Don’t Rock the Boat: Why Stability Matters for Historic Floating Vessels

The National Register of Historic Vessels consists of over 1,500 craft of all types, spanning the full breadth of British maritime history. Some 200 of these vessels form the National Historic Fleet – vessels of outstanding importance as the best surviving representatives of their type, meriting high priority for conservation. 

But what happens when a vessel has outlived its original purpose? 

Many have been given a second life as static floating vessels, often undergoing transformations into museums, restaurants, office spaces, hotels and other public spaces. However, whilst they no longer go out to sea, they still float, which means stability and structural safety remain important. Despite this, gaps in UK legislation have resulted in a lack of stability criteria for static floating craft and structures, leaving many of our most important historic ships at risk. 

Supported by Lloyd's Register Foundation’s small grant programme, the ‘Don’t Rock the Boat’ project, led by National Historic Ships UK (NHS-UK) and maritime engineers Beckett Rankine, set out to produce Stability Guidelines to help owners assess, manage and improve the structural safety of the vessels in their care. 

With Foundation funding, we were able to conduct extensive community and stakeholder engagement to gauge how stability and risk are considered and mitigated. Our partners, Beckett Rankine, provided knowledge and expertise, including consultation with international museums. We also engaged a consultant to conduct vessel visits across the UK, resulting in nine registered UK static floating vessels being surveyed during the project. 

Our research found that, in some vessels, significant internal machinery had been removed below the waterline, though only one had undergone major changes to the superstructure (involving the addition of new floors above the weather deck). These modifications have potentially large impacts on vessel stability.

‘During conversion, all items of machinery and weapons systems were removed to allow these spaces to be opened up and repurposed.’ (Anonymous vessel case study published in Stability Guidance)

Location and function determined other potential risks. For example, vessels moored amongst busy traffic were at greater risk of being struck by other craft, and ships open to the public have greater health and safety requirements. Vessels that had to travel to undergo maintenance were also vulnerable to damage and loss on route. 

‘The main risks have been identified as the hull being hit by debris.’ (Anonymous vessel case study published in Stability Guidance) 

We discovered that whilst most vessel custodians had considered the stability of the vessel, including conducting some form of stability assessment, this was not always consistent, and the level of knowledge varied significantly. Most did have an active stability booklet (a requirement for operational vessels) but previous stability tests were often unclear or incomplete. For larger organisations, ensuring policy and procedures were disseminated and understood by staff and volunteers was also a challenge. 

The complex nature of historic vessels and the lack of legislative clarity make managing the safety of static vessels extremely difficult. With this project, we aimed to support vessel custodians in caring for their craft and all those on board. 

Our Stability Guidance sets out to demystify some of the considerations around vessel stability, break down existing legislation, and advise vessel owners on how to provide a safe space for workers, volunteers and visitors. 

A recognition that vessel projects are driven by multiple objectives, with different levels of funding available to them, was essential for developing practical guidelines. We aimed to demonstrate best practice through exemplar case studies, while presenting the staged response of a risk-based approach to ensure any vessel custodian can start to take steps that ensure safety requirements are met. 

Our guidelines include a helpful decision flowchart and example risk assessments, which set out the different stages of assessment in a manageable checklist. 

We also emphasise the importance of engaging specialist expertise where required and that any decisions taken should be made in conjunction with other NHS-UK guidelines, including those on conservation, health and safety, access and climate change. 

Since publication in February 2025, our Stability Guidelines have provided clarity and set a standard for best practice in the sector. The project has also improved our understanding of static floating vessels in an international context and the unique position of the UK where, without specific codes and standards, we are able to create a flexible, heritage-focused response. 

Our guidance is freely available via the NHS-UK website.  

"We would like to thank all those involved in developing this paper, the vessels who agreed to act as case studies, and Lloyd's Register Foundation, whose funding made the project possible." Hannah Cunliffe, Director of NHS-UK.