A plastic filling between two sheets of steel

A new composite system of steel and plastic makes ships more stable and durable – as well as more economical.

A new Sandwich Plate System (SPS) from BASF and London-based Intelligent Engineering is ushering in a new era in shipbuilding and may be able to completely replace classical steel construction.

The system was given the name ‘sandwich’ for a good reason: Two layers of steel are tightly bound together by a plastic filling. This core consists of a special mixture of a polyurethane (PUR) elastomer that is both durable and elastic.

As a result, SPS components are much stronger than the conventional steel constructions. Ships built with the SPS method are also lighter and their materials last longer.

In the traditional construction method, hulls and decks typically consist of steel plates that are between one and two centimetres thick. These must be reinforced with welded-on stiffeners. The hull of a medium-sized tanker incorporates approximately 60 kilometres of welds. This leads to significant labour and material costs during construction and repairs. In addition, the welds form weak points in the humid environment because they are the first places to rust and are also susceptible to fatigue.

SPS is claimed to be superior to this steel construction in many aspects. The system’s strength makes it possible to reduce the number of reinforcement elements needed; approximately 50% of the labour-intensive welding is eliminated.

The additional advantages of SPS are clear when it comes to repairing worn decks.

‘It’s as quick and easy as laying carpet,’ says Dr. Jens Dierssen, a spokesman for Elastogran, a BASF subsidiary.

‘Instead of a time-consuming process where the old deck is ripped out and replaced, with SPS the existing deck is retained and cleaned.’

Spacer bars are laid and a new deck plate welded on. Afterwards, the cavity between the steel plates is filled with the PUR elastomer.

‘This basically functions like a compound glue,’ says Dierssen.

‘We mix the two liquid starting ingredients directly on site, and inject them into the hollow space at a pressure of 150 bars.’

The plastic solidifies within a few hours, giving the deck new stability. SPS allows the renewal of up to 200 square metres of deck per day, as opposed to the 20 square metres per day possible using conventional methods, allowing ships to be in drydock for shorter periods of time.

P&O has already used the method in the renovation of the decks of four of its ferries.

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