I would like to make a cuben packraft

[Brendan Swihart]

I kinda hesitate to get involved here, but if you really want to push the envelope, buy some 30d heat sealable nylon. Cuben is expensive and will not hold air. Aside from Richard, who knows more about fabrics than 99.9 percent of people on this site, you have several other people saying it's not a good idea. I'd trust a neoair (or hell, a cheap Target air matress) 100x before I'd get in a cuben raft, and I've used cuben quite a bit. If you're going to do it just because people are saying you shouldn't, then I guess godspeed.

[Luke Schmidt]

I'm definitely thinking make a raft, just maybe a bit different. MYOG packrafts have been tried by one or two people but I don't think the idea has been fully explored. I also wish someone would do a better job of documenting the experience (might make a good BPL article).

Some things I'd think about…

-Cuben vs. Nylon (the weights really aren't that different) Durable cuben isn't much lighter then nylon. Given its stretch Nylon might actually be more puncture resistant then cuben.
-Weight Savings vs. Durability. If you go from .75 oz cuben to 1.4 oz cuben or similar nylon you increase durability a lot and I really don't think the weight game would be that much, maybe 3-6 oz. You will NOT feel that extra weight in your pack, especially since you'll have a PFD, paddle, etc.

Two other ideas

1. packrafts were not noted for their good performance on big rivers, lakes and bays. I'd read up on the newer models and what makes a good flatwater raft if you plan on doing rivers in this thing.
2. Another area for creative weight savings might be the other gear used for pack rafting. PFDs and paddles might be a good area for some creative projects (please wear a PFD when you use your creation, I've swam in big rivers and its no fun).

Regardless of what you make I hope you take good notes and have a good time. I'll look forward to hearing from you.

[Ken Thompson]

Why not try a cuben PFD first? A lot less material. Would be stressed to a similar degree holding you up. Two pieces and an inflation valve. What do you think?

[P. P.]

First of all, let me take a moment to say I'm glad to be able to post again. YAY!

I love the idea of a cuben raft. I'm an avid packrafter. However, I don't think a cuben pfd would be equal to the stress and pressure to which a raft would be subjected. Unless you sit on it and ride it down a river…………….

[Ken Thompson]

True, but it would be a way to see if it would hold air long term. You could stress test it easier than a full size boat. Thinking weights and swimming pool here.

[Hiking Malto]

Iceaxe,
What about combining a couple of small neoairs for flotation in a outer cuben sleeve. That would allow your flotation portion to have dual use. On a related note, I just made a bunch of cuben items over the last couple of weeks. I made new food bags to replace the 1.5 zpacks bag that went on my PCT hike. The new sacks were 100% waterproof but when I filled the old sacks up with water there were dozens of tiny holes in what appeared to be a very serviceable food bag.

Finally, I'm an engineer but can relate to your comment about the motivation of being told it can't be done. In a former life I invented a casting process using aluminum molds. After doing scale up I called a major AL manufacturer to make sure that the alloy that I was using was optimized. I was told by the experts that what I had already accomplished couldnt be done. I guess the experts were wrong.

Sounds like you have a new adventure planned. Look forward to hearing the details. Or you could tell me to go f off! :)

[a b]

GG man, would never tell you to do that! It is your enthusiam for life that is an inspiration to me.
Your idea of a sleeved floatation raft is quite interesting. May not save any weight but would be a hybrid approach with built in safety of multiple chambers. Thanks. Hey Ken, your picture just reminded me of that hand drawn picture from Colin Fletcher's book. He used just such a PFD to cross rivers.. He also used it as a hat! Thanks PP and all. I will be sure to share pictures of the launch in my local resevoir.. It could be pretty hilarious.. Perhaps the first cuben submarine.

[Ken Thompson]

For big rivers, what about one of these offerings?

http://www.gaboats.com/

[David Chenault]

I think the in-elasticity of cuben would be a major problem, but no harm trying (save to the wallet).

The lightest rafts I'm aware that are currently available are the Flytepacker and the Supai Adventure Gear Canyon Flatwater 2. They appear to be fairly equivalent products.

[Lawson Kline]

I would save your money. The PET version of cuben fiber is NOT air-tight at all. Sure it might be the day it comes from the factory but after a little use pin-holes form and it will leak air.. An air molecule is much much smaller then a water molecule and is the reason it works decent for drybags but not so good for air-tight structures. All that said, when I was making dry bags I had Cubic Tech make me an airtight CT5K material using a 1 mil Weldable Polyurethane Film on both sides. It was EXPENSIVE ($30+ meter), Heavy (5.5oz sq yard) and had to be welded at a super low temp due to the Dyneema fibers. If you left the material in the sun for a long period of time it would weld together by itself. All and all it was pretty a cool material but needed some tweaks. It would of made a good drybag material but not a good packraft material as a 1mil film is still very thin for an air-tight material. From what I understand 2-3 mil is the minimum and if you went this thick you might as well use an off the shelf 70d or 200d TPU material since the film/coating weight would be the same. Good Luck : )

[Jordo _99]

Been following this a bit but figured that everyone else had pretty much covered it…

I like that you're willing to try something new and push limits….However, this just seems pricy and time consuming for a result that almost certainly isn't going to accomplish much other than being able to say "told you I could do it" (It will probably float but it's not going to wear/age well at all and will be prone to failure).

By all means, if you have the time and money, go for it. I'd love to see it…I'm just confused as to the intention of using cuben against the overwhelming recommendations against it. If it were me, I'd be paying a bit more attention to all the red flags people are waving so it makes me wonder why you're so adamant about using cuben anyway.

so…why stick with cuben when the responses are heavily against it?

[Colin Krusor]

David, thanks for mentioning the Supai boat. I wasn't aware if it. I learned about two new packrafts in this thread (the Supai and the Feathercraft mentioned by Luke). The Supai is 11 oz lighter than the Flytepacker, making it the lightest packraft available (that I know of) by a substantial margin. I might consider buying one of these.

[a b]

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[Franco Darioli]

So simple, makes you wonder why no one has come up with the same concept before.
One small problem I have is visualising how you are going to get into that raft so that the sides become "rigid"
BTW, keep in mind that the air inside those balloons can cool down pretty fast once in the water.
Anyway this has inspired me to have tacos tonight.

[Colin Krusor]

Ah! You argued earlier in this thread that cuben is not as prone to leaks as people think, ab, so I assumed that you were considering using the cuben as an airtight barrier.

I think your plan to use an inflatable bladder inside a cuben envelope is much more promising. Is this the basic design you had in mind (below)?

I had thought of making a heat-sealable nylon packraft/kayak in roughly that design, too. It seems that it might track better and have better speed than a conventional packraft. I think it would still be nearly as wide as a packraft at the widest point, though (in the middle, where you squeeze between the tubes). It has occurred to me that lower drag might be achievable with a large central tube with two small lateral tubes, but at the cost of much less stability:

I made a down-filled inflatable sleeping pad for my wife a while ago using the bladder-in-envelope design:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=56903

The thin, heat-sealable polyurethane film that I used for the bladder weighed about 1.2 oz/yard. I definitely would not use anything thinner. It is a tough material but it's fragile at that thickness. The envelope was M90 nylon taffeta, but I considered using cuben (and Steve Evans suggested it in the thread). However, according to my math, replacing the nylon envelope with 0.51oz cuben would only reduce the weight by about 15%, because the majority of the weight is from the bladder material. The bladder needs to be larger than the outer envelope to prevent it from being under any tensile strain when it is inflated. If you use the same bladder material I used and 1.4oz cuben, the weight of the material becomes nearly the same as heat sealable 30D nylon (2.5-3oz/yard). You can only improve upon 30D nylon from a weight standpoint if you use an ultrathin bladder material and/or a lighter weight cuben (like the 0.74 oz stuff).

Don't forget to add a (fabric?) vent somewhere (probably at least two) on the cuben, so air can escape from between the cuben and the bladder while you're inflating the bladder.

[Jordo _99]

Well I was with the group that was under the impression that the idea was for Cuben to be the balloon and have a single layer…I have far more confidence in this idea.

Definitely keep us updated on this. I was always interested in how it would work but now I'm hooked to see the design that's being hinted at.

If it's similar to the canoe-like raft Colin posted a picture of, then it might be interesting to have a sleeve for a sleeping pad to go down the center to help support the entire structure…just as idea.

[Alpo Kuusisto]

I tried this summer to build a 'kayak' inspired by the shelter systems tarp kayak:
http://www.shelter-systems.com/kayak.html
Idea was to make a fabric shell, about size and shape of a small whitewater kayak. Then insert a standard closed cell foam mattress on the bottom to create some shape and a six foot pole (cut from the riverside willows or aspen) on top of it to stiffen the frame. Backpack was stuffed in stern and finally kayaker climbed in, his feet filling the bow.
Paddling was quite awkward, but possible. The boat didn't have any initial stability but would float so deep it was actually quite easy to keep upright (swimmer can't tip over). Stern volume was too small even with 50 liter backpack, so feet were much higher than butt making paddling a good workout for the abs.
Unfortunately there are no photos and the 'boat' is already cut in half to help with cutting a new slightly longer shell for next summer.

Pros of this design for a cuben packraft would be:
+ takes only two sq. yards of fabric so would be ridiculously small
+ not too many seams
+ doesn't need to be airtight
+ with a small puncture, slowly fills with water but the structure doesn't collapse
And cons:
– paddles flatwater even worse than Alpacka
– probably impossible to self rescue
– swims deep
– previous combined with poor initial stability makes entering and exiting difficult.
– you need the willow, or carry a pole
– you need the mattress and backpack too, and pfd and paddle of course

Hope I could give some ideas for the cuben raft project, and would welcome any ideas how to continue with my boat. The goal is a sub 5 pounds packraft that would be better to paddle flatwater than Alpacka. Probably made out of heat sealable PU coated nylon.

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