General question here...... If you require approx. 110 lbs of overhaul ball weight to keep tension on the crane cable, will you require 440 lbs on a 4 part (double sheave) rigging? How is this accomplished? Do most cranes have extra overhaul balls? Novice operator here, trying to learn before I fowl my cable. T.I.A.
If you have more than one part you won’t be using a ball, you’ll be using a block. The block will be built heavy enough to keep proper tension on the number of parts it can reeved with.
OK.... so my two sheave block weighs approx. 80 lbs. That doesn't seem like it will be heavy enough. It is obviously less than the overhaul ball.
My headache ball weighs 150 pounds, using 9/16 rope. When I rig my small snatch block (weighs about 20 pounds or so) to achieve a 2 part line, I rig the block to the ball, the rope down thru the block and then secured at the boom tip. That works fine, my big block for when I rig for a 3 part line is so heavy (250-300 pounds?) it does the same thing, keeps enough tension on the line to not ratnest on the spool. Good point/question, but there seems to be enough waffle room for a lighter downhaul weight to do the job, at least for my 30 ton boom truck.
Is that perhaps a snatch block not a hook block or standard crane block? Ive seen some boom trucks have an aux snatch block to allow for reeving more parts of line. What kind of crane? Pictures of what your working with? You can upload picks using the upload file at the bottom of the post screen. Its just to the right of the post reply button.
Some pictures.... The block is a 342 Mckissick rated at 7.5 ton. This is on a TM250 1974 grove. This lift I am planning for is 9,000 lbs. so not requiring four lines, but more than one. I am trying to use what came with the crane but also wanting to know in advance what will work and what won't.
That block may have come to you with the crane, but it didn't come from grove for that crane. Its likely off a old overhead crane from a shop/factory. The weight needed on the block, is determined by how much cable is hanging on the back side of the boom. If you have 50' of boom out, there's 50' of cable on the back side of the boom. The weight of the block pulling down, must be more than the weight of the cable on the back side of the boom. If its not, when the block gets close to the tip of the boom, the weight of the cable on the back side of the boom- will overcome the weight of the block, and it will pull the block up into the tip sheaves. So if you are running 9/16" cable, and have out 60' of boom. 9/16" cable is .59lbs/ft. 60'x.59=35.4lbs. So the block needs to be pulling down a effective weight of more than 35 lbs (with 60' of boom out). Only 1/4 of the weight in a 4 part is pulling down on the back side cable, so 200lbs of block or so- should be enough to hold it down. Also remember when its cold, the sheaves don't turn real fast, and if you pop the lever into cable down real fast, its probably going to overrun the sheaves and make a mess of the cable stack on the winch. Slow is better in cold weather. Time to look for another block.