How do I bridge a small river .

K

Kevin the grey

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Aug 26, 2005
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I do not know if this is appropriate here but here goes .

I have a small river to cross 25 feet x two feet deep . The bridge must be easily built by one man with not the greatest physique in the world . I would rather work with what is around such as small trees and stakes . I,ll throw in some poly cord rope as that is what is available . I already built a beautiful bridge out of pallets that was destroyed through neglect . I do not wish to spend that much effort so my bridge can be destroyed , It has to be simple and easily dismantled . It would have to serve 150 men with one hand free . They are carrying bows and other archery related equipment in the other hand . Most would be sure footed . There will be the occasional older person and child . There is not much current though with rain that can change somewhat .
 
If you have more pallets available they would still be one of the better materials to work with. I would make a floating bridge from pallets lashed together and secured by ropes to trees on the banks and by several posts driven into the bank. I would use two posts per pallet. The posts would be on the downstream side. I would build the bridge one pallet at a time and secure each pallet to its posts. When all pallets are in place I would lash them together and to the bank. This should be manageable for one builder.

If only one person at a time stands on a pallet I am assuming it would keep him out of the water. You need to test that with your pallets. If floatation is inadequate slip some extra wood inside the pallets. By the way, I would rotate the pallets such that the boards that you walk on run cross-wise to your path. This allows you to stick extra wood between the pallet layers without it being swept downstream.
 
For what it's worth I used to cross a tight one inch cable strung between trees over a river like you describe. There was another cable overhead for stability. These were very tight connected to really big pines. Mac
 
believe it or not, I used to make those knid of bridges when I was 14. You can use 2 long tree trunks, held in place on each bank with wooden stakes. then lash smaller (say 2inch thick) lengths of tree trunk or limbs across the 2 main beams like a peer. You can drive in a couple of large stakes in the center and lash the main beams to them to reduce bounce, of breaking. Of course, this kind of bridge will rot to failure in a season. It might be best to invest in some treated lumber and build one that you can use for years.
 
Do you have two trees close enough to each other and to the river that could be felled across it? By this I mean trees thick enough to support a heavy man midstream. Trees this size would be hard to move around by yourself. You might need to bring a come-along (hand winch) to move the trees into position. You might get by with lighter trees if you lash floats to the center of the span.

If you had a chain saw you might use it to partially flatten the top side of your trunks. If you lash the trees tightly together you might make a walking surface by filling in the crack between them with rocks and packed dirt.
 
I think a floating design in a river with any kind of current is asking for trouble. A couple of posts driven into the river bed for center support would present much less drag and simplify things greatly. Would this be possible? Can you be more specific on the size of the trees available?
 
thanks . lashimg trees is proabably the way to go . perhaps with a stake or boulder support in thr middle . All I have is poly rope which doesn,t bind tightly . I can tie a good knot I sometimes find it is hard to keep the lashings reasonably tight .
 
Kevin the grey said:
All I have is poly rope which doesn,t bind tightly . I can tie a good knot I sometimes find it is hard to keep the lashings reasonably tight .
Click to expand...
One thing you can do is to use a 'winder' like a tourniquet, and then lash down the 'winder'.You can't make it any tighter than that.

:) Doc :)
 
Two parallel logs staked at their bank ends to prevent rolling, and a "rail" of rope to steady, a hiking staff that reaches the stream bottom on the downstream side is my suggestion. Alternate the smaller ends and larger butts of the logs. You should only have to tie them in the middle to keep them from sagging independently. lay a piece of wood over and under making a log sandwich, tying outside the logs on either side. This will easily handle one hiker at a time. They do need their hands free however. Otherwise, one large log and they "walk the plank" and depend on their balance without the rail rope and staff.

Codger
 
Codger 64 these are ordinairy human beings . Give them a staff and they will pick their teeth with it . L:O:L

It has to be stable to the point that they can keep one hand free . I think the guide rope might be a good idea .
 
Eh, be very,very careful with ropes and cables strung across streams. The forces can get enourmous very quickly.

Take a 200-lb load (not a heavy archer with gear) and make it bob a little bit. That's all of a sudden a 400-lb load. If your biggest guy with his gear is 300 lbs, plan for a 600-lb load.

If your rope or cable is hanging at 15 degrees above horizontal with a bobbing 300-lb weight in the middle (600-lb load), then tension in the cable is almost 2500 lbs. Flatten the cable to 10 degrees and the tension is 3500 lbs. This is actual force, not with a safety factor.

I have crossed rivers myself using climbing equipment and setting up a "Tyrolean traverse." If you do that, you need a *really* strong rope designed for such things. Think 7/16" kernmantle static line. Then you can put a sling on a pulley and get people across in the sling using another rope to work the system. Do the gear separately to ease the load.

If you do the lashing trees bit, you will need to make a "deep beam" or truss. It will be difficult to make one big enough, and with enough lateral stiffness, to do the job. I think I would try a triangular cross section first, say 4-5 feet deep and half that wide.

Probably the most expedient method is to fell a tree and do the time-honored "butt scoot straddle" to get across :)

Scott
 
Butt scoot is not an option . Some of these boys do indeed approach 300 pounds with gear . I,m 250 myself in my skivvies . Some have bows approaching and beyond 1000 bucks . A little mishap and they are gonna cry on my shoulder . The rope available is pretty ordinairy 1/2 inch flemish twist poly rope . I will try to rig it as a hand rail on the bridge instead of it actually going tree to tree either that or a combination of the two . Thanks for the advice on the rope .
 
OK, so the guys have big bucks to spend. Spend it. :rolleyes:
Make a steel cable suspension bridge with a wood slat deck (Indiana Jones) and a rope or cable rail on each side. 150' of steel cable, and wood for slats, a few cable clamps and turnbuckles.

Codger
 
Codger its a fact of life that the more they have the more they want . Its hard to get volunteers let alone get them to open their wallet . L:O:L
I,ve seen guys with 40 thousand dollar trucks with hitches on them that look like they are meant to haul a train . Try and get them to pay a 5 dollar range fee and they cry, pull out 3 dollars in change and try to convince me why they shouldn,t have to pay even that much .
 
The materials I described are not that expensive. I'd make the lard ass rich boys wade the creek while I explained what I needed to make a simple suspension bridge so the next trip they could all stay dry. I've forded two, three, even four foot deep creeks with my boots and gear held high to reach a prime hunting spot. Maybe a butt scoot log would inspire them as an alternative. I get the same guys with my pool service and construction. They'll spend a dollar to try and save a dime while telling you about their condo in Florida or their new boat that cost more than my house. You just have to find a polite way to say "pony up big boy", or else be prepared to do the bridge out of your own pocket. I wouldn't give the type rope you mentioned much consideration. 1/2" twist poly rope would be asking for trouble. Do it right, or do it rustic, or don't do it, IMHO! Good luck and let us know what you come up with!

Codger
 
I have located a small shoal that nearly extends to one shore . I am going to front it with some large rocks to stabilise it and use that as a stepping off point for my bridge . It practically halves the distance and so a low bridge to the other shore shouldn,t be a biggie . Thanks for all the suggestions .
 
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