Bespoke Sea Chest Blanking Tool for Cruise Liner with Franmarine

Date: August 2025

Background

Franmarine was engaged to undertake a critical underwater maintenance project at an Australian port, requiring the safe replacement of internal valves within a vessel’s sea chest. The operation demanded a highly specialised blanking solution capable of isolating the intake while withstanding significant operational pressures.

After initial attempts with standard off-the-shelf equipment proved unsuccessful, Franmarine turned to Ausco for engineering support. Drawing on decades of subsea intervention engineering experience, combined with precision design, advanced manufacturing, and rigorous testing, Ausco collaborated closely with Franmarine to deliver a bespoke solution that met both the project’s technical demands and stringent safety requirements.

Key Features

Custom-designed sea chest blanking tool tailored to vessel specifications.
Engineered to withstand pressures up to 20 PSI under extended duration testing.
Manufactured with precision machining for accurate fit and durability.
Redundancy measures included, such as hold-back lines for added security.
Validated through rigorous FAT testing, simulating real-world subsea pressures.
Designed for diver-friendly installation with torque application exceeding 80 Nm.

Challenges

Undertaking this project presented several significant challenges as outlined below:

Difficult fitment: Standard blanks failed due to dimensional and access constraints.
Custom engineering needed: A tailored tool was required to fit through the sea chest cut-out while tolerating pressures up to 20 PSI.
Tight timeline: The blank needed to be designed, manufactured, and tested rapidly to avoid vessel downtime and compliance risks.
High consequence of failure: Any leakage or valve failure could result in uncontrolled flooding, with the potential to sink the vessel.

Solution and Outcomes

Testing & Validation

The bespoke blank was tested to withstand 20 PSI for 12 hours, replicating subsea pressures and validating performance under real-world conditions. FAT results gave Franmarine’s dive team confidence in the tool’s capability prior to installation.

Safe & Controlled Execution

Franmarine’s divers installed the blank using torque in excess of 80 Nm, secured further with a hold-back line for redundancy. CCTV and HD photography documented the procedure for quality assurance and reporting. All operations were carried out in compliance with AS/NZS 2299.1:2015 occupational diving standards

Outcomes

Successful isolation: The sea chest was safely blanked, enabling the valve replacement with-out incident.
Efficient delivery: The entire operation was completed within the planned two-day schedule.
Safety assured: No incidents occurred despite low visibility and confined working conditions.
System restored: The sea chest grating was reinstated to operational standards, ensuring long-term integrity.

Conclusion

This project highlights the strength of collaboration between Franmarine and Ausco, and showcases how Ausco’s subsea intervention engineering expertise – combined with advanced design, manufacturing, and testing capabilities – can deliver safe, reliable, and efficient solutions to complex marine challenges.