Statistics

[Aja]

Reading the post below on Replacing Standing Rigging and Olewill's question at the end of his post on where a rigging failure had occured set me thinking.

There are plenty industry reports available from car manufacturers, Insurance companies, Top Gear opinion polls even, where knowledge and the likelihood of of car failures is pretty well open knowledge.... "everyone knows about the thingy that always goes first on the Rover/Subaru Mini 10000 injection...."

Is there any information available in the marine environment - e.g. from Insurers tables on the likelihood of (say) "....rigging failure is going to be at the lower rigging screw on the starboard cap shroud ..."

If not, why not?

Donald

 

[KenMcCulloch]

Because of small sample sizes and confounding variables. Cars are produced in huge numbers so faults and failures emerge in numbers that can be analysed to show patterns. With yachts the sample sizes are much smaller, with far fewer examples of each type, and even within those 'populations' much variation in terms of both rigs (masts and rigging from different suppliers and set up in different ways) and of course in how they are used.

Take Folkboats for example. Regular racing, lots of changes in rig tension through winding on the backstay, reefing late and so on will produce different and greater stresses than more leisurely cruising. Even though there are 000s of similar boats the only pattern evident might be related to how they are used. That would make it difficult to establish predictive validity in relation to, say, failures of particular components. The variations across the population of all Folkboats in respect of their setup 'confound' any predictive patterns that might emerge in relation to the way they are sailed.

 

[sarabande]

I am not sure that I agree entirely.

If a "point of failure" database existed, it would show common consistent positions where rigging failure takes place: a toggle failure in a Folkboat is a toggle failure on a RTW yacht.

The beneficial outcome would be to be able say that, f'rinstance, for any shroud that passes over a spreader with an included angle of less than 145 degrees, the failure rate is three times greater than for a more than one of 145 degrees.

There are so many variables though, that

1 setting up the technical database
2 inputting test data
3 defining reports
4 collecting real life data
5 inputting said data
6 running reports against "what-if" simulations

would be a very long and expensive business, And there I agree that the available data source set is probably far too small, unless every insurer and rigger joined in.

I'd go the other way, and shove all the tech data into a clever engineering app, and predict failures from that, and match theory to real world events. Any disparity is likely to be down to human failure to put things together properly, design rigs to known limits, or experience localised stresses or impacts outside the design parameters.

 

[Aja]

I seem to remember that for one of the round the world races one boat had problems with forestay fittings and when they looked they all had it.

Then another race possibly one boat had problems with keel delamination and the rest were re-engineered whether they had it or not...
Now surely if 1x19 wire and 'x' rigging screws were know to fail and insurance companies were advised through claims then riggers and others would (surely0 be advised to stop fitting these - or am I being naive?

Donald

 

[ex-Gladys]

I think the issue with rigging is iy's all a "hand made" process. In other words the rigger takes wire and fittings and makes up the rigging to your sizes. The "manual" process of swaging or whatever those fittings on must be the main variable?