Do shipping containers float?

Are shipping containers waterproof?

Shipping containers are not necessarily waterproof, but are weather-resistant. Their robust steel construction and tightly sealed doors protect cargo from rain, ocean and river splashes, and most external moisture. However, their seals often degrade quickly once they hit the ocean, allowing water to seep in.

Standard containers fill with water within days or hours, depending on impact damage and construction. Refrigerated containers, also known as reefer containers, offer slightly more protection but aren't entirely waterproof. Shippers often use specialised packaging to protect sensitive goods, such as insulated liners and thermal blankets to control moisture, and shock-absorbing materials like foam or airbags. 

What happens to shipping containers lost at sea?

Shipping containers lost at sea either float temporarily or sink to the seabed, depending on their weight and contents. Floating containers can remain on the sea's surface for weeks, travelling significant distances carried by ocean currents. Eventually, they take on enough water until they sink. Sunken containers become difficult to retrieve and may release their contents over weeks, months and even years, leading to environmental concerns, especially if they carry plastics or chemicals. Plastics degrade into microplastics, contributing to long-term pollution, and chemicals can poison marine life. 
 
When shipping containers hit the seabed, they create obstacles for fishing operations, damage sea life (especially if they contain hazardous materials) and threaten undersea infrastructure like cables. Sometimes, sunken containers become makeshift homes for marine life, as artificial reefs that coral and other organisms colonise. Retrieving sunken containers is often expensive and impractical, especially in deep waters, so most are left on the seafloor. However, advancements in underwater robotics are making it easier to locate them. 

How do containers stay on ships? 

Containers stay on ships thanks to precise stacking and sturdy securing systems. Crews ensure heavier containers are stacked at the bottom of shipping vessels and lighter ones on top to maintain balance. Each 20 or 40-foot container is secured vertically using twist locks and horizontally with lashing rods. 
 
Some ships have cell guides, metal rails that hold containers in place, adding an extra layer of security. Stowage planning software helps crews optimise container placement, enhancing stability and safety for each journey. Additionally, crews inspect and make adjustments during voyages to ensure all containers remain tightly secured. 
 
Also, some containers are equipped with sensors and tracking devices, such as Radio Frequency Identification (RFID) tags, allowing for real-time condition monitoring. It helps shippers quickly respond if containers are at risk of becoming unsecured. 
 
Strict regulations set out by the International Maritime Organisation (IMO) for container weight and securing methods help minimise risks, ensuring that containers stay firmly in place throughout each trip. Port State Control (PSC) plays an essential role in ensuring safety. PSC inspectors from different countries have the authority to check whether vessels comply with all IMO safety standards before they set sail.