How to Eskimo Roll a Packraft

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RomanDial
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How to Eskimo Roll a Packraft

Post by RomanDial » Sat Nov 21, 2009 1:08 pm


alaskabackcountry
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Re: How to Eskimo Roll a Packraft

Post by alaskabackcountry » Sun Nov 22, 2009 1:50 pm

Regarding the thigh straps: does anyone have any thoughts on using the lightweight attachments from Alpacka vs. the metal D ring types made for bigger boats?

Obviously the thin fabric from alpacka would be lighter. Is strength going to be a major issue? Perhaps more of an issue on the front or rear? I'd love to hear some thoughts from those who already have their boats set up this way.

Thanks for all the beta so far.

-Kevin

alaskacreeker
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Re: How to Eskimo Roll a Packraft

Post by alaskacreeker » Mon Nov 23, 2009 8:16 pm

The reason behind using larger d-ring patches is so the stress from the pull of the thigh straps is concentrated over a maximum area. If you use tiny little d-rings, there will be a ton of stress pinching just one small spot in the fabric, which might rip the boat, especially if you roll a lot. That large d-ring isn't only a few extra ounces and disperses the forces of rolling much better.
Timmy J.
www.alaskawhitewater.org
"Screw it, let the revolution begin..."

RomanDial
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Re: How to Eskimo Roll a Packraft

Post by RomanDial » Tue Dec 15, 2009 5:55 pm

Kevin --

The lightweight Alpacka tie-down used on a thigh strap equipped boat ripped off after ripping in half. The owner of the boat replaced that with the big D-ring style, about 4.5 inches in diameter. Weighs 1 oz instead of 1/4 oz.

FYI

http://packrafting.blogspot.com/2009/12 ... -ride.html

Alpacka Raft LLC
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Re: How to Eskimo Roll a Packraft

Post by Alpacka Raft LLC » Wed Dec 16, 2009 1:53 pm

Yes, we talked to Luc (who had the grab loop blowout rolling). Very cool experiments going on, but this helps illuminate why Sheri (the Alpacka inventor / prez. for those readers who don't know) isn't jumping straight into rolling boats, thigh straps, etc... she's looking at things from fabric to other components to deck design, asking questions like "what are the big implications for design and safety?" I just spoke to her, and she raised the point that the boats weren't designed, as-is, for rolling or for the sort of water you really need a combat roll in, so there's a tremendous amount for her to investigate.

That highlights some of the community / Alpacka synergy: in a variety of uses, the community is doing innovative things with the boats, also a bit out of the design or testing spec... as happens when you've got adventurous souls :D . Sheri's dedicated to providing a tough, thoroughly-tested platform.

Current Alpacka grab loops: not tested for rolling.

sheri

Re: How to Eskimo Roll a Packraft

Post by sheri » Wed Dec 16, 2009 9:38 pm

I don't have the info as to exactly which way Luc's grabloop tore. I need to know more to make a real judgment on what happened. In the email Luke wrote to Andrew he stated that the fabric itself tore. Don't know whether the webbing tore first or the fabric itself. Can't really make an assesment until I find out exactly what happened. In general though that grabloop should be plenty strong. Still I would lean towards a slightly different configuration on the grabloop and also with a slightly larger base. Rolling does not create more than 350 lbs. of stress which is what we have found the grabloops can fail at. So perhaps the grabloop was faulty, the glue job was faulty, the allignment was faulty, etc. etc. etc. If the pull line was placed wrong and the glue job was not great all the way around then the grabloop can pull off. Gluing this fabric well is a little trickier than it looks.

One word of caution on putting the D ring grabloops from ARK or anywhere else. If the base in Vinyl or PVC and not Urethane you will also probably get failure down the road. Make sure the base is Urethane. Over time most gluing of Urethane to Vinyl or PVC fails. The glues are not designed to work across the different fabrics.

Cheers, Sheri

RomanDial
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Re: How to Eskimo Roll a Packraft

Post by RomanDial » Thu Dec 17, 2009 2:21 pm

This is what I put on my boats as described on Alaska Raft and Kayak's web site:
http://alaskaraftandkayak.com/store/nrs ... -1065.html
NRS D-Ring For Bandits

Add these urethane coated nylon D-rings to your NRS Bandit inflatable kayak.
These can be used for strapping in gear or installing thigh straps in your boat.

Use urethane specific glue for installation such as #1901 Clifton Urethane Adhesive.

4 patches
1" D-ring
4" patch diameter

mhay
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Re: How to Eskimo Roll a Packraft

Post by mhay » Thu Dec 17, 2009 2:27 pm

Speaking for Luc here, but he explained the grab loop "tear" to me the other night. The grab loop pulled off the boat when the outer layer of plastic(?) on the boat peeled off the inner fabric of the boat. So it was more of a mechanically induced delamination of the boat material than a tear.

mike

RomanDial
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Re: How to Eskimo Roll a Packraft

Post by RomanDial » Thu Dec 17, 2009 2:50 pm

Wondering if maybe it's related to the small diameter of the patch Luc used?

Alpacka tie-downs are 3 inches in diameter (~7 sq inches); the bigger NRS Bandit ones are actually 4.5 inches (~16 sq inches).

So, doesn't double the area halve the pressure, if pressure equals force divided by area? And wouldn't it be the outward pressure acting on the glue or fabric laminate that would cause the failure?

Hig or Shaggy or other engineering/physics types, can you check my physics here?

Shaggy
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Re: How to Eskimo Roll a Packraft

Post by Shaggy » Thu Dec 17, 2009 5:31 pm

That's act3ually a little conservative, but close, Roman. I calc that a 4.5 inch circle has about 225% the surface area of a 3 inch circle. Additionally, though, the actual weld or glue area can have a different geometry and % of the total area. EX: an rf-welded grabloop is a concentric circle surrounding the central sewn-on loop. So, not only is the area of adhesion different based on attachment method, but that can change the mechanical forces too (ex: peeling vs. shearing).

Hig's the real wiz at this, though.
All posts are personal opinions only.

"Boldness has a genius, power, and magic." -Goethe

Hig
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Re: How to Eskimo Roll a Packraft

Post by Hig » Tue Dec 22, 2009 2:29 am

Well... if the failure was simultaneous failure of the entire glue surface, then it would be exactly the surface area difference you're describing that was important. But that's probably fairly far from the case.

In this case, and in many gear failures, the failure probably begins at a point. Once a tear starts, there's a tremendous amount of force concentrated at the tip of the tear, so it tends to continue. That's why you might knick a piece of packing tape in order to tear it. So in this case I would look to the details of where the loop intersects the patch. The simplest explanation is the thickness of the patch where the loop joins it. The Alpacka patch is thinner there, so the tear initiates more easily. It may be that it's worth looking at the details of the stitch. Are Alpacka patches, or some subset of them, over-stitched leading to weakened fabric?

My guess is that a carefully designed patch carefully applied could be far lighter than those beefy ones that Roman has been using. It's on my list to experiment with this... I'm not really that concerned with rolling, but I'm curious to see how a light setup might improve general paddling. So I'll try to build it to be light but still strong enough to roll with, and then maybe I'll never test that strength. :)

lucmehl
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Re: How to Eskimo Roll a Packraft

Post by lucmehl » Thu Jun 16, 2011 4:24 pm

The tie-down loop in question was defective- the two layers of the patch were only glued together for half of the patch. I put stabond between the unglued surfaces as well as on the boat/patch bottom. The patch (strong-side hip) ripped along that glue/no glue seam, and took a little bit (4x4 mm) of the blue material off the boat, leaving a white bald spot.

I put Alpacka tie-downs on Tomas' boat and he ripped a patch (strong side hip) during a pool session. The stitching failed that holds the webbing to the patch.

I've put the Alpacka tie-downs on 3 or 4 other boats and have had no problem with those.

So in my opinion... it is still worth using Alpacka tie-downs instead of the heavy D-rings. But plan to replace them when they rip.

-Luc

MikeC
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Re: How to Eskimo Roll a Packraft

Post by MikeC » Sun Aug 05, 2012 8:14 pm

FWIW, NRS is selling a 'packraft specific' d-ring type patch. They are lighter, have a webbing loop instead of a d-ring, and they are tempting for those of us counting grams in our overall setups.

I glued some of these into a Yak about 2 months ago, and the one that sees the most force (at my right hip) finally failed last night. The glue job held, but the webbing part tore out of the patch.

I've been practicing my rolls in a local lake 3+ nights per week so this thing has been seeing lots and lots of force. I suspect that they might work for folks that already have a bomber roll and don't often need to use it.

Doesn't seem worth the paltry difference in weight to me, especially given the time it takes to glue these in and wait for them to cure.

In short, going forward, I think the standard d-ring patches are probably the best overall choice--at least at the hips.

RomanDial
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Re: How to Eskimo Roll a Packraft

Post by RomanDial » Mon May 27, 2013 11:13 pm

Besides coming back from Mexico last winter with big drop inspiration, Luc showed me this: http://www.kayakshed.com/jackson-kayaks ... ckband-kit

It's a whitewater kayak backband. You clip it in with locking carabiners to your metal D-ring set up and you are locked in.

Combine it with a 4" thick minicell foam semicircle for your feet, and your roll will be easier to nail -- you'll be locked in like a hardsheller.

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