therefore livelihood is at stake) continue to recommend balsa is cost. Its a cheaper option so therefore most often used.

This ignores the fact that epoxy is also almost universally recommended by the same designers and is vastly more expensive that polyester. If cost was the king of reasons why would the designers not also stipulate polyester in their kits? I think we all know the reason.

Cost is just one small factor. Its a factor, small though. As another has pointed out, in the cost of an entire build, 10% of the shell cost is about 5% or less difference in final sail away cost, so I dont buy the balsa is cheaper argument.

I also dont buy the "Ive seen too many balsa repairs to consider it" argument prevalent among debates like this, there is a very considerable thread in another place on this and it almost exactly mirrors this one in its themes and arguments, most anti protagonists still conveniently ignoring the fact that the actual "experts" the kit designers nearly all choose balsa most of the time in even their most expensive high end models where cost is clearly no object to the purchasers.

Its a shame the polycore kit maker did not survive, but perhaps there is a reason and that balsa kit players survive to this day. Its a shame Oram decided to stop but I am sure it was not because he favoured balsa.

Disclaimer, I am building a balsa kit boat and used polycore for my furniture.

Redreuben
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Re: Balsa VS foam core

Post by Redreuben » Thu Dec 19, 2013 2:02 pm

Well as can be seen by the issues raised, there are pluses and minuses for both.

Guess it depends on how you think each of these effect the way you intend to use the boat and your skill sets etc etc.

Just a further thought that some may choose to consider.

Foam derives from petrochemical.

Balsa is a renewable resource. Go well with this resin, http://www.ecopoxysystems.com

Happy Building. :D

groper
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Re: Balsa VS foam core

Post by groper » Sat Dec 21, 2013 9:20 am

Balsa has much higher mechanical properties than standard PVC foam. To get the same mechanical properties from foam you'd have to go upto around 160kg/m3 density - which is available but the cost is astronomical, circa 300 bux per 15mm sheet of plain foam. Std 80kg/m3 foam is Half this, with balsa cheaper again.

MM , you can't use polyester with balsa or any other wood on a boat... well you *could* but you'd be an idiot for doing so. Epoxy is the only resin that's considered waterproof enough for longevity. Many timber boats became water logged over the years and we finally figured out why... theyre not expected to last 10 years when built with PE from what we've come to learn. PE and VE have enough porosity for osmosis to occur whereas epoxy is considered virtually impervious extremely low porosity. They didn't know any better back in the day tho... But some 3rd world countries still build them like this on the cheap, bash em around and throw em away a few years later type of thing.
This is why you won't ever see a modern designer use anything but epoxy with a balsa core or ply wood design, regardless of cost.

Cost is always a factor, in ANY building project, in ANY industry.

Duflex balsa core, is very cost effective. High strength to weight ratio product, no labour to laminate them yourself. It's hard to beat this combination of mechanical properties vs real cost inc labour. Hence it's success in this market. Do you really believe that you wouldn't have blinked twice if the cost of your kit went from $70k upto $110k just for the flat packed sheets? Well that's the difference between foam duflex and balsa duflex...

You don't see much balsa core in full blown racing yachts tho... Anyone care to reason why?

Redreuben
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Re: Balsa VS foam core

Post by Redreuben » Sat Dec 21, 2013 10:46 am

groper wrote:
You don't see much balsa core in full blown racing yachts tho... Anyone care to reason why?
It's not very suitable for infusion. So it's heavy.

groper
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Re: Balsa VS foam core

Post by groper » Sat Dec 21, 2013 3:05 pm

Well yes, incompatibility with infusion is one part of it, and the increased weight is another.

Which brings me to another gripe I have with the taped seam panel construction method... There is literally hundreds of kilos in extra weight from so many tape joins... And every extra kilo, costs about $20 in epoxy and tape and micro fibres... I figure my boat has about 300kgs of unnecessary weight and added about $6k to my building costs. Then there is the time to do the seams and fair them out afterwards.... I'm convinced there is a better way... I'd definitely explore the option of building a giant female mold and infusing the whole thing in one shot. All decored parts done beforehand, inserts placed, edge closures done and only a few taped joins to bond the large sections.... I think the savings in weight and epoxy would pay for the extra materials to build the mold... Total time to build would be less tho. So a lighter boat for less work, similar cost.

44c
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Re: Balsa VS foam core

Post by 44c » Sat Dec 21, 2013 3:40 pm

To build the mould you have to build the plug - and fair it. It's unlikely to save work.

Holding your boat together isn't unnecessary weight! Really, the tapes and the corresponding resin for them don't result in a heavy boat. Compare Schionning or Oram boats to moulded production boats, or the Fusion 40. Even with female moulded parts, foam cores and resin infusion, the Fusion 40 is heavier than a similar size Oram or Schionning.

Balsa is still used on racing boats, but generally in highly loaded structural areas. Racing boats need to be as light as possible, aren't expected to have long lives, and don't need to be able to take the knocks of cruising. So for the less loaded parts, foam works fine.

mahnamahna
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Re: Balsa VS foam core

Post by mahnamahna » Sat Dec 21, 2013 6:16 pm

groper wrote: This is why you won't ever see a modern designer use anything but epoxy with a balsa core or ply wood design, regardless of cost.

Cost is always a factor, in ANY building project, in ANY industry.
This is the point I made, perhaps not well because you seem to think I am arguing the opposite. I mentioned Polyester only because it is cheap but for the obvious reasons is never used for composite boats and only to counter the argument that balsa is used because its cheaper. My point being that cost in most cases is NOT the reason designers and builders choose balsa.

Foam is offered but not often used, and on some boats built by boat yards for clients with fat wallets. There has to be a reason for this. So cost does not fully explain balsa use among those that have the choice of any material because they have less limited budgets. Some of the new G force race bred cats that Schioning was initially commissioned to design (then later added the design family to its range) was ultra light weight racing oriented cruisers, and they use ultra light weight balsa at 80kg or almost identical properties to foam. Why use balsa then? On boats that are leaving sheds at north of $1 million?

I suspect that the reason is because it works well, regardless of the downsides and provided all proper building methods are used, but that goes for any material. Given all that is known, and all the for and against arguments, balsa is still my choice, regardless of the rot risk. Well that is not quite true, I chose balsa because I did not have the confidence at the time in my ability to loft from plans, and ply boats required that, kit cut boats did not. Now I have confidence I might choose a ply boat but given that I probably only have one build in me, that is unlikely to happen. But you never say never. But I am still very happy with my choice. A proven system from proven materials. People that deny that balsa is a proven material with comments like "Balsa has no place in boat building" are in denial IMO.

I also fully understand and respect those that are building with other materials, I wish them well and will admire their boats.

groper
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Re: Balsa VS foam core

Post by groper » Sat Dec 21, 2013 11:14 pm

44c wrote:To build the mould you have to build the plug - and fair it. It's unlikely to save work.

Holding your boat together isn't unnecessary weight! Really, the tapes and the corresponding resin for them don't result in a heavy boat. Compare Schionning or Oram boats to moulded production boats, or the Fusion 40. Even with female moulded parts, foam cores and resin infusion, the Fusion 40 is heavier than a similar size Oram or Schionning.

Balsa is still used on racing boats, but generally in highly loaded structural areas. Racing boats need to be as light as possible, aren't expected to have long lives, and don't need to be able to take the knocks of cruising. So for the less loaded parts, foam works fine.
I don't think your comparing apples to apples there Alan, molded production boats don't often use sandwich construction but usually more solid glass and gel coat layups which is where the weight Gains come from.

It's unessesary weight because the laminates are not continuous... If it were a full sandwich build, but without the tape joins in a fully molded continuous layup around all the chines etc the weight would be even less. I reckon I've used almost a full drum of resin and almost 2 full rolls of glass cut into tapes to join stuff together... It's quite wasteful IMHO... Rob Denny!s philosophy follows this same train... Reduce the secondary bonding and taping to a minimum and there are some large gains to be had...

You don't have to build a plug either.... I was thinking more along the lines of direct female molding... Jon sayer has done some designs thatue this technique for some of the race boats he has designed... It's a step in the right direction provided you have handle on infusion which is an integral part of making the system labour/time efficient.

44c
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Re: Balsa VS foam core

Post by 44c » Sun Dec 22, 2013 7:26 am

groper wrote:
44c wrote:To build the mould you have to build the plug - and fair it. It's unlikely to save work.

Holding your boat together isn't unnecessary weight! Really, the tapes and the corresponding resin for them don't result in a heavy boat. Compare Schionning or Oram boats to moulded production boats, or the Fusion 40. Even with female moulded parts, foam cores and resin infusion, the Fusion 40 is heavier than a similar size Oram or Schionning.

Balsa is still used on racing boats, but generally in highly loaded structural areas. Racing boats need to be as light as possible, aren't expected to have long lives, and don't need to be able to take the knocks of cruising. So for the less loaded parts, foam works fine.
I don't think your comparing apples to apples there Alan, molded production boats don't often use sandwich construction but usually more solid glass and gel coat layups which is where the weight Gains come from.
This is simply incorrect. Many production multihulls use foam core sandwich construction. Many others use Balsa core. Boats like the Katanas use resin infusion, foam cores, even a high percentage of carbon fibre. Yet they are incredibly, almost inexplicably heavy.

In fact I don't think there IS a production cat made entirely of solid glass. Some are solid glass below the waterline, but AFAIK, NONE of the boats currently in production are entirely solid.

The Fusion 40 as I mentioned, is moulded, resin infused and foam cored, but is heavier than most similar sized Duflex boats. It's heavier than my boat, which is considerably larger.

groper
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Re: Balsa VS foam core

Post by groper » Sun Dec 22, 2013 9:33 am

Well from the pics ive seen of the fusion assembly, it looks as tho they use foam core in parts of it, but huge areas of it are solid glass aswell -the chamfer panel area shows the core in the bow area and under the bulkhead locations and on the bridedeck floor - but solid glass everywhere else; ... then there is all the bonding flanges on every section and all the bulkheads which are all solid glass etc.... the smaller complex shaped pieces would have no core at all...

Have a look at this pic - theres almost no core at all in just about the entire pic, just a little bit here and there in the flat areas and around the edges which helps hold the parts shape so theyre a bit more dimensionally stable for assembly.
Theres many reasons why the fusion is so heavy and i suspect its the same with most production boats... yes they might use SOME core material, but its not fully foam cored everywhere and its not the way i was thinking of building and its not really comparing apples to apples ie a fully foam cored boat. The other boats you mentioned, i dont know about, but theres clearly many reasons why production boats end up heavy...

But the main point is this - your boat, my boat, and every other duflex kit boat out there, would be at least a couple hundred kilos lighter, if all the seams did not need to be taped and joined, but were instead made in a single continuous large piece.

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