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Structural maintenance programmes are growing, in number and complexity, requiring a new innovative approach and an overhaul of decades-old approaches to vessel crack repair, to unlock cost, time, environmental and safety benefits. With an aging global fleet and new stress points emerging on existing vessel structures as a result of retrofitting and refits, it is becoming more pressing for ship owners and operators to look for cost effective solutions to vessel crack repair.

In order to inform maritime industry leaders of the complexities surrounding these new market challenges, and to provide further insight into the available solutions, such as our Sandwich Plate System (SPS), which offers a safe, efficient and environmentally sustainable solution with schedule and financial savings, we are providing a series of virtual presentations to members of the Royal Institute of Naval Architects (RINA).

We recently delivered our first presentation to RINA’s London branch and were pleased that the session received strong interest from members. It was a pleasure to answer a raft of questions on the various applications of SPS and on multiple user cases, answers to which you can find in the Q&A below:

Q&A: Sandwich Plate System (SPS): A Structural Composite

How do you deal with inspections?
If a crack has appeared on a vessel’s hull, it can be inspected from the outside to ensure it has not grown. Inspection criteria are discussed and agreed at the SPS design and approval stage.

What material do you use for the exterior plate of SPS?
In most circumstances, the SPS top plate and perimeter bars are generally the same grade as the existing structure or a higher grade if improved is strength required. However, there are some unique instances in which we have used stainless steel or aluminium as the top SPS plate. For example, there is an FPSO newbuild now operating in the North Sea which has enhanced oil recovery tanks, built with carbon steel but with a stainless-steel SPS top plate. This enhancement was done during the construction phase.

What is the relative cost of SPS repair versus a renewal?
We are cost competitive in the maritime market. This is mainly because the application of SPS is up to four times faster than conventional solutions, which means your vessel does not stay dockside for prolonged periods. For example, on a bulk carrier tank top over 600sqm, the whole tank top can have SPS applied within 10 days alongside at a quay. Likewise, for the offshore market, including below the water line repairs, our SPS solution is 10 to 11 times cheaper than the alternative of having dive boats alongside. The solution is also cost-effective in that it is a class approved permanent solution and therefore promises longevity.

After installation of the SPS how do you verify the internal integrity of the polyurethane core?
We go through an extensive quality assurance process when installing SPS and aim for a surface profile of greater than 60 microns. We also check the humidity level inside each cavity between faceplates by blowing dry air through the cavity before injecting the polyurethane. Additionally, following the installation of SPS, we collect a sample of the polyurethane, which has passed through the cavity, and carry out a shore D hardness test on it. We also perform a leak test on the cavity to ensure the liquid polyurethane does not leak from the cavity. After the elastomer has set, each cavity is tested to assess the cavity fill and to check for voids or air pockets.

Is there a maximum or minimum service temperature?
In most cases, temperature is not an issue. We have installed SPS in extremely hot climates and extremely cold climates and tailor each SPS order to your specific customer criteria. We have also received class approval to install SPS on the outside of a vessel to upgrade to ice class standards. The polyurethane elastomer core is an engineered material that has been specifically developed for the anticipated extremes of the full range of operating temperatures between -45 degC and +100 degC.

What is the maximum time an SPS system has been used on a vessel?
SPS is designed to last the lifetime of a vessel.  Our longest installation is our first one, completed 21 years ago on a Ro-Ro vessel in November 1999 and the ship is still in operation.