Materials

A nice tear through the fibres of the core rather than joint failure.

Tried to jimmy open some of the joints...ended up driving the chisel with a hammer....

The soup is almost ready!

The timber got a good boil on the stove

19 October 2011

I have been exploring the various grades of marine ply available for the dinghy build and as with most things all is not what it seems when in comes to “marine” ply. As I mentioned over in the Dinghy build page I have discovered various grades and standards of ply and I had to make a decision on whihc one to buy. this post gives you the final update on that decision. I discounted the cheap ply from Bunnings and Mitre10 simply because I could not get any real handle on how good or bad it was, only a brief visual inspection of th top sheet and then its you take what you get. So that one is out. Lets jump to the other end of the spectrum and briefly talk about the Hoop Ply with AS2272 cert. This is the rolls royce of the plys. It looks really good and the quality is obvious. But there are two penalties with this. First PRICE…expect a factor of 2 or 3 in higher price. Second weight, expect say 10~20% more weight.
At this stage I have really narrowed the field down to a “real” BS1088 complient Gaboon or Mahogany ply. Gaboon is a species of timber that is close to mahogany. Its lighter in ply form than Mahogany, ~9kg per sheet versus 10~11kg per sheet in mahogany. Again theere is a price differencial…gaboon is about 30% dearer than mahogany ply. However you will find variations around these prices. These is a direct corrolation between quality and price…naturally.
I have decided to go with the Mahogany ply.
Testing for quality.
Two of the cheif quality issues are dencity of the core, ie. no voids and the quality of glue used in manufacturing.
Visual inspection is really the only practical way I can check for voids and then it is really only on the outside edges but generally speaking its fairly easy to get a quick overall impression of the quality even by sirface qualities. The ply sample I got and the ply I have seen in the shed seems good, so that box ticked.
Second one is the glue. There is a test called the boil test where you stick a sample of the ply in boiling water, if the glue is not BS1088 complient it will fail in the heat.. Well naturally I did this with the sample. Here are the photos. The last photo is the teller…when I put a chisel through the timber, the cores split not the glue joint. This was after 1 hour boiling in salted water, then 2 hours sitting in the cooling pot then another 1 hour boiling. I put the chisel through when it was still warm in case there was any resetting of the melted glue. After this test i am happy with the quality of th timber I am buying.

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Hi, you are welcome to comment and I'm looking forward to reading it. Regards Mick

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