Port inspection: reading the waterline and the hidden side of quays between the tides

Port facilities divide into mooring facilities (quay walls, piers, dolphins), protective works (breakwaters, revetments) and cargo-handling and ancillary items (aprons, crane foundations, fenders, bollards). The main drivers are seawater corrosion of steel, chloride attack on concrete, wave and berthing impacts, and loss of fill behind the wall.

In Japan, under the technical standards for port facilities, each facility needs a maintenance plan and must be inspected and diagnosed according to it. The national inspection guidelines combine routine patrols with periodic inspections at least every five years (every three years for priority facilities), plus extraordinary inspections after earthquakes or storm waves.

Above water the work is done on foot and by boat; underwater it relies on divers. Under piers, inspectors slip in by small boat at low tide and look up by torchlight. Steel thickness is measured by divers who first scrape away shells and weed, then apply an ultrasonic gauge.

At the root of the pain: quays built in the high-growth era are ageing all at once, and divers and port engineers are in short supply. Many berths cannot stop cargo handling, so inspection has to slot in between ship movements.

Ports call for a combination of aerial, surface and underwater drones. Aerial drones cover the overview and superstructure, surface vessels the pier soffits and waterline, and underwater vehicles the wall face and seabed.

Ports are hostile to every kind of drone. Under piers it is dark and GNSS-denied. Over the sea there is wind and swell. Underwater, turbidity and current can limit cameras to tens of centimetres.

• Water, spray & humidity: salt spray damages aircraft; water reflections fool downward sensors; in murky water sonar beats cameras. Water, spray & humidity
• GNSS-denied: under piers, choose aircraft that localise visually or with LiDAR. Underwater there is no GNSS, so manage position with acoustic positioning or tether length. GNSS-denied
• Darkness: it is dark under piers even at noon. Use lit aircraft and consistent exposure. Darkness
• Wind & turbulence: sea wind is unobstructed, and it swirls around quay corners and piers. Wind & turbulence
• Magnetic disturbance: sheet piles, cranes and moored hulls upset compasses. Magnetic disturbance

Another obstacle is ships. Working berths have large vessels and cranes, so when and where to launch a boat or ROV must be agreed with port operations.

Port inspection rates each member’s degree of deterioration (in stages such as a–d), evaluates the performance of the facility as a whole and sets repair priorities. Drone data helps in the steps before rating: finding, measuring and comparing.

Responsibility for inspection lies with the port authority (usually a local government) or the facility owner. How drone and ROV data are used is for the manager to judge and record, within the technical standards and inspection guidelines. The national government also compiles information on new technologies for port inspection — see the MLIT Ports and Harbours Bureau.

For flying, Japan’s “specified flight” rules apply (over densely inhabited districts, within 30 m of people or property, etc.). Quay cranes and moored ships count as property. Most international ports have restricted areas under the SOLAS maritime security framework (the ISPS Code), so you cannot enter or fly without permission from the port authority and the facility security officer. Work on the water may also need procedures with the harbour master (Japan Coast Guard) because of vessel traffic. Compare countries in world regulations.

Internationally, PIANC, the World Association for Waterborne Transport Infrastructure, brings together international experts to publish technical reports and guidance.

• Under marine growth: steel covered in shells and weed must be cleaned before its surface can be seen. Cleaning is still mostly divers’ work.
• Reliable thickness measurement: ROV-mounted gauges are improving, but cleaning, coupling and recording consistently is still often more reliable by hand.
• Visual inspection in murky water: heavy turbidity defeats cameras. Sonar shows shape but not fine cracks.
• Voids under the apron: invisible from above. Ground-penetrating radar or coring is needed.
• Rating and usage restrictions: deciding whether a berth can be used is the manager’s responsibility.

In the early morning, with no ships moving, a small uncrewed boat slides out from the end of the quay and photographs the deck soffits as it threads under the pier. At the same time a tethered ROV descends along the sheet piles, recording the wall at the same depth and position as last time. An aerial drone measures the apron and spots a few millimetres of settlement.

Divers go down only at the few places the data flags. Port engineers compare deterioration rates across facilities and decide which quay to repair and when — that, at least, is how the editors see it.