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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).

Meanwhile the seas have become crowded with commercial shipping. Some countries in 2007 are increasing the number of ships in their fleets by 20% a year. There will be 7,000 container ships on the sea in 2008, the largest carrying 10,000 x 20ft container stacked 18 layers high on their decks. This increases the likelihood of container collision. Container collision sounds strange but piled high as described they fall off ships. Whilst some containers sink, others float just below the surface, depending on the buoyancy and packaging of the cargo they contain. The risk of colliding with a container is higher in busy shipping lanes and during winter and spring when storms make it more likely that containers are washed overboard from freighters.

The problem with waterborne objects is keeping a look out for them. As they often reside just below the surface it is not practical to place a watch on the bow for days on end and they are completely imperceptible at night or in high seas.


Why address this?
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.

How to address this?
A simple response to the limited risk in some boats is to mount a bulkhead damn board just on the forepeak as presented with a marine plywood board in figure 1.

Steel or aluminium boats tend to crumple and are not as susceptible to holing in a collision but wood or fibreglass vessels are vulnerable. Particularly blunt nosed yachts that do not tend to ride up - see figure 2.

Implementing a bulkhead damn board on these vessels can be a viable and measured response to this possibility. If the board height is measured correctly, and an allowance for the bow to be down after a holing is factored in, the boat will not sink even if holed in the forward cabin area. It thereby makes the forward cabin into a water tight compartment in moderate seas or at least buys the crew time to access the situation and effect jury repairs. A collision aft of the cabin would be more likely to be a glancing blow so the consequences should be less severe - the notable exception of course being the Titanic.

A bulkhead damn board need not have to be a permanent fixture but may be 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.


With thanks to:
Michael Harpur, Yacht Obsession.





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