John Cobb- Crusader/Railton Special

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Pullman99
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Re: John Cobb- Crusader/Railton Special

Post by Pullman99 » Sat Sep 29, 2012 8:30 am

Today, 29th September 2012, is the 60th anniversary of the death of John Cobb at Loch Ness in 1952. His initial run with Crusader that day resulted in a recorded speed of 206.89mph thus making Cobb the first person to set a speed in excess of 200mph on water. As we know, sadly, on his return run, it is believed that a major structural weakness in the design of Crusader's forward planing shoe caused the craft to crash. This subject has been commented on by several contributors here. A truly Great Briton who is remeberd by many today.

As Novie has mentioned, I understand that the Speed Record Club is holding a gathering at the Cobb Memorial at Drumnadrochit today so, hopefully, any Forum contributors present may be able to contribute a further post or two.
Ian Robinson
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Excelsior2007
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Re: John Cobb- Crusader/Railton Special

Post by Excelsior2007 » Sat Sep 29, 2012 3:36 pm

Thanks for pointing that out, Pullman99. I had forgotten that this was the day of John Cobb's death.

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sheppane
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Re: John Cobb- Crusader/Railton Special

Post by sheppane » Sun Sep 30, 2012 3:29 am

Pullman99 wrote:Today, 29th September 2012, is the 60th anniversary of the death of John Cobb at Loch Ness in 1952. His initial run with Crusader that day resulted in a recorded speed of 206.89mph thus making Cobb the first person to set a speed in excess of 200mph on water. As we know, sadly, on his return run, it is believed that a major structural weakness in the design of Crusader's forward planing shoe caused the craft to crash. This subject has been commented on by several contributors here. A truly Great Briton who is remeberd by many today.
To be completely accurate, Crusaders accident took place shortly after exiting the measured distance on the first run, as the craft ran into a series of swells, believed to have been caused by the cruiser Maureen, which had moved from its stationary position shortly before the attempt was made. It had resumed is stationary position in the measured distance, but it's swell had not dissipated but instead was reflected back on to the course by the steep lock side, notwithstanding the start of the record attempt being delayed for about 10 mins. The swells impacted Crusaders weak front shoe, causing it to eventually fail. A very brave man lost his life.
'When you go down into the arena, you know that sometimes, you're likely to get your nose punched. You do it with your eyes open. You take the risks'

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Mike Bull
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Re: John Cobb- Crusader/Railton Special

Post by Mike Bull » Sun Sep 30, 2012 10:38 am

From the little I've read, the front shoe was known to be weak, failing even, and was being shored up by people who begged Cobb to return the boat to the builders for proper strengthening work!? :shock:
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Dominic Owen
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Re: John Cobb- Crusader/Railton Special

Post by Dominic Owen » Sun Sep 30, 2012 8:35 pm

I've wondered often whether this had something to do with it;
Crusader bow plane.JPG
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rob565uk
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Re: John Cobb- Crusader/Railton Special

Post by rob565uk » Sun Sep 30, 2012 11:14 pm

Mike Bull wrote:From the little I've read, the front shoe was known to be weak, failing even, and was being shored up by people who begged Cobb to return the boat to the builders for proper strengthening work!? :shock:
According to the much disputed account provided by the book "The Last Crusader", just prior to Cobb's fateful last run, Commander Peter du Cane pleaded with Cobb to allow him to return the boat to Vosper's yard for substantial strengthening work on the forward planing shoe, but Cobb was keen to go for the record before having to depart to take up his Chairmanship of the Falklands Island Company. Internal timber strengthening had already been added to the shoe and apparently du Cane finally agreed that provided 190 mph was not exceeded and conditions were very calm, Cobb could probably secure the record with the boat as it was.

I have never seen Dominic's pictures of Crusader before, but they appear to show a definite crease in the surface of the shoe.

There is no doubt that Cobb was a very brave man and an exceptional record breaker. His LSR efforts and especially his 1947 record of 394 mph in the Railton Mobil Special inspired many other record breakers. He exceeded 400 mph in one direction in 1947 and 16 years went by before Craig Breedlove achieved a two-way average of over 400 mph (407.45 mph) in the 3-wheeled Spirit of America in 1963.

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sheppane
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Re: John Cobb- Crusader/Railton Special

Post by sheppane » Mon Oct 01, 2012 12:01 am

My understanding is that it was not the shoe itself that was weak, but rather its interaction with the wooden hull, in terms of its mounting, and flexibility thereof. I believe there is a pretty good description of the supposed problem, in Hook's Last Crusader, although that book is written from a Vosper perspective.
I believe Steve may be able to shed much more light, although understandably, he may want to keep his powder dry for his Cobb book project
'When you go down into the arena, you know that sometimes, you're likely to get your nose punched. You do it with your eyes open. You take the risks'

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Dominic Owen
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Re: John Cobb- Crusader/Railton Special

Post by Dominic Owen » Mon Oct 01, 2012 12:37 am

rob565uk wrote:I have never seen Dominic's pictures of Crusader before...
They're a couple of frames I took from some raw editorial footage of the boat being transferred from trailer to loch.
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Re: John Cobb- Crusader/Railton Special

Post by malcolm uk » Mon Oct 01, 2012 6:47 pm

The BBP operations team were at the Cairn when wreaths were laid to remember John Cobb at the time of the accident 60 years ago. We were able later in the day to gather useful data regarding wakes and washes from moving craft. Inspite of their experience with World Record attempts the role of the operations team for K6 and their actions that day meant they were probably culpable in the accident which took place.
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KW Mitchell
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Re: John Cobb- Crusader/Railton Special

Post by KW Mitchell » Mon Oct 01, 2012 11:22 pm

It is important to understand that Crusader fell foul of the little-known effects of dynamic instability. This was elegantly enunciated by the Norris brothers following analysis of cinematographic recordings of Crusader's demise (The Engineer, 1957).

They showed that the craft suffered violent pitching oscillations of 5-6Hz, initiated by swell, which led to the collapse of the front wedge. Such instability was shown to be related to the height of the CG above the wedges and their inherently large moments therein, plus factors relating to the 'spring-rate' of the wedges. The issues are discussed in further detail - together with the lessons learnt in relation to K7's design - in Neil's book 'Donald Campbell Bluebird And The The Final Record Attempt' pp's 198/9.

It is also possible to argue that even if Crusader's front wedge had been strengthened, such extreme forces on a single front wedge would have led to failure - and - even if Cobb had been able to run on perfect water that fateful day, a speed would have eventually been reached whereby the oscillation was inevitable.

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