Hook Height – Vertical Clearance -- Lift,
Aren’t they all the Same?
NO! They each have significantly different meaning and to use the wrong one, as is frequently done, can have disastrous consequences.
A. Crane Clearance
This can be measured in a number of ways so make sure your using the right term for the dimension you require.
- Clearance from floor to the lowest building obstruction
- Clearance from the floor to the bottom of the crane girder
- Clearance from the floor to the hook
- Even floor to the bottom of the runway
B. Height of Lift or Hook Height
The distance from the floor to the crane hook in the highest position. This dimension is critical in most applications as it determines the height of the runway from the floor and is dependent on the inside height of the building. On a Double Girder crane, the hook can withdraw in between the girder (see figure 2 below). This may not be usable space, depending on the size of the object you lifting.
3. Hoist Lift
Hoists come in incremental drum lengths. You may require only 20 ft of lift, but the drum may have 28 ft of wire rope on the drum. Don’t be confused by a vendor quote regarding the term “Lift”. Make sure you ask for both numbers and make sure if the hoist has more rope then necessary, that the hoist is equipped with a lower limit switch. This will prevent the hook from hitting the floor and unraveling the remaining rope off the drum.
1. Hoist lift dimension
The hook up dimension and the available rope on the drum are two different measurements. Make sure you know which one is being quoted.
2. The Vertical Measurement has 4 different factors
a. Floor to bottom of girder
b. Floor to hook
c. Floor to top of runway
d. Floor to lowest overhead obstruction
3. Pay special attention to the configuration of the crane to make sure your dimensional assumptions are appropriate.
Probably the best tool to avoid confusion is simple line drawings. The old saying a picture is worth a thousand words is never more accurate than in this circumstance.