It is probably best to have one of our experienced estimators look at your job if you have any doubts, be we realize that this is not always possible. There are many variables involved in setting up a crane to do a job. Some things to look for on the job site are power lines that may be in the way, underground utilities and septic tanks, trees or other obstacles, having enough area to position the crane, as well as ground conditions(ie—muddy or sandy ground, pavers, stamped concrete etc.). Once you have determined that there are no impediments that can preclude us from getting the crane into position, then we need to determine the actual job dimensions.
The most important dimensions to determine the size of the crane and boom length needed to get your job done are as follows:
- Distance away from the building or obstacle to be lifted up onto(for jobs at ground level this is obviously the only dimension you will need). If there is room to pull right up to the structure or to get as far away from the structure as need be, this dimension does not really need to be provided by the customer since we can determine the optimal distance away to position the crane(sometimes it is better to be farther away from the building so as to be able to boom the crane down more to reach farther in on the structure). Where this dimension becomes important is when there is an obstacle that prevents us from moving right up against the structure; an example would be that there might be a landscaped area between the building and the road. It is important to note here that you need to consider where the center of rotation (see glossary) of the crane will be. On a typical medium sized hydraulic crane there is a distance of approximately 12’ from the back of the crane to this point as well as from either side with the outriggers out.
- Height of the building or structure to be lifted to. This is a crucial measurement. The only reliable way to get this measurement is to use a tape measure( a laser will work in some cases) and to drop it off the edge of the structure. While a guesstimate is better than nothing sometimes a difference in height of only a few feet can mean the difference between being able to do the job or not.
- Distance from the edge of the structure to where the item will be lifted. On a job where the crane can get perfectly in line with the item to be lifted this is pretty straightforward, but there are many cases where the crane’s position will be laterally offset from the item. In such a case it is often better to provide us with the straight line measurements of the distance in and the distance that the crane will be offset rather than trying to determine the distance in by guessing where the crane’s boom will be in relation to the structure; by providing the exact straight line measurements we can determine the exact measurements using trigonometry.
- The weight of the item to be lifted is also most crucial. It is important to note here that crane load charts list the gross capacity of the machine. Several deductions need to be made to determine the actual net capacity of the machine; some of these deductions are the weight of the hook block or headache ball, the weight of the wire rope, the weight of a hanging stowaway jib, as well as the weight of rigging such as spreader bars, shackles, etc. Therefore if the load chart lists a capacity of 4000lbs at a specific boom length and radius, it will not be possible for this machine to lift an item with a weight of 4000lbs since the weight of the items to be deducted would take the gross weight above the capacity of the crane.
As you can see, there is quite a bit that goes into lift planning. On more complicated jobs we often have to visit the site a few times to make absolutely sure of our game plan. If you are uncertain of any of the above it is advisable to have us come out to do a site survey; this is free of charge. Many times, however, by simply calling us we can figure out what type of machine you need to get your job done.
Listed below is a job calculator spreadsheet for our 165 ton Demag. Feel free to download it, but please realize that it is like a beta product and has not yet been completely rid of bugs. It tends to work fairly well with the main boom only, but the jib setups are a bit buggy.
Download Spreadsheet [.xls]