Cranes work on weight not boom length.
It's the lower sections that will test you, the closer you get to ground. Even a 25t franna has near 30m of stick.
If you have a CSI Yellow block rated 2000kg SWL you'll be cutting off 250kg chunks max to stay within the SWL.
That tree is good for around 1000kg/m3.
So you want to be cutting off 0.25m3 which is 250kg
So at
800mm dia what length block can you cut to get the 250kg?
To get volume of a cylinder formula is
Quote:
π is symbol for pie (3.1416)
r is symbol for radius (use m not mm)
|
πr2 x h but we need to know what length to cut the log so
h=.25/(πr2 )
Answer is
0.5m (close enough)
Want to test me
(3.1416 x (0.4 x 0.4))x0.5= 0.251m3 which is 250kg
But now it's
1100mm dia so how high, lets try it
h=.25/π x (0.55 x 0.55)
h=
0.263m long Hope you get it, just shows how a small increase in dia of 300mm halved your length.
It's murder on your gear and a porty sucks at lower log like that, the capstan winch is way superior as you can pull in slack when the piece gets pushed off.
Every block you cut means resetting the pulley and tying everything up ... you'll be up there a while and that's after lowering out the branches. This is where people straighten out 50kn biners coz they dont do the math.
That block will go 7x it's own weight at the pulley if you let it run and are pretty good, it can go 10x or more easily if too many wraps lock it up.
As you get closer to the ground it gets worse as there is less rope out. Also,
how do you tie up an 1100mm dia piece that's only 263mm long? How do you push off a 250kg block?
You asked the cost of a crane, I ask you the cost of what you are doing to your gear and yourself? Also, the customer pays for the crane but who pays for your back, broken gear, injuries, damage etc?
Lets say we have only 20m of 1m dia, that makes that whole barrel weigh in at 15,700kg