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  1. #21
    Senior Member 3club's Avatar
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    rethink

    A 30 foot span sounds like fun, nice long sways side to side!

    It sounds like the more weight you put in, the lower you get, so stretch is definitely coming into play. Also, it sounds like it might be stretching more over time (hours). Before making changes, I'd figure out exactly what is stretching.

    You'll need a helper for this. Get in and have your helper measure each side as precisely as possible. Add more weight and remeasure. Repeat after being loaded (the hammock, not you) for a few hours or overnight. See what changes.

    In a friend's setup, his tree straps were nylon and the source of significant stretching. I would recommend wrapping the webbing as many times as can reach, and then attaching to all the loops at once, thereby minimizing stretch there. You can't do that with a marlin spike. Since this isn't backpacking, I'd just use a big cheap hardware store steel S hook.

    Remember that everything stretches, even amsteel, and the amount is approximately proportional to load and inversely proportional to strength, so changing from 2000 lb strength to 4000 lb will cut your stretch in half. At 30 feet, even just a 1% stretch is almost 4 inches.

  2. #22
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    Ah, quite an enlightening answer, especially about the Amsteel stretching numbers. Thanks!

    So one possible solution (if I can't shorten the distance between hanging points), is to get larger diameter Amsteel for less stretch. Unfortunately, I didn't get to use the hammock yesterday to do some experimenting.

  3. #23
    Senior Member shumway's Avatar
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    Did you try the thing that Demostix mentioned (marking the whoopie at the bury)? Are you making sure to milk the buries on your whoopie slings so they grip nice and tight? Are they home made whoopies? How long are the buries?

  4. #24
    Senior Member 3club's Avatar
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    Another thing to question, is it the kind of stretch that recovers by itself? So if you wake up and find yourself close to the ground, and then get out for half a day, does it go back up by itself somewhat?

  5. #25
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    "Did you try the thing that Demostix mentioned (marking the whoopie at the bury)? Are you making sure to milk the buries on your whoopie slings so they grip nice and tight? Are they home made whoopies? How long are the buries?"

    -No, I haven't had a chance to do the marking at the bury yet.
    -I was milking the whoopies as much as I could by hand before hanging. But I did notice after the major sag incident, the whoopies were much more milked than I could have ever done by hand (30 lbs of finger force vs 350 lb of people is no competition to tightening whoopies)
    -Home made 6' whoopies using the long pictorial somewhere on this forum
    -The buries are however long as were detailed in the pictorial

    Oh and I take my hammock in for the night every day for the following reasons:
    1) Since I'm new to hammocking, I want to practice hanging, taking down, adjusting, etc
    2) I don't want my hammock, carabiners and whoopies exposed to the Seattle elements and possible bird poop. The only thing I leave outside are the tree straps.

    There is still a little light left outside, maybe I'll try putting my tree strap higher on the tree side and some of the other suggestions.

  6. #26
    Senior Member 3club's Avatar
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    Also, if you're considering trying heavier rope and making new slings, I'd suggest making really long ones so you don't need all the extra bits to make up the length required. Remember too that the recommended bury length is stated in "fids", which is a measurement of the rope diameter, so if you use rope twice as thick, you'd want your burries to be twice as long too.

  7. #27
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    Well, with the little light I had left, I reset my suspension sag ridgeline to 98", then tried going from big tree to plum tree. Testing Mr. Plum Tree with just pushing down on hammock with my hands, I am not trusting it. So right now, my 30' distance is all I have for now.

    I raised the big tree attachment point by only one foot this time, and of course, deck rafter height was unchanged.

    Outcome of tonight's adjustments? I like the suspension sag ridgeline of 98". I may try 99" next time. I milked everything by hand, and swung a bit to get some extra weight to help further milk the buries. I heard a creak again on the tree end whoopie/extension loop.

    What would be better to cover my distance issue: longer tree straps or thicker whoopie slings?

  8. #28
    REV's Avatar
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    simple solution.


    move the deck closer to the tree.

    one more thing (if its not been suggested) is maybe do a slippery half hitch with the whoopies tail at the bury to see if that helps.
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  9. #29
    Senior Member 3club's Avatar
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    Fiddling with fids

    I've seen both that a "fid length" is 21 times the rope diameter, and also 7 times the rope circumference. But 7 times the circumference would be 22 times the diameter. Close enough.

    According to Samson's whoopie sling splicing instructions, the bury should be 3.5 fids. You can always go longer if you want.

    If you upgrade to 1/4" rope,
    1/4" diameter x 3.1415 = 0.79" circumference
    0.79" x 7 = 5.5" fid length
    5.5" x 3.5 fids = 19.24" minimum bury
    I'd probably make it an even two feet.

    Now, your angle:
    Assuming 30' span, tied 9' high at ends, 5' high in middle (15' from end). That's a 4' drop over 15', that's about a 15 degree angle, or about 4x tension factor if my math's not screwed up.

    360 pounds between the lot of you (150+180+30), 180 on each side, but then x4 = 720 pounds tension on each side.

    1/4" amsteel has 8600 lbs average breaking strength. 1/8" has 2500. For most of the length of the sling, the rope is doubled (to the tree and back again), so double the strength. (That doesn't mean the overall strength of the sling is doubled, because of the weakest link, but for considerations of stretch, most of the length is twice as strong.)

    For 1/8", 720/5000=14% of it's breaking strength, at which you should expect about 0.6% stretch, over a ten foot length, = about 0.72".

    For 1/4", 720/(8600x2)=4.2% --> 0.2% stretch. Over 10' = 0.24".

    Given the geometry of your setup, each inch of stretch should cause about 3" drop.

    Strength and stretch estimates based on http://www.samsonrope.com/index.cfm?rope=192

    Upon further consideration of your situation, stretch of the hammock itself doesn't come into play, because of your structural ridge line. Because of the length between deck and tree, and the fact that it's intended to support an entire family rather than an individual, I recommend upgrading the ropes for everything, including the ridgeline. If you upgrade the webbing straps, you should make them heavier, not longer. The straps are the stretchiest part of your suspension, so you want to minimize their length.

    Just another thought: we talked about moving the deck and moving the tree, but have you considered digging a hole 15' from the deck and dropping an a 4x4 or a round cedar post? Put it half way between the deck and the tree and you can hang two hammocks! Use two posts and you could hang five hammocks in a diamond pattern like this: <|>

  10. #30
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    Wow, thanks so much for the calculation help, 3Club!

    Well, the plum tree that I don't trust, is halfway between the deck and the big tree, so that is a good candidate instead of permanently installing a post. I think I will get some towing straps from Harbor Freight to do the reverse direction pull so the plum tree doesn't snap on me.

    If I understand everything correctly, using the plum tree (and a reverse direction strap to keep the plum tree stable), I should still be able to use my 7/64" whoopies, correct?

    If that doesn't work, then I will get thicker Amsteel to make new whoopies and a suspension sag ridgeline.

    Thanks again!

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