CASE CN6 - Float Requirements for Portal Cranes, P. Malone
Float Requirements for Portal Cranes
Symptom: Portal cranes were experiencing difficulty going around curves.
This was evident by the high pitch sound of metal to metal contact as a number
of cranes transverse the curves around drydocks.
Collection of Facts: A west coast shipyard proposed that the float that
provides a means for cranes to go around curves, designed on portal cranes,
should be redesigned so they would operate by the available centrifugal force
generated by the crane going around a curve. Float has lateral or sideways
movement capability that is built into portal crane running gear. This
lateral movement is necessary because the geometry of the rectangular crane
frame on a curved track does not allow the corners of the crane to touch both
rails (See Figure 1). This phenomenon occurs because the ends of the crane do
not fall on a radial line.
If a given crane is operated on a curve of constant radius, the gage can be
adjusted so no float is required. However, if cranes of the same gage, but
different lengths/wheel configurations, are operated on the same curve,
different gage adjustments are required. Therefore, a compromise alignment