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Plywood Testing


Quiet

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Earlier this year I put up a few posts regarding sourcing suitable plywood in Australia. I ended up going with Hoop Pine Marine ply and am currently cutting the frames for a Ravenswood. (Very slow progress I know, but that’s another story).

 

At the time I thought some simple testing of the plywood might be in order, so I took 2 off-cuts and hung them on the back fence over winter. One was left raw, the other coated with 2 coats of pure tung oil.

 

Winter here tends to have a lot of heavy fogs that hang around all morning and lots of nights below freezing. Once things get damp they can take ages to dry.

 

After a full winter the tung oiled sample is like new. The raw sample has numerous small mould spots all over it as a result of staying damp for extended periods. Neither sample looks remotely like delaminating so the glue seems fine. The raw sample also has fine cracking along the grain on all exposed surfaces. My guess is this is a result of the water that soaked into the plies freezing and expanding during the night and so cracking the timber, much the same way it gets into fine cracks in rocks and eventually splits them apart. That’s just a thought bubble though and if people have other theories or better explanations I’d be happy to hear.

 

The samples are back on the fence now. I want to see how they cope with our hot, dry summers. In particular I want to see how the tung oil stands up to our rather ferocious UV levels.

 

In the meantime, back to the Ravenswood. Thank goodness it isn’t a race.

Ply Weather Test 1.jpg

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Quiet:

A good test, but requires quite a bit of patience. Accelerated tests of this sort sometimes are done by boiling the test piece. I see two recommendations coming out of your test: 1) Treat your frame with oil, and 2) don't hang your boat on a fence. As encouragement in building your Ravenswood (I hope), I've attached a photo of mine in New York Harbor.

Fair winds, Andy

libertyswim1.jpg

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2 hours ago, andy00 said:

Quiet:

A good test, but requires quite a bit of patience. Accelerated tests of this sort sometimes are done by boiling the test piece. I see two recommendations coming out of your test: 1) Treat your frame with oil, and 2) don't hang your boat on a fence. As encouragement in building your Ravenswood (I hope), I've attached a photo of mine in New York Harbor.

Fair winds, Andy

libertyswim1.jpg

And, don't boil your boat - at least limit boiling to the stringers,  unpainted skin, and sinew.

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The problem with the boiling test is that many waterproof glues will fail under heat. Epoxy is a prime example, great glue but if you boil it it will soften and come apart.  

 

Baltic birch is another example, very weather resistant but if you boil it, it will fall apart really quickly once the glue gets hot.  

 

Since our kayaks don't see 200+ degree water I think that the boiling test is really irrelevant. 

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Thanks Benhardt57, I looked at them early on in my selection process and might trial the ply at a later date. Problem was, I couldn't be sure the Baltic Birch they sold was the same as Jeff recommended. Heard lots of good things about the Hoop Pine so ended up going with that. So far it seems to be really nice to work with and the glue is definitely waterproof.

 

Andy00, I promise I won't hang the kayak from my back fence. Having said that, it's amazing how much protection the tung oil gives the wood. The test sample really does look like new, with none of the dirty weathered appearance timber gets when left outside raw. Thanks for the inspiration picture. There's not much I can do about the current slow progress and it's nice to see completed craft. Gives me something to aim for. The building is fun in itself as well so whilst it will be nice to see a finished kayak, I am thoroughly enjoying the journey along the way.

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  • 2 weeks later...

Hi Teasea

 

I ordered the plywood from Boatcraft  Pacific http://boatcraft.com.au/ . They have a number of distributors around the place. Have a look on their website and see if there is one near you. Being in Canberra, I needed to get it shipped here. They were great to deal with, answered all my questions and processed the order without delay. Be aware though, it’s not cheap stuff! Very nice to work with though and was able to get all frames from half a sheet, so that makes the price per kayak more reasonable..

 

As you are in Sydney, you might be able to have a look at the birch ply from DMK Forest Products http://dmkforestproducts.com.au/wisa-birch/   mentioned earlier in this thread and see if it’s like the stuff Jeff recommends.

 

Looking at the spec’s for both Birch and Hoop Pine on the Wood database http://www.wood-database.com/ , it’s evident that both timbers are classed as having poor rot resistance so oiling the frames is a must (see the results from my over-winter test earlier in this thread). Amazing the difference this makes. The Hoop Pine is rated as lighter than the birch, but also correspondingly weaker so when I cut the frames I increased the thickness of the frames by 10-12 mm to compensate.  So if Jeff has made a frame 20mm thick, I increased it around 30mm. Easy enough to do and there shouldn’t be any weight penalty due to the lighter timber. The resultant frames certainly feel quite strong.

 

Only  a few frames to go and I'll get into the stringers and gunwales. (Thank goodness for a friend with a table saw). A good timber yard fairly close, so these will be Western Red Cedar. Also need to start the coaming and laminated beam. There are a few Aussie timbers that are meant to be quite good for bending so I will be investigating those.

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