jfm
Well-Known Member
Nice Lakesailor there
- I just realised my post 115 repeated what Tranny said in 114 - apologies Tranona. 
Owner wins claim against UK builder
- Thread starter Asm
- Start date
- I just realised my post 115 repeated what Tranny said in 114 - apologies Tranona. 
Angele
Well-Known Member
I'm coming to this late, and only read up to post 60ish so far (but I'm continuing to read so may have caught up by the time anyone replies to this post), but no one appears to have questioned in detail whether the forces involved are likely to have exceeded the crucial 40.5kN needed to have smashed even a properly made 20mm laminate, other than by guessing the size of the hole.
As Newton told us, the force required to bring the boat to a stop = mass x acceleration.
Mass of a "dry" boat is 27.5 tonnes. Call it 30,000 kg laden. The suggestion is that the boat was doing at least 6kts. Now, 1 kt is about 0.5m/s, so 6kts is 3.0m/s.
If the impact of the rock on the p-bracket is the thing that brought the boat from 6kts to stationary, it is impossible for the impact to have lasted for more than a fraction of a second (or else the rock would have entered the boat by a distance of a metre of more, which clearly it didn't do). So, let's say the impact of the rock on the p-bracket brought the boat to stop in about 1/3 of a second (makes my maths nice and easy). That is an acceleration of 10m/s/s. The force required to do that is mass x acceleration = 30,000 x 10 = 300,000N or 300kN. That is a heck of a lot more than the critical 40.5kN.
So, a key issue here is how much of the boat's momentum was absorbed by the initial impact with the bow riding up onto the rock. Unless it is more than 90% (reducing the speed to less than 0.6kt), I struggle to see how the force of the impact could have been less than 40.5kN so as to have been insufficient to disintegrate even a properly built hull.
Anyone spot any flaw in my maths?
As Newton told us, the force required to bring the boat to a stop = mass x acceleration.
Mass of a "dry" boat is 27.5 tonnes. Call it 30,000 kg laden. The suggestion is that the boat was doing at least 6kts. Now, 1 kt is about 0.5m/s, so 6kts is 3.0m/s.
If the impact of the rock on the p-bracket is the thing that brought the boat from 6kts to stationary, it is impossible for the impact to have lasted for more than a fraction of a second (or else the rock would have entered the boat by a distance of a metre of more, which clearly it didn't do). So, let's say the impact of the rock on the p-bracket brought the boat to stop in about 1/3 of a second (makes my maths nice and easy). That is an acceleration of 10m/s/s. The force required to do that is mass x acceleration = 30,000 x 10 = 300,000N or 300kN. That is a heck of a lot more than the critical 40.5kN.
So, a key issue here is how much of the boat's momentum was absorbed by the initial impact with the bow riding up onto the rock. Unless it is more than 90% (reducing the speed to less than 0.6kt), I struggle to see how the force of the impact could have been less than 40.5kN so as to have been insufficient to disintegrate even a properly built hull.
Anyone spot any flaw in my maths?
kcrane
Well-Known Member
If you assume the forward part of the hull didn't hit the rock, but that the rock hit perhaps part way down the prop shaft and pushed the boat up as the rock ran along till it clanged the P bracket, then in my head the time it took to stop would be a lot longer than 1/3rd second. The energy would also be dissipated along vectors not entirely the reverse of the direction of travel wouldn't it?
Angele
Well-Known Member
Hmm! Fair point. The front of the bow did hit the rock. There is discussion about the boat riding up onto it. (See last sentence of para 20).
However, the judge does talk about failure as a result of a vertical load, suggesting that it was not the collision of the p-bracket with the rock that brought the boat to a stop.
Still, staggering forces involved in bringing a big boat to a stop, aren't they? And the vertical forces would have to be tiny in comparison in order for them to fall below 40.5kN (essentially a "glancing blow").
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Tranona
Well-Known Member
Think you will find it was the prop that hit the rock - logical - rather than the P bracket. Part of the calculation of forces involved the amount of deformation of the prop shaft. See para 26 of the judgement for details of the arguments.
Angele
Well-Known Member
Save for the amount of energy permanently stored within the deformed prop shaft, the force transferred to the P bracket is the same whether it was the P bracket or the prop that hit the rock, so long as the prop remained attached to the shaft and the shaft to the P bracket. Hence the way structural engineers convert evenly distributed loads to point loading etc. At least that was the way it was when I did structural engineering calcs at university!
Interestingly, the para talking about the bending moment comes up with values for the horizontal or vertical loading required to achieve that moment (even if the lower value is taken) that are way in excess of 7.7kN and likely more than 40.5kN. Admittedly, this doesn't prove that a vertical force of more than 40.5kN was applied to the P bracket, but the onus was on the plantiffs to prove, on a balance of probabilities, that it wasn't and there is a plausible scenario here that says it may have been. I'm surprised the defendants didn't make a big issue of this, but the judge seems pretty much to dismiss the point in para 29.
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Tranona
Well-Known Member
Yes, that is why they brought in the idea that the force can be determined by the size of the crack, and as that was unknown for certain, it was estimated through establishing the waterflow. However, as we have discussed at length above, that estimation seems to be based on assumptions that are easily challenged. What is even more surprising as I mentioned earlier they ignored the fact that at some point after the grounding the crack had "grown" to 30", suggesting that a greater force had been applied at some point.
JumbleDuck
Well-Known Member
Though, as I said, the force required to grow a crack from 6" to 30" crack might easily be less than the force required to make the initial 6" crack. Depending, as you said, on the exact thickness profile of the laminate. Crack growth is funny stuff - it's all about energy, not forces, and can behave in unexpected ways.
Angele
Well-Known Member
Agreed. I've now read all the posts, so I'm up to speed, and reread the judgement.
Such a bad outcome for Pearl that the judge concluded the evidence on (vertical) impact force was inconclusive, and so it was all down to the size of the hole and, as others have stated, the "expert opinion" is based on flawed assumptions. If greater reliance had been put on the possibility that the vertical force was substantial, then the outcome would surely have been different.
A 30 tonne boat would not have to come to a final rest on a P bracket or prop at any great speed for the vertical force to exceed the crucial 40.5kN, even if a substantial proportion of its weight was being supported by another part of the boat already in contact with the rock or by its buoyancy.
petem
Well-Known Member
Whilst I agree that if Pearl had hired some decent lawyers they might have got away with this but from a moral perspective they were building potentially dangerous boats and they paid the price for this. (JFM, perhaps it's a good thing that you weren't defending them!)
I wonder if this action may lead to a string of claims against Pearl? If I owned one I'd be having it surveyed immediately so I could be at the front of the queue of owners demanding that their vessels are made safe.
Does anyone know what Pearl are going to do to check the other boats they have built (assuming they haven't done this already)? The decent thing would be to check them all for hull thickness. In fact, they should have done this as soon as they learned of the potential issue. I also note that there's no mention of this incident on their website. If they were confident of their product surely they would make a statement to reassure current and potential owners? Perhaps they think this will blow over.
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petem
Well-Known Member
Yeah but the thickness of the hull may be critical for the next Pearl that grounds. The hulls are strengthened in these areas for a reason.
MapisM
Well-Known Member
Ermm... I'd rather want the shafts attached to solid P-brackets also for other good reasons, regardless of grounding!
Not that this is meant to dismiss your concern - rather the opposite, in fact.
petem
Well-Known Member
Does it? Perhaps the owner was disgusted that he paid £100,000's for a boat and was supplied with one that was potentially dangerous. And we're not privvy to whatever conversations he had with Pearl following the incident. I wonder what his side of the story is.
petem
Well-Known Member
Reading this...
http://civillitigationbrief.wordpre...witness-statement-i-signed-its-just-not-true/
...sounds like the whole trial was a shambles.
But at the end of the day, he "argued the vessel was not of 'reasonably satisfactory quality' and unfit for use as a luxury pleasure craft", and was probably right (albeit he was very lucky to win £450k and not just the cost of making good the thin hull).
http://civillitigationbrief.wordpre...witness-statement-i-signed-its-just-not-true/
...sounds like the whole trial was a shambles.
But at the end of the day, he "argued the vessel was not of 'reasonably satisfactory quality' and unfit for use as a luxury pleasure craft", and was probably right (albeit he was very lucky to win £450k and not just the cost of making good the thin hull).
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jfm
Well-Known Member
that website you linked to was a waste of electrons if ever I saw one Pete
. The blog advises solicitors to make sure witness statements are true before signature. We'll I never! I'd never have thought of that. Such is the quality of this blog it contains the statement "A yacht, built by the defendant, sank having struck another yacht."
Angele
Well-Known Member
Yes....... But evidently not enough, even if built correctly to spec. 40kN is nothing for a boat with a mass of 30,000 kg.
petem
Well-Known Member
that website you linked to was a waste of electrons if ever I saw one Pete
But there's a lot of sloppy solicitors out there. I'm reminded of an incident we had with my MiL's (now deceased) solicitor a few years ago. She was sued by a local firm of estate agents who were claiming fees from a house sale (she changed agents and the first agent claimed they had introduced the eventual purchases - we were totally unaware of this). The court had written to my MiL's solicitor and the first we heard about the hearing date was on the Friday (the case was to be heard on the Monday). Needless to say we had no time to prepare a case. The judge was not impressed and we lost. A couple of years later I smiled when I read this http://www.bbc.co.uk/news/uk-england-gloucestershire-25137568 (same guy).
Yes, I noticed that. The blogger is obviously lacking in attention to detail himself.
petem
Well-Known Member
You're missing my point. If you hit rocks at planing speed you're probably gonna sink a plastic boat (however thick the hull). But hit a sandbank at a lower speed and the difference between 7mm and 20mm may save your life.
But I don't understand why Pearl haven't made a press statement. Considering the boat was built some time ago (2007?) surely they could say that this was an isolated incident, skipper was negligent, quality assurance has been improved, customer have nothing to worry about, blah, blah, blah.
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Tranona
Well-Known Member
Don't think anybody did try and argue that. The claim was for breach of contract - the boat was not built to the agreed specification.
There was a potential secondary claim under s14 of the SOGA but it was not necessary to pursue that as the claim under contract was successful.
On the evidence given a claim under s14 would arguably have been much more difficult.
oldgit
Well-Known Member
H,mm ...running a boat,presumably with enough navigational stuff to equip Skylab, hard aground at high speed on a plainly marked well known hazard out side your home port in broad daylight, with good visability and good sea conditions ....
