Jim Timber
1/4 bubble off
Or rather, a long or short logging arch?
I know there's a zillion threads on making these things, but what I haven't found is the justification for the two schools of thought on them. I'm about to cut metal and start building my own, and am trying to nail down which features make the most sense, without ever having used either one.
A short arch allows the butt to drag, and a long one (usually) raises the whole log.
Raising the whole log makes it easier to pull (less drag), and reduces trail erosion, but also reduces the inherent safety of self braking which potentially means danger to the operator if the log tries to out run the vehicle (an issue on hills).
Dragging the log, even at the very end of it, increases the amount of dirt (potentially) packed into the bark, potentially damages the log from abrasion, and I'd imagine requires more fuel due to increased friction. This may or may not be true in winter with snow pack.
Longer arches need more support, as the load is higher and thus a higher CG and more leverage on the legs. The entire log is also supported by the arch, so there's additional weight not left on the ground as with a short arch.
Now here's where it gets muddy... With the longer arch, you're limited in how tight of quarters you can maneuver if the log is fully elevated and locked to the backbone of the frame. If the load must pivot on the arches axle center line, you're potentially left with a very large turning radius if you have a big stick in tow due to the excessive "tail swing" (like a school bus has). Conversely, with a short arch (one that just lifts the front enough to be pulled), you have the same problem, but slightly different in that you don't have the advantage of the middle axle to rotate about - which means if you do make a sharper turn, you're potentially scrubbing on trees and causing damage.
There's a guy who came up with an arch called the "praying mantis" which is very similar to a design I had come up with independantly, and that allows the arch to grow and shrink as the size of the load varies - I just wonder how necessary that really is in the real world?
It seems to me, the larger the log, the more you'd want it to drag, as that would balance the relationship of easy hauling to operator danger if the load were to overtake the tow rig.
There's also the issue of allowing the log to pivot at the pick-up point. Wouldn't it be more desireable to allow some movement there as long as the tail end was dragging? I'm seeing youtube videos where they're hell bent on lashing the tree to the frame to keep it straight, but anyone who's ever seen a tandem semi trailer knows that middle pivot allows much better navigation of turns.
As you can see, I'm torn between both.
I know there's a zillion threads on making these things, but what I haven't found is the justification for the two schools of thought on them. I'm about to cut metal and start building my own, and am trying to nail down which features make the most sense, without ever having used either one.
A short arch allows the butt to drag, and a long one (usually) raises the whole log.
Raising the whole log makes it easier to pull (less drag), and reduces trail erosion, but also reduces the inherent safety of self braking which potentially means danger to the operator if the log tries to out run the vehicle (an issue on hills).
Dragging the log, even at the very end of it, increases the amount of dirt (potentially) packed into the bark, potentially damages the log from abrasion, and I'd imagine requires more fuel due to increased friction. This may or may not be true in winter with snow pack.
Longer arches need more support, as the load is higher and thus a higher CG and more leverage on the legs. The entire log is also supported by the arch, so there's additional weight not left on the ground as with a short arch.
Now here's where it gets muddy... With the longer arch, you're limited in how tight of quarters you can maneuver if the log is fully elevated and locked to the backbone of the frame. If the load must pivot on the arches axle center line, you're potentially left with a very large turning radius if you have a big stick in tow due to the excessive "tail swing" (like a school bus has). Conversely, with a short arch (one that just lifts the front enough to be pulled), you have the same problem, but slightly different in that you don't have the advantage of the middle axle to rotate about - which means if you do make a sharper turn, you're potentially scrubbing on trees and causing damage.
There's a guy who came up with an arch called the "praying mantis" which is very similar to a design I had come up with independantly, and that allows the arch to grow and shrink as the size of the load varies - I just wonder how necessary that really is in the real world?
It seems to me, the larger the log, the more you'd want it to drag, as that would balance the relationship of easy hauling to operator danger if the load were to overtake the tow rig.
There's also the issue of allowing the log to pivot at the pick-up point. Wouldn't it be more desireable to allow some movement there as long as the tail end was dragging? I'm seeing youtube videos where they're hell bent on lashing the tree to the frame to keep it straight, but anyone who's ever seen a tandem semi trailer knows that middle pivot allows much better navigation of turns.
As you can see, I'm torn between both.