Motorcycle + Hammock

[lukaledoux]

So in preparation for my big trip this spring, I bought a Hennessy Hammock and managed to find a post on ADVRider about only needing 1 proper anchoring point + your motorcycle to be able to setup camp.

Well I'm pleased to say it's totally possible! Simply align your bike slightly off axis with the hammock line, so that the weight is transferred into your suspension, and a little into the kickstand. Putting her into first keeps it from rolling back and the weight of the bike seems to be enough to prevent it sliding back too. I don't have much clearance from the ground but it works!

My dog got all excited and brought me a stick. Also note the use of an old pan for preventing the kickstand from sinking in. The ground is really soft right now (spring time!).

 

[Carlos840]

You are a brave man! This has trouble written all over it...

 

[bdevries]

You are a brave man! This has trouble written all over it...

this x2....

 

[tejkowskit]

What are you tying out to on the bike? I ask because the weight begin pulled on your bike is more than your body weight.

Here's an equation to see how much weight is really being put on each tie out point; in your case a tree and the bike:

W=weight
Y=angle of hammock suspension
Z=weight on your motorcycle
(0.5xw) / sin(y) = z

 

[Water Bear]

That is awesome. Also your dog is great.

What are you tying out to on the bike? I ask because the weight begin pulled on your bike is more than your body weight.

That seems backwards. I assume you got your result from a free body diagram where the tension in each cable is assumed to be the same and the angle assumed to be the same. (Seems like an OK model).

The maximum tension force happens when the angle is 90 degrees. Your equation at 90 degrees yields W/2, which makes sense since the tree supports half the weight, but is notably lower than W.

Fun fact: For a rope of uniform density tied between two trees with an equal angle between the rope and the horizontal at each tie point, the tension force in the middle of the rope is lower than at the ends. You can derive this result with classical physics and some elbow grease.

Edit: You're right, the maximum doesn't happen at y=90 degrees, its when y=0, when the tension is infinite. I guess as long as the angle is below sin^(-1)(1/2) then the tension is less than the weight.

 

[tejkowskit]

That is awesome. Also your dog is great.



That seems backwards. I assume you got your result from a free body diagram where the tension in each cable is assumed to be the same and the angle assumed to be the same. (Seems like an OK model).

The maximum tension force happens when the angle is 90 degrees. Your equation at 90 degrees yields W/2, which makes sense since the tree supports half the weight, but is notably lower than W.

Fun fact: For a rope of uniform density tied between two trees with an equal angle between the rope and the horizontal at each tie point, the tension force in the middle of the rope is lower than at the ends. You can derive this result with classical physics and some elbow grease.

edit: never mind.

I'm not a mathematician, but am avid hammock camper. All the research I have done when making my own hammocks used that formula. Sources: Hammock Camping 101Just Jeff's Hammock Camping PageHammock Hang Calculator | The Ultimate Hang

You are correct in that I gathered it from the assumption that the angle is the same on each end, but it is not backwards. I don't know, and have not seen how to factor the weight on a hammock if the tie outs are at different heights on the trees or distances from the trees, but the principle remains.

Weight is divided in half because there are 2 tie out points, not only when angle is 0 degrees. If there were 4 tie out points, you would multiply by .25. You are right that maximum tension happens at 0, but the force applied depending on the angle of the hammock suspension is factored into the equation by sin(angle).

I get that the formula doesn't directly apply to OP's situation, but it may still be cause for concern. Would hate for OP to fall on his butt or damage his moto.

If the hammock suspension is slack then the weight isn't as great. If the hammock is too slack then OP's butt may touch the ground as the tie out point is already low to the ground.

I suppose my original post should have read, "Be careful of your suspension angle as it may put too much stress on the bike."

Edit:Slack as in > 30° as 30° is the optimal hang angle for hammocks

 

[lukaledoux]

What are you tying out to on the bike? I ask because the weight begin pulled on your bike is more than your body weight.

I'm tying to both passenger rails, they are quite strong. I am aware of the suspension angle potentially increasing the load on the bike, which is why I've opted to have it basically as low as possible without touching the ground. Additionally, having the tree anchor point a little higher helps by taking more of the load.

Cue youtube math: https://www.youtube.com/watch?v=NNv-groL_B0

I'm really not worried about the bike. Worst case scenario, I drop a couple inches to the ground in the middle of the night. Bike is unlikely to topple over at that angle.

 

[tejkowskit]

Looks like you did your homework and are comfortable with it :thumbup:

Have you seen how to hang with 1 tree and a long pole (fallen tree branch) tied out and staked to the ground? If a long enough pole is available it would allow you to set up more horizontal instead of on a slope.

Edit:http://youtu.be/57I_HLsEnbc
He ties out to a fallen log, but it still works if you have tent stakes or make tent stakes out of dead branches.

 

[Water Bear]

I'm not a mathematician, but am avid hammock camper. All the research I have done when making my own hammocks used that formula. Sources: Hammock Camping 101Just Jeff's Hammock Camping PageHammock Hang Calculator | The Ultimate Hang

You are correct in that I gathered it from the assumption that the angle is the same on each end, but it is not backwards. I don't know, and have not seen how to factor the weight on a hammock if the tie outs are at different heights on the trees or distances from the trees, but the principle remains.

Weight is divided in half because there are 2 tie out points, not only when angle is 0 degrees. If there were 4 tie out points, you would multiply by .25. You are right that maximum tension happens at 0, but the force applied depending on the angle of the hammock suspension is factored into the equation by sin(angle).

I get that the formula doesn't directly apply to OP's situation, but it may still be cause for concern. Would hate for OP to fall on his butt or damage his moto.

If the hammock suspension is slack then the weight isn't as great. If the hammock is too slack then OP's butt may touch the ground as the tie out point is already low to the ground.

I suppose my original post should have read, "Be careful of your suspension angle as it may put too much stress on the bike."

Edit:Slack as in > 30° as 30° is the optimal hang angle for hammocks

Yea, you were right, it's not backwards. The force balance is 2Tsin(y)=W. I am in fact a dope.

The one thing to correct in what you said is the following. sin^(-1)(1/2) is 30 degrees. This is "optimal" because for lower angles y, the tension force on the bike is greater than the weight, but for angles between 30 and 90 degrees the tension force is lower. the minimum tension force happens when y=90 degrees.

In other words, the more sag he has in that set-up, ie the lower to the ground it is, the less force is put on his bike.

 

[lukaledoux]

Awesome, great video! Looks so sketchy but it works, that's the beauty of physics! :rockon:

Looks like you did your homework and are comfortable with it :thumbup:

Have you seen how to hang with 1 tree and a long pole (fallen tree branch) tied out and staked to the ground? If a long enough pole is available it would allow you to set up more horizontal instead of on a slope.

Edit:http://youtu.be/57I_HLsEnbc
He ties out to a fallen log, but it still works if you have tent stakes or make tent stakes out of dead branches.

 

[tejkowskit]

The one thing to correct in what you said is the following. sin^(-1)(1/2) is 30 degrees. This is "optimal" because for lower angles y, the tension force on the bike is greater than the weight, but for angles between 30 and 90 degrees the tension force is lower. the minimum tension force happens when y=90 degrees.

In other words, the more sag he has in that set-up, ie the lower to the ground it is, the less force is put on his bike.

Right. I should a clarified. Optimal angle for greatest comfort with low(er) force*.

Awesome, great video! Looks so sketchy but it works, that's the beauty of physics! :rockon:

Haha I would be skeptical to do this. Perhaps your motorcycle is the better option.

Do you put a coaster under your kickstand to distribute weight and keep the kickstand from sinking into the ground?

 

[lukaledoux]

Yes, there's an old pan underneath. I'm not sure it would be necessary if the ground were dry and hard but right now it's really soft.

Right. I should a clarified. Optimal angle for greatest comfort with low(er) force*.


Haha I would be skeptical to do this. Perhaps your motorcycle is the better option.

Do you put a coaster under your kickstand to distribute weight and keep the kickstand from sinking into the ground?