I’m planning an 8’-0" fun gun. I’m going to bag 1/8" poplar ply onto 1.5 lb EPS. On the rails I was going to use 1 layer of doorskin ply (that would be under the deck and bottom skins) and then layer on 1/8" strips of balsa and cork.
My question is how far back do I need to cut back on the rails? Is 1" (8 layers!) enough? Too much? And would the 1" rails be strong enough to do away with a center stringer? Finally I was thinking of doing all this with 5 minute epoxy. How much will I need? Does anyone know a inexpensive supplier?
If you can create some sort of cross section template, you’ll have a much better idea as to how much rail to build up. A thin sharp rail will take less material than a full rail.
The more you shape the taper of your deck/rail crown area, the less rail build up you’ll have to do and the less material it will require… I’ve seen some cross sections that were nearly rectangular and required a fair amount of build up.
Your perimeter door ply under the deck and bottom skins sounds like a good way to do it but in previous discussions, some feared it would make a board too stiff. Tough call as to whether a stringer should be added or not. It will add weight and stiffness but increase strength.
I’ve purchased 5 minute epoxy in squeeze bottles that worked OK for this sort of thing. System Three has it in various sizes and they are quite helpful if you have any specific questions. With a lot of layers you will have a lot of surface area to cover and it may take more than you think.
I’ve tried using 5 minute epoxy from the hardware store with horrible results. It’s very weak stuff. Maybe RR’s is better. I did have good luck with 30 minute stuff though, it comes in 16oz dishes. Get some of the extra-strong packing tape from Office Depot to hold on the rails while it cures.
What’s the doorskin for?
You might consider using 3/16 instead of 1/8, it’s still easy to bend as long as it’s not really firm balsa. You can always put in some relief cuts. 1" is probably good, although I don’t know how strong cork will be.
Do 1" for your first one, because it so hard to estimate how much to thin the blank before adding the skins back on. 1" will allow you to take the very blocky rails you’re likely to get, down to a reasonable radius…
I use either foaming pu glue or laminating epoxy for attaching rails, depending on the material. You’d go crazy trying to mix up & use batches of 5 minute epoxy over the length of a board.
I do use it, however, for very small pieces like the bits inside the buttcrack of a fish. Manageable, in that kind of application.
Thanks for all the feedback. The build schedule is for 1/8" skins top and bottom with 6oz over. It would would have perimeter rails of 1/8" doorskin (luan mahogany ply) and 1/2" of balsa on either side ( cork wouldn’t have any structure). I realize that’s a lot of stringer. I was thinking of eliminating the center stringer.
Should I go with 1 lb EPS? Would 4 oz be adequate? Remember it is a gun. I’m planning on using it in 1 1/2 to double overhead waves.
I’m also torn between 5 minute epoxy, putting on one piece at a time (easier, costlier) or just gluing up all the pieces with regular epoxy and taping it on (messy, more problems). This is going to be my first vac project. If I f…k up the second method could be more expensive.
I once worked for a custom furniture maker and after clamping up a particularly complex piece that took four people holding parts and putting clamps on, I asked him, “Have you ever designed something that you couldn’t build?” His answer, “No. If I did that I’d be an architect.” Guess he didn’t like architects.
Lillibel, I think you could eliminate all the vertical plywood (doorskin stringers) - center & at the rails. With a plywood deck & bottom & balsa rails, you’d be fine. Maybe Shwuz can chime in, he’s built quite a few like that…
I had a second thought, though, and that is that I’m not planning on using a rocker table, so I think a center stringer is a must to keep the rocker. Could I bag both top and bottom skins at once? Or is it better to do them one at a time?
I’ve never actually done ply skins before, but I can tell you where the problems will come.
compound curves are the biggest problem. Unless you plan your shape and deck crown very carefully, you’ll run into areas where the deck needs to curve up into the nose rocker and also curve down/across to meet the rails. It won’t bend that way. So, you need to plan your deck shape so that in areas where you have rocker, you have no crown on the deck. That is the main reason why I’ve always done my skins with strips of balsa instead of sheets of ply, so I can have more freedom in shaping my deck. I did some veneer boards a couple of years ago, and had to make ugly relief cuts all across the nose where I had compound curves.
Definitely do your skins one at a time, it’ll take more time, but only one thing to screw up at a time.
You probably don’t need all those stringers, but yes, the center will help hold your rocker on the inital bagging. Once you have one skin on, though, it shouldn’t be a problem.
Thanks for the warning Shwuz. Will I still have problems with bender ply? I figure the bender ply will bend really easy across the board and the normal flex of ply would take the rocker. I’ll try to keep the deck as flat as possible at the nose flip. What do you think? The bottom will be flat.
Silly, I can’t imagine trying to do more than one layer at a time with only a couple minutes working time, that’s why I was thinking to scarf pieces together and glue one layer at a time.
Did anyone see my post about cooking the blank to fo away with a vent plug?
I can’t wait to get started on all this stuff. On June 22 I have to go and get my surfer’s ear drilled out, so I’ll will be dry docked all summer…dreaming about using the 8-0 come winter…
“compound curves are the biggest problem. Unless you plan your shape and deck crown very carefully, you’ll run into areas where the deck needs to curve up into the nose rocker and also curve down/across to meet the rails. It won’t bend that way. So, you need to plan your deck shape so that in areas where you have rocker, you have no crown on the deck. That is the main reason why I’ve always done my skins with strips of balsa instead of sheets of ply, so I can have more freedom in shaping my deck.”
Hi Shwuz,
Makes perfect sense. In the case of strips, they would probably act the same way as ply if glued together first then laid onto the deck? Ever tried this? I’m thinking maybee Paul Jensen has experience with this issue. Paul?
Gorrila glue for the first layer is pretty bullet proof
Man, gorilla glue might be bullet proof but not fool-proof. When I did my rails, it was the first time I used the stuff and I guess I used too much, because the stuff expanded a lot and made big ugly gaps between the rail and the foam. How do you guys make that stuff work?
