Dutch's site says the fabric is rated at 400lbs but I hear that making a bridge hammock instead of a gathered end hammock will derate the fabric some.
Thanks!
Dutch's site says the fabric is rated at 400lbs but I hear that making a bridge hammock instead of a gathered end hammock will derate the fabric some.
Thanks!
https://www.hammockforums.net/forum/...hammocks/page2
Info in that thread... though his Dutchness has yet to chime in on his products.
Good read, sounds like it should be fine but is close to the limit. I also should probably get .75 poles instead of .65.
How do the poles fail if too much weight is on them?
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Hey there, the poles are under compression, so likely they won't fail without an outside intervention (like a kick from below under weight, or something). On the Ariel I built with 2.4, the weak point is where the pole tip enters the Amsteel. There the pole, fabric, and rope all meet, and I believe it's the hammock's weakest point.
I had a spectacular failure once—ended up on the floor REALLY fast—and sent a pole tip through the fabric when it slipped from its rope seat. Even with the tear in the hammock body, I wouldn't worry about anyone laying in it. I certainly don't think twice about getting in it.
Let me know if there's more I can tell you!
"We are the greatest bulldozers to walk erect. Will we ever permit Mother Nature–truly our mother–to do her thing, undisturbed and unmarred? Will we ever be content to play a passively observant role in the universe, and leave off this unceasing activity? I do not wish man in control of the universe. I wish nature in control, and man playing only his just role as one of its inhabitants."— Randy Morgensen, 1971
Originally Posted by Beeip
What happens with the poles under excessive compression is closer to buckling failures http://www.bing.com/images/search?q=...ng&FORM=RESTAB
I'm just a carpenter not an engineer so here's my version:
Picture a 2x4 standing there... now put a bunch of weight on it so it's under compression.
Things are pretty good- but as you point out- if you go and kick it in the middle or grab it you're introducing a totally new force that only compounds the problem and could cause it to fail even if it was doing perfectly fine under compression. Currently I build light gauge structural multi story buildings for a living. We put lateral bracing in at third points so that our studs (under compression) cannot twist or shift in any axis to prevent buckling.
I have seen the poles visibly bend when used incorrectly. I blew out several wooden poles in my earliest experiments and got lucky. So for those who are thinking of picking up tree branches... wood shatters it doesn't buckle.
If you overload a pole it basically will buckle (at the ferrule) and begin to bend like a bow that is being strung.
This should cause you to freak out.
Take it a bit further with your bow and arrow and start drawing the string- you are basically increasing compression force, which is causing the bow to bend. Because a bow has elasticity it can handle this. An aluminum pole doesn't have this ability, so if it starts to bend at all it's probably not all that far away from the ferrule collapsing and failing.
So you drew the bow back... and suddenly it cracked in half in the middle. This could realistically happen in any direction relative to the pole... so flip a coin.
Tails- it explodes out in a direction away from the occupant.
Heads- It ends up inside the occupant.
Easton Aluminum's biggest product is arrow shafts for good reason.
Don't mean to be overdramatic about this.
But we do seem to have a rash of folks interested in pushing the weight limits and sizes of bridges. I'm happy to accept any blame for encouraging it.
200 ish pounds, with a 36" .625 bar with a single ferrule midspan is a safe bet.
250 ish pounds with a 36" .75" bar with a single ferrule midspan is a safe bet.
It might be worth thinking on a bit... that Warbonnet makes more bridges than anyone and hasn't exceeded these limits.
Do not go below 80% of bar length for your dog bones- compression on your bar increases quite a bit.
Do not go above 250lbs unless you really understand what is going on.
Fabric has vastly improved even in the last few months.
So yes... fabric can hold lots more weight than it used to. Shockingly so even. Fabric failure is actually pretty low on the spectrum of bad things that can happen.
And all our construction techniques have improved as a community (mostly via Grizz).
At the end of the day though a bridge hammock is designed to take all the forces of the occupant and transfer them to the suspension and the poles.
So we may be past the point where the fabric fails... but all that really means is that we are transferring ever larger loads to the suspension and poles.
Sure two layers of 400lb rated fabric probably won't fail when you sit down... and now that there is some Kevlar webbing available that won't snap either.
The poles haven't changed. In fact... some poles have entered the market that are not as high quality as Easton poles. That's a mildly scary combo.
Yes... a 40" bar gives you a flatter lay than a 36" bar... but what did you do to compensate for using a longer bar in your design?
But you can't just slap Grizz's design on a photocopier and hit 111% and call it a winner.
Hearing a rip and getting a good bump in the butt is a learning experience.
Poking a hole in the hammock body sucks- but it's a relatively small deal.
Poking a hole in your body sucks- even more so in a recessed bar bridge where that pole is right above your head.
Fair enough! I didn't mean to sound flippant or dismissive of safety (I'm a paramedic after all—I'd prefer not to be a patient!). I'd rather not be on the business end of a flying aluminum pole. Chalk this up to my being "well-intentioned, yet misinformed." Always humbled by the knowledge kicking around here.
"We are the greatest bulldozers to walk erect. Will we ever permit Mother Nature–truly our mother–to do her thing, undisturbed and unmarred? Will we ever be content to play a passively observant role in the universe, and leave off this unceasing activity? I do not wish man in control of the universe. I wish nature in control, and man playing only his just role as one of its inhabitants."— Randy Morgensen, 1971
I quoted you... but wasn't picking on you (or anyone).
On the one end of things- I'm with Bic (Hiker Dad bridge)... it's doesn't need to be rocket science to roll some 1/2" webbing into fabric and shove some poles in.
End bar bridges with rolled webbing edges are not bad and if you had a failure the bars are outside the body of the bridge at least.
So I've done more than my share of "Don't be scared.. try a bridge"
I've posted pictures of me standing in a bridge directly under a pole much larger than 36".
But I've made a good 100 of them. I have broken poles. I even got punched in the face once and still have a small scar on the bridge of my nose. Could just as easily have an eye patch.
The wood pole failures I had were at my shins... and I got splinters but they blew away from me at least.
I use PVC pipes to test poles in case they were to break that would catch any flying metal.
I believe I am still the only one to sort out both the lightest ( .490 poles and 9.125 ounce total weight with a 200lb weight limit) and the heaviest bridges (still in testing but going strong)... that's not to brag.
That's just to point out I have a pretty informed opinion... and not being an engineer I didn't get those things accomplished by running the math. I built stuff that broke then built more stuff that broke.
While fabric can fail... that's just disappointing.
We have reached a point though where the fabric is no longer first thing to go.
And since I have yet to even come close to a dynaglide failure I really doubt we will ever see the suspension fail.
I was building with 1/2" grosgrain in lieu of webbing for quite some time so that's not the weak spot.
That leaves the poles... and nobody knows what the thresholds are for those. (increased trekking pole conversions without much thought given to them are a bit troubling too)
Very careful design is the key to pushing the poles in a recessed bar bridge... not the fabric.
200lbs is a good magic number for a reason...
Super glad to see more people pushing bridges... just a bit worried too.
Good stuff, Bill. I'll add a tangential anecdote. I was using a trekking pole as a spreader, and I decided to try putting a sewing machine bobbin into the suspension for the tip. The hole in the center of the bobbin is close enough to the diameter of most trekking pole tips that there isn't room for it to swivel, so the angle of the suspension triangle was imparting a bending force to the tip. The 4" hard rubber shaft of the tip section bent until it cracked, and either the bobbin popped out from between the Amsteel lines or the tip came out of the bobbin. Anyway, everything went flying (bobbin, trekking pole), but missed me. I figure a sewing machine bobbin used with a standard aluminum spreader bar is trying to bend it, but the aluminum spreader is strong enough to resist it. Still, I'd prefer a connection attachment that kept all the forces in compression.
Yes... not being a trekking pole user personally I was surprised by the subtle differences in tips and design that could be big issue. I got a few sets to play with and had good luck with the cascade tech cheapies, but the Fizban UL poles many like are a bust.
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IMG_4291.jpg
The cascade tech fully collapsed is just bout perfect for my micro bridge. I haven't tried yet but I think a similar thing could be done well for a 36" pole. These would replace a 26".
IMG_4292.jpg
This is a very "clean" conversion IMO. The shaft sticking out of the handle is also the dowel and happens to be the exact same pole diameter of the middle section. So in this case the upper shaft is like a ferrule (but outside) the joint is good and the poles stack each other's wall across perfectly and I'm not relying on any locking mechanics as the bottom is fully collapsed. This tip seems made for a bobbin too.
You make an excellent point though I hadn't thought of much and bears careful consideration ... the weak point is the tip to pole shaft connection and a perfect illustration of a compression failure with even a minor off axis load.
Now that I think on it; either here or in person Grizz mentioned he discovered the same thing and talked to gossamer gear about it. It seems the verdict was to have the tip break instead of the very expensive carbon shaft. Makes sense for the average user... but that's not great news for trekking pole/bridge conversion either. It just rang a bell as I typed so maybe he can elaborate more. But when Grizz and WV reach a similar conclusion I'd call that gospel.
Last edited by Just Bill; 04-01-2017 at 11:45.
That tip through the handle looks great, do you have any other pictures of how you made it?
I know Grizz has popped a circle out of cork handles with a dowel but I think the new Cascade poles are rubber at the tip.
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