Implications of Bonded Structural Grids in Production Boats

[coopec43]

Originally Posted by Pete7

Plus both yachts, this one and the Evans Beneteau, survived hard groundings and live to sail again, all be it with some serious work, but sail again. What's not to like. The hand built HR is nice, but as he says twice the price.

Pete

Sadly another 100+ fin keeled boats didn't survive.
Keels A B C D E F G H I J K L M N O P Q R S T 1 Keel Failure ...

http://www.cedomare.com › uploads › 2018/09

XLS

6, 1, FINISTERE, 2018, 23-Feb, Bunbury and Return Ocean Race, Keel Broke off ... 15, 10, POLINA STAR, 2015, 4-Jul, Cruising, Keel Broke Off, Sank, No ... /keel-detatchment-and-capsize-of-sailing-yacht-cheeki-rafiki-with-loss-of-4-lives



Then there's missing and overdue yachts.

https://boatwatch.org/boat-watch-net...erdue-vessels/

[Jim Cate]

Originally Posted by coopec43

Sadly another 100+ fin keeled boats didn't survive.
Keels A B C D E F G H I J K L M N O P Q R S T 1 Keel Failure ...

http://www.cedomare.com › uploads › 2018/09

XLS

6, 1, FINISTERE, 2018, 23-Feb, Bunbury and Return Ocean Race, Keel Broke off ... 15, 10, POLINA STAR, 2015, 4-Jul, Cruising, Keel Broke Off, Sank, No ... /keel-detatchment-and-capsize-of-sailing-yacht-cheeki-rafiki-with-loss-of-4-lives



Then there's missing and overdue yachts.

https://boatwatch.org/boat-watch-net...erdue-vessels/

I'd like to point out that careful perusal of that list shows that nearly all of the lost keels were on out and out race boats... Vendee globe and mini-transat sorts of boats. The Polina Star was quickly determined to be a design and execution flaw in a newly stretched build... very few examples of failures of cruising boats shown.

So, IMO repeatedly using this compilation to discredit fin keeled cruising boats is not very convincing. There are a hell of a lot of them out there that have intact keels.

However, I will say that I'd not ever want to own a boat where a haulout and survey are needed after each grounding. I've thumped the bottom enough times whilst cruising in distant waters that such a requirement is sufficient to disqualify a design for me.

Jim

[coopec43]

Originally Posted by Jim Cate

I'd like to point out that careful perusal of that list shows that nearly all of the lost keels were on out and out race boats... Vendee globe and mini-transat sorts of boats. The Polina Star was quickly determined to be a design and execution flaw in a newly stretched build... very few examples of failures of cruising boats shown.

So, IMO repeatedly using this compilation to discredit fin keeled cruising boats is not very convincing. There are a hell of a lot of them out there that have intact keels.

However, I will say that I'd not ever want to own a boat where a haulout and survey are needed after each grounding. I've thumped the bottom enough times whilst cruising in distant waters that such a requirement is sufficient to disqualify a design for me.

Jim

Why do keel failures happen and what can we do to prevent it?

https://www.yachtingworld.com/news/k...ng-facts-60006

https://www.youtube.com/watch?v=qmRIrh2hK5U

[coopec43]

Despite all caution, ground contact cannot be completely ruled out. Anyone who drives onto a sandbank normally has little to fear except for a little scratched anti-fouling paint. Nevertheless, Holger Flindt recommends looking under the boards upon any grounding: "If water penetrates, the position of the keel bolts has changed or hairline cracks appear, this points to structural damage. If nothing can be seen from the outside, crew can find any cracks in the keel seam or major damage to the keel bulb by diving down. After hitting the ground, the insurer should be informed immediately, and they will accompany you through all necessary steps. Also it is important to know: With a good insurer, the inspection costs after an instance of grounding are usually covered.”


https://www.pantaenius.com/de-en/ins...-of-incidents/

I can't help thinking it's a bit like taking the family sedan off road if you plan serious cruising.


But as others have pointed out there is probably not much risk for most yachts when sailing in well charted waters and where hazards are known.

[Dockhead]

Originally Posted by coopec43

Despite all caution, ground contact cannot be completely ruled out. Anyone who drives onto a sandbank normally has little to fear except for a little scratched anti-fouling paint. Nevertheless, Holger Flindt recommends looking under the boards upon any grounding: "If water penetrates, the position of the keel bolts has changed or hairline cracks appear, this points to structural damage. If nothing can be seen from the outside, crew can find any cracks in the keel seam or major damage to the keel bulb by diving down. After hitting the ground, the insurer should be informed immediately, and they will accompany you through all necessary steps. Also it is important to know: With a good insurer, the inspection costs after an instance of grounding are usually covered.”

https://www.pantaenius.com/de-en/ins...-of-incidents/

I can't help thinking it's a bit like taking the family sedan off road if you plan serious cruising.

But as others have pointed out there is probably not much risk for most yachts when sailing in well charted waters and where hazards are known.

I had a long keel encapsulated ballast boat. I was more nervous about groundings in that, than in my present bulb keel boat.

When fiberglass meets rock at speed, a lot of bad things can happen. With solid lead it's a different ballgame.

I don't think any fiberglass long keel boat is stronger than the best fin keel boats.

If you want to reach a different category of strength from that, then you need a steel hull.

[coopec43]

Originally Posted by Dockhead

I had a long keel encapsulated ballast boat. I was more nervous about groundings in that, than in my present bulb keel boat.

When fiberglass meets rock at speed, a lot of bad things can happen. With solid lead it's a different ballgame.

I don't think any fiberglass long keel boat is stronger than the best fin keel boats.

If you want to reach a different category of strength from that, then you need a steel hull.

I think you are being unrealistic

Of course a solid lump of lead will take a lot of punishment but what about hull/keel join? Will the hull be able to handle 20 tonne of yacht coming to an abrupt halt?

My home-built f/g keel would be 1½ inches thick, The flat slabs of lead have been carefully laid in each section of the keel then polyester resin has been poured over that to fill any voids. But that is how all production encapsulated ballast boats are built?

"An encapsulated keel has a fiberglass cavity laid up with the original molding. The builder then fills the cavity with a ballast mix including a dense metal such as iron or lead and a glue such as concrete or resin. For example, Gulfstar used a concrete and lead slurry".15 Dec 2009

(Many insurance policies require the fin keel yacht owner to notify the Insurer of any grounding)

"Even a deviation of 20 metres there can have consequences." And depending on the type of yacht concerned, this can lead to serious damage. In the worst case, not only the keel bulb, but the entire structure of the yacht is affected. "In our experience, mid-length keels with an older design are often better protected against grounding" (Insurance expert Holger Flindt)

https://www.pantaenius.com/de-en/insights/journal/prevention/prevention-pantaenius/news/grounding-why-theres-an-increasing-number-of-incidents/

[Dockhead]

Originally Posted by coopec43

I think you are being unrealistic

Of course a solid lump of lead will take a lot of punishment but what about hull/keel join? Will the hull be able to handle 20 tonne of yacht coming to an abrupt halt?

My home-built f/g keel would be 1½ inches thick, The flat slabs of lead have been carefully laid in each section of the keel then polyester resin has been poured over that to fill any voids. But that is how all production encapsulated ballast boats are built?

"An encapsulated keel has a fiberglass cavity laid up with the original molding. The builder then fills the cavity with a ballast mix including a dense metal such as iron or lead and a glue such as concrete or resin. For example, Gulfstar used a concrete and lead slurry".15 Dec 2009

(Many insurance policies require the fin keel yacht owner to notify the Insurer of any grounding)

"Even a deviation of 20 metres there can have consequences." And depending on the type of yacht concerned, this can lead to serious damage. In the worst case, not only the keel bulb, but the entire structure of the yacht is affected. "In our experience, mid-length keels with an older design are often better protected against grounding" (Insurance expert Holger Flindt)

https://www.pantaenius.com/de-en/insights/journal/prevention/prevention-pantaenius/news/grounding-why-theres-an-increasing-number-of-incidents/

Yes, my keel is "mid-length". Lower-aspect lead bulb keel, with the bulb flattened so that the boat can be dried out on it. This is typical of Northern-European built high end (non-mass produced) boats, actually universal. Not the best nor the worst sailing performance, but probably the strongest structure possible short of a metal boat. Here for example an HR 53:



I've seen a few encapsulated keels split from hard groundings. Fiberglass is much softer than metal.

With a fin keel, the question is the engineering of the joint, and the structural system. The strength of that varies greatly among different boats, and some of them -- like that Hanse in the video -- are quite vulnerable to structural damage. Others are built like brick houses. I would take a better built fin keel into a hard grounding any day, over an encapsulated keel in a fiberglass boat. YMMV.

You are less likely to rip the keel off of an enscapsulated keel boat but much more likely to have a hull breach, as the soft part of the hull goes all the way down to max draft. The way the FRG encapsulation is filled may or may not stop flooding through the breach, but won't stop the breach itself.


What concerns sailing performance -- some people don't care, and that's fine. But for those who do care, the construction of encapsulated keels, which has a lot of concrete or resin or even worse, voids, below the waterline, besides metal, exacerbates the bad shape of long keels (airfoils and hydrofoils give much higher performance, with higher aspect ratios) by making them also much less dense, which increases wetted surface and drag. This is why they are not my cup of tea, but of course, YMMV.

[LittleWing77]

Originally Posted by danstanford

...I am one of the folks who made a conscious decision to have a fin keel for performance reasons despite the fact that other keel designs would clearly have a better result hitting a rock 4' deep. Not defending my choice but rather saying I knew the implications.

Yeah, Dan, but com'on!

You've chosen a J-boat. For Racing. On Lake Ontario.

You're certainly not going to be crossing oceans or even coastal cruising...

LittleWing77

[jtsailjt]

Originally Posted by Dockhead

I had a long keel encapsulated ballast boat. I was more nervous about groundings in that, than in my present bulb keel boat.

When fiberglass meets rock at speed, a lot of bad things can happen. With solid lead it's a different ballgame.

I don't think any fiberglass long keel boat is stronger than the best fin keel boats.

If you want to reach a different category of strength from that, then you need a steel hull.

“Stronger” doesn’t tell the whole tale and it would be interesting to know what sort of boat you consider to be the best fin keel boats.

If you’re talking about even the best high aspect fin, there’s no getting away from the tremendous concentrated forces that the combination of a long moment arm and a small cross section yields. I’m sure you’ve seen these boats with the aft part of the keel rotated right up into the hull and cracking it like an eggshell. Some end up on the bottom shortly afterward but some make it to a nearby boatyard and are repaired at great expense. Ive seen these hauled out and some were very expensive, high performance yachts that many would consider to be “the best.”

More moderate fins with lead ballast bolted on are probably the best for withstanding hard groundings with minimal damage just as long as the keel bolts are inspected to ensure they haven’t developed microscopic cracks that could lead to failure, but very few are inspected because keel bolt failures are infrequent and it’s an expensive process. These keels have some of the groundings energy used to transform the shape of the lead and the remainder is spread over a much larger area than with a more aggressive fin. The damage from even a hard grounding can usually be repaired with some filler and paint.

Encapsulated ballast boats with fins usually have a shape similar to a moderate bolted on lead keel but with the ballast completely encapsulated there is zero chance of bolt failures allowing it to break loose and the boat sinking as a result. However, the damage from a hard grounding can be much more expensive to repair, especially if sea water penetrates into any voids around the ballast, and doubly so if the ballast used is a ferrous metal.

So, for as an owner/skipper responsible for paying the boats yard bills, for a hard grounding I think I’d rather be in a boat with a moderate fin with bolted on ballast, but if I wasn’t going to have to pay for repairs I think I’d choose encapsulated ballast as the safest. Even the best boats with aggressive fins are much more vulnerable to catastrophic damage from a hard grounding than are the other 2 types.

Then there’s another option I can think of and that’s a design where the boat has no keel and instead has ballast encapsulated in the bottom of the hull with a large bronze centerboard that is both ballast and fin but would flip up in a hard grounding, minimizing damage. Ive only seen one of these, a Ted Hood design that was a 49 footer and the owner said it sailed very well.

[coopec43]

Originally Posted by jtsailjt

sinking as a result. However, the damage from a hard grounding can be much more expensive to repair, especially if sea water penetrates into any voids around the ballast, and doubly so if the ballast used is a ferrous metal.

So, for as an owner/skipper responsible for paying the boats yard bills, for a hard grounding I think I’d rather be in a boat with a moderate fin with bolted on ballast, but if I wasn’t going to have to pay for repairs I think I’d choose encapsulated ballast as the safest. Even the best boats with aggressive fins are much more vulnerable to catastrophic damage from a hard grounding than are the other 2 types.

Then there’s another option I can think of and that’s a design where the boat has no keel and instead has ballast encapsulated in the bottom of the hull with a large bronze centerboard that is both ballast and fin but would flip up in a hard grounding, minimizing damage. Ive only seen one of these, a Ted Hood design that was a 49 footer and the owner said it sailed very well.

Maybe the Kraken yacht?

"It is named the ZERO keel system “because it has zero bolts and zero risk of falling off the hull. The encapsulated lead bulb also provides a low centre of gravity and a sleek hydrodynamic shape to enhance performance.”
​
https://www.krakenyachts.com/zerokeel



https://www.krakenyachts.com/krakendesign

[Dockhead]

Originally Posted by coopec43

Maybe the Kraken yacht?

"It is named the ZERO keel system “because it has zero bolts and zero risk of falling off the hull. The encapsulated lead bulb also provides a low centre of gravity and a sleek hydrodynamic shape to enhance performance.”
​
https://www.krakenyachts.com/zerokeel

https://www.krakenyachts.com/krakendesign

Few naval architects would agree with that they write on the Kraken website about skeg rudders:

"So why have almost all large modern production cruisers abandoned their skegs?

"And why – even more surprisingly – is this habit spreading to serious blue water cruisers? Why are so many unsupported spade rudders now hanging under blue water cruising sterns?
​
"The answer – predictably - lies in the cost."

https://www.krakenyachts.com/skeghungrudders

This is nonsense. Modern boats have spade rudders because they perform much better. These guys seem to build yachts (in very small numbers) for people with weird structural prejudices.

Skeg rudders are far worse hydrodynamically, than spade ones, and they are not necessarily stronger. My boat has a partial skeg, and it is one design element which I don't like. The best rudder for a boat which is intended for sailing is a really strong spade rudder, like what Steve Dashew designed for his boats, and like what most high end builders are now using. A spade rudder can be made just as strong as you want it to be, and it is far better for sailing performance. The rudder is a foil just like the keel, and its hydrodynamic performance is crucial for sailing performance.

The only structural failure I ever heard about in a Moody yacht (which were built for more than 150 years up until the late 2000's) was a broken skeg. It is harder to make a strong skeg, than it is a strong spade rudder.

And the structural value of encapsulating a keel of the shape of the one on the Kraken yacht? Zero. That will be less strong than a well designed bolted on keel. That is purely designed to appeal to someone's irrational prejudices.

[boatpoker]

How about a liner that never was bonded to the hull !

Liner Bonding Failure

[marshmat]

Originally Posted by Dockhead

Few naval architects would agree with that they write on the Kraken website about skeg rudders:

"So why have almost all large modern production cruisers abandoned their skegs?

"And why – even more surprisingly – is this habit spreading to serious blue water cruisers? Why are so many unsupported spade rudders now hanging under blue water cruising sterns?
​
"The answer – predictably - lies in the cost."

https://www.krakenyachts.com/skeghungrudders

This is nonsense. Modern boats have spade rudders because they perform much better. These guys seem to build yachts (in very small numbers) for people with weird structural prejudices.

Skeg rudders are far worse hydrodynamically, than spade ones, and they are not necessarily stronger. My boat has a partial skeg, and it is one design element which I don't like. The best rudder for a boat which is intended for sailing is a really strong spade rudder, like what Steve Dashew designed for his boats, and like what most high end builders are now using. A spade rudder can be made just as strong as you want it to be, and it is far better for sailing performance. The rudder is a foil just like the keel, and its hydrodynamic performance is crucial for sailing performance.

The only structural failure I ever heard about in a Moody yacht (which were built for more than 150 years up until the late 2000's) was a broken skeg. It is harder to make a strong skeg, than it is a strong spade rudder.

And the structural value of encapsulating a keel of the shape of the one on the Kraken yacht? Zero. That will be less strong than a well designed bolted on keel. That is purely designed to appeal to someone's irrational prejudices.

Absolutely correct. The "skegs are stronger" argument comes from a fundamental misunderstanding of structural mechanics.
In fact, it is *much* easier to design and analyze the structure of a spade rudder: it is just a cylindrical member, with two points of support and a distributed load. It's an easy first-year undergrad engineering calculation to find all the stresses, the reaction forces on the bearings, etc.
A skeg-hung rudder, by contrast, is a system of coupled bending loads between two members of different materials and different section shapes. That's far more difficult to analyze, and if you try computing a sensitivity analysis on it, you find that the results are wildly different if you assume tiny changes in manufacturing method or material quality. If anyone says "skegs are inherently stronger", then I can be about 95% sure that said person actually knows nothing at all about the structures or the math involved.

Originally Posted by boatpoker

How about a liner that never was bonded to the hull !

Liner Bonding Failure

That's horrifying. And far too common.
Now and then, I see people coming to the defence of boatbuilders after the likes of David Pascoe and Wallace Gouk and Steve D'Antonio point the finger at stuff that's obviously shoddy, obviously poorly designed, and obviously installed without any knowledgeable quality control. I've even seen a few claim that because a boat is CE-marked and RCD compliant, that the builder obviously knows what they're doing, and wouldn't ever make dangerous mistakes. Then you get something like an Oyster 825 just spontaneously disintegrating.
Paperwork exercises like RCD are no substitute for having actual, qualified engineers perform (and independently review) the design calculations and the manufacturing drawings, and put an actual QC process in place to ensure that mistakes get caught and corrected.
And I think it's been obvious for at least a decade, now, that bonded-in structural liner grids present a lot of challenges for both in-factory QC and for later inspection. The part that frequently gets damaged is just too well hidden, and the failure modes are often what NASA calls "criticality 1" – i.e. the potential for rapid, total loss of crew and vehicle, with no redundancy and no easy way to get early warning of imminent failure.

[danstanford]

Originally Posted by LittleWing77

Yeah, Dan, but com'on!

You've chosen a J-boat. For Racing. On Lake Ontario.

You're certainly not going to be crossing oceans or even coastal cruising...

LittleWing77

Laughing, you are right LittleWing, I am not crossing oceans in my trusty little girl and I would choose a very different boat if I was. Sometimes I ask myself why I am here on a Cruising Forum and the answer is that I like the people!

The point I was trying to make originally was related to the way the structures act if they hit a rock at speed which the boats (YouTube boats in question) seem to have done. Does the glued in grid allow an amount of flex that does not rip the keel off of the boat when this might happen allowing the boat to get back to the dock prior to repairs?

Obviously we cannot ever tell from impact to impact but the question remains about if the heavier built glassed in frames would just stop without damage or would there be different types of damage?

[marshmat]

Originally Posted by danstanford

Laughing, you are right LittleWing, I am not crossing oceans in my trusty little girl and I would choose a very different boat if I was. Sometimes I ask myself why I am here on a Cruising Forum and the answer is that I like the people!

The point I was trying to make originally was related to the way the structures act if they hit a rock at speed which the boats (YouTube boats in question) seem to have done. Does the glued in grid allow an amount of flex that does not rip the keel off of the boat when this might happen allowing the boat to get back to the dock prior to repairs?

Obviously we cannot ever tell from impact to impact but the question remains about if the heavier built glassed in frames would just stop without damage or would there be different types of damage?

There is no requirement for a boat to flex enough to cause damage in a grounding. Indeed, while grounding damage might be tolerable in a pure racing design, I think there's broad agreement among naval architects that a cruising boat should be able to take the ground at a fair fraction of hull speed without any risk of structural damage.


Some boats do suffer structural grid flex in this situation. When they do, the damage is often hidden between bonded layers that you can't see. That's a problem.


Boats aren't cars. A grounding is not a sudden impact of the whole boat with a rigid immovable object; you don't need a crumple zone to dissipate energy and you don't need single-use sacrificial structures. The keel tip does suffer that impact, but the rest of the boat is supposed to dissipate the energy into the water and come to a controlled (if abrupt) halt. Whatever structure carries loads between the keel and the hull is supposed to be strong enough to convert the sudden point load at the keel tip into a rapid pitch-down motion of the hull. The backstay has to be strong enough to control the inertia of the mast. The kinetic energy of the boat gets safely dissipated as a wave propagating laterally outward from both sides of the bow. You don't need to, and shouldn't, sacrifice any structural components to accomplish that.