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post #1 of Old 07-01-2005 Thread Starter
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the concept of unsinkable yachts

If you are in the market to buy a new yacht then think long hard before you part with your hard earned dollars or pounds or whatever before you lay them down for a boat that makes a claim to unsinkability.

The concept itself is nothing new. Sadlers used it years ago. Etap have legitimised it even more with certification. There are also several ways it can be done and there is plenty of material out there on the Net that discusses the use of foam, floatation bags and even closing compartments.

Sadlers and ETAPs though use double skin technology with GRP. It is not to be confused with Whipple shield technology in spacecraft either - in that sense it is very low tech!

It is easier to provide unsinkability on glass boats. Remember the Boston Whaler. It is certainly more difficult on a steelie or even a heavy timber or even aluminium boat. Although some of the other methods are more appropriate with those materials. One noted marine architect I spoke to said it was easy enough to do in any boat and I agree with that - his reason for not designing such safety into all boats was the lack of interest. Maybe it is like cars years ago when the manufacturers claimed "safety does not sell" as their excuse for not including it in all vehicles.

What the boat manufacturers do not tell you if you are buying an "unsinkable yacht" and worst still when you approach them are not prepared to say is what happens when the keel sheers. The truth is it happens and when it does the results can be disasterous in any boat.

Why it is important to understand the limits of unsinkability in the buying decision is that boats that are being sold as "unsinkable" come at a premium so if you are going to pay the extra you may as well know that the concept of unsinkabilty is limited to just that.

When the keel sheers an enormous weight is suddenly removed from the boat. When it happens, and recent Sydney-Hobart yacht races show that it does, most boats either sink or just turn turtle.

It is all very well for marketers like ETAP to say their boats are unsinkable but the reality is that is not much comfort when the boat is upside down and you are trying valiantly (usually in heavy seas) to hold onto what little grip or flat section there is on the bottom. The boat certainly won''t right once the keel is gone and indeed with so much floatation low down in the hull the thing will turn turtle very quickly. Hey even I learnt that in the bathtub!!!!

The reality is that "unsinkability" is just that - there is no guarantee that the boat will stay upright. So do not be seduced by the claims that it can still be sailed when it is flooded. That does not happen in all circumstances. Even though the brochures and deliberate floodings described in them are designed to make you feel warm and fuzzy about such things.

There is a lot of obstacles out there in the ocean, some living, some not, and a keel is not made to take that much impact. You don''t have to be a rocket scientist to understand that any pressure at the bottom of the keel translates into a lot more pressure at the top with fin type keels. It is all to do with leverage. And I am not talking about dingies here - I am talking about craft that weigh or displpace many tons.

Whatever the manufacturers claim the bottom line is and history has shown that fin keels just cannnot take that sort of punishment.

Maybe it is time ETAP too considered longer keels otherwise all cruisers who want that concept will be better off to resort to other boats with inflation bags or closing compartments to stem the flow rather than opt for foam core plastic boats which despite the claims are still delicate in such circumstances. Remember steel has about 27 times more impact strength than fibreglass of the same dimension.

That does not even take into account that the present foams all take on some water albeit some less than others. There is also the nasties that love to eat that stuff. They too are matters that the manufacturers don''t want you to know.

At least if you buy an unsinkable boat after reading this you will know that they do in fact have limitations and what to expect. For most of us though I wonder whether all that hype is really worth the extra expense. I for one don''t think so. Probably the reason why ETAPs are not volume sellers either.

Johnno is offline  
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