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Old 27-11-2015, 07:03   #121
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Re: Oyster Problems?

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Originally Posted by neilpride View Post
The laminate thicknes around the keel stub is ridiculous , Hard to see a minimum inch of glass right there, is just BS in all the aspects....
This was my immediate reaction as well. Really surprising as older and much smaller Oysters I have known have far thicker glass even several feet from the keel stub.

There seems to have been almost no adhesion between the skin and what appears to be a matrix above. It looks rather like the skin was bearing nearly the entire load of the keel, with little actual reinforcement from the beams above.
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Old 27-11-2015, 07:06   #122
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Re: Oyster Problems?

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Originally Posted by Bill Seal View Post
It's interesting that none of the sub-structure seems to have failed. It looks like they were depending on the peel strength of the hull laminate. I wonder if they just glue the winches on with their magic accumpuckey.
This is a major departure from traditional build technique for Oyster. Obviously not a good one.
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Old 27-11-2015, 07:22   #123
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Re: Oyster Problems?

It is the Chan to keel clan the hoses the a connect different sections of the ma in bilge
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Old 27-11-2015, 07:32   #124
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Re: Oyster Problems?

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Originally Posted by Polux View Post
In fact the keel structure depends on the hull laminate strength or in other words on the hull integrity. The forces transmitted by the hull should be absorbed by a large part of the hull to prevent what happened here assuming no defective built. The relative small part of the hull that delaminated indicates that the forces were not sufficiently transmitted and absorbed by a large part of the hull.

And bonded agents had to be brought by somebody as the responsible for this, even on a hull that has the keel structure laminated to the hull
I have to say that the image you posted of the 885 hull in construction leaves me less than impressed with the reinforcing structures of the newer Oysters. Some of the stringers seem slim for the size of craft and discontinuous (bending round to accomodate yet to be added internal structures it would appear), or rather inappropriately bent. Also very few rib structures… in older, far smaller, Oysters these are rarely more than 3 or 4 feet apart and often much less. Also the stringers used to continue right up the sides of the vessel. In this case I presume those large triple windows obviate this… but I wonder if there is sufficient compensation, perhaps in the accomodation bulkheads, or have they simply dispensed with the super seaworthiness of the Matthews era?
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Old 27-11-2015, 07:46   #125
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Re: Oyster Problems?

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Originally Posted by Alessiocannoni View Post
The weight of the boat in cruising conditions (1000 l of fuel and 1000 of water + sails and all the stuff) was 66 Tonn, (I measured by load cells in September in Gosport by load cells because the Oyster didn't do it), the mast 1 m shorter than the n. 1, the main in mast fourling main (don't ask me why please); seems that Rob is not involved in the structures, chooses on the deck hardware, funny way to adjust the boat asset, this aspect seems to be cured by Oyster technical department, I say seems because all their technological and building solution are secrets (fortunately nobody can copy)
Dear Alessio,

Thank you very much for your invaluable contributions here. Your participation is extremely welcome and appreciated.

Yours Aye,

Steven
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Old 27-11-2015, 08:14   #126
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Re: Oyster Problems?

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Originally Posted by Muckle Flugga View Post
This is a major departure from traditional build technique for Oyster. Obviously not a good one.
Since Rob Humphreys is designing Oysters they have a similar keel structure, that is what is used on the vast majority of modern yachts.

The question if this one was well dimensioned or not is another question.

There are many recent Oysters circumnavigating and doing ocean passages without any problem.
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Old 27-11-2015, 08:25   #127
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Re: Oyster Problems?

Quote:
Originally Posted by Polux View Post
Since Rob Humphreys is designing Oysters they have a similar keel structure, that is what is used on the vast majority of modern yachts.

The question if this one was well dimensioned or not is another question.

There are many recent Oysters circumnavigating and doing ocean passages without any problem.
Well… this thread suggests things might be otherwise than they appear.
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Old 27-11-2015, 08:42   #128
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Re: Oyster Problems?

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Originally Posted by Muckle Flugga View Post
I have to say that the image you posted of the 885 hull in construction leaves me less than impressed with the reinforcing structures of the newer Oysters. Some of the stringers seem slim for the size of craft and discontinuous (bending round to accomodate yet to be added internal structures it would appear), or rather inappropriately bent. Also very few rib structures… in older, far smaller, Oysters these are rarely more than 3 or 4 feet apart and often much less. Also the stringers used to continue right up the sides of the vessel. In this case I presume those large triple windows obviate this… but I wonder if there is sufficient compensation, perhaps in the accomodation bulkheads, or have they simply dispensed with the super seaworthiness of the Matthews era?
That appreciation goes with your way of thinking:

"‘Structural engineering is the art of modeling materials we do not wholly understand into shapes we cannot precisely analyse as to withstand forces we cannot properly assess in such a way that the public at large has no reason to suspect the extent of our ignorance.’"

Structural engineering is not different on their finality and objectives regarding building a bridge, a boat, a car, an airplane or a building. It can be well done or inadequately done but it is the way things are built today, with science computer analyses and a lot of high tech means and knowledge, and not only boats.

Regarding your analyses I have no idea if it is wrong or right and I bet that even an experienced naval architect would have to consult its structural engineer and this one would have to look at the calculations and scantlings to be sure if you are right or wrong.

By the way that quote that you appreciate so much has nothing to do with boat building and boat building structural engineer, it is a 37 year old citation made by a civil engineer. If that quote was true many of the bridges, buildings and structures built since then would have collapsed. Happily it is not the case, at least in what regards the vast majority of constructions. Or maybe they are all good artists
http://www.burnsmcd.com/Resource_/Pr...-Engineeri.pdf
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Old 27-11-2015, 08:47   #129
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Re: Oyster Problems?

I have to say I am also not impressed by the skin thickness. It is much less than on my boat. I recently installed a keel cooler and had to use a hole saw to make the hole. The plug was 1.25 inches thick, about 3 ft to the side of the centreline.

That said, I don't think the load from the keel should have been capable of ripping apart even half an inch of fibreglass over the huge area that would have been in tension.

The keel broke off in the lower half of the keel stub. This should be an enormously strong area, the strongest part of the boat, with a very large cross sectional area to spread the stresses.

The bolts nor the strength of their support were an issue here, unlike in many other failures.

Among many extraordinary things I noticed, when the keel fell off it managed to peel the skin off both port and starboard sides in doing so. I'd love to understand what went on.

Looking at the flanges coming out of the keel, they appear to be the wrong shape. As the keel stub is a tapered triangular shape in cross section, so should the keel stub flanges be made ideally, so as to be maximally strong and rigid, yet they are straight. I can't see how the parts inside the keel stub would have been put together, but by not making the ribs triangular in shape they are presumably relying on laminate adhesion to hold many of the the stresses. Perfect production control and of material quality will be needed also. Not an ideal combination at all. I think the flanges look thin too. It is in this keel stub that the failure will have started I believe.

The displacement of the 825 is 56 tons lightship compared to 61 tons for the same sized predecessor model, the 82. It looks like they might have lightened the structure a little, though they might have done this with a design that is intrinsically lighter such as by using some cored materials.

I wonder if boat builders stress test their structures as they are being built to ensure the quality of materials and processes is correct? Commercial building builders do it daily when using concrete for example.

I hope we get to see a very detailed engineering analysis and report on this soon.
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Old 27-11-2015, 08:48   #130
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Re: Oyster Problems?

Quote:
Originally Posted by Polux View Post
That appreciation goes with your way of thinking:

"‘Structural engineering is the art of modeling materials we do not wholly understand into shapes we cannot precisely analyse as to withstand forces we cannot properly assess in such a way that the public at large has no reason to suspect the extent of our ignorance.’"

Structural engineering is not different on their finality and objectives regarding building a bridge, a boat, a car, an airplane or a building. It can be well done or inadequately done but it is the way things are built today, with science computer analyses and a lot of high tech means and knowledge, and not only boats.

Regarding your analyses I have no idea if it is wrong or right and I bet that even an experienced naval architect would have to consult its structural engineer and this one would have to look at the calculations and scantlings to be sure if you are right or wrong.

By the way that quote that you appreciate so much has nothing to do with boat building and boat building structural engineer, it is a 37 year old citation made by a civil engineer. If that quote was true many of the bridges, buildings and structures built since then would have collapsed. Happily it is not the case, at least in what regards the vast majority of constructions. Or maybe they are all good artists
http://www.burnsmcd.com/Resource_/Pr...-Engineeri.pdf
Well a fair few have… in fact. And many that have not were built well beyond the margins of uncertainty. You do notice that the first paragraph of your post contradicts the first line of your final paragraph, don't you?
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Old 27-11-2015, 08:50   #131
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Re: Oyster Problems?

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Originally Posted by Muckle Flugga View Post
Well… this thread suggests things might be otherwise than they appear.
I don't follow. Your comment regards this:
"The question if this one was well dimensioned or not is another question.
There are many recent Oysters circumnavigating and doing ocean passages without any problem."

There is one Oyster with problems, a boat that was not designed to be a 90ft but that resulted by an adaptation from a 82ft boat made by Oyster.

There are many recent Oysters circumnavigating or that have circumnavigated.

These are two facts.

What do you mean that this thread suggests regarding the other recent Oysters that have circumnavigated and have been sailed extensively without problems?


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Old 27-11-2015, 09:31   #132
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Re: Oyster Problems?

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Originally Posted by neilpride View Post
The laminate thicknes around the keel stub is ridiculous , Hard to see a minimum inch of glass right there, is just BS in all the aspects....
....15 mm.....and the thickness of the fiberglass of the frames into the stub about 6 mm....
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Old 27-11-2015, 09:53   #133
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Re: Oyster Problems?

Would it be too much to ask to see a detailed design drawing showing how that keel is attached? and maybe a stress analysis of that attachment with both static and dynamic loading?
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Old 27-11-2015, 10:10   #134
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Re: Oyster Problems?

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Would it be too much to ask to see a detailed design drawing showing how that keel is attached? and maybe a stress analysis of that attachment with both static and dynamic loading?
Almost certainly such an analysis would be proprietary to the NA and/or builder. So, yes, it probably is too much to ask.

But even so, it appears that any such analysis would be pointless. The failure happened in a place and manner that surely the designer did not consider a possibility.
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Old 27-11-2015, 10:33   #135
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Re: Oyster Problems?

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Would it be too much to ask to see a detailed design drawing showing how that keel is attached? and maybe a stress analysis of that attachment with both static and dynamic loading?
No, it would certainly be needed to understand what happened. Unfortunately the only ones that will have it are the technicians and experts that are going to investigate the accident. it makes all the sense to wait for the conclusions. The only thing for sure is that something was wrong on that boat and that the accident did not occur due to an impact.

Regarding more or less educated speculations I have posted already some by boat builders, experts in composite boat building and NAs, published on the Yacht de magazine. They point to different causes and I don't think that without enough information we will be able to do better than them, quite the contrary.
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