Interesting thread and Idea. I’ve been obsessed with reducing the weight on my hollows for years. The largest weight loss has come from reducing the weight of the rail band in conjunction with increasing the dome in the deck of the board. This does three things to reduce the weight. The rail width is reduced both top to bottom and side to side because of the enhanced dome in the deck, and because I create my perimiter frame prior to inserting any type of interior frame I am able to route out the interior of the rail to make a completly hollow rail. The enhanced dome in the deck alongside a good interior frame can cancell out the need for any interior carbon fiber or lamination.
I’ve used quite a few combinations, depending on what I’m constructing the internal frame out of. Epoxy mixed with fairing filler works great, though it can add alot of weight. I’ve used polurethane glue on my last few boards, and I am very happy with it. Doesn’t really add any weight. Hey, you’re in the area. We should try to connect some time.
I’m a big fan of PU glue too. Especially the Elmer’s version of foaming gorilla-type stuff. Living where we are, it helps to have something unaffected by the cool & damp
I’d love to see your setup & your work in person. I have a flexible schedule, especially during the week…send me a PM (click my username & choose ‘Send a Private Message’)…I’m a fairly dedicated west Marin longboarder, but might have some stuff you’d be interested in anyway…and I’d certainly not pass on the chance to see what else you’re up to.
I finished making all of the balsa sub-frames for the ribs at work today (I love my job at the hobby shop, I can build my surfboard on the clock). These sub-frames are the basic rib structures which are made of a 3 plies of balsa. They are intended to hold the shape of the board and act as a jig to install other parts which carry the majority of the load. Each rib is composed of 11 individual pieces of wood. Each piece of wood is positioned to give the maximum strength and spread the stress around the lightening holes. I also threaded 2 strands of carbon tow under tension through the ribs. The tow will be anchored to the rails.
I came up with an interesting way to work with the tow. The strands of carbon are not adhered to each other at all, when you work with it, it can unravel and make a mess, also it can take up alot of space and require excessive amounts of glue to adhere it to a structure. What I do is cut off 10 ft at a time, clamp one end in a vise and the other in a drill. I thin 15 min epoxy with 50% alcohol. Then I brush the mixture onto the tow. Then I wind it up in the drill (about 150 turns) while keeping as much tension as possible. Meanwhile all of the resin is squeezed out of the tow. I wipe this off with a paper towel. This just leaves just enough resin to make a round rope that is VERY flexible and easy to work with.
I assemble the whole rib with the carbon tow entirely with thin and medium viscocity Cyano-Acrylite Glue what modelers call C.A. glue or super glue. The best part about the glue is that it dries in seconds and wicks into the grain of balsa and between the fibers of carbon to make a very strong bond that is also light weight. My entire frame will be constructed exclusively with super glue. Epoxy is sooooo heavy!! plus you have to mix it and wait.
here is the current weight analysis of the parts.
stringer subframe: 3 oz
rib subframes (starting from rear)
1: 1/8 oz
2: 3/16
3: 1/4
4: 5/8
5: 1/2
6: 1/2
7: 1/2
8: 3/8
9: 3/8
10: 1/4
11: 1/8
Total weight: about 6 1/2 oz and it actually looks like a board now!! all the major parts interlock without any glue
Looking good, what is your next move? Bottom skin?
My hollow had a flat deck and I had to build the rail out 1 1/2". The board weighs 23 lbs. I agree, if you use more cross members you can use a thinner skin and save alot of weight. The domed deck will also give you less rail to build up but my experiments show that it is near impossable to put foil into 1/8"ply. without it kinking if it is domed. Think about bending a toilet paper roll.
You cannot bend it if the material cannot stretch in two directions. Bending ply. only bends in one direction.
I am thinking about thick veneer backed with glass that applied to the frame while still green a la Paul Jensons post.
i have to wait for my carbon parts to arrive this week. Then I will fill in the truss inside the stringer, laminate it with carbon on top and bottom. Then Glue the ribs, and sub stringers, Then make the kevlar C-Channel rail supports, Then fill in the frame work for the deck, which is over the ribs (making each rib an I-beam) , Then sheet the botom with 2 ply veneer, then sheet the top
I bought a 8" drill press today from a place called Harbor Freight. They have a huge selection of crappy low quality tools but for the price you CAN’T turn it down (for what Im gonna do with it, I think it will hold up fine). It was only $49.99 WOW. and I got an 11 peice hole saw set for $2.99 Im gonna lay the first layer of sheeting up in the hole saw drill press and go to town!! They also have a nice looking scroll saw there for $49.99 I will grab it tomorrow. Im not sure if this place is a franchise but if it is you should check it out!!
I have the rail frames attatched. they are a 3-ply lamination of balsa and kevlar. 1) 3/32" balsa runing lengthwise 2) 5 oz kevlar tape 3) 1/16" balsa (grain running top to bottom
I assembled the rail with thinned epoxy. 1 part resin, 1 part hardener, 1 part alcohol. This allows me to use a brush to lay on a thin light coat. Then all the parts are clamped down while the resin cures. I am a strong believer that easiest way to lower weight in a structure is by using less glue. Thinning epoxy is a great way to use less resin. As the alcohol in the epoxy evaporates, it leaves a thin layer of resin that is thuroughly saturated through the balsa and kevlar. It is just enough to hold it all together. pics coming soon, hold tight.
By the way I had a great skim session today on the gulf. When a cold front approaches FL, usually a strong low pressure forms over Georgia. This sucks up a nice south swell right along west FL. The skim rolls right up to the sand with nice thigh to waist high left lines!! Very fun
Here is the stringer with the 1/4" carbon tube truss Next to it is one of the unidirectional carbon laminates. One for the top of the stringer and another for the bottom. also there is the kevlar tape that I will use to laminate the rails
close up of the stringer. You can see the slots for the ribs. I took the pics right before I covered up the truss with the other balsa sheer web.
Here are some pics of the board after building the kevlar balsa rails but before sanding them
close ups
the concave in the bottom. I have since sanded it so it is not so V shaped
After sanding the kevlar rails. That shit is a bitch to sand. I went through 2 used belts and one new belt on my belt sander, and I went through 2 sanding blocks to get the rails smooth!!
Finally, here are a few pics of my shop. As you can see I like my airplanes!!!
PLEASE GIVE ME SOME FEEDBACK!!! I WANT TO HEAR YOUR OPINIONS!!!
im installing Futures fin boxes. The mounts for the fin boxes will double as extra support in the back of the board. I know it looks a little empty there.
