When DIY goes wrong. (Bridge Hammock spreader bar fail)

[kerryandjane]

Hi guys. I'm in the middle of constructing my first "Grizz Bridge Hammock" (A.K.A. Rhino Bridge) and wanted to share a mishap.

Bridge Spreader Fail..jpg

I thought the 10mm x 1090mm (1.5mm thick) aluminum pole I used was total overweight and overkill for what i'd be using it for but I guess not. It buckled when I was testing for a good hang angle..... These could have been my US$150 CF hiking poles

Reason for breakage (other than obesity) i'm guessing it's something to do with suspension triangle head length 30" vs spreader bar length 42" (It's just what I had around. Bar too long for a short suspension triangle (Too much squeeze on the pole.... longer suspension triangle = less stress on pole.).

Any other guesses? I've got $5 in materials in this project but plenty of hours. The google-fu and progress is ongoing.

[gmcttr]

If the triangle dogbones are only 30" compared to 42" spreader bars, than yes, that's a poor ratio.

But, 10mm tubing is not large enough. I don't think I would even trust 10mm solid rod. Also, I'm guessing they are made from a soft, low tensile strength aluminum while the tubing that is usually used is a high tensile strength tempered aluminum.

[GrizzlyAdams]

If the triangle dogbones are only 30" compared to 42" spreader bars, than yes, that's a poor ratio.

Yes. Having a triangle side be at least 75% and closer to 80% of the spreader bar length is one of my constant mantras. 30/42 = 71%. Well into the danger zone.

But, 10mm tubing is not large enough. I don't think I would even trust 10mm solid rod. Also, I'm guessing they are made from a soft, low tensile strength aluminum while the tubing that is usually used is a high tensile strength tempered aluminum.

Agreed again, that looks like soft aluminum you could bend over your knee.

I'm glad it wasn't your CF poles too...

[kerryandjane]

Finally had a chance to test and retest today. Thanks for the replies Grizz and Gmcttr. Amazingly helpful with all your comments/examples/pictures/videos elsewhere.
I also found out why my poles ended up longer than they should have been in the first place; Taiwan has their own inches measurement. 36" on their tape measure is 42" on my trusted tape measure. (I looked at about 4 they had lying around.)..... I learnt something.

The aluminum poles i've got are weak but will work till my Questoutfitter .625" poles arrive.

[Newton]

Finally had a chance to test and retest today. Thanks for the replies Grizz and Gmcttr. Amazingly helpful with all your comments/examples/pictures/videos elsewhere.
I also found out why my poles ended up longer than they should have been in the first place; Taiwan has their own inches measurement. 36" on their tape measure is 42" on my trusted tape measure. (I looked at about 4 they had lying around.)..... I learnt something.

The aluminum poles i've got are weak but will work till my Questoutfitter .625" poles arrive.

I did a little internet research and found that an inch in Taiwan is 1.19291339 U.S. inches long. It's rather curious that a tenth of a foot, old U.S. surveyors measurements, equals 1.2 U.S. inches. 12 Taiwan "inches" would equal 14.31496068 U.S. inches or 1.19291339 U.S. feet.

A foot in Taiwan, a chhu'n, is 30.30 cm in length. So it begs the question. When is a foot not a foot?

Learning all the time we are!

[stevebo]

Glad you figured the problem out! I had a similar issue last summer----I DIYd a griz bridge, and was experimenting with poles and pole sockets/ways to connect dog bones to spreader bars. As I was laying in the hammock, one of the spreader bar sockets let loose and the spreader bar launched it self into the woods like an arrow out of a bow! Im really glad about 2 things 1. i tried this at home first 2. no one (including my self) was in the way-----theres alot of pressure on the spreader bar, and when this baby took off it was pretty impressive! Good luck with your new hammock!

[aquaholic]

i of course didn't fully test my system when i headed to the woods, and of course the wind blew and the rain fell that night. so about two hours into my slumber my 3/4" wood dowel (who knew lowe's sells trekking poles ) let go when i guess a gust of wind pushed the tarp (aka 1mil dollar store drop cloth) against the end of the pole at an angle and i got dropped about 10 inches. being still 1/2 an inch or so off the ground i just turned around and let my feet dangle. worked out ok, but not what i really wanted as my first hang. my spread was 36", held in place using a lashing through a 2" loop in my webbing, that part worked well, but i realized after i got home that when i measured my lines out i didn't add enough to cover my knots, duh-huh, so my triangle was about 4 inches shorter than i had planned. live and learn...i hope. rest of my group got a good laugh though, so mission accomplished. i even stayed dry.