Monday, December 15, 2008

[ferry disaster] greed and ignorance

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First, the news:
A wooden ferry carrying about 100 passengers has sunk in the Philippines, with at least 22 people drowned and about another 30 missing.

The ferry Maejan was approaching Aparri in Cagayan province in the north of the country when its bamboo outrigger broke in heavy seas off Ballesteros.

Passengers panicked and some leapt into the sea, creating instability on the vessel, which then capsized.



As you'll see in the top photo, the outrigger consists of two parts. The spindly arms extending outwards are called the akas and the long log in the water is the ama.

Now look at the photo above of a Hawaiian outrigger under sail. You can see that the ama has very little inherent buoyancy and far less weight, so it's only a balancing act of the crew which keeps the whole platform upright.

It acts in much the same way as poles do in skiing – they’re not designed for pushing hard against the snow – they’re only there for delicate balance.

There is designed to be one ama only, which skims a metre above the water on the "upwind" side [ignore the tiny float on the other side for now] and this long plastic float is kept there, skimming, only by the crew's skill and constant movement.

Furthermore, this ama is designed to be used in conjunction with sail, which gives it nice counterbalance and therein lies the stability. It's not designed for use on a power boat which has no sideways, sail assisted stability.




The south-east Asian variety of the ama really does use an actual log, joined by spindly akas, which don't need to be strongly made because as mentioned already, they are not designed to absorb pressure - they're designed only for delicate balance.

If any downwards pressure were to be put on these amas, then they would instantly go under the water and the boat would roll.

Now, the moment you design amas either side of the central hull [the boaty part of the boat], you have created a trimaran, not an outrigger any more. You are asking the amas for something completely different – you are asking them to absorb sideways and downwards pressure.

Therefore spindly akas and non-buoyant amas are no longer of any use [check the ferry in the top photo again] and must be discarded in favour of far more buoyant and sturdy amas, as in photos 3 and 4.

Also, in 4 below here, you can see that the central hull has no inherent stability whatsoever. It is of concave design near the waterline, [by comparison with a normal convex shaped hull] and the trimaran hull is, by definition, top heavy above.




The reason it is designed this way is that if you have a narrower beam [width] at the water line, this in turn means a more efficient, longer shape and less wetted area, which in turn means either more speed or in the case of a commercial craft, more fuel savings.

Clearly, a ferry company is interested in that.

Where the ferry company makes its mistake is in choosing the western trimaran central hull, a wedge shape balancing on its sharp end, combined with a south-east Asian, spindly, log design ama either side, designed to be used with a normal hull shape and not to be used as waterline balancing floats.

In other words, they want a trimaran for fuel efficiency reasons, plus speed, but are not prepared to use the key design component of that – the buoyant amas, which are expensive to build and add weight.

Any expert could tell them that as long as the weather is fine, they may survive but in bad weather, with passengers on board, they're all dead.




Now look at the commercial ferry above. Even with a normal, rounded shape, stabilizers below and a wide beam [width], this boat is rolling in the heavy seas.

So can you imagine what the ferry in the top photo would be doing in such seas? The moment high seas alter its balance, over goes the ferry and in the Philippines region - they do go over and people do die quite regularly.

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