Plywood Moth

You're here in New York, Oceanboy2000? Psych!

Have you been in touch with Scott Sandell in Sag Harbor? Scott, prime agitator for Modern Moths here in the U.S., is the "staff" of Mothballs Magazine: http://www.mothboat.com/USMMCA/newsletters.htm

I'm building a Classic Moth in Ardsley, and am planning to use this sandwich panel as a plywood substitute: http://www.yachtacoustics.com/nvt_CD/pdf/materials/MAS_Comp.pdf

Best plywood supplier in our area is
Maurice L Condon Co
(914) 946-4111
250 Ferris Ave
White Plains, NY 10603

I hear there's a place in Yonkers where you can buy a wide assortment of veneers.

Here's the U.S. mothists' Yahoo group: http://groups.yahoo.com/group/Mothboat/
We even have a New York mothists web site: http://homepage.mac.com/rlarson6/NYMN.htm

Welcome aboard!

 

stephen! that is all to awesome to hear! im currently in buffalo but due back to nyc in mid january. This moth project thread has really taken off in less then a day! The project currently stands as a new heater purchased for the garage, a gallon of epoxy waiting for me at the supply store tomorrow, the homemade scarfing jig almost done, and the wood pannels stuck at the store after the door to the van broke. tomorrow shoudl be a big day though! at least i hope. thanks for your input~dan

 

Many of the Australian scow moths built in the 70's were often 1.2mm ply. The lighter 3mm sounds perfect for a bit more durability.

The one in the picture belongs to my brother but resides in my garage at the moment. They often had the ply on an angle like this on cedar stringers about 5" apart. Decks were thin too but with a layer of light fglass or kevlar on the underside they would flex but never break (only where you walk).

 

doorskin ply

A cheap source of 3 mm ply are door skin panels. These are the 3 x 7 foot panels used to skin interior doors and are available at Home Despot and/or Lowes (at least in the Norfolk, Va area) for about $7/sheet. Typically, the panels have one "good" side and one side with lots of patches, etc. This isn't great stuff (two v. thin veneers and a v. fat middle layer of mystery wood), but the price does permit experimentation, and as noted in earlier posts, 3 mm is lighter than 5 mm. Some lots of door skin appear to be assembled with water proof glues and other lots delaminate if you spit on them, so if you don't plan to coat with expensive epoxy (which kinda defeats the purpose of buying cheap ply) you need to take a cut-off and soak it in hot water to see if it's water proof or not. Even if not WP, door skin panels are useful at the pattern making stage. Unfortunately, door skin panels are not stocked universally through out the Home Despot kingdom, so if planning a visit to friends, or attending a regatta in the Norfolk area I occasionally bring a stack of sheets home, lashed to the roof racks or sandwiched between boats.

Have fun.

imptoo

 

the door skins were mentioned to me by a freind as well, since the luan never made it home last night i should make a few quick calls to see if i can at least take a look at the stuff somewhere around here. Question though, you mention covering the hull in epoxy. I have heard many schools of thought on this one and im sure this is going to start a whole new wave of replies. I have heard of those with marine ply still giving it a coat of epoxy, others not. I have heard of those with exterior ply giving a coat, and others not. What is everyones thoughts on this?~dan

 

another quick question guys and girls....ive found a supplier of 1/8 luan and MANY other plywoods in my area http://op6.activant-inet.com/LENCO/nlcatalog.asp this is very good news! any opinions on the 1/8 plys avaliable?

 

plywood supplier

I looked at the cabinet grade plywood and the stuff listed as P18L Lauan is most likely the doorskin variety. It has also been used in cabinet shops for ultra-cheap cabinet backs. My bet is that it's not waterproof glue.

This means that when the boat gets scuffed and takes-up water, the laminates will begin to come apart with little ceremony and with them will go your boat in that area.

You'd have to be VERY careful with your boat to avoid any scuffing, scratches or dings that will penetrate the epoxy glass barrier. If you are not that careful (and who is, after all, with a bargain priced boat) then do get the plywood that at least has waterpoof glue to hold it together.

Skip all that if you can mount and dismount from the boat in the water without ever contacting a hard surface. Likewise for getting it on the roof of the car.

I've seen doorskin boats that have lasted for many years and they simply amaze me. I guess it comes down to how much irritation you would have if the boat started to come undone on you after one season of hitting it. If you only have that expectation, then get right after it my man, it's all just time and money, anyway. You aren't going to cross an ocean so the serious durability/safety lecture is inappropriate.

Chris

 

to coat or not to coat

I've heard some peeps say they would "never paint with glue or glue with paint".

Indeed, "painting" plywood with epoxy resin is expensive and, if the ply was manufactured with water proof glues, somewhat redundant. But, on the flip side, epoxy coating does give a useful increase in panel stiffeness. This is particularly useful in the case of roll tanks, humpy fore decks etc. One can resin coat the back side of the panel prior to fitting it to the boat and then fit it while the resin is in the green stage. This permits the use of thin ply, which will bend more easily (without all those annoying cracking sounds), in components that will subsequently be subject to high(er) loads than the rest of the hull. If one also skins the backside of that panel with say, 4 oz cloth, one may discover that some interior structural beams, knees, stringers, etc can be safely dispensed with. The weight savings of this last strategy can be calculated in advance in as much as most of the resin and hardener remain after catalysis (unlike the solvent component of paints); so what you apply is what you get. Additionally, one can use multilple layers of thin ply panels laminated together with resin over a jig or mold to acchieve a curved, localized component with the required strength. In the case of bending, thinner is better...

In Moth Boating, over-building is probably a rate limiting obstacle to development: if your existing boat lasts too long, you won't have the motivation to design and build something faster for next season.

imptoo

 

I would go for the 1/8" luan. I would worry about how waterproof the glue really is, so I would probably coat it really well with epoxy. And here's a trick.
Don your respirator and grab a heat gun, heat up the resin where you are spreading it with a paintbrush. This will drop the viscosity and will also warm the air inside the wood. Bubbles will come out. As the wood cools, it sucks resin back in. Pretty cool.
Suprise, but over on Sailing Anarchy another guy from New York is thinking o doing a Moth build as well. Scott is dancing a jig in Sag Harbor. Merry Christmas Scott.
SHC

 

ok guys, i have some 1/4 luan and set about scarfing together the pannels, and what an incredible pain, i cant imagine 1/8th! The new plane i have is garbage, and setting up the jig for ply that thin is turning out to be tricky. i have some more test material left and im thinking maybe a belt sander?~dan

 

OK.
First youneed a big enough flat surface tosupport the edge of the plywood. Annother piece of cheapo thick plywood on some saw horses or trash cans will work.
Put some masking tape on the edges.
You want an 8:1 scarf joint.
Draw a line 2" from the edge for 1/4"
Or 1" from the edge for 1/8"
Tack the plywood to the stiffer stuff so that the edges line up.
Wail away with any tool you want to make a flat or slightly concave bevel.
A 5" grinder is the usual "professionals" choice.
The masking tape will tell you when you have gone too far.
Untack and put aside.
Do the same thing to the next piece.
Un tack it and put it aside.
Put a piece of plastic over the thick piece of plywood.
Tack piece 1 down about 4' from one end.
Be sure to line up the long edges so the piece you end up with will be straight.
Apply epoxy to scarf.
Plop the other piece on top. Line up the feather edge with your pencil line. line up the long edges. Tack it in place.
Now put a piece of plastic over the3 scarf joint and using a piece of straight wood as a batten, nail the pieces together. Drywall screws work well too, but the goal is to have a nice smooth transition between the pieces and large surface clamping is the only way to get there.
Nailing the pieces to a third piece is the only way to make sure they don't swim all over the place.
It's really hard to do a beautiful job of this, Ive been at it for 30 years and they still don't look all that good to me.
An alternative scarf is to cut a zig zag pattern about 4" wide. Use a sheet rock knife to match the other side. Interlock the pieces and laminate a layer of 10 oz glass on the inside.
This may effect how the panels roll up, but it can be less frustrating than the scarf joint.
Don't fret too much. Wood is pretty smart and sometimes it takes a while to out wit it.
Good luck.
SHC

 

Thanks

thanks so much for the run thru! i just got in from the garage after building a new jig to cut the scarfs and glued them up as a trial for the epoxy in the garage overnight, it shold be interesting to see how it goes in the colder temps. i have my fingers crossed. I think i may have made the scarfs a little steep though, so i may go thru it your way in the morning, it seems alot less risky, and all or nothing. thanks again for the proccess.~dan

 

for holding down the plywood edge to be scarfed I often use doble sided carpet tape. If you try this be careful, tape must be not too sticky otherwise you risk damaging the feather edge when you pull away the plywood from the scarfing table.
Marco.

 

Imortant:
set the tape 5 mm. back from the edge of the table.
Marco.

 

I find it easier to make consistent scarfs that match by doing a stack at once.
Draw a line at ~ 25mm the edge ( 3mm ply ) on each piece needing a scarf, and arrange the pieces in a stepped stack, with the lines and edges aligned.

Then you can grind/sand/plane the scarf of all 6 or 8 bits at once.