inexpensive plywood

True Steve, you don't "need" wet/dry cycling, unless you're trying to make a determination in a few days, at which point the WBP type-1 test will yield the most useful results. A dishwasher can be helpful here. It's not a true type-1 test, but it's gets pretty close and will usually sort the men from the boys.

 

Correct.

 

thats a pretty slick idea Par

 

don't you have to be single to do the dishwasher test?

 

A dishwasher exception notification form, can be picked up from the APA branch nearest you or by request from the local post office. I think they charge a copying fee, but it's less then a buck . . .

 

adaptability

Par, I enjoy the fact that you can build them plain or fancy, know the difference and build accordingly. My rowing boats are built throw-away because there is always a new idea to try, and building an expensive boat is only a waste of money to me. I've lowered sheer strakes, modified a transom and added more vee in a bow area. not pretty workmanship, but it allowed me to find out if the boat could be improved and the improvement carried on into the next build. All seat of the pants stuff, cheap ( $400-$600) per boat but fun to build and then race. latest was a skin on frame 16' that was built by eye-ball only and rows very well. One race had 35mph gusts and 15/20 more or less continously. She behaved like a real lady while other designer boats had a world of trouble. Just dumb luck on my part.

 

if the original poster just google Hannu's Boatyard he will have all the designs he needs and the testing of different glues on the ply expained.

 

I just ordered 54 sheets of 3/4 exterior AC Pine for our barge project. It is a south american product from a company called Arauco. We will test it prior to use but the comments i have head from builders and the company emails back and forth seem very promising. $32 a sheet . It too has very few plugs on the c side and it appears a lesser number of substantial internal voids but the first sheet we sill test with and cut up to see whats she is made of.

 

Arauco ply is made with radiata pine and from experience it looks really nice in the store but checks like an SOB in the sun. I have also had a few chunks of the surface layer split and lift from the other layers. This is on a curved surface and under stress so it might be an anomaly.

 

Nice to hear from someone who has used Arauco ply,the checking sounds much like what Fir ply does and shouldnt be a problem if it is being glassed, the delaming is a concer though.
Joe, what sort of testing are you planning on doing? please keep us informed.
Steve.

 

the only test we were thinking of was the diswasher test. We will also be slicing up the top sheet in the bundle for use in other parts of the project but to also look for voids.It got beat up a little and will not be used for the primary construction. On our design the only curved surface is the slope on the bow. All other surfaces are completely flat and all joints are at 90 degrees and all exterior surfaces will have at least one layer of 8 oz glass and at least 2 layers of resin. All outside corners will also have an additional layer of 4" biaxial tape and the corners rounded. For the bow slope we were going to make cuts on the back side to ease in the slight bend of the 3/4 ply. Sounds like maybe we should put a little extra glass on that section.

Lewis, For the layers that separated on a curve, was it a glue failure or wood failure. We have also had some minur failures in that form even with marine ply but the curves might haave been more than the wood could take. These were in repairs and not initial construction.

Todays plans are to dig some steel i beams out of the snow and make a construction platform to begin construction on. All of my trailers are high enough were we will be up beyond a comfortable height when buiulding so im thinking of just building a skid that cn be leveled up and then when ready just pulled out of the shop with the tractor. Were building it upside down so it will have to be flipped then put back in the shop for final operatoins. Were still doing a lot of thnking on the subframe for the crane mounting.

 

Here is a pic (small) and a link to a bigger pic of the damage. It started as a section of lifted wood and I simply broke out the splinter. That is a standard sized 1/4" driver bit beside it for comparison. Notice it is right down to the glue with almost no trace of wood on the glue. It looks like it could have used a bit more glue or perhaps more pressure. I will fill with epoxy and plan on glassing the entire deck with 2 oz cloth to seal the deal.



and the link to the big one: http://www.angelfire.com/ego/lewisboatworks/Stuff/Misc/ChipB.JPG

 

what was the radius of that bend. the bow of the barge will be about 6 feet

 

That looks like a big fat pain in the but, what are the chances of gluing back in the piece that came out and then sealing it in with glass, its less epoxy that way which keeps the characteristics of the material more even, rather than have a big blob of epoxy under the glass which might want to expand and contract differently than everything else.

 

What I see in that picture is lots of checking and some delamination. What caused the delam isn't really as important, though I'll bet on pith, pitch or just plain old application errors. I've found that if sheathing Douglas fir, you need a minimum of 10 ounces of cloth, to prevent the checks from "bursting through". It depends on the thickness of the outer veneer in the plywood and of course the quality of the plywood.

If the area is ground back to good fabric contact, then filled with a structural mix, it'll expand and contract at the same rate, as the rest of the encapsulated panel. If this plywood panel isn't encapsulated, then you're screwed and this sort of thing will happen over and over. Plywood doesn't "move" like solid woods do with environmental changes, but it does move. This small movement in time will shear the sheathing, unless the sheathing is heavy. Encapsulation removes this movement from the equation and then everything acts as one monocoque piece.