Definition
Modular installation is the erection discipline covering structures and equipment fabricated off-site as complete or near-complete units, then transported and positioned into their final location using SPMTs, skidding systems, or marine transport — shifting engineering risk from the erection site to the fabrication yard and the transport interface between them.
Fabrication yard tolerances meet site conditions
A module built to tight tolerances in a controlled fabrication yard still has to fit its final position on site, where foundations, adjacent structures and access constraints were fixed independently of the fabrication programme.
The transport interface is its own risk category
Moving a module from fabrication yard to final position — by SPMT, skid, or barge — is a distinct engineering problem from either building the module or lifting it into place, with its own load cases, route engineering, and structural checks.
Off-site build compresses on-site programme
The commercial case for modular installation usually rests on reducing time spent on the constrained or expensive site itself, which means the transport and final positioning operation is under pressure to be fast as well as safe.
SPMTs move completed modules from fabrication yard to quayside, or directly to their final position, using hydraulic suspension to keep the load level across uneven ground and all-wheel steering for precise final positioning.
Float-over installation extends the same modular logic offshore, delivering a complete topside module to its substructure by vessel rather than by road or rail transport.
Strand jacking is frequently the final step once a module reaches its position, lifting or skidding it the last distance onto its permanent supports.
The Bullwinkle jacket demonstrates the modular-installation transport interface directly: the completed jacket had to be skidded from its fabrication yard onto a launch barge across a 77-ft gap before it could sail — a transport operation distinct from, and just as commercially exposed as, the offshore installation that followed.