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Old 17-05-2021, 03:37   #1
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Implications of Bonded Structural Grids in Production Boats




Interesting video. The guy had a hard grounding in an almost new Hanse which required extensive structural repairs.
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Old 17-05-2021, 03:56   #2
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Re: Implications of Bonded Structural Grids in Production Boats

Thanks for that: very interesting.


If I could afford an expensive yacht I don't think I'd go past an Island Packet.


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Old 17-05-2021, 05:43   #3
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Re: Implications of Bonded Structural Grids in Production Boats

FWIW, I am certainly not a marine architect nor do I wish to attempt to defend any method of boat construction.
In both this case and Expedition Evans, the boats had hard groundings followed by sailing away and then getting repaired. Is this enough to defend this type of construction? As I understand it, the grid functions as a kind of fuse allowing the boat to flex rather than break.
I haven't hit anything hard yet although I have touched bottom in a shallow channel a few times but just imagine the loads and stresses 10 tons of boat coming to a stop when a lever extending out of the boat stops. Would a more conventional construction just spread the loads and cope with it?
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Old 17-05-2021, 05:51   #4
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Re: Implications of Bonded Structural Grids in Production Boats

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Originally Posted by danstanford View Post
FWIW, I am certainly not a marine architect nor do I wish to attempt to defend any method of boat construction.
In both this case and Expedition Evans, the boats had hard groundings followed by sailing away and then getting repaired. Is this enough to defend this type of construction? As I understand it, the grid functions as a kind of fuse allowing the boat to flex rather than break.
I haven't hit anything hard yet although I have touched bottom in a shallow channel a few times but just imagine the loads and stresses 10 tons of boat coming to a stop when a lever extending out of the boat stops. Would a more conventional construction just spread the loads and cope with it?

It seems to me like the hull to grid bonding is too weak and too brittle if they de-bond in a grounding. If it's done well, I'd expect the grid to prevent the hull from flexing significantly, leading to localized damage in the impact area, but the stiffness of the grid should prevent things from flexing beyond that area (much like heavy glassed in stringers in a conventional build).
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Old 17-05-2021, 06:03   #5
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Re: Implications of Bonded Structural Grids in Production Boats

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Originally Posted by danstanford View Post
FWIW, I am certainly not a marine architect nor do I wish to attempt to defend any method of boat construction.
In both this case and Expedition Evans, the boats had hard groundings followed by sailing away and then getting repaired. Is this enough to defend this type of construction? As I understand it, the grid functions as a kind of fuse allowing the boat to flex rather than break.
I haven't hit anything hard yet although I have touched bottom in a shallow channel a few times but just imagine the loads and stresses 10 tons of boat coming to a stop when a lever extending out of the boat stops. Would a more conventional construction just spread the loads and cope with it?

There are a lot of variables. Very high aspect keels (concentrating the forces at the hull-keel joint) will produce more stress on the joint for a given impact force. Combination of that, with a less strong (or at least durable) structural system like a glued-in grid, makes the boat more subject to structural damage in case of a hard grounding.


I don't think this is necessarily bad -- it's lighter, MUCH cheaper, much better performance, and the relative vulnerability of this approach may be acceptable to many (probably most) sailors. If structural damage were really common then insurance rates would penalize such boats, but they don't, as far as I know.


You can make the keel less vulnerable be reducing the aspect ratio so spreading the load over a wider base. Plus building a stronger structure which is fully laminated in, and tied in with stringers and ring frames. There is actually no limit to how strong you can make a bolted-on fin keel (notwithstanding the prejudices of some full-keel enthusiasts) -- it's all just a question of engineering, and how much money/weight you're willing to spend on it.



But this approach (lower aspect keel, strong structure) is MUCH more expensive, and a lower aspect keel gives worse sailing performance than a high aspect, torpedo keel like in the video.


Like everything in sailing, it's a tradeoff. My boat is the second type, with a bulb keel but relatively low aspect, and with very costly structural system. It's a reasonable compromise, still decent sailing performance (sail rings around any full-keeler), and sailing in rocky and not completely charted waters as I do (and sometimes entirely uncharted), I do feel better knowing that hitting a rock will not cause any damage. Tested in reality when I hit a completely uncharted rock in Finnish waters once, without the slightest effect on the structure (verified by survey). But sailing upwind, I sometimes miss the hydrodynamic performance of a high aspect torpedo keel. Everything is a tradeoff.
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Old 17-05-2021, 06:28   #6
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Re: Implications of Bonded Structural Grids in Production Boats

Thank you Dockhead for finding this video. People have asked me advice on repairing fin keels and this is a great video to show the work necessary. I feel very sympathetic for this owner who I believe now understands the construction differences between boatbuilders. With regard to the repair itself. Obviously removing the entire grid would be a huge task but Iíve seen it done. A new grid laminated in with epoxy and Plexus where one cannot laminate, produces excellent strength. There is really no need to ďtestĒ the polyester as the engineering numbers of laminating with epoxy or polyester are well understood.
The debonding of interior cabinets was again valuable to illustrate how difficult it is to know the extent of the damage. Iíve seen a keel hull joint protected by an exterior band before and it too requires a bit of engineering and the correct epoxy to account for keel to hull flex. The manatee crew fell into fits of laughter at the size of the bilge pump and sorry, but the idea of plastic ball valves. They are firm believers in aluminum vessel construction and consume huge quantities of beer justifying this by the claim the flat cans are necessary for future construction.
Alright, Iíll be serious.
Some time ago a competent sailor came into an OEM who produced a fast and extremely popular racer cruiser to buy for his older children. One month later the boat was back at the factory having hit a rock. We had to agree with the insurance company it was a complete write off. If we gave him all new interior cabinets, a new grid, all the epoxy, glass etc. and the crew did the repair on weekends for a third of regular yard labor...it still remained a total wreck.
Consumers want fast boats with large interiors and the amenities of a condo.
Bomb proof construction is costly. A comfortable motion at sea is no longer a selling point. Survivability? Look at the requirements for passenger vessels and them ask yourself why the yacht you will have your loved one sail in, cannot meet these minimum standards. There was an advertisement many years ago showing a vessel which had bounced across a reef and survived hull intact. Maybe a Pacific Seacraft? You donít see adds like this anymore. So ends my rant.
I truly feel sorry for this gentleman and hope he never grounds out again. Again, thank you Dockhead as this post is so very important, truthful and informative.
Happy trails to you.
Captain Mark and his manatee crew who uses our huge dewatering pump for water fights with fire boats.
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Old 17-05-2021, 06:30   #7
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Re: Implications of Bonded Structural Grids in Production Boats

Very interesting video and would have thought that the "integrated" grid would have been more than just glued to the hull w/bondo/thickened polyester resin. Even more surprised to hear the owner knew before he purchased the boat that the grid wasn't laminated to the hull. Are these boats that much cheaper than a boat w/ a properly laid in grid?

Always nice to have the lighter faster boat, but at what price? Would be nice to have minimum build specifications for these grid hulls that would include lamination of the grid to the hull. Not all initial boat purchasers will go through the deep dive to see how the grid is tied to the hull and never know in advance the boat would potentially be totaled after a hard grounding.
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Old 17-05-2021, 06:35   #8
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Re: Implications of Bonded Structural Grids in Production Boats

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There was an advertisement many years ago showing a vessel which had bounced across a reef and survived hull intact. Maybe a Pacific Seacraft? You donít see adds like this anymore. So ends my rant.
Isn't this a question that arises when does not bounce up and over the reef but rather stops dead in the water conveying all the stresses into the hull?

As referred to by Dockhead, 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.
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Old 17-05-2021, 06:37   #9
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Re: Implications of Bonded Structural Grids in Production Boats

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Originally Posted by Manateeman View Post
Thank you Dockhead for finding this video. People have asked me advice on repairing fin keels and this is a great video to show the work necessary. I feel very sympathetic for this owner who I believe now understands the construction differences between boatbuilders. With regard to the repair itself. Obviously removing the entire grid would be a huge task but I’ve seen it done. A new grid laminated in with epoxy and Plexus where one cannot laminate, produces excellent strength. There is really no need to “test” the polyester as the engineering numbers of laminating with epoxy or polyester are well understood.
The debonding of interior cabinets was again valuable to illustrate how difficult it is to know the extent of the damage. I’ve seen a keel hull joint protected by an exterior band before and it too requires a bit of engineering and the correct epoxy to account for keel to hull flex. The manatee crew fell into fits of laughter at the size of the bilge pump and sorry, but the idea of plastic ball valves. They are firm believers in aluminum vessel construction and consume huge quantities of beer justifying this by the claim the flat cans are necessary for future construction.
Alright, I’ll be serious.
Some time ago a competent sailor came into an OEM who produced a fast and extremely popular racer cruiser to buy for his older children. One month later the boat was back at the factory having hit a rock. We had to agree with the insurance company it was a complete write off. If we gave him all new interior cabinets, a new grid, all the epoxy, glass etc. and the crew did the repair on weekends for a third of regular yard labor...it still remained a total wreck.
Consumers want fast boats with large interiors and the amenities of a condo.
Bomb proof construction is costly. A comfortable motion at sea is no longer a selling point. Survivability? Look at the requirements for passenger vessels and them ask yourself why the yacht you will have your loved one sail in, cannot meet these minimum standards. There was an advertisement many years ago showing a vessel which had bounced across a reef and survived hull intact. Maybe a Pacific Seacraft? You don’t see adds like this anymore. So ends my rant.
I truly feel sorry for this gentleman and hope he never grounds out again. Again, thank you Dockhead as this post is so very important, truthful and informative.
Happy trails to you.
Captain Mark and his manatee crew who uses our huge dewatering pump for water fights with fire boats.
Yeah, everything is a tradeoff.

I wouldn't mind my loved ones in such a boat as long as they weren't sailing in remote areas (like 99% of sailboats don't), AND so long as I could get insurance at reasonable cost to deal with the rare catastrophe. I don't think such a boat is actually dangerous for normal coastal cruising (and even less for sailing offshore in mild latitudes where there's nothing to hit). Boat built like this are cheap, light, and have fantastic sailing performance. Those are great arguments.

I wouldn't want it for my own use, however, because I do sail in rocky, poorly-charted and uncharted areas, sometimes a thousand miles from rescue. But that's a 1 in 100 use case. For that, I'm pretty happy with my present boat, but better (because of the problem of ice) would be a metal boat, which is what I would use if I were building from scratch.
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Old 17-05-2021, 07:46   #10
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Re: Implications of Bonded Structural Grids in Production Boats

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Consumers want fast boats with large interiors and the amenities of a condo.
Bomb proof construction is costly. A comfortable motion at sea is no longer a selling point. Survivability? Look at the requirements for passenger vessels and them ask yourself why the yacht you will have your loved one sail in, cannot meet these minimum standards. There was an advertisement many years ago showing a vessel which had bounced across a reef and survived hull intact. Maybe a Pacific Seacraft? You donít see adds like this anymore. So ends my rant.
Manatee & Crew,

SO true. People buying boats today charter a couple different versions of bendy-toys and then think they know everything there is to know about "bluewater" sailboats.

My all time favorite clueless quote was the guy who said he owned a 38 foot Island Packet with such a high freeboard he couldn't imagine a wave washing over it. I guess he'll learn, if he ever actually goes sailing across a real ocean.
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Old 17-05-2021, 08:01   #11
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Re: Implications of Bonded Structural Grids in Production Boats

This is well worth reading: https://assets.publishing.service.go...ort_8_2015.pdf and annexes https://assets.publishing.service.go...eekiRafiki.pdf

It is a MIAB official report on a case where a Beneteau had grid bond failure, went on passage, lost its keel and everyone died.

It is a bit sobering, and I expected the used prices for bonded boats to fall after this became more widely known (because it can be both difficult to inspect for and even more difficult to repair). But it may well be that this customer base just does not really care enough about the safety issues and the cost/ease trade-off makes sense for them.

In a follow-up investigation, MAIB did a random inspection of a whole bunch of bonded grid boats sitting in storage in UK yards and found a significant number of them had cracked bonds unknown to their owners.

Keel Summary Points:

1. Matrix detachment is possible in yachts where a GRP matrix and hull are bonded together. The probability of this occurring will increase with longer and harder yacht usage. There is therefore a need for regular structural inspection by a nominated competent person as part of a formal verifiable procedure, as well as before embarking on an ocean passage.
2. Owing to the continuous nature of a matrix where solid floors are in place, particularly where the keel is attached to the hull, it may be difficult to readily identify areas where a detachment has occurred. There are differing opinions among surveyors and GRP repairers with regard to what are appropriate methods of inspection and repair, including the circumstances in which the keel should be removed. There is therefore a desire for best practice industry-wide guidance to be developed.
3. Any grounding has the potential to cause significantly more damage than may be subjectively assessed or visually apparent, including matrix detachment. It is therefore important that all groundings, including those perceived to be ‘light’, result in an inspection for possible damage by a suitably competent person.

There was suppose to be a follow-up process to create better guidelines for original construction process control, inspection techniques and process, and repair processes . . . But I think unfortunately the industry dropped that ball completely - was not interested.
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Old 17-05-2021, 14:33   #12
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Re: Implications of Bonded Structural Grids in Production Boats

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But I think unfortunately the industry dropped that ball completely - was not interested.
Well, sure! The boats are selling just fine as they are, so why change?

Jim
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Old 17-05-2021, 14:56   #13
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Re: Implications of Bonded Structural Grids in Production Boats

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Well, sure! The boats are selling just fine as they are, so why change?

Jim
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.

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Old 17-05-2021, 15:15   #14
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Re: Implications of Bonded Structural Grids in Production Boats

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Well, sure! The boats are selling just fine as they are, so why change?

Jim
yea, sure, but it would be nice to have a better idea of how to inspect for this damage, and how best to fix it. I would think that would be in everyone's best interest. . . . except it would take a little effort, and would raise the PR profile of the bonding drawbacks.

It is nice that two yachts 'survived' . . . but do remember that everyone died on Cheeki Ra ki.
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Old 17-05-2021, 15:44   #15
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Re: Implications of Bonded Structural Grids in Production Boats

If you purchase a new car, you have a reasonable assurance that it has been driven straight into a wall, tee boned, driven into a cement block at an angle. In my SUV there are warnings about roll overs on the visors with little cartoons of a car on two wheels. You have headrests, seatbelts airbags. A safety latch on the hood. Instructions for child seats, child door locks. Much the same in small private aircraft and much more in commercial passenger aircraft.
Survivability is an integral part of engineering design.
Admirality Courts have played a huge part in the creation of rules and regulations for safety at sea. Passenger vessel structural inspections, safety equipment inspections and operator competence testing have significantly improved safety.
Iím not advocating mandatory standards as stringent as for cars. I like the idea experimental aircraft can be built and flown. If one chooses to build a vessel or have a vessel built to whatever design they can imagine...fine. Two conditions. Do not carry any means for a mayday. Second, no children aboard. No one should risk their lives to save you as you have chosen to sail ďexperimental classĒ.
As children cannot weigh the dangers, they are not willing participants.
I think these two rules would produce very interesting vessels and would advance vessel designs. A number of great auto safety features came from race cars.
The real issue here is DISCLOSURE.
The vessel owner states it precisely...ĒHad I KnownĒ...
Well he knows now doesnít he. Well if my SUV has a big unremovable warning about roll overs...why not boats.
Why Iíve made fun of the Ken, Barbie and the cat sailing blogs is there is little disclosure of the true costs, heartache, misery and dangers.
Some feel I post too much gloom and doom. Others understand Iím trying to present the view of the prudent Mariner. The joy of this forum is that it provides readers with multiple perspectives.
I doubt some OEM builders will ever change. Thank goodness for custom yards.
Build whatever you wish. When I first went ocean racing the boots were wood, we had no radio direction finder..no radio at all. No one expected to be rescued. It was simply dangerous. Yachting was experimental class. Things have changed and isnít it time for full disclosure? Isnít it time to let someone point out flaws without being personally attacked or dismissed with snarky quips?
Iíd like to think itís still Yachting.
Again, I sincerely thank Dockhead for finding this amazing story.
Happy trails to you
Captain Mark and his manatee crew hard at work building boats from beer cans
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