JEM Watercraft

very interesting link to some tests done on f/glass to ply bond , it seems that humidity is the thing to watch

http://www.glen-l.com/wood-plywood/fibe ... ywood.html

The ISO 12215 standard describes that the moisture content of encapsulated or over-laminated wood for structural purposes should not exceed 15%. This means when calculating backwards that it is not possible to make a good structural bonding if the relatively humidity is more than 60%.

I'm not sure that would be a good statement. "Relative humidity" is calculated on the amount of water within a medium (air) compared to the amount that it can carry at that temperature.

To assume that moisture from air is quickly transmitted into wood may not be a valid assumption. But, most pointedly, wood and air have different capabilities to hold water.

Don't we measure moisture content of wood by % of weight gain?

Actually the relative humidity in air and the moisture content in wood has a lot to do with each other. Wood that is dry will interact with the relative humidity in the air so the moisture content in the wood is 1/4 of the relative humidity in the air.

Therefore with a relative humidity of 60% in the air the moisture content in the wood will be 15%. If you then bring the dry wood into your workshop with lets say 40% relative humidity in the air the moisture content in the wood will quickly get to a new equilibrium at 10%.

Darn ....

I live in the land of heat and humidity , commonly called Florida. Which leads me to this thought.......

All the boats I have made , none of them have been in less then 60% humidity , more like 80% to 100%. My shop has a ceiling fan for circulation and ventilation with the doors and windows wide open.

Only one time they were closed , when I was working on a kayak for a 90 day period and we had two hurricanes .... YEP.. I still went out and worked on the kayak. Closed the shop up and went to work on the boat.

I never have had a problem with the epoxy or glassing during those conditions but the epoxy is from a Florida company so it might be designed for use in our humidity.

Chuck.

Yep, I am with Chucky on this one. Over half of my boats have been built in times of extremme heat and humidity.

Atmospheric at anywhere between 80 & 100 percent with ambient temps in the shed between 90f & 110f. I have found that my cheap ply will absorb moisture from that air and my sweat and warp more than the good stuff (if not held flat till stitched) but it hasn't seemed to affect bonding properties.

Just a small point raise.

It didn't necessarily say that bonds made at high humidity were particularly weak or were going to prematurely fail, just that if they fail the bond may fail. It must be fairly marginal too, as there were only "some failures at the plywood/fiberglass interface".

Some of us will come into contact with hard surfaces at high speed at some point, make sure you carry out a full inquest into the demise of the craft should there be any damage and lets see what real life results tell us.

I don't think your boats will fall apart just yet.

Mick, during summer we have low humidity if you'd like to pop down to Melbourne and build a craft so that comparisons can be made operating in the extremes of Australian weather/climate, please let me know.

I'll supply the materials, have a large shed and brew my own beer and wine (which is good, though I am biased).

Tor

I'm sorry I can't my allow my designs to be part of this until I've been sent samples of the "materials".

I have done that with the canoe I made from 1/8th inch wood by bouncing down a white water river for four days. Rick-o-sheying down river without any damage.

"O" By the way .... the river was closed by the authorities right after we left as unfit/unsafe to paddle even for experienced white water paddlers and there plastic boats.
You might of guessed by now , when we pulled off 5 days later they opened it up as we were loading up to go home. The ranger came by our camp and remover the unsafe sign ( River Closed) and put one up that advised to use CAUTION ( Experienced paddlers only) when on the water.

Damages , capsized one time , wet and cold but that was me , the canoe had a few scratches on the bottom of it from bouncing on and off the rocks but nothing to worry about. The graphite and epoxy worked real good going over rocks.
It was some NASTY water in that river , in the main area and even along the banks when pulling out at night for camping. I had to use rocks to hold the ropes when camping since dirt was not there.

By the way , I was not the only person who swam in that river , several of the guys did and even the aluminum canoes ended up with dings and dents in them. I was thinking that is the nice thing about wood , it flexes. It was NOT a fun trip. The camping was great the rapids sucked and that river was nothing but rapids with a 50 to 100 yard smooth stretch , just enough to bail your boat out and keep going before the next mess that would spill over into your boat. Waves at the rapids from 2 to 4 feet high was the normal , a few places higher.

Chuck.
PS.. Am I going back there and paddle again.... ....Not in this lifetime

Unfortunately this is part of the Validation Protocol and Technical Plan to complete the comparison of a Qld canoe vs a Victorian canoe, however there is enough scope to include a matrix of samples and consider the merits of a trans Pacific build also.

Sorry Matt, it doesn't travel well, all the sediment gets kicked up...



Then lets not worry to much about the bond strength unless we're working outside in the rain...

Tor