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Old 12-12-2015, 09:42   #361
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Re: Oyster Problems?

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Originally Posted by Dockhead View Post
...
My guess is that you are universalizing your own experience in your own cruising grounds, and misapplying it to the rest of the world. I have never, myself, come close to grounding in the Mediterranean. The shores there are -- everywhere I have sailed -- steep-to with lots of depth right up to the edge of the shore. There are no tides to speak of. The charts are excellent, even in parts of the Med we think might be less civilized, like Turkish and Croatian waters. There are no shallow passes which require taking chances, to get through. I haven't seen much in the way of shifting sand bars.

.... At the risk of boring everyone by repeating it, I would never buy myself, nor recommend to any of my friends, a boat which has a keel which is not strong enough to withstand a pretty violent grounding. In my opinion, such a keel is appropriate only for hard core racers or performance nuts, sailing in very controlled conditions, or in cruising grounds where grounding is extremely unlikely.
Certainly I talk about what I know, but I do not only no know the med as well as the North coast of Spain that is called the "Death Coast" for a reasons related with the many shoals. Both Portugal and North of Spain have tidal waters. I know also that many boast with this type of keel make circumnavigations without any problem.

I agree with you that keels should resist groundings but that does not mean that they did not need to have the structure repaired later. Most have on any type of boat.

My disagreement with you is the assumption that the type of keels used on performance boats is necessarily more fragile than other types of keels and it is very funny we were discussing this on a thread regarding a keel of the type you seem to consider more strong, on a boat built by a very reputable brand, that failed with an year of use without never have been grounded, even lightly.

As you can see on this one, more than an hard grounding, with a lot of pounding by big waves over rocks, the keel is still there:
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Old 12-12-2015, 09:48   #362
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Re: Oyster Problems?

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Originally Posted by sailorboy1 View Post
Maybe this is thread drift, but:

It is my understanding the keel that ripped off the hull of the Oyster in question never experienced any grounding. Probably the only example of a keel just falling off a boat with no "help" ever out of all the stories of lost keels I can recall.
Then maybe your memory needs a refresher.... Our Hunter 450 keel came loose and saltwater intrusion corroded the keel bolts without the boat ever experiencing a hard grounding, or showing any evidence of any grounding... a topic discussed by you, others and myself on this forum extensively. Design was the problem, a design issue that could be easily and relatively cheaply remedied by the manufacturer if it chose to do so.

Structural deficiencies inherent in any boat design whether it be an Oyster, Beneteau or Hunter can cause the keel to come loose, which is what's being discussed on this thread.
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Old 12-12-2015, 10:15   #363
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Re: Oyster Problems?

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This has nothing to do with what you are defending regarding keels to be able to sustain hard groundings with any sort of damage.

That would correspond to cars being able to crash without sustaining any damage.

That is not the case and quite contrary modern cars are designed to destroy themselves on an absorbing way when crashed. Modern cars will sustain a lot more damage on a crash than 40 year old cars but the passengers will have a much better possibility of not sustaining damage.

As it was already pointed out modern keels are designed not to fall out even when sustaining an heavy grounding and the interior structure is designed to absorb the shock while sustaining some damage. That makes the shock less violent, protecting better the crew and giving more possibilities of not losing the mast.

As it was already pointed out very few modern boats are lost after a hard grounding and they can be sailed to a shipyard for repairs.





ROFLMFAO! Now boats are designed with keel "crumple zones" like cars! Priceless! This guy is almost as entertaining as Trump.
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Old 12-12-2015, 10:18   #364
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Re: Oyster Problems?

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Yes I agree with you. There is talks about making another RCD category above the maximum existing one. It exists that category in what regards racing offshore or in what regards professionally charted boats in UK.

Does not mean that the one that exists will be modified in what it stands for, just as you say, a bigger safety margin.

The reason that lead me to have an interest in boat design was precisely that, to be an educated buyer but I would never guess what you have to learn to be just that

As this Oyster case shows traditional solutions are not necessarily safer solutions even if most tend to look at the past to be assured that they are "proven" and safer design solutions.

There is also a tendency to mix luxury in what regards finish and interior quality with sound quality in what regards structural solidness and seaworthiness. Again this case is a good example.


The whole point here is that Oyster veered away from their "traditional solution" to the sort of thing you are constantly espousing, and this was the result. Everyone here but you can see that a return to the traditional solution is exactly what is called for.
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Old 12-12-2015, 10:31   #365
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Re: Oyster Problems?

I disagree strongly with the notion that it is ok to design a keel that cannot take a hard grounding without a repair being likely. A boat is actually like a car, contrary to Polux's analogy in so far that it is normal for a car to survive a low speed crash (7kt say,) just like a boat with a strong keel can do. If you hit anything hard enough it wil be damaged of course, so how strong to make the keel is a question of degree and what is reasonable to achieve.

Given that it is easy to make it strong enough and that there is little downside, cost or performance wise. Given that there is a high probability of grounding and the consequences of a failed keel are life threatening, all this is good reason why to make the keel strong enough to take a grounding is the right thing to do.

Tha Oyster 825 keel was a terrible mistake of bad design/build and so is the First 40.7 for a whole set of totally different reasons. I have to say I am shocked that Polux is defending the First design and to imply it and other designs that are based on similar design principles are acceptable. They are so clearly unacceptable in my view.
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Old 12-12-2015, 10:49   #366
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Re: Oyster Problems?

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The whole point here is that Oyster veered away from their "traditional solution" to the sort of thing you are constantly espousing, and this was the result. Everyone here but you can see that a return to the traditional solution is exactly what is called for.
I thought this was the most remarkable acknowledgment in their public statement.

So do the photos we've seen with the green squares constitute some sort of grid liner? I have no idea what this type of structure looks like, especially from the outside in! If so, is this a scenario where the "old" method they are now returning to is commonly known as "stick built," whereas what failed was the type of grid liner/matrix commonly associated with many production boats? I'm sure this is overly simplistic, especially since there also seemed to be a lot of concern about thin sections of laminate.
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Old 12-12-2015, 10:54   #367
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Re: Oyster Problems?

Quote:
Originally Posted by poiu View Post
I disagree strongly with the notion that it is ok to design a keel that cannot take a hard grounding without a repair being likely. A boat is actually like a car, contrary to Polux's analogy in so far that it is normal for a car to survive a low speed crash (7kt say,) just like a boat with a strong keel can do. If you hit anything hard enough it wil be damaged of course, so how strong to make the keel is a question of degree and what is reasonable to achieve.

Given that it is easy to make it strong enough and that there is little downside, cost or performance wise. Given that there is a high probability of grounding and the consequences of a failed keel are life threatening, all this is good reason why to make the keel strong enough to take a grounding is the right thing to do.

Tha Oyster 825 keel was a terrible mistake of bad design/build and so is the First 40.7 for a whole set of totally different reasons. I have to say I am shocked that Polux is defending the First design and to imply it and other designs that are based on similar design principles are acceptable. They are so clearly unacceptable in my view.
I agree with you, of course, but let's not confuse two issues -- keel shape, and construction method.

Polux is saying several different things, which we need to keep straight. They are not all consistent with each other, and not all are wrong.

1. He is defending high aspect keels and says that they can be designed to be quite strong.

2. He is saying that only idiots go aground, so designing massively strong keels is not all that important.

3. He is saying that the longish keel (compared to the real racing type -- hence "traditional type") of the Oyster did not prevent the keel from getting ripped off.


Proposition 1. Is certainly true, but it's a simple matter of geometry and lever arms, that all other things being equal, a keel with a longer interface with the hull will be stronger. And the curve of strength vs. keel length will be very steep at the beginning.

Propostion 2 has a manifestly false premise, but we have discussed that.

Proposition 3 is true, but it's a red herring. It's intentional obfuscation to call that Oyster keel "traditional". It was not quite as thin as the most aggressive designs, but it was in no other way "traditional". It was lightly and badly built, contrary to "traditional" approaches which would make the hull-keel interface a massively strong part of the structure. Not just "high end" boats, but many mass produced boats have well engineered hull-keel interfaces.
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Old 12-12-2015, 10:55   #368
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Re: Oyster Problems?

Quote:
Originally Posted by poiu View Post
I disagree strongly with the notion that it is ok to design a keel that cannot take a hard grounding without a repair being likely. A boat is actually like a car, contrary to Polux's analogy in so far that it is normal for a car to survive a low speed crash (7kt say,) just like a boat with a strong keel can do. If you hit anything hard enough it wil be damaged of course, so how strong to make the keel is a question of degree and what is reasonable to achieve.

Given that it is easy to make it strong enough and that there is little downside, cost or performance wise. Given that there is a high probability of grounding and the consequences of a failed keel are life threatening, all this is good reason why to make the keel strong enough to take a grounding is the right thing to do.

Tha Oyster 825 keel was a terrible mistake of bad design/build and so is the First 40.7 for a whole set of totally different reasons. I have to say I am shocked that Polux is defending the First design and to imply it and other designs that are based on similar design principles are acceptable. They are so clearly unacceptable in my view.

How strong without damage is something Polux can think about it if he have the bad luck to run hard aground in a atoll / Pacific/ thousand miles from any civilization....
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Old 12-12-2015, 11:01   #369
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Re: Oyster Problems?

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* * *

Hydrographic surveys are not primarily intended for pleasure vessels, but for normal shipping. It is EXACTLY the boat with a small draft, like this, which is MOST at risk of grounding, because waters at those depths are not surveyed thoroughly, practically anywhere, and are anyway subject to constant changes due to the action of waves and currents.

* * *

Charts are not infallible, and become less and less infallible, the further you get away from areas surveyed for shipping, . . .
Critically important points, imho, and probably only obvious to some in hindsight.
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Old 12-12-2015, 11:03   #370
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Re: Oyster Problems?

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I thought this was the most remarkable acknowledgment in their public statement.

So do the photos we've seen with the green squares constitute some sort of grid liner? I have no idea what this type of structure looks like, especially from the outside in! If so, is this a scenario where the "old" method they are now returning to is commonly known as "stick built," whereas what failed was the type of grid liner/matrix commonly associated with many production boats? I'm sure this is overly simplistic, especially since there also seemed to be a lot of concern about overly thin sections of laminate.
"Stick built" refers to how the furniture is installed. Versus hull liner, with prefabricated joinery.

What we see in the photos looks to me like a Plexus bonded (it's green, right Minaret?) grid matrix. I doubt if that boat has a liner.

It was not the bonded grid matrix which failed, however -- it was the "brackets" -- the vertical GRP parts, which were only 5mm (!) thick), of the keel stub. Once that failed, then the whole mass of the keel was supported by the bond between the keel stub skin and the outer skin of the hull, which then failed in turn. I am not a marine architect, but it looks so obviously weak -- how in the world it meets classification, I have no idea.

A more "traditionally built" keel would be solid lead right up to the bottom of the hull.
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Old 12-12-2015, 11:05   #371
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Re: Oyster Problems?

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I thought this was the most remarkable acknowledgment in their public statement.

So do the photos we've seen with the green squares constitute some sort of grid liner? I have no idea what this type of structure looks like, especially from the outside in! If so, is this a scenario where the "old" method they are now returning to is commonly known as "stick built," whereas what failed was the type of grid liner/matrix commonly associated with many production boats? I'm sure this is overly simplistic, especially since there also seemed to be a lot of concern about overly thin sections of laminate.

No no, is not the classic plastic grid liner droped in a hull glued here and there, its a post bond glass job with some short of foam or syntethic core covered in FG making a spider web of grid structure... its curious but the whole bottom section break apart without pulling the structure, could be a bad batch of resin , contamination or who know.... Minaret maybe know better ,,,, I guess they are thinking in make the hulls thicker , special the keel stub, probably changing the foam sections for something more apropiate or a full redesign of the inner structure, in any case this issue call for more FG , or who know, maybe a cored bottom with a solid keel structure...
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Old 12-12-2015, 11:08   #372
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Re: Oyster Problems?

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Originally Posted by Polux View Post
Certainly I talk about what I know, but I do not only no know the med as well as the North coast of Spain that is called the "Death Coast" for a reasons related with the many shoals. Both Portugal and North of Spain have tidal waters. I know also that many boast with this type of keel make circumnavigations without any problem.

I agree with you that keels should resist groundings but that does not mean that they did not need to have the structure repaired later. Most have on any type of boat.

My disagreement with you is the assumption that the type of keels used on performance boats is necessarily more fragile than other types of keels and it is very funny we were discussing this on a thread regarding a keel of the type you seem to consider more strong, on a boat built by a very reputable brand, that failed with an year of use without never have been grounded, even lightly.

As you can see on this one, more than an hard grounding, with a lot of pounding by big waves over rocks, the keel is still there:
I agree with you, of course, that high aspect keels can be made strong, and in fact can be made extremely strong with the right engineering and materials.

So obviously not every longer keel, no matter how badly built, will be stronger than every high aspect keel, no matter how expensively and well built, it is. It is a logical fallacy to claim that one failure of a longer keel proves that high aspect keels are just as strong.

In fact, it is a reasonably simple question of lever arms and geometry of the keel-hull interface. You need much stronger materials and much stronger means of attachment, to get the same strength out of a high aspect keel, and at some point there is no material, not even carbon nanotubes, which will make up the difference.

So let's not mix up these issues. The Oyster in question was shockingly badly built, and that was the cause of the accident. Even an old fashioned full keel with barn door rudder, can fail, if it's built badly enough.
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Old 12-12-2015, 11:09   #373
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Re: Oyster Problems?

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Originally Posted by poiu View Post
I disagree strongly with the notion that it is ok to design a keel that cannot take a hard grounding without a repair being likely. A boat is actually like a car, contrary to Polux's analogy in so far that it is normal for a car to survive a low speed crash (7kt say,) just like a boat with a strong keel can do. If you hit anything hard enough it wil be damaged of course, so how strong to make the keel is a question of degree and what is reasonable to achieve.

Given that it is easy to make it strong enough and that there is little downside, cost or performance wise. Given that there is a high probability of grounding and the consequences of a failed keel are life threatening, all this is good reason why to make the keel strong enough to take a grounding is the right thing to do.
I don't think any modern car can survive even a 7 km/h without quite big damages. Volvo used to advertise their car can do just that in the 80's, but they were strongly build and had the bumper far away from the chassis. Now all cars are made to protect the passangers and thus deform easily at the front while keeping the middle of the car much less deformed. I think airbags would go if a car hits a strong wall at 7 km/h and thus making most cars beyond repair.

It's good question to ask how hard grounding a boat should be able to handle. I don't think there are many boats that can handle 7 knots hard groundings without damage, but also I don't think there should be any boat loosing its keel in it. By hard I mean hitting a steep rock (granite or other hard, not sand or loose small rocks) and bouncing back from it. It certainly is not at all easy to desing and make such a keel struckture without loosing performance and not making the boat very expensive.

I don't think a First 40.7 not having damaged from previous groundings would loose its keel in the hard grounding described above.
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Old 12-12-2015, 11:10   #374
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Re: Oyster Problems?

Quote:
Originally Posted by Dockhead View Post
"Stick built" refers to how the furniture is installed. Versus hull liner, with prefabricated joinery.

What we see in the photos looks to me like a Plexus bonded (it's green, right Minaret?) grid matrix. I doubt if that boat has a liner.

It was not the bonded grid matrix which failed, however -- it was the "brackets" -- the vertical GRP parts, which were only 5mm (!) thick), of the keel stub. Once that failed, then the whole mass of the keel was supported by the bond between the keel stub skin and the outer skin of the hull, which then failed in turn. I am not a marine architect, but it looks so obviously weak -- how in the world it meets classification, I have no idea.

A more "traditionally built" keel would be solid lead right up to the bottom of the hull.
Dock, stubs are very popular for many brands, ask Minaret in how well build is the Nauticat keel stub, they are a really well design when the builder try to link a keel with a hull, they act like a proper bilge sump and the stub if is build it right can sustain lots of punishment without breaking the hull, add to this a strong inner structure and the result is a strong as hell keel conection...
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Old 12-12-2015, 11:12   #375
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Re: Oyster Problems?

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How strong without damage is something Polux can think about it if he have the bad luck to run hard aground in a atoll / Pacific/ thousand miles from any civilization....
But that happens only to morons . . .

So Polux has nothing to worry about.
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