Sunday, March 28, 2010

FV Trident Inquiry – the Joint Panel of Experts

The Aberdeen Press and Journal informed us this weekend about the latest goings-on in the Trident inquiry. It was thus that we learned that Mr Martin Pullinger, [*] naval architect and retained expert for the majority of the Trident victims’ families, was criticised by the advocate acting for the vessel’s designer for having formed an opinion on Trident’s stability "without the knowledge required", a claim which the advocate defended by citing Mr Pullinger’s decision to defer matters relating to the Trident’s seakeeping ability to Professor Colin MacFarlane.

We are thus given to understand that Professor MacFarlane’s unique expertise in the arcane subject of seakeeping should preclude other experts from having opinions not only on the subject of seakeeping but also on issues of stability in general (issues deemed up until now to be the bread and butter of any naval architect).

How odd is it then to read pages 64 and 65 of the transcripts of evidence from the inquiry for the 4th of November 2009 about the following exchange, which took place during that day’s hearings:

Cross-examination by MR ANDERSON: […] Well perhaps you could tell us then, Professor MacFarlane, what exactly is it about the prevailing sea conditions which has combined with the specific sea-keeping characteristics of the Trident to cause this to capsize?

WITNESS [Professor MacFarlane]:  I do not know […] I do not know the specific sea-keeping characteristics of the Trident at this stage which combined with those sea conditions caused it to capsize.

SHERIFF PRINCIPAL YOUNG: Sorry. You don’t know?

[1] Mr Pullinger, it’s been reported, has refused to concur with the conclusions of the Joint Panel of Experts  - which did not mention static stability as a potential contributing factor to the loss of the vessel - and has submitted his own report to the inquiry. 

Sunday, March 21, 2010

FV Trident Formal Investigation – the distance from reality

Toto, I’ve a feeling we are not in Kansas anymore” (Dorothy Gale, from the film The Wizard of Oz)

With every day that passes, it becomes more and more apparent that the UK government would very much like the Trident court of inquiry to dismiss the findings of the original 1975 public investigation and conclude instead that the loss of the vessel and its seven crew was caused by some reason other than deficient stability. 
In fact, the cause for the loss that has been proposed by the inquiry’s Joint Panel of Experts (JPE), after many years of deliberation, and which the Government is vigorously promoting is that:

 “The cause of this capsize is attributed to specific sea-keeping characteristics of the vessel combined with the prevailing sea conditions at the time”

To arrive at the above conclusion, without or in spite of the available factual evidence, a few premises need to be introduced beforehand, which when you use a long enough chain of estimative processes, approximations and other abstractions of reality, and when you are not constrained by empirical verification, can be quite easy.

In order to demonstrate and produce evidence about the behaviour of the Trident in various sea conditions the Maritime Research Institute Netherlands (MARIN) was hired to construct a physical model of the vessel, which was tank tested in the weather conditions specified by the inquiry Joint Panel of Experts (JPE), as well as a Fredyn numerical model, which was tuned using the tank testing results from the physical model.

Trident’s weight and centre of gravity details, normally derived from an inclining test, used by MARIN to build their models were, however, a step further from reality since they had been obtained from sister vessel data and negotiations amongst the parties represented at the inquiry.
The weather conditions, specified by the JPE, inconsistent with several eyewitness testimonies and the findings of the original investigation [*], were derived from two weather hindcasts – i.e. other approximations of reality – and then processed for the purpose of providing the necessary parameters for the model. 
How this processing was done and how reliable its outputs were, we may never be able to fathom. All we really know is that the conclusions drawn by the inquiry experts from these hindcasts suggest that, on the day when the Trident was lost, the winds and the sea waves were much bigger than the testimony given at the time of the 1975 inquiry indicated.
What is more, the MARIN physical model was only run for a limited number of wave settings, leaving the scientists to analogise freely as to the reactions of the model to other sea conditions.

Then, of course, the error propagation comes into play and, in the end, the results obtained from this combination of successive abstractions of reality, with their accumulated errors and subjectivity, doesn’t inspire great confidence.

In short, it can be argued that testing the behaviour of a vessel whose displacement and centre of gravity at the time of her loss are not accurately known, under weather conditions the parameters for which appear to have been interpolated from extrapolations, by means of a model which incorporates a number of possibly debatable assumptions and suppositions as well as a series of further abstractions, validating this model against another model, observing it through a very limited number of tests and assessing the test results using yardsticks and norms that have not been accepted in the wider maritime community, takes us a some distance from reality and from a level of certainty than we might consider suitable to a fatal accident investigation.
[*] If we understood correctly the press reports on this subject, the victims’ families were prevented from appointing their own weather specialist. (Aberdeen Press and Journal, 02 November 2009, Trident families’ weather expert is disallowed)

Saturday, March 06, 2010

FV Trident inquiry – variable factors and conditional probabilities

In the Aberdeen Press and Journal of 5 March 2010 we read about the dialogue that took place between Ms Ailsa Wilson QC (representing the Advocate General) and Professor MacFarlane (expert witness for the inquiry) concerning the stability of the FV Trident:

"Ms Wilson said: "The feeling among the group [i.e. the relatives of those lost on the Trident] is that Trident had survived for 18 months and sailed in much worse conditions to those during the loss, so she must have been a risk.
Mr MacFarlane said he did not see the logic in this, adding: "If she survived much worse sea conditions and more difficult conditions then I don’t see how it could be said that she had a stability problem. That doesn’t seem logical to me.""

If the testimony mentioned above is accurately reported, then we have to accept that the concerns expressed thereafter by Mrs Jeannie Ritchie, one of the Trident widows -“We seem to be going round in circles and being baffled by science,” she said - may be well grounded.
For it appears that, in response to one of the relatives’ reasoned arguments as to what may have caused the vessel to capsize, Professor MacFarlane chose to give a rather superficial and possibly misleading response, neglecting to explain that a vessel’s stability - that gives a vessel its resistance to capsize - is not a constant, but a variable property, which depends on a number of variable factors, such as the disposition and weight of fuel, water, ice, fish etc., and that his answer would only be true, if the Trident’s stability had been exactly the same during her last as well as her earlier trips.
The underlying logic behind the proposition put forward by the relatives is really quite simple: if we assumed that the probability of any given vessel capsizing is dependent upon two principal factors:
  • The intact stability of the ship – where the probability of capsize is inversely proportional to the ship’s stability reserves – which is, as mentioned above, a variable
  • The sea conditions in which the ship is sailing – where the probability of capsizing is relative to the size of the waves
then, for the Trident’s trips, which she had successfully completed earlier and where the sea conditions were worse, we would have to conclude that the stability of the vessel was better.
By virtue of the same logic, we would also have to conclude that, on the Trident’s last voyage, taken in more benign sea conditions, but ending with the capsize of the vessel, it must have been the vessel’s stability that was worse. The suggestion, therefore, is that it was the stability rather than the wave height, which led to the capsize and loss of the vessel.

The obvious question that follows from here is - what level of intact stability did the Trident have at the time of her loss?