Charlestown Harbour is a small historic port in Cornwall, originally built in the late 1700s. The Grade II-listed harbour is the last open Georgian Port and a UNESCO World Heritage Site, featuring an inner and outer harbour separated by a flap lock gate.

Beckett Rankine designed and project-managed repairs and regeneration work for Charlestown Harbour, including the work package to replace the lock gate.

Salvaging after storms

In 2021, winter storms inflicted significant damage to the outer harbour and water entered the historic stone wall, leading to a section collapsing into the sea.

Beckett Rankine was brought on board to design and oversee the repairs.

The site is difficult for construction equipment to access. We implemented a creative solution by importing large quantities of crushed rock from a nearby quarry to build a temporary causeway that gave a solid platform for construction.

We also faced the challenge of keeping the waves outside the harbour and away from the works, especially at higher tidal levels. Our solution was to fill empty shipping containers with some of the crushed rock, placing them in the Harbour entrance as a temporary breakwater. This simple and practical measure proved highly effective and kept the waves at bay, even when the tide came in.

Once work was complete, the containers were removed and recycled, and the quarry rock was reused on other projects.

The old lock gate fails

The lock gate finally succumbed to winter storms in October 2024, with a breach that drained the water from the inner harbour.

Beckett Rankine helped to co-ordinate the emergency response, which included transporting historic ships to a nearby harbour and installing a temporary cofferdam to protect the harbour.

New lock gate design

As the existing lock gate was determined to be unsafe, we devised a modular replacement gate that updates and reinforces the original design while meeting modern design and safety standards. Importantly, the new lock gate is also designed to improve the harbour’s climate resilience and remain aesthetically in character with its heritage.

The modular design enabled ease of transport and installation, as well as ensuring that future repairs or replacements can be localised in sections for faster, more sustainable and cost-efficient maintenance.

Many of the new features enable the gate to withstand larger waves, which is a growing concern as climate change increases the wave forces entering the harbour.

• The inner flood tanks are designed to resist greater wave impacts. They are also fitted with a Stillwell system to empty quickly if required.
• The storm locks – weighing 200kg each – protect the winches and prevent the gate from being forced open by strong waves.
• An intentional void between the gate and walkway allows waves to pass over the top during high tide, rather than hitting the gate directly.

The original gate had no functioning sluice gates for 20 years, so these have been reintroduced in the new design to help with maintenance. At 60% open, the sluice gates are powerful enough to fill an Olympic swimming pool in 7 minutes, or the equivalent of 10 household baths each second.

Additionally, hard-wearing timbers were added to protect the gate when vessels pass over it while open, as well as modern safety features such as flashing lights, barriers and walkway safety netting.

Out with the old

In April 2025, the original lock gate was lifted and removed by ConstructEx – the first time since it was installed in 1971.

The gate weighed in the region of 50 tonnes, with around 20 tonnes being mud and fouling alone. It was lifted manually over a three-day period, with the support of strategically placed chain blocks that were digitally monitored for careful, even movements.

The old gate has been recycled, though Charlestown Harbour kept some parts to feature in heritage displays about the harbour’s engineering history, including the 55-year-old winch.

In with the new

Throughout summer 2025, the gate, sheave and winch designs were finalised and preparatory works began.

The new gate installation involved a complicated process throughout the 2025/26 winter, as works could only be carried out during the narrow window of a Spring tide. A temporary barrier was put in place to protect the gate and inner harbour from waves, particularly important during winter storms.

The gate modules were transported to Charlestown via road and assembled on a pontoon in autumn 2025. The project team carried out precision engineering to fine-tune the bearings and alignment, then lifted the gate into position in December.

In January and February 2026, the winches and sheaves, walkway, and safety features were the final elements to be installed. The project team then carried out a series of test to ensure the gate is fully operational and safe.

Next, the inner harbour will be re-filled so that Charlestown Harbour can open once again, celebrating the occasion with a public event in Spring 2026.

Challenges

The project team faced a multitude of challenges, largely unique to the project, that required creative solutions and flexibility to overcome.

• Winter weather windows
  The works needed to take place in the ‘dry’, with the inner harbour drained. As a result, on-site activity was limited by weather conditions and tide windows, while also under pressure to limit the exposure to waves during construction.
• UNESCO World Heritage status
  The harbour had to remain as close to its current condition as practically feasible to maintain its protected status. The potential impact on the historic fabric of the harbour was considered for each tool or methodology, with minimal evidence of the works left after the project was completed. This included designing the replacement lock gate to be as visually similar as possible to its predecessor.
• Lack of historical data
  There were no drawings available of the original gate, and limited historical information on the harbour’s construction generally. This added a layer of complexity to meeting the UNESCO requirements, leading to an almost archaeological approach to early research and investigations.
• Unexpected harbour wall repairs
  During preparatory works, we discovered that parts of the harbour walls were made from mundic concrete. This historic aggregate, which is made from the byproduct of mining, was popular in the early 20^th Century and is almost unique to the region. Unfortunately, it is also prone to deterioration, and so concrete repairs to the harbour walls were needed.
• 100 tonnes of mud
  Once the inner harbour had drained, it was discovered that an enormous quantity of mud was blocking access to the gate being removed. This added a considerable amount of time to carefully remove without compromising the harbour structures.