Power transformers for substations and power plants ship without radiators and bushings, often without oil and filled with nitrogen or dry air. Transport weight can be tens to hundreds of tonnes, with a high centre of gravity that is not always central. The manufacturer supplies a transport drawing with weight, CoG position, lifting points, jacking points and lashing points.
Transformers are usually loaded onto MPP or heavy lift ships with ship cranes, or onto barges by shore crane or rolled on with modular trailers. When lifted by ship cranes, the transformer’s weight effectively acts at the boom head, so GM drops and the ship heels; anti-heeling tanks and the crane heel limit must be prepared in advance.
The core and windings inside the tank can be damaged by shocks that leave no visible trace. Manufacturers therefore fit shock or impact recorders with acceleration limits per axis. Records are checked at every handover, and the stowage position on board is chosen to keep accelerations low during the voyage.
Cargo characteristics
| Parameter | Typical range |
|---|---|
| Transport weight | Distribution transformers < ~10 t; power transformers ~50–400+ t |
| Centre of gravity | Often high and off-centre; marked on the tank and in the transport drawing |
| Lifting and jacking points | Manufacturer lifting lugs or trunnions and jacking pads; only these are used |
| Shock recorder | Fitted by the manufacturer; acceleration limits (g) per axis set by the manufacturer |
| Fill medium | Pressurised nitrogen or dry air; pressure monitored in transit |
| Accessories | Radiators, bushings and conservator shipped separately in crates |
Stowage & securing principles
Lift to the rigging plan
The rigging plan uses manufacturer lifting points, a spreader beam where needed, and includes rigging weight. Sling angles are kept so lug loads stay within limits.
Stability during the lift
GM is calculated with the transformer at the boom head. Maximum heel is limited by crane and ship, and anti-heeling is ready before the piece leaves the quay.
Grillage and bearing
The transformer sits on grillage or steel beams that bear on its base as shown in the manufacturer’s drawing and carry the load into strong ship structure.
Low and near amidships
Accelerations are smaller near amidships and low in the ship. Stowage in the hold or on a midship deck helps keep shock recorder readings within limits.
Sea-fastening
Welded stoppers on the grillage or deck resist longitudinal and transverse forces, with lashings to the transformer’s lashing points. No welding on the transformer tank.
Monitoring
Shock recorder and gas pressure are logged at loading, during the voyage where possible, and at discharge as part of the handover.
Pre-loading checks
-
Transport drawing with weight, CoG and lifting points
Why it matters: The basis for the rigging plan, stowage position and sea-fastening design.
-
Crane SWL at outreach including rigging weight
Why it matters: Rigging weight is easily forgotten and pushes the crane over its limit.
-
GM during the lift and anti-heeling readiness
Why it matters: The ship can heel beyond the crane limit as soon as the piece is lifted.
-
Deck, hatch cover or tank top strength under the grillage
Why it matters: Transformer point loads can damage structure if not spread.
-
Shock recorder active and initial reading logged
Why it matters: Without a baseline, damage cannot be traced to a stage.
-
Nitrogen or dry air pressure
Why it matters: Falling pressure signals a leak and the risk of moisture ingress.
-
Marine warranty surveyor approval and weather window
Why it matters: Sea-fastening and lift plans usually need approval before the operation.
Common risks
- CoG in the drawing not matching reality, so the transformer tilts when lifted.
- Shock recorder exceeding limits because of stowage at the ship’s ends or high on deck.
- Stopper welding on the transformer tank damaging it.
- Grillage not bearing on the correct base areas.
- Excessive heel during the lift because anti-heeling was not prepared.
- Loss of gas pressure and moisture entering the tank.
Frequently asked questions
Why are transformers fitted with shock recorders?
The core and windings can shift from shocks without any visible external damage. The shock recorder logs accelerations in transit so owner and carrier can tell whether the manufacturer’s limits were exceeded and at which stage.
How is the transformer’s CoG used in planning?
The CoG from the transport drawing feeds the ship’s combined CoG, the load on each grillage bearing and the force in each lashing. The combined CoG calculator helps with early estimates before detailed calculation.
Are lift and stability calculations in STOWAGE.ID official?
No. The Heavy Lift and Project Cargo modules are rolling out in stages, and results are shore-side planning. The stability booklet, the class-approved onboard loading computer, the crane manual and the surveyor’s approval remain the official reference.
General guidance for education. Follow the vessel’s Cargo Securing Manual, the shipper’s instructions and the surveyor’s directions.
Shore-side planning & decision support. The class-approved onboard loading computer remains the official reference.