Multipurpose (MPP) ships have unobstructed box-shaped holds, movable pontoon tween decks and ship cranes that can often work in tandem. They are flexible: one voyage can carry breakbulk, containers, steel and project cargo. Dedicated heavy lift ships have much larger cranes and anti-heeling systems for lifts of hundreds of tonnes.
When a crane lifts a piece, its weight effectively acts at the boom head, not at the cargo’s position on the quay. The ship’s KG rises and the transverse moment causes heel. The ship’s GM during the lift, anti-heeling tank capacity and the crane’s heel limit must therefore be checked before the lift starts.
Heavy pieces usually stand on grillage or steel beams to spread the load into the tank top, tween deck or hatch covers. Sea-fastening is designed from the expected route accelerations and is often reviewed by a marine warranty surveyor, especially for high-value project cargo.
Typical sizes & characteristics
| Parameter | Typical range |
|---|---|
| Typical size | MPP ~5,000–25,000 DWT; dedicated heavy lift ships of similar or larger size |
| Cranes | MPP usually 2–4 cranes of ~40–250 t, often able to work in tandem; heavy lift ships up to hundreds of tonnes per crane |
| Holds | Box-shaped, 1–3 long holds, movable pontoon tween decks |
| Anti-heeling | Anti-heeling tanks and pumps to offset the moment during lifts |
| Hatch covers | Strong pontoons for deck cargo, with load limits per panel |
| Typical cargo | Project cargo, breakbulk, steel, heavy vehicles, modules, small craft, containers |
Typical ranges for the vessel class, not data for any specific ship. For planning, use your vessel’s stability booklet and capacity plan.
Cargo spaces & how they are modelled
Box holds
Holds are modelled as box spaces with tank top load limits and clear height. Long and irregular pieces are drawn in their real shape.
Pontoon tween decks
Pontoon positions set the heights of the lower and upper holds. Each configuration becomes a cargo space variant with its own load limits.
Deck and hatch covers
Large deck pieces sit on hatch covers or beside coamings with per-panel load limits and space for sea-fastening.
Crane reach
Crane SWL versus outreach is modelled so cargo positions can be checked against single and tandem crane capacity.
General stowage rules
SWL and outreach
Cargo weight plus lifting gear (spreader, slings, shackles) must stay below the crane SWL at the outreach used, with margin for tandem lifts.
Stability during the lift
GM is calculated with the cargo weight at the boom head. Maximum heel during the lift is limited by ship and crane, and anti-heeling tanks are prepared beforehand.
Grillage and point loads
Heavy pieces sit on grillage that carries the load into strong structure. Load per m² and point loads are checked against tank top, tween deck or hatch covers.
Sea-fastening
Stoppers, lashings and welding are designed for the route’s longitudinal, transverse and vertical forces. No welding directly on the cargo body without the owner’s consent.
Cargo CoG
Project cargo centre of gravity comes from the cargo owner’s documents and is marked on the piece. An off-centre CoG affects slinging, heel and sea-fastening design.
Common mistakes & risks
- Lifting gear weight left out so the crane works above SWL.
- GM during the lift not checked and the ship heels beyond the crane limit.
- Cargo CoG in documents not matching the actual piece.
- Undersized grillage so point loads damage the tank top or hatch covers.
- Sea-fastening welded to parts of the cargo not designed to take load.
- Wrong pontoon tween deck configuration so cargo does not fit or space is wasted.
Frequently asked questions
Why does KG rise when a crane lifts cargo?
As soon as the piece leaves the quay or deck, its weight hangs from the boom head. For stability, that weight is treated as acting at boom head height, so KG rises and GM falls for the duration of the lift.
How does an MPP differ from a heavy lift ship?
An MPP is a versatile ship with medium cranes that carries many cargo types. A dedicated heavy lift ship has much larger cranes, strong anti-heeling systems and deck structure for very heavy pieces.
When are the MPP and Heavy Lift Planner available?
The MPP and Heavy Lift module is the fourth wave together with Project Cargo and is rolling out in stages. Its stability results are shore-side planning; the class-approved onboard loading computer and stability booklet remain the official reference.
Shore-side planning & decision support. The class-approved onboard loading computer remains the official reference.