Could use some feedback for lamination/composite project

[Anonymous]

1st X post.

[Anonymous]

I’m going to be making a combination UL Pulk/shelter and bicycle trailer/shelter. For fiber reinforcement on the top/ceiling panel, I’m using a combo of 3.7 oz/yd2 S-glass and 1.4 oz/yd2 e glass for the top of the panel and 1 layer of the 3.7 S-glass for the bottom of the panel (since it won’t be under any significant load, I might just use one layer of the S glass on the top and bottom).

I’m trying to figure out what a good, inexpensive, and lightweight core material would be? I know foam would work pretty good, but I’m trying to stay away from it for environmental reasons.

So far I’ve considered honeycomb core cardboard, balsa wood, and a plywood of some kind. The cardboard would be the cheapest and lightest I think.

Any suggestions or other ideas for a core material?

 

[James Marco]

Styrofoam/foam panels is perhaps the lightest, but it adds nothing to strength in compression. Compression is what holds two layers stiff/rigid. As it tries to fold up under stress, you will find it quickly compresses, loosing any strength it had from the separation. One skin is tensioned, the other side is compressed. I would suggest a light wood, like balsa or cedar to mitigate this. This maintains strength over the entire tension of the fabric on one side and has high compression resistance on the other side. Generally a much stronger shell.

Even cardboard is not the best, though you do have a little more strength, given at least a 1/2″ thickness. Again, it compresses easily so overall, you are better off with a 1/4″ layer of solid wood than a 1/2″ layer of cardboard reinforcing web. I have used quite a bit of web in cabinet doors under mica, or regular doors with a wood frame. But mica is relatively rigid before adding the glue. Using a fiberglass skin, I am afraid you will end up sagging into the web pockets leaving a waffle effect on the surface. We won’t discuss air bubbles.

The ultra fine 1.4oz will likely add more weight than what you add in strength over simply adding two layers of heavier glass in satin weave…a 3.1 or 3.2oz satin weave aircraft grade glass. It kind’a depends on how you build it up. Normally, plain weave will have a lot of tiny pockets. Satin weaves generally use about 1/2 (maybe a bit less) as much epoxy over a plain weave S glass, even though the S glass is a bit stronger. So, the reduction in epoxy (weight) with satin weave generally offsets using two layers of plain weave S glass. The two layers of 3.2oz Satin means you get a total of around 6.4oz vs 5.1oz you are planning. But, the weight will be roughly the same. So, the satin weave is actually somewhat stronger (even though S glass has higher strength) and about the same weight after applying it. It is just more expensive, though a portion of this can be recovered through using less epoxy. I usually use about 20% acetone in the epoxy AFTER MIXING A BATCH and before using it. This lets it penetrate the satin weave a bit better. (I normally recommend MAS/Crystal Clear epoxy, not the West blueish tinged stuff.)

For a pulk, you need heavier cloth. The light fabrics are not enough to prevent tears/scratches. I used three layers of 3.2oz satin weave on a strip canoe and got the weight down to 17lb for 13.75′. A person dragged my boat half full of water over a rocky shoreline after dumping it. He put a 8″ gash in the bottom over a broken rock (duct tape patched it up temporarily.) Generally, the fiberglass is not strong enough, even with three outside layers, to prevent digs. For the pulk side, I would recommend at least two 10oz layers, maybe three.

Did I read that right, is that what you were looking for?

[David Thomas]

1/8″ 3-ply plywood, also called “doorskins” are what I used in 3 single and one triple sea kayak.

They were only $10 for a 4′ x 8′  back then, 20 years ago and they were, conveniently, a stock item at Home Depot.

I debated whether to think of it as (6-ounce) fiberglass-reinforced wood, or wood-cored fiberglass, but they each added their own strengths to the resulting craft.  All my boats are working boats so they get dragged over the rocks and run up on barnacle-covered beaches at full speed.  They’ve held up fine.

A friend who made a number of cedar strip canoes and dories would use clear fiberglass above the waterline for the better looks and carbon fiber below, believing it to be more slippery on the rocks.

[James Marco]

David, nice boat. I assume that was stitch and glue?

I have seen a couple boats with graphite bottoms. I never used it, but can well understand it’s need. I usually use a 1/8″ nylon line soaked in epoxy laid over each stem. This handles most beaches up to about 5-10 years. Then it can be sliced off and new added.

Ha, hey, he dumped the canoe in a short stretch of white water, and was in a hurry to get out of the water. He just grabbed the boat and, adrenalin fueled, dragged ~500# of boat & water up the beach.

Anyway, I agree with your assessment. Wood cores add strength, and stiffness to the laminate making it much stronger than adding up the strengths of fiberglass and plywood individually. My first boat was cobbed together back in the latter 70’s after Scientific American released the Strip Built Canoe article. Built of 5/4″x1/4″ mahogany/white oak it was a 4seat lake rowboat. I believe I have built about a dozen or so since then…mostly solo canoe-yaks. Anyway…

It is hard to beat glass/vinyl composites for pulks. Cheap and easy to pull with crossbars.

[Anonymous]

Hi James,

Thank you for the advice/info. I have a lot to learn about lamination composites. Re: glass/foam combos, my understanding is that surfboards are commonly made out of a foam core with something like two layers of 3.7 oz/yd2 S-glass for the top/deck and one layer on the bottom, or one layer of S glass with a layer of E glass for the top/deck and one layer of S glass for the bottom. Not surprisingly, they don’t handle focused/pointed impact stress all that well (like banging against sharp rocks or coral), but they manage to handle all the other extreme stresses (torsional, compression, etc) pretty well and are fairly durable if built correctly.

The fiberglass/core layer is only for the roof of the pulk. When in pulk mode, it will be somewhat raised on two long skis, so I’m not too worried about abrasion and impact (minus the occasional branches or what not).  I suppose there is “some” possibility of it getting flipped over at times.  While I prefer to not use foam, I’m not totally against it, and a skin layer of high density 1/8th EVA foam on top of the roof composite would provide a lot of protection for the fiberglass underneath, as well as a bit more insulation.

Re: Honeycomb cardboard core, you wrote, “Using a fiberglass skin, I am afraid you will end up sagging into the web pockets leaving a waffle effect on the surface. We won’t discuss air bubbles.”

Yes, I am somewhat concerned about such possibilities.  On the other hand, people have successfully made cardboard bikes, skateboards, snowboards, surfboards, and furniture both with and without fiber reinforcement using glues and epoxies, so I figured a roof reinforced with S-glass and epoxy that generally won’t be subjected to much stress might be ok.

One of the things I’ve looked at is Baltic Birch plywood.  I can get it for a bit cheaper than balsa core. Know anything about it?

However, it would set me back some 60 dollars (using 1/4″/5-6 mm), whereas the honeycomb core cardboard would be about 38 (maybe less if I can find it locally), but with more length to work with.  I would be forced to make a 6 ft long roof if using balsa or baltic birch plywood core. I’d prefer to have it a bit longer since I will be sleeping in it.

If I could find some high quality, non warped, 1/8 plywood like David mentioned, I’d be open to using that though.  Certainly would be a lot cheaper and more convenient since it comes in larger sizes. I do have both a a couple Lowes and Home Depots close by. I suppose I don’t want the pulk/bike-trailer/shelter to be too light, otherwise wind or what not will too easily blow it over.

Btw, speaking generally and to no one in particular, S-glass is about 25% stiffer and higher tensile strength than E-glass, and actually has higher tensile strength than common/standard carbon fiber at same sized fibers, but carbon fiber’s tensile strength to weight ratio comes out a bit higher than S-glasses and it’s stiffness to weight ratio is moderately higher.  However, the S-glass is still significantly less expensive than carbon fiber.  It’s also generally, all around more durable, or so I’ve heard/read.  Carbon fiber is better for parts that need very high stiffness and tensile strength at lowest weight possible. For like certain high end race car, race boat, or race bike parts.

 

[Anonymous]

The rest of the pulk/bike trailer/shelter will be a combo of general, cheap lumber 2×4 type material for the somewhat triangular frame (maybe with a very light E-glass fabric+epoxy over it) and fabric+climashield apex+dyneema/spectra type cord for the rest…  Let me explain a bit.

Eyelet screws will be screwed into the inner part of the frame at intervals, and dyneema type cord will be strung through to make a wide spaced net.  On top of that (and connected directly to the top of the frame), for the floor will be a two layers of 1.7 Robic nylon with Climashield Apex in between. Think of an uber strong and durable hammock. EVA Foam pads (which I already have) will be further insulation for sleeping and/or putting rough/abrasive/sharper stuff on.

The sides (3 sides, two sides and back) fabric will be a combo of 3 oz/yd2 siliconized, highly water resistant, slightly breathable nylon outer fabric, with a backing of 1443R Tyvek or PP nonwoven fabric (making it WPB) next to same, Climashield Apex core, and 1 oz Robic for the inner.  Besides all the venting of moisture from the WPB sides and the more breathable floor, there will be a “window” vent in the roof with removable/exchangeable (velcroed) WP+insulation, non DWR WPB fabric, and mesh panels–probably right under the head-sleeping area.

The back fabric panel will function as an adjustable “door”–meaning it can be made to be flat against the rest of the structure for maximum insulation, or pulled out some for increased ventilation in nicer and warmer weather.

Minus the removable 12″ fixed caster type wheels (overkill you might say, but the bicycle will have a small gas engine on it) and permanent long skis, depending on core material used in the roof and exact dimensions (either 48″ [at widest part] x72″ or 43″ [at widest] x84″) in the main structure, I guesstimate it will weigh somewhere between 40 and 65 lbs.

The bottom part of the narrower nose [40″] end will be hinged to the corresponding part of the roof, so that from the back, it will be able to be raised and supported by two carbon fiber hiking poles (one on each side) or collapsed. The general design is based on the pulk-shelter used by an Arctic type explorer, but modified to be both much more breathable and lighter and to do double duty as a bike trailer. His biggest issue was condensation buildup because he had a lack of venting and used primarily WP materials (he had a plywood floor and WP fabric sides).

It’s probably the most ambitious project that I plan on building so far. It’s both for recreational use in the present and for the ultimate bug out shelter potentially for the future.

If I could get sponsors and save up some money meanwhile, I’d consider doing an ultra trip–bike down to the tip of South America and fly self and the pulk-shelter to Antarctica for some kind of excursion there.

[David Thomas]

Don’t fret about low-weight being blown around in the wind.  Yes, it will happen, but don’t build the weight in – add water or rocks if you want more weight at times, but you’ll never want it when you’re pedaling up hill.

I’ve had thoughts about a pulk-shelter for myself on skis/snowhoes or for dog-sledding buddies.  No need to set up a tent, just crawl into a totally wind-proof, insulated coffin with enough head room to sit up.  I’d use stitch-and-glue construction like those Pygmy kayaks I built (their plans, my jigsaw).  I imagine a false floor with about 6 inches of depth for storing food and gear down low where it will add the most to stability.

I wish those Jet sleds (available all over up here and cheap) came longer, like 7 feet long.  I’ve considered buying two, and joining the front 80% of one with the back of another with some lumber stringers for stiffness and welding the joint in the HDPE.

They also make additional HDPE strips to attach to the bottom if you want it to track even more.

[James Marco]

Justin,
You wrote:
“…my understanding is that surfboards are commonly made out of a foam core with something like two layers of 3.7 oz/yd2 S-glass for the top/deck and one layer on the bottom, or one layer of S glass with a layer of E glass for the top/deck and one layer of S glass for the bottom.”
Yes. But I am sure you do not want the 2″ thick foam that accounts for that strength. If you don’t mind the thickness, sure, it can work. The separation between the surfaces adds strength. There are formuli for that, but generally you get good to excelent strength in the 1″-2″ thick range. Very roughly you can think of this as trading the compressive strength is traded for tinsel strength along the opposite surface, not allowing the compression to collapse the substrate. (Not quite true, but close enough.)

Yes, I do not dispute that S glass is about 20% stronger. But, it takes 100% to epoxy it. Satin weave glass takes about 66% less epoxy for the same weight cloth. I can get a smooth surface in two coats. With plane weave, it takes three coats. Adding dissimilar glasses, really does nothing for the laminate (I use three layers outside and 1 layer inside the canoes.) It DOES improve overall strength somewhat and impact resistance/abraision resistant a lot. Really a balanced laminate is the strongest/weight, but with asymmetrical loads/impacts/scrapes/sharp digs, sometimes it doesn’t make sense to keep them symmetrical. Also, S glass is a bit stiffer to work with and doesn’t conform to any curves as easily. Depends on your design.

“Yes, I am somewhat concerned about such possibilities. On the other hand, people have successfully made cardboard bikes, skateboards, snowboards, surfboards, and furniture both with and without fiber reinforcement using glues and epoxies, so I figured a roof reinforced with S-glass and epoxy that generally won’t be subjected to much stress might be ok.”
Your call, I would not do it.

Baltic birch is usually 5’x5′ pieces. I use it for jigs in the shop. It is fairly hard and normally made with no voids, giving it high compressive strength. If you want more than 5′, you generally have to special order it or laminate it edgewise. Think of this as two crenelated edges joined with regular wood glue. The length of the crenelations are longer than the strength of the wood, so generally there is only a little loss of overall strength. Not difficult, just hard to make things work perfectly over the length of the plywood joint. I believe there was a section on that in one of the boat building books….hmmm….(“Ultralight Boatbuilding”??) I don’t remember offhand. I made up a small table out of some plywood scraps, but never bothered with more. Some of the stitch & glue panels were closer to 13′ to 16′ long. Never particularly cared for the rough edges on the boat, though. As you say, door skins will work for you. Usually you can get these in good birch, too. I would lean to mahogany to avoid any wood rot.

One problem with carbon stuff, is that it is not transparent. This is perhaps the biggest downfall. Aramids are also not transparent, but you can usually get them in multiple colors. You can always beef up a laminate. You cannot change it’s color.
Anyway…

[Edward John M]

I’m not sure that what you want will work well on snow.

I have been advised many times and it has been my experience that “Long, Low, Skinny and Flexible is the best solution for load dragging on snow

I have made and used a ski based sled with a flat top, long and wide enough to sleep on and it was a pig anywhere but on smooth graded track

Also it is getting much harder to find old downhill skis suitable for making such sleds from since the introduction of shorter super-shaped skis

Like David Thomas above I have though about taking a Paris Expedition sled and stretching it by adding in a centre section but in practice I find adding an extra shorter sled is more efficient and easier and has more flexibility in use

[Edward John M]

This is what I use as I know my verbal description is a little lacking

[James Marco]

I found this on the web. It describes the basic failures with fiberglass. Tension, compression and shear are all discussed with some mention of foam cores and poly web cored/cardboard laminates.
http://www.ericgreeneassociates.com/images/Failure_Modes.pdf

[Anonymous]

Hi David,

Good point about adding extra weight in the form of water etc.and not worrying too much about the lightness. Thank you for the practical advice.

 

Hi Edward,

Would agree that the width I’m looking at is not ideal. I’m factoring in the sometimes accompaniment of my spouse sleeping in the shelter. I’m probably going to go no wider than 44″ at the widest (tapering down to 40″ at the other end). Also, I wouldn’t be lugging around a ton of weight–I’m towards the UL (and not having to have a tent will help). I see used long skis here and there–yes, getting harder to find, but I could also make my own–wouldn’t be too hard since bindings etc wouldn’t be part of the picture.

Btw, this design is loosely based on the below “Pulka-Hut” by Cameron Smith, who used his for a few years in Iceland and overall quite liked it except for the condensation build up and that it was kind of cramped/small.

Here’s a short Y.T. video featuring it (there is also a more in-depth article out there somewhere about his experience with it):

 

Hi James,

Thank you for the further feedback and the link. Lot’s of complex factors to consider for sure.

 

A general update:  I’ve been doing a lot of research into cores as to pricing, weight, and general properties. I’ve decided to chuck out the plywood idea because while pretty economical (if using non exotic materials) and fairly light weight, I would still need to have something for insulation and that’s an extra expense that’s not necessary if I go with the right core to begin with. For a little while, I was looking at some Paulownia plywood and even eyeing the Paulownia tree in my back yard. But the Paulownia plywood is pretty thin (2.7 mm) and not really insulating enough.

The tree in my backyard would be a lot of work and at least 25 dollars extra in expense (since I would need to get a milling attachment for my chainsaw). Then I would have to wait some 7 to 9 months or so for it to dry enough to use.

I’ve narrowed it down to choosing between 3/8″ Balsa core (bit pricey–about 90 dollars with shipping, but pretty light and good all around core, somewhat sustainable, and fairly insulating) and 3/4″ high density EVA foam, which I can get for a bit under 30 dollars including shipping–very good insulation and even lighter. Like I said earlier, would prefer to not use foam because of environmental reasons (btw, I’ll be using a 30% bio based, lower toxicity epoxy to help offset this as well). However my cheap side is definitely tempted.

Decisions, decisions. I need to order other materials from the same company that sells the balsa, so chances are I’ll probably go with the balsa core.

Meanwhile, I’m trying to complete the current project I’m working on before I start the above one. I’m chopping out the majority of the main tubes of my steel framed bicycle and replacing them with a bamboo/carbon fiber composite.  Unlike most projects of this sort, I’m wrapping the entire bamboo pole in a layer of c.f.  I don’t trust the quality of the bamboo I’m using and want it to be very durable and strong.  The fattest tube section I’ve cut out weighs 1lb and 7 oz and the tube I’m replacing it weighs about 10 oz.

However, this is less about weight and more about vibration dampening/ride comfort. Cutting out a couple of pounds is just a little side bonus (also saving a bit a weight by replacing the gears/derailer with a lightweight 1 speed conversion kit.

(I’m doing a two part epoxy approach, using West Systems G-Flex directly on the bamboo because of the greater flex and for any potential expansion/contraction, and then a top layer of Entropy Super Sap to increase the stiffness a bit. If it happens to crack a bit, at least I have the G-Flex layer to fall back on…or so I hope).

 

 

[Author]

Posts