Oyster Problems?

[Muckle Flugga]

Meanwhile back on topic for old vs. new Oyster. I attach a couple of photos from an example from the early 90s. One is of a core from a nondescript area of hull well forward and to starboard of the keel, the other I have annotated with a crude arrow indicating its position in the actual hull interior view. Note the massive and densely placed stick built, part of the hull, structural grid around this simply ordinary part of the hull. Also note that the section is solid, came out completely dry after more than a couple of decades afloat, and is 27mm thick. Compare that to the absurd 15mm in the keel stub structural areas of a much larger "new design" Oyster.

Apologies for the mirroring, but these were shot in "photobooth" and then flipped horizontally.

[Dockhead]

Originally Posted by minaret

So was she repaired or not? I count at least 5 holes in the hull on the port side, some quite large.

Yes, but I have to say -- the keel looks firmly attached, and the rudder broke off in a way which appears to have left the shaft intact in the hull. The hull itself seems to have held up pretty well.

Probably still totaled if it was full of water, but I would say that structure has performed very well indeed.

[driftwoodcove]

This topic is interesting from a design perspective, in that the thing that seems to be the problem is rarely the problem.

In a design that utilizes beams for strength, the thickness of the skin doesn't provide much stiffness. This is true for all sorts of thing(the best example is a house). The skin provides sheet strength, keeping the beams straight and aligned.

The important design characteristic shown in those pictures is the design and placement of the keel support beams, and the strength of the attachment of the keel to those beams. It is clear that the axial beams sheared off at the cross-beam attachments. The skin just went along for the ride.

Because the cross beams were so far from the keel, the axial beams likely flexed(the keel has a huge cross-force), causing fatigue. The cross beam placement looks troublesome to me. I wonder if the inner bulkhead supporting the rigidity of the hull around the mast was compromised in the stretch design at the "encouragement" of the owner.

The only skin thickness that really matters is between the 2 keel beams. In all other areas, it just has to resist impact, and oilcanning between the beams.

I have a friend that designs high end industrial equipment. I have asked him several times why he uses so much extra structure in his equipment(it makes it heavy). He said it is advertising, and freely admits it is not necessary. If it looks strong, people think it is strong.

Heavier is only stronger if it is heavier in a place that would break otherwise. Often heavier is weaker, if it puts more stress and less flexibility in places you didn't think about. I was much stronger when I weighed 250 lbs(I am 280 now).

Chris

[Muckle Flugga]

Originally Posted by driftwoodcove

This topic is interesting from a design perspective, in that the thing that seems to be the problem is rarely the problem.

In a design that utilizes beams for strength, the thickness of the skin doesn't provide much stiffness. This is true for all sorts of thing(the best example is a house). The skin provides sheet strength, keeping the beams straight and aligned.

The important design characteristic shown in those pictures is the design and placement of the keel support beams, and the strength of the attachment of the keel to those beams. It is clear that the axial beams sheared off at the cross-beam attachments. The skin just went along for the ride.

Because the cross beams were so far from the keel, the axial beams likely flexed(the keel has a huge cross-force), causing fatigue. The cross beam placement looks troublesome to me. I wonder if the inner bulkhead supporting the rigidity of the hull around the mast was compromised in the stretch design at the "encouragement" of the owner.

The only skin thickness that really matters is between the 2 keel beams. In all other areas, it just has to resist impact, and oilcanning between the beams.

I have a friend that designs high end industrial equipment. I have asked him several times why he uses so much extra structure in his equipment(it makes it heavy). He said it is advertising, and freely admits it is not necessary. If it looks strong, people think it is strong.

Heavier is only stronger if it is heavier in a place that would break otherwise. Often heavier is weaker, if it puts more stress and less flexibility in places you didn't think about. I was much stronger when I weighed 250 lbs(I am 280 now).

Chris

Well… ok, but skin thickness also determines resilience to holing due to impacts in the water, either with the earth or with floating objects.

Further, surely if the skin thickness in question is the main structural component of the keel stub itself… it matters rather a lot!

[Muckle Flugga]

Originally Posted by neilpride

I doubt very much the solid object theory, why? well I guess the only massive object floating in the oceans are Shipping Containers, if they fall from the top of a wave in one of this containers is Game Over ASAP, then they continue sailing, with the stereo fixed,,, other stuff you can see sometimes floating around is wood logs , driftwoods, but I cant believe they are able to dislodge a keel, long time agoo I bump in a massive piece of wood with my boat with the result of a depth sounder log broken and few scratches in the hull... the 40,7 underbody shape don't like to much to pound to windward or fall of from waves , the Bang is fenomenal and the whole boat suffer ,,,,

There are very many other massive objects floating in the worlds oceans than shipping containers, especially after events such as the tsunamis. Even large plastic containers hold enough water and have enough area to present enormous inertia, but plenty of bits of metal as well as massive tree trunks, buoys adrift, really you name it, out there.

[Muckle Flugga]

Originally Posted by Polux

…
The disagreement here regards having boats that can sustain a hard collision and can be sailed to safety but have to be repaired versus boats that can sustain hard collisions without any need of repair (if that can be possible).

… Regarding hitting a container normally the first part to be hit is the forward section of the hull and regarding that if one really wants to be safe and consider that eventuality frequent, the best is to change for a steel hull or at least an aluminum one.

Finally has these pictures of Sydney 38 that ended up thrown big waves to the rocks show:

...

On this movie you see a very light small French cruiser racer, with the same type of keel, hitting at high speed a big whale in the middle of the Ocean. No problem for the boat or keel that did not need any repair...only for the sailor that hurt is back.

A funny thing, the boat name was "Baleine Blanche" that means white whale

Your words regarding "changing to steel and/or aluminium" show you are at least cognisant of the risks and the fact that thin fiberglass is particularly vulnerable. It also follows, rather obviously, that massively built fiberglass is far better than a 5mm or 6mm twin skin with core, as is the build on many of the production boats you are constantly defending. This is simply obviously true. It is equally obviously true that you can get away with sailing a circumnavigation in a ballasted and buoyed plastic bathtub if you so choose, but is it prudent? Are you more or less likely to survive a serious collision or grounding? I think you equivocate constantly to bolster what appears to be an agenda. You suggested in some thread recently, I think, that you work in the industry… is this the case? Do you work for a yacht builder?

As to your suggestion that you will definitely hit the likes of a container with the bows rather than keel this is complete nonsense. Such structures will float corner up, if at all, meaning you can hit it at above the surface, all the way down to the keel tip, first. It is entirely chance. Really that suggestion was a bit of pure fantasy for the convenience of your entrenched argument.

Your penchant for anecdotes as argument is showing in the video of the whale strike. Fun video, but one has to say: so what? It is like showing a single dashcam video of a non fatal car accident with a bus and extrapolating to say all car accidents with buses will be non fatal. Or were you really trying to suggest that a blue whale is incapable of damaging a plastic boat?

[poiu]

Credit to Polux. If only keels were made of what he is made from. He keeps getting knocked, only to bounce back each time like a toughened superball.

[neilpride]

Originally Posted by driftwoodcove

This topic is interesting from a design perspective, in that the thing that seems to be the problem is rarely the problem.

In a design that utilizes beams for strength, the thickness of the skin doesn't provide much stiffness. This is true for all sorts of thing(the best example is a house). The skin provides sheet strength, keeping the beams straight and aligned.

The important design characteristic shown in those pictures is the design and placement of the keel support beams, and the strength of the attachment of the keel to those beams. It is clear that the axial beams sheared off at the cross-beam attachments. The skin just went along for the ride.

Because the cross beams were so far from the keel, the axial beams likely flexed(the keel has a huge cross-force), causing fatigue. The cross beam placement looks troublesome to me. I wonder if the inner bulkhead supporting the rigidity of the hull around the mast was compromised in the stretch design at the "encouragement" of the owner.

The only skin thickness that really matters is between the 2 keel beams. In all other areas, it just has to resist impact, and oilcanning between the beams.

I have a friend that designs high end industrial equipment. I have asked him several times why he uses so much extra structure in his equipment(it makes it heavy). He said it is advertising, and freely admits it is not necessary. If it looks strong, people think it is strong.

Heavier is only stronger if it is heavier in a place that would break otherwise. Often heavier is weaker, if it puts more stress and less flexibility in places you didn't think about. I was much stronger when I weighed 250 lbs(I am 280 now).

Chris

Quite true, a spider web of beams and partitions make a thin hull strong,, question could be where is the red line? 10 mm , 12, 5, 17 ? in a 90 ft yacht,,,I dont want to sound repetitive but in keel stubs the only way to make it strong is layers of glass , lots,,, based on calculations or in previous models.. and still those 15 mm in hull bottom sounds inadequate no matter how well the beams and the stringers are in place.... but is just my opinion...

[neilpride]

Originally Posted by Dockhead

Yes, but I have to say -- the keel looks firmly attached, and the rudder broke off in a way which appears to have left the shaft intact in the hull. The hull itself seems to have held up pretty well.

Probably still totaled if it was full of water, but I would say that structure has performed very well indeed.

Without more details hard to make a clear opinion, but my 2 cents, hull cracked and holed, bulkheads toasted, mast step gone, keel structure toasted, furniture if there is any , shifted and out of place, what we see on those pictures its a hull airlifted dropped in the ground, cant say the structure perfomed really well without see the interior,,,,, we have 2 boats with really expensive repairs in the yard after Hurricane Gonzalo, they fall off from the stands, one holed and with 2 main bulkheads split cracked , the deck also bend ,,, the other , 2 jack stands penetrated the hull skin making a horrible damage inside,,,, they are here waiting for their owners.... I guess a big wave cacht the Sydney 38 and airlifted to the rocks, placing the boat there in one Bang!! maybe not much waves pounding the boat hour after hour.....

[Muckle Flugga]

Originally Posted by poiu

Credit to Polux. If only keels were made of what he is made from. He keeps getting knocked, only to bounce back each time like a toughened superball.

Yes, I do give him credit. I think him intelligent, very knowledgeable, and a skilled polemecist. We all have biases. His are particularly clear. I just wish he wouldn't blandly argue for pretty much all modern production yachts as if they were all equal, and equally suited to any task set for them, no matter what. What many who argue with him are saying is basically this: for long range unrestricted ocean service with great confidence it is better to have a boat designed specifically for that purpose, just as it is better to go end to end of the Sahara in a Land Cruiser rather than a quattro family sedan with a spoiler. No matter how many times it is said, no matter what parts of the whole he concedes (and he has conceded pretty much all of it, piecemeal), he will defend the mass production road vehicle as being "just as good" as the rugged, desert designed 4x4, by pointing to a Renault Clio that has driven from Accra to Khartoum. Challenged about any feature of that, he will usually then equivocate by pointing to some souped up rally version which has successfully won the East African rally… or the fact that three banger production road vehicles were taken across the Kalahari on Top Gear, if you get the analogy. That these things happen or are possible makes it no less true that the more appropriate vehicle for the journey is, and always will be, the likes of a Land Cruiser, as it happens, particularly an older model, entirely serviceable by the driver with an ordinary tool set.

[Muckle Flugga]

Originally Posted by driftwoodcove

This topic is interesting from a design perspective, in that the thing that seems to be the problem is rarely the problem.
...

Chris

I hadn't noticed that it was only your second post, just wanted to say thanks for the interesting perspective and welcome aboard!

[Polux]

Originally Posted by minaret

Don't know how we got onto hard groundings, as this started with CR which suffered only soft groundings before total keel failure.

You don't know that and in fact not only that is not stated on the MAIB report as the way they put it seems to suggest they think otherwise:

They say on the MAIB report:

"Cheeki Rafiki suffered what was described as a ‘light grounding’ "

But then they describe the structural works needed and those are not consistent with a light grounding:

"Cut flanges off six bays, grind back hull, laminate and sides of structural floors. Bond structural floor to hull with GRP, lightly rub down and apply wax gel. Drill off limber holes, refit pipes and floors. "

One of the other several light groundings described as "dropped on to the ground’ when in the trough of a wave."

In what regards what the owner of the boat described light groundings you seem to miss three points:

1- The charter company that owned the boat was the surely very interested into describing previous groundings as light otherwise the blame of the accident would fall over her due to improper maintenance of the boat.

2- On a charter boat you will never know what charters do to the boat and even if the boat is hard grounding they would never say that because it would be a sure way to lose the caution. I remember some years ago a charter boat that was hard grounding so hard that it lost the keel. The boat had not water ingress and was delivered to the charter company without the keel and without reporting any grounding.

3- The extension of the only report of a repair made to the structure of the boat after the first grounding is not consistent with a light grounding.

Regarding all that the MAIB report says:

"Anecdotal evidence collected throughout the investigation suggests that the frequency of grounding, particularly when racing, may be higher than reported. A decision on whether or not a grounding triggers a subsequent inspection for damage, and possible repair, is often based on the skipper’s assessment of whether or not it was a ‘light’ or ‘heavy’ grounding. This methodology is highly subjective and, throughout the investigation, considerable variation of opinion existed as to what constituted a ‘light’ or ‘heavy’ grounding..."

Originally Posted by minaret

And as stated many many times, the whole issue is that the type of keel and hull construction you so love cannot be "surveyed and properly repaired" without astronomical expense, vastly more so than traditional forms of construction. It says it right there in the MAIB report. ..

I would expect that someone that works on the boat repair business would be more accurate in what regards the statements he makes. In fact no such thing is said on the MAID report and quite contrary it is stated that several First 40.7 have been repaired in a structural way after suffering groundings. If the cost was so astronomical as you refer the boats would be toasted. What the report says is:

"MAIB inspectors visited five GRP repairers who had undertaken repairs to Beneteau First 40.7 yachts following matrix detachment.

Of these five repairers: 1. Three were of the view that the matrix flanges should be removed and surfaces prepared in way of the detachment before the matrix was then re-glassed to the hull with a combination of appropriate matting. 2. One was of the opinion that any remaining bonding paste between the matrix flange and hull should be ground out, with the flange left intact, and fresh bonding paste re-applied before the matrix was then glassed to the hull with a combination of appropriate matting. 3. One considered that either of the two methods was valid.

Beneteau had provided advice on its recommended repair method in documentation issued to its after sales and dealer network. This advice recommended that a flange of at least 5cm be retained and that the bonding paste should be ground out and replaced before the matrix was then glassed to the hull, in order to retain the ‘I’ beam effect and matrix stiffness. All of the repairers agreed that the keel should be removed when necessary to effect keel repairs, a point confirmed within Beneteau’s advice.

All of the repairers agreed that it was very difficult to identify areas and the extent of matrix detachment, particularly in the vicinity of the keel owing to the clamping effect of the keel bolts and washer plates. However, the single most agreed method for detecting matrix detachment was the use of a hammer to tap on the matrix and to listen for changes of tone. Two of the repairers suggested a further method of landing yachts ‘lightly’ on their keels, and watching for deflection of the hull."

This is not consistent with what you claim "cannot be "surveyed and properly repaired" without astronomical expense, It says it right there in the MAIB report. .."

If that was the case several 40.7 that were grounded would not have been repaired. The only think that the MAIB report says is that "very difficult to identify areas and the extent of matrix detachment, particularly in the vicinity of the keel owing to the clamping effect of the keel bolts and washer plates.". You state it like if it was impossible without an "astronomical expense".

What that means to me is that for a proper identification of damage on the bonding of the matrix the keel should be taken off. That was not the case on the repair that was made on the boat.

Regarding the causes of the accident they say:

"a combined effect of previous groundings and subsequent repairs to its keel and matrix had possibly weakened the vessel’s structure where the keel was attached to the hull. It is also possible that one or more keel bolts had deteriorated. A consequent loss of strength may have allowed movement of the keel, which would have been exacerbated by increased transverse loading through sailing in worsening sea conditions. "
....
"The repair invoice following Cheeki Rafiki’s grounding in August 2007 indicates that the resulting damage was in way of six bays. Photographs taken of the keel bilge area prior to the vessel’s departure on the ARC trans-Atlantic Ocean race 2013 show areas of renewed gel coating, indicating the result of a previous repair. At least two of these areas are in bays immediately either side of bays where the keel was bolted to the hull (Figures 16 and 17). Given that detachment had probably occurred in the two repaired bays, it is possible that detachment had also occurred in way of the keel but had not been detected because of the clamping effect of the keel bolts, the keel not having been removed."...

The repair invoice also indicates that the repair was not carried out in accordance with Beneteau’s recommended method contained in the advice to its after sales and dealer network.

https://assets.digital.cabinet-offic...ort_8_2015.pdf

[neilpride]

So whats your plan if you ran aground a 40,7 in a remote place, and the matrix is compromised?

[neilpride]

Beneteau had provided advice on its recommended repair method in documentation issued to its after sales and dealer network. This advice recommended that a flange of at least 5cm be retained and that the bonding paste should be ground out and replaced before the matrix was then glassed to the hull, in order to retain the ‘I’ beam effect and matrix stiffness. All of the repairers agreed that the keel should be removed when necessary to effect keel repairs, a point confirmed within Beneteau’s advice


As far I know I never see this document or advice from Beneteau, can you provide a link?

[Polux]

Originally Posted by driftwoodcove

....
The important design characteristic shown in those pictures is the design and placement of the keel support beams, and the strength of the attachment of the keel to those beams. It is clear that the axial beams sheared off at the cross-beam attachments. The skin just went along for the ride.

Because the cross beams were so far from the keel, the axial beams likely flexed(the keel has a huge cross-force), causing fatigue. ...
I have a friend that designs high end industrial equipment. I have asked him several times why he uses so much extra structure in his equipment(it makes it heavy). He said it is advertising, and freely admits it is not necessary. If it looks strong, people think it is strong.

Heavier is only stronger if it is heavier in a place that would break otherwise. Often heavier is weaker, if it puts more stress and less flexibility in places you didn't think about. I was much stronger when I weighed 250 lbs(I am 280 now).

Chris

Yes, I agree with all that. But in this case, because the stub was part of the hull the skin thickness on that area would also bee important. In the end all the efforts of the keel are transmitted to the hull and the hull has to be solid enough to take them without coming apart or flex excessively.

That has not to do only with the thickness of the hull, but with being it cored or not (a cored hull will flex less and will be more resistant to the forces transmitted from the interior) and with good engineering regarding the correct spread of charges by the hull.

On this case, that I think you identified correctly to being due to the structural axial beams that shared, that was due probably to excessive flex that caused precocious material fatigue. That Flex probably was due not only to an optimistic dimension of those structural parts but also to the hull thickness around the stub and the part of the hull above that allowed for excessive lateral flexing.