Wednesday, January 21, 2009

Tons of wet balsa

A few weeks ago a debate on the use of balsa core began on our KSSboat group on Yahoo. It was lively and informative. It also went onto the Multihull boat builder steamradio forum (email is: Anyone who has read what I have written will know my view – Balsa loves water and rots very quickly. It is impossible to ensure the water does not get to the balsa core and there is nothing at all to gain anyway. We got lots of feed back. We learnt of lots more reasons not to use it. We learnt of a very long list of designers who are promoting its use. The only explanation of this is that they have not seen what I have seen of cores and that they are swallowing the sales pitch, which has gone to the extent of balsa becoming an industry standard. It should never, ever be in any boat – unless the objective is to build in redundancy and reduce resale value. One only has to flip through one of the multihull magazines to see the extent of its use. It is in most of the boats in build pictures, particularly owner build. Seems that most plans come without any warnings of the dangers of balsa or instructions to get the best results.
If this sounds harsh on other designers, put your self in the shoes of an owner – here is a quote from one owner on Balsa core.

"If there are no voids in the layup, water doesn't spread through it and cause rot, even with such poor workmanship.? It is a better practice, of course, to completely seal balsa from all contact with water. As the owner of several tons of wet balsa core (in a C&C monohull) and some dry balsa (in an F25c), allow me:

1. Anyone who thinks balsa core is better than foam is either a sadist or is not the brightest bulb in the chandelier.
2. Even if he/she had the most perfectly laid up laminates on earth NOBODY will believe this when the boat comes up for sale.
3. He/she will NEVER recoup the cost of the extra labour involved in the utterly futile attempt to achieve a perfect balsa layup throughout the entire project.
Having said that, if the object of the exercise it to demonstrate that piss actually flows uphill, my advice is 'go ahead'." T.H


Robert said...

End grain balsa is prewarmed to dry it for about 24hrs and then fully incorporated in the sandwich lay up straight away. The end grains suck up the resin and it is thus that the wood is sealed forever. If the balsa is not thoroughly dried it is likely it will delaminate later resulting in soggy messses. Using this method ensures the keying of end gran balsa to the resin/glass will be superior to that of foam but the result is slightly heavier than a foam sandwich due to extra resin being sucked up. Foam doesn't suck up resin.

Happy sailing, Derek! Bob Willcox.

Tony said...

You would have to be peddling the stuff Bob, check out tests at "The coastal passage" to see how the wonderful duflex product sucks ink stained water completely through the panel in less than a minute.

Its enough to make a duflex builder head off to the shed with a box of matches (after checking the policy was paid up).

Might as well start epoxy coating cardboard!

Robert said...

No, I don't sell balsa core. What I say is that provided the balsa is thoroughly hot dried immediately before use and provided there is a good surplus of resin for the wood grain to suck up then the balsa is fully sealed. Of course it will need constant watching when afloat and designers should allow for the weght of the extra resin needed to effect a proper seal. I would recommend PVC foam rather than balsa for its reliability but balsa can work if design allows for extra weight, if the drying and subsequent lamination are done conscientiously (no using balsa straight from its pack)and all subsequent mods and repairs are done keeping the balsa dry and sealed. Balsa does need a lot of care but it is so cheap!

Robert said...

In addition everything in life costs either time or money or both. If you use balsa core it is cheap to buy but it takes a lot of time to lay it up properly and a it will occupy a lifetime of constant, good care to maintain it. If you have the money buy foam, if you haven't, buy balsa and devote a lot of time to it.