Hook Coverage, What is it and Why is it Important?

Overhead Crane Hook Coverage

If the purpose of your new crane is to provide max storage of say, steel coils in your warehouse or maybe you need to lift something on the edges of your building, be careful. The physical dimensions of the cranes' mechanical components provide constraints that are expensive if not impossible to overcome.

Side Approach

End view of bridge crane looking down runway.

End view of bridge crane looking down runway.

The "Side Approach" is that lateral dimension, the left to right movement of the trolley hoist. It's a measurement of how close to the side walls you will be able to get your hook. Even without any other obstructions like building knee braces, roof drains or heaters, the physical width (wheelbase plus overhang) of the hoist and trolley will be a dimensions constraint that's hard if not impossible to overcome. 

Application Tricks Available

  1. Hoist are not symmetrical (usually), so there will be a short side and a long side.
  2. Different brands have different side approach dimensions, so shop around.
  3. The wire rope drum orientation can be perpendicular or parallel to the bridge girder. Therefore, long lift applications would be helped by a perpendicular drum orientation.
  4. Chain hoists, because they don't need a drum, frequently provide better end approach. Note that chain hoists are usually suited to, at best, moderate duty cycle applications and usually under 10 ton capacity.

End Approach

End view of end truck, showing wheelbase of crane and end view of double girder hoist.

End view of end truck, showing wheelbase of crane and end view of double girder hoist.

Where the Side Approach dimension is governed by the width of the trolley/hoist, End Approach is a longitudinal dimension and dictated by the overall length of the end truck. Again, due to things like electrification and walkways, this dimension is not necessarily equal on both sides of the crane. 

Application Tricks Available

  1. Although end trucks are normally symmetrical, the crane layout may not be. Considerations like walkways, line shaft bridge drives and festoon conductors, can provide a dimensional advantage to rotate the crane for better end approach.
  2. A specially designed, "spacer saver" end stop can sometimes save over a foot, but are more expensive.
  3. A runway dog-house in which the runway protrudes through the end wall, thereby allowing part of the end-truck to extend beyond the end of the building has been used in extreme cases. It's called a "dog-house" because from the outside of the building is looks like two dog-house sized appendages will be sticking out of your building. The worst case scenario is if the dimension problem is your fault, from that day forward, these two warts sticking out of the end wall of your building may be called "Bill's Memorial Doghouse." And if you're really unlucky, the maintenance crew will put a sign on both sides, emblazoned with your name. In spite of the looks, the concept works and might just save your bacon.
Any resemblance to persons living or dead should be plainly apparent to them and those who know them. All events described herein actually happened, though on occasion the author has taken certain, very small, liberties.

Note; if you choose to rotate the crane 180 degrees to gain end approach on one end of the building, your conductor bar will now be on the wrong side to feed the crane. If the runway has not yet been installed this is easy. If the runway has been installed or it would be too costly to feed the power from the other runway, conduit can be run from the formerly powered side of the crane to the opposite side in a pinch.