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Old 01-01-2016, 19:21   #856
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Re: Oyster Problems?

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Originally Posted by TJ D View Post
it was found that Kevlar on the outside was in fact too brittle and would shatter upon impact.
There has been extensive research on 'crash mitigation' outside the marine world. There are three (relatively obvious) conclusions . . .

(1) The single most effective technique is to design a structure with a progressively deformable layer of material in front of the crash panel. This deform-able layer will absorb and spread a lot of the impact shock load (like a car bumper). In a boat hull you can specifically design the local core to act in this way (rather than its usual high stiffness per strength priority). Or you can put a second deformable coring and the crash panel behind the 'normal' hull structure. . . . . depending on how much weight you are willing to add to have serious crash protection.

(2) Kevlar fibers are less brittle than carbon . . . . but s-glass is less brittle than kevlar. So an S-glass crash panel would be even more effective . . . .but a bit heavier than kevlar

(3) Use seriously high grade epoxy with toughening nano particles is the highest leverage thing you can do without any weight increase. It would add cost but it would be insignificant in just a bow crash section. But Guegon does not make/sell it and I believe to-date they have only ever been used in the marine market in the AC72's and are not well known or understood by most marine designers.

None of this had much to do with the oyster . . . Which I personally believe was primarily a qa bond failure, secondarily combined with inadequate structure for the dynamic loading.
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Old 02-01-2016, 05:04   #857
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Re: Oyster Problems?

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Originally Posted by estarzinger View Post
,,,
None of this had much to do with the oyster . . . Which I personally believe was primarily a qa bond failure, secondarily combined with inadequate structure for the dynamic loading.
What do you mean by qa?
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Old 02-01-2016, 06:21   #858
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Re: Oyster Problems?

I'm a steel boat guy because that's what I built 25 years ago, and that's still what I own and sail. However, I follow the engineering and structural threads very closely, out of general interest in sailing and the industry of sailboat production, both for racing and cruising.

That said, what will be the long-term consequences for older high-tech boats? It's one thing to build a racing boat with fairly exotic internal grids and layup schedules, built to be competitive for a few years. But how about the guy who buys the ten or twenty year old racer or even production cruising boat that was built according to the style or fad of that era, when it's almost impossible to survey what is happening inside the skins, especially in high load areas like the keel joint?

Short of destructive testing (not conducive to further sailing with that boat hull) how does the 3rd or 4th owner know if a boat is still safe to take to sea? Just by the manufacturer's reputation? What about when the manufacturer has tried and changed various layups and core materials etc many times over the decades? And there might even be problems with particular hulls even on the same production series? "Oops, I don't think that bond was quite right. Oh well, the rest of the layup will make up for it."

One thing I know is that the keels don't fall off of the solid layup uncored GRP boats built from the 60s to the 80s, at least, not that I am aware of. (Assuming the keel bolts are accessible for inspection etc, if it's an external lead or iron keel.)

And I strongly believe that in the real world, it must be assumed that every used boat on the market has taken some hard groundings that severely stressed the keel joint, possibly leading to ingress of saltwater into places where it will do damage, to the keel bolts, hull core, etc. How can you tell if an older boat constructed of what used to be considered exotic layups is safe to take out in high winds and big waves?

I think there are a lot of "iffy" cored high-tech plastic boats out there. I've heard some very sick "crunching" sounds from cored boats making minor docking errors. Over time, what is happening inside, if there is core damage or water ingress? Is there an element of Russian Roulette to buying and sailing hard an older boat with an exotic construction from the 90s, 2000s and so on? Complex construction methods that had their day in the sun, and then were rejected or superseded for a variety of reasons?

I like to sleep well even when pounding through waves, and worrying about the hull splitting open or the keel falling off precludes that.
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Old 02-01-2016, 07:17   #859
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Re: Oyster Problems?

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Originally Posted by Travis McGee View Post
I'm a steel boat guy because that's what I built 25 years ago, and that's still what I own and sail. However, I follow the engineering and structural threads very closely, out of general interest in sailing and the industry of sailboat production, both for racing and cruising.

That said, what will be the long-term consequences for older high-tech boats? It's one thing to build a racing boat with fairly exotic internal grids and layup schedules, built to be competitive for a few years. But how about the guy who buys the ten or twenty year old racer or even production cruising boat that was built according to the style or fad of that era, when it's almost impossible to survey what is happening inside the skins, especially in high load areas like the keel joint?

Short of destructive testing (not conducive to further sailing with that boat hull) how does the 3rd or 4th owner know if a boat is still safe to take to sea? Just by the manufacturer's reputation? What about when the manufacturer has tried and changed various layups and core materials etc many times over the decades? And there might even be problems with particular hulls even on the same production series? "Oops, I don't think that bond was quite right. Oh well, the rest of the layup will make up for it."

One thing I know is that the keels don't fall off of the solid layup uncored GRP boats built from the 60s to the 80s, at least, not that I am aware of. (Assuming the keel bolts are accessible for inspection etc, if it's an external lead or iron keel.)

And I strongly believe that in the real world, it must be assumed that every used boat on the market has taken some hard groundings that severely stressed the keel joint, possibly leading to ingress of saltwater into places where it will do damage, to the keel bolts, hull core, etc. How can you tell if an older boat constructed of what used to be considered exotic layups is safe to take out in high winds and big waves?

I think there are a lot of "iffy" cored high-tech plastic boats out there. I've heard some very sick "crunching" sounds from cored boats making minor docking errors. Over time, what is happening inside, if there is core damage or water ingress? Is there an element of Russian Roulette to buying and sailing hard an older boat with an exotic construction from the 90s, 2000s and so on? Complex construction methods that had their day in the sun, and then were rejected or superseded for a variety of reasons?

I like to sleep well even when pounding through waves, and worrying about the hull splitting open or the keel falling off precludes that.
I fail to see what all your considerations has to do with Oyster or even with performance boat building.

Certainly the buyer of a high tech high performance cruising boat can care less about if the boat is going to last 25, 30 or 35 years for the simple reason that in 15 years will be no more a high performance cruising boat and if that is the kind of boat he likes and wants he will have another, probably much sooner than that.

But regarding longevity of high tech racing boats, that seems what you are talking mostly about ant talking about those 25 year old kevlar ones that made the Witbread/VOR circumnavigation races they are still around sailing, as well as much older boats that made that race.

You can track the history of the old racing boats that made that circumnavigation race here. Probably the information will interest you since it is about the longevity of what were once high tech boats.

Whitbread/Volvo boats - where are they now | The Daily Sail
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Old 02-01-2016, 13:15   #860
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Re: Oyster Problems?

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Originally Posted by Polux View Post
What do you mean by qa?
Quality assurance . . . . Meant that I suspect something was not done correctly in the build procedure . . . Probably surface not prepared correctly, but could have been any of several other possible errors.

Combine that with not enough load spreading at the high strain point(s) and the skin flexed itself right off the structural grid
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Old 02-01-2016, 14:08   #861
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Re: Oyster Problems?

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Maybe someday some of these guys will catch on that racing has absolutely nothing to do with cruising. How likely are you to ground a boat during a Sydney-Hobart? Now compare that to how likely you are to ground a boat during a full seasons cruise in any popular cruising ground.

My prejudice against cored hulls is mostly a "gut feel" thing. But being in engineering I have learned to pay attention to the gut.
So you have a thin layer of glass, balsa or foam, and then another thin layer of glass. If the glass does not adhere permanently to the balsa, what you have left is a thin flexible piece of glass for strength. As a theoretical "system" the inner/core/outer is rigid and strong. But if the adhesion breaks down you have almost nothing.
The assumption that the glass matrix will adhere long term to balsa, seems wildly optimistic to me. Back that up with how many I have seen with delamination (glass not adhered to the core) after years it makes no sense to me. Glass layup shrinks and continues to shrink and change shape at a lesser rate over time. So much so that builders have to support it to keep it in shape after layup.
It's just one bad assumption after another to me.
It seems to me if a hull could be built with the glass work tying the inner and outer shell together, maybe a hexagon type of matrix it would be great, but it is very hard and expensive to do in reality... although it's done with high temperature metals in some aircraft parts.
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Old 03-01-2016, 15:15   #862
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Re: Oyster Problems?

Another weird accident to a Humbreys designed boat:Dismasted by an Atlantic Rogue Wave | Sailing With Zest

Almost as bad as keel falling off?
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Old 03-01-2016, 15:56   #863
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Re: Oyster Problems?

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Originally Posted by estarzinger View Post
(3) Use seriously high grade epoxy with toughening nano particles is the highest leverage thing you can do without any weight increase. It would add cost but it would be insignificant in just a bow crash section. But Guegon does not make/sell it and I believe to-date they have only ever been used in the marine market in the AC72's and are not well known or understood by most marine designers.

Why does the AC72 need abrasion resistance? Is it because they are built so on edge that a minor incidental scrape could damage them?

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Old 03-01-2016, 16:13   #864
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Re: Oyster Problems?

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Originally Posted by Cheechako View Post

It seems to me if a hull could be built with the glass work tying the inner and outer shell together, maybe a hexagon type of matrix it would be great, but it is very hard and expensive to do in reality... although it's done with high temperature metals in some aircraft parts.
Honeycomb comes in many flavors and not just high temp. Perhaps Minaret could explain why they don't use honeycomb? I don't see why it would be any different to use than any vac bag job. Cost is an object?
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Old 03-01-2016, 16:23   #865
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Re: Oyster Problems?

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Honeycomb comes in many flavors and not just high temp. Perhaps Minaret could explain why they don't use honeycomb? I don't see why it would be any different to use than any vac bag job. Cost is an object?
Carbocraft racing shells (rowing boats) were made with core of aluminium honey comb with some kind of carbon fibre/glass fibre inner and outer layers. They were top class shells in their time (1980s).
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Old 03-01-2016, 16:28   #866
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Re: Oyster Problems?

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Another weird accident to a Humbreys designed boat:Dismasted by an Atlantic Rogue Wave | Sailing With Zest

Almost as bad as keel falling off?
Ha ha ha !!!

Another wooden boat with wooden chainplates???

Yep. I have seen this take before: like some designers believe the forces from the rig do not need to be transferred all the way to the hull/grid/frame.

Actually the problem is maybe not so much the mistake the designer or builder made but the fact that it took a while to come up: if it failed early on, the design would have been corrected. Same old thing always: build it well, see where it breaks, then build it better. Boat building the old(-er) way!

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Old 03-01-2016, 19:20   #867
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Re: Oyster Problems?

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Originally Posted by colemj View Post
Why does the AC72 need abrasion resistance? Is it because they are built so on edge that a minor incidental scrape could damage them?
It was not intended for abrasion resistance in the ac72 application. The toughened Nano resin can be tuned to improve many properties. . . . Technical reading if you are interested http://www.dtic.mil/dtic/tr/fulltext/u2/a478357.pdf

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Honeycomb comes in many flavors and not just high temp. Perhaps Minaret could explain why they don't use honeycomb? I don't see why it would be any different to use than any vac bag job. Cost is an object?
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Carbocraft racing shells (rowing boats) were made with core of aluminium honey comb with some kind of carbon fibre/glass fibre inner and outer layers. They were top class shells in their time (1980s).
Honeycomb core has been used on many boats. Nomex (Kevlar) honeycomb core has been widely used in high performance applications. Polypropylene honeycomb core is less expensive and widely used - we had some on hawk, it is good for sound insulation in addition to good stiffness/weight, so we used in our engine room panels. Oracle used aluminum honeycomb on their ac72 - high stiffness/weight but that has corrosion issues with carbon skins so is not generally used on boats expected to last very long.

Making sure you have a reliable skin bond to the honeycomb, without also filling the honeycomb with resin, requires some knowledge/skill/experience, but is a "solved problem".
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Old 03-01-2016, 20:49   #868
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Re: Oyster Problems?

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I




Making sure you have a reliable skin bond to the honeycomb, without also filling the honeycomb with resin, requires some knowledge/skill/experience, but is a "solved problem".
Well I'll say. Honeycomb cored flight surfaces have been the de rigueur for many years. "Some knowledge" is true but we ain't just patching a panga here, some simple skills are required but bonding honeycomb is pretty standard stuff.
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Old 04-01-2016, 05:12   #869
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Re: Oyster Problems?

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Another weird accident to a Humbreys designed boat:Dismasted by an Atlantic Rogue Wave | Sailing With Zest

Almost as bad as keel falling off?
Interesting story and interesting 23 old design, quite light for an 11m boat (5020kg) specially considering that almost half of it is ballast.

The wave impact was so big that the shroud pull on chainplate broke the deck and the main bulkhead:

"Our tête-à-tête was interrupted by the loud roar of a mammoth breaking wave on the port side, further forward than any previous waves. I remember us staring at each other with “WTF?!” looks and then both turning toward the sound. There followed an even louder bang, accompanied by the sickening sound of tearing wood as we were hit by the wave. The lights went out and the boat felt as it if had been thrown sideways to starboard. "

Amazingly the boat was not capsized, or maybe not, with that huge B/D ratio instead of a rolling movement the big wave just induced a sideways big slide certainly with the boat almost lying flat on the water.

Regarding the accident, the skipper on the lesson's learned, does not blame the boat obviously thinking that all small boats can encounter situations that are over the breaking point of the boat and that rough "mammoth" wave was one of them.




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Old 04-01-2016, 05:19   #870
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Re: Oyster Problems?

Structural failures often are about the joints, connections or nodes between structural elements. Even a cored assembly to act as a composite must have proper bonding between the skins and the core.

Transferring forces from one member to the next must involve a "node" and these are often where failures occur in failures of complex systems.

I wonder how much research is done related to joining what seems to be very strong elements... is the "tabbing" able to perform under stresses that the hull or the bulkheads, stringers etc can? I hope so. :-)
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