DavenHelen
regular
Reged: 06/09/2005
Posts: 516
Loc: UK, Lancashire
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Your quote was "the probability could be absolutely zero".
Disagree, unless you are saying that if we remove all know causes, there will never be an incident in which a liferaft is required. You are confusing Probability based on events which have happened and Probability based on the likelihood of them happening in the future.
I would challenge your statement, "The number of incidents is not related to the number of voyages or number of miles." and "They are not randomly distributed across the population, but only occur in a narrow range of specific circumstances."
You appear to be saying that increase in usage will not lead to circumstances that need LRs You can analyse the incidents to understand the circumstances but you cannot prevent similar circumstances from reoccuring.
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Dave
"There are 10 types of people in the world - those who understand binary, and those who don't".
Edited by DavenHelen (15/05/2008 10:23)
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jordanbasset
regular
Reged: 31/12/2007
Posts: 175
Loc: Shropshire
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Hi, thanks for the figures re re serious injuries on the road, they are useful and enables people to assess their own risks.I believe I have travelled in my live so an average around of 15,000 miles per year. If I multiply that by 50 years ( not including time as a child when passenger and assuming I will not see 70) that comes to 750,000 miles, which as a ratio to 10 million miles is around a 1 in 13 chance of being seriously injured or killed. I think that is a big enough risk to justify a seat bealt. In addition serious road casualties went down considerably when seat belts were made compulsory (probably together with generally safer car design one of the single biggest improvements to safety on the roads) if no one wore seat belts the number of serious accidents would go up and the risk would be even greater. Perhaps if you rarely travelled by car the statistical likelyhood would be low.
What would be interesting is similar figures with regards to life rafts over miles travelled, but as has been already mentioned it seems such figures are hard to come by
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"Without question, the greatest invention in the history of mankind is beer. Oh, I grant you that the wheel was also a fine invention, but the wheel does not go nearly as well with pizza."
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Tranona
regular
Reged: 10/11/2007
Posts: 1084
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Sorry, please get yourself a book on basic statistics. Probability is defined exactly as I described. There is no way you can predict events. You can only count past events and then project forward.
I can say that on the basis of the evidence there is a 60% chance if you are hit by a ship your boat will disintegrate and 40% chance that it will stay afloat long enough for you to be rescued or take to your liferaft. This is based on total of 5 reported incidents. I can also say that in a planned evacuation there is a one in three chance that the liferaft will not inflate. Based on a sample of 3, all with very different causes.
Now you should see why statistics are useless in understanding this issue.
Imagine how the daily papers could present the figures
"3 out of 5 yachts disintegrate in collisions!!!"
Somewhere at the bottom they might say that there have been only 5 collisions in 12 years, and probably would not bother to explain that an 8 metre yacht does not stand a chance against a 15000 ton ferry.
You can sail all your life and if you don't go near big ships, don't go out in extreme conditions and have a sound ship the probability of you needing to use a liferaft from the data available is in fact zero.
As to your last point, yes you can prevent foundering by not getting into situations where it might happen. However while we continue to cross the channel and dodge ships there is always a chance that a collision will occur. The fact that it happens so rarely suggests that everybody is fully aware and takes precautions, Radar, AIS, Mk1 eyeball etc.
Read the reports and then you will know what to do to avoid foundering.
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DavenHelen
regular
Reged: 06/09/2005
Posts: 516
Loc: UK, Lancashire
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“Sorry, please get yourself a book on basic statistics.”
Got plenty thanks.
“Probability is defined exactly as I described. There is no way you can predict events. You can only count past events and then project forward.”
Probability is about expected outcomes based on existing data. As there have already been Liferaft incidents then likelihood/chance of future incidents is non zero unless you intend to bias the sample by removing inconvenient data.
“I can say that on the basis of the evidence there is a 60% chance if you are hit by a ship your boat will disintegrate and 40% chance that it will stay afloat long enough for you to be rescued or take to your liferaft. This is based on total of 5 reported incidents. I can also say that in a planned evacuation there is a one in three chance that the liferaft will not inflate. Based on a sample of 3, all with very different causes.
Now you should see why statistics are useless in understanding this issue.”
Except we are not talking samples here, this is population. In the first case, we are looking at 5 incidents out of the total population, so it is perfectly acceptable to to make those statement. In the second case you are making predictions based on a small sample size and should couch your statement in terms of the Confidence Intervals and the Power of the test. Unsure as to why you think that this makes Statistics useless.
“Imagine how the daily papers could present the figures
"3 out of 5 yachts disintegrate in collisions!!!"
Somewhere at the bottom they might say that there have been only 5 collisions in 12 years, and probably would not bother to explain that an 8 metre yacht does not stand a chance against a 15000 ton ferry.”
That is Newspapers for you.
“You can sail all your life and if you don't go near big ships, don't go out in extreme conditions and have a sound ship the probability of you needing to use a liferaft from the data available is in fact zero.”
For certain values of “big”, “extreme” and “sound”. The problem is most sailors will have to go near big ships at some point, will get caught out when the weather deteriorates and will have unforseen problems with their boat.
“As to your last point, yes you can prevent foundering by not getting into situations where it might happen. However while we continue to cross the channel and dodge ships there is always a chance that a collision will occur. The fact that it happens so rarely suggests that everybody is fully aware and takes precautions, Radar, AIS, Mk1 eyeball etc.”
Yes.
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Dave
"There are 10 types of people in the world - those who understand binary, and those who don't".
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nct1
regular
Reged: 21/02/2004
Posts: 387
Loc: UK
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I guess we will have to agree to differ on that point, to my mind a liferaft does act in the same way as seatbelts and airbags. You have choices, you can chose to have a car with an airbag or not, and believe it or not, some people still chose not to deploy seat belts, on the basis that they have never needed one to date !
Having a sound yacht is of course easy if you replace it with a new one every 3 years and have all system surveyed independently every year.
But most of us have a budget and run older boats, and anyone that has ever run an older car knows, systems will break down due to old age, and often without warning, despite regular servicing and independent surveys (MOT).
The 2 F7's I was in were not forecast, and blew up within 20 minutes in one case, so you cannot guarentee not to be in bad weather.
My reasoning for having a liferaft is not based on the statistical liklihood of needing one, it is simply that at sea there will be occasions where systems could fail and the rescue services cannot come to your aid before the boat goes down.
I want a fallback position as a last resort.
I do not want to leave it to chance that I will never need a fall back position.
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Fireball
regular
Reged: 15/11/2004
Posts: 7179
Loc: Chichester
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That is fine - nobody has said you shouldn't have a LR ... we are just putting the point across that statistically speaking you don't NEED one ...
I don't think you can do a direct comparison with LRs against seatbelts or airbags ... whilst seatbelt is compulsory in the UK, airbags are not.
Anyway - when driving a car you are in collision avoidance/potential accident situations many times even in a short journey, whereas at sea the sailing yacht can pretty much take care of itself and an accident potential is usually minutes rather than seconds away.
The prolonged argument comes down to some ppls opinion that everyone NEEDS a LR onboard whilst others (like myself) disagree that they are a necessity and it then becomes (for non-commercial use) a personal decision based on individual circumstance.
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Don't be sad boy, people die all the time, just like that, why you could wake up dead tomorrow. - Homer Simpson
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Chrusty1
regular
Reged: 27/02/2008
Posts: 847
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You must really enjoy these threads?........don't the words, banging, head, and wall mean anything to you? I have got a sore head just reading all this!  
I will just add this, seems to me that if people want to carry a Life Raft, then fine......if they don't then that's fine as well, it's up to each individual to make their own choices, speaking for myself, I don't have one, I can't afford one, and if I could afford one, there are things that are more important to me to spend my money on. To my way of thinking, the best liferaft is the one you are sailing in.
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Captainslarty
regular
Reged: 12/08/2007
Posts: 2012
Loc: Currently La Coruna Spain
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The CBA factor dictates that I cant be bothered reading ALL this post.. but...
IF you dont have a raft, you are relying on others or drowning.. your choice...
but, to rely on others is selfish..
buy a bloody raft.. or stay in the marina. 
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PM me for info re SSB's etc. Bought, sold, repaired, fitted and optimised.
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Chrusty1
regular
Reged: 27/02/2008
Posts: 847
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1. Not all people sail from Marinas.
2. Not all sailors can afford a bloody liferaft.
3. Not all sailors need a bloody liferaft.
4, Some sailors are capable of making sure that they have their boats set up to make sure that they don't ever need a bloody liferaft.
5. Some sailors do not rely on others to get them out of trouble.
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Fireball
regular
Reged: 15/11/2004
Posts: 7179
Loc: Chichester
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Quote:
The CBA factor dictates that I cant be bothered reading ALL this post..
Your life - your choice!! 
Quote:
but...
IF you dont have a raft, you are relying on others or drowning.. your choice...
Which says that you believe a LR to be a necessity - ie, if you don't have a raft you WILL drown if others don't save you first ... it isn't as simple as that - first off, you need to be in a situation where deployment of LR is required and indeed possible - which statistically speaking you are more likely to win the lottery this weekend using 1 set of numbers ... (good luck - if you do, can you buy me a LR? )
Quote:
but, to rely on others is selfish..
Even if you do end up in a LR you are dependant on others to collect you from said LR .... so you are also being selfish ....
Quote:
buy a bloody raft.. or stay in the marina.
If I could justify the marina spend then I'd probably have purchased a raft ... I can't so I haven't .... so as I'm not in a marina I can go sailing without a LR now?
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Don't be sad boy, people die all the time, just like that, why you could wake up dead tomorrow. - Homer Simpson
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