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Keeping afloat after colliding with a waterborne object

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What is the issue?
The risk of colliding with a floating or waterborne object such as a whale, tree or a freight container is very low. Sadly marine experts believe two centuries of whaling may have reduced whale numbers to 1% of the original population. There are now believed to be as little as 10,000 humpback whales in the North Atlantic were 240,000 roamed (1.5m worldwide).

About a container an hour is being lost overboard
Photo: Paul Townsend
But the risks of colliding with a container is increasing as the seas have become increasingly crowded with commercial shipping. As of 2018, there were 52,183 ships in the world's merchant fleets moving around 170 million containers each year. At any given moment there are 5-6 million shipping containers on enormous cargo ships sailing across the world’s oceans. These containers bringing vital commodities as well as consumer goods to billions of people worldwide.

But the increase in containerisation and container movement means more of them get lost in transit which increases the likelihood of a vessel colliding with one. It’s estimated that 10,000 of these large containers are lost at sea each year. That's about one container falling overboard every hour on average. Few, if any, are ever recovered and not many are reported because, unless someone gets hurt, or something lands in a marine sanctuary, there is no legal repercussions for these losses.

Almost all containers that go overboard will sink eventually. But, depending on the buoyancy and packaging of the cargo they contain, some can float just a handful of centimetres above the surface for a long time. Indeed if a container is filled with the right amount of polystyrene it could stay in that state for years on end. A 20-foot steel container can displace 37 tons and a 40-foot container can displace more than 70 tons. So one of these containers awash has the mass of an unmarked rock at sea afloat and the sharp corners of these reinforced steel boxes has all the piercing capabilities of one.

Lost containers may not all sink or float as high as this
Photo: US Coastguard

The problem with these, as with all waterborne objects, is keeping watch for them. As they often lie just below the surface it is as good as impossible to see them and they are completely imperceptible at night or in high seas. The risk of colliding with a container is also higher in busy shipping lanes and during winter and spring when storms make it more likely for the highly piled containers to fall or get washed overboard.

Why address this?
The oceans are vast and we should not be obsessed about containers, yet we should be mindful of this problem. The consequences of hitting a large floating object such as a large tree or container could be severe. Depending on the construction of the boat, the shape of the bow, the collision type - head on strike, glancing blow, or scraped by - the damage could range from a minor scrape to sinking within minutes.

'All is Lost' starring Robert Redford is based upon a fictional container strike
Photo: J.C. Chandor External link

How to address this?
Watertight bulkheads are the best answer by far, but many yachts do not come with these as standard. A simpler response to the limited risk in some boats is to mount a bulkhead 'damn board' on the fore and aft cabins on any vessel with a rudder that may be subject to flooding caused by a damaged rudder or prop shaft support strut.

Steel or aluminium boats tend to crumple and are not as susceptible to holing in a collision. If it is possible to provide extra reinforcing in the bow it would be advantageous and particularly so if the bow would not have them ride up over the debris. Wood or fibreglass vessels are much more vulnerable. Particularly so modern lightweight blunt-nosed yachts that would not tend to ride up, and their keels and fin rudders are another exposure.

Bolting in place a bulkhead 'damn board' made of marine plywood, up to about ¾ of the way up the passageway, will create watertight compartments in the event of a collision. Because they cost little and may be so easily installed they could be considered a measured response to this possibility. Should there be a collision these should create watertight compartments in moderate seas or, at the very least, buy the crew time to access the situation and effect repairs.

Mass production boats with their blunt noses, fin keels and exposed rudders are
vulnerable in collision situations.

Photo: Michael Harpur

The bulkhead 'damn boards' need not be a permanent fixture, rather securely bolted in before departing. A more elaborate solution would be of course to fit a watertight bulkhead, but this would be a much more expensive option.

If one is further concerned areas to look at are vessels with encapsulated keels and stems that are more likley to ride up. It is also possible to strengthen the keel support by using strong bolts with wider washers. It is also worth checking if there is anything one can do, to strengthen the rudder and other underwater fittings. An abandon ship plan that works in under a minute is also advisable.

Traditional vessels offer safely encapsulated keels, protected rudders and tend
to ride up on any debris that is struck

The situation should improve in the future. The International Maritime Organization (IMO), the United Nations agency responsible for the safety and security of shipping and the prevention of ships' pollution, began to develop measures to prevent the loss of containers. New regulations requiring the gross mass of a container to be verified before it is loaded onto a ship came into force on 1 July 2016. These regulations are targeted on the optimum stowage of containers to help prevent container stacks collapsing and being lost overboard and any associated injury, loss of life, or related navigational danger.

With thanks to:
Michael Harpur, Yacht Obsession.
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