New Beneteau's - How is the decks secured to the hull?

[CarlF]

I expect the hull to deck joint is done with Plexus and the self tapping screws are just there to hold it together while the Plexus cures. A properly done Plexus joint is stronger than bolts and backer plates. Of course, doing it "properly" requires good procedures at the factory as there's no way to check it after the parts have gone together.

I'd be very surprised if there isn't some sort of structure under those U bolts. It could be as simple as a small fiberglass three sided box under the deck that is attached with Plexus to the deck and acting as a knee to where it is also attached with Plexus to the hull. I expect there is also a structural bulkheaad/crossbeam within 6" of where those shrouds come through to resist the inward compression from the shrouds that would bow the deck. I do wish the U-bots were a size bigger. Wouldn't cost much.

While Beneteau is certainly a price built boat, something as visible as losing masts would quickly become a sales problem.

[DeepFrz]

It's not the Plexus itself that is the worry or the weak point but the method of glueing a bulkhead, for instance, to the hull but of not removing the gel coat from the bonding area. Now you are not depending on the strength of the glue but the strength of the gel coat bond to the fiberglass. We have seen a number of failures, on this forum, where the bond failed either at the gel coat bond or where the item was glued to plywood and the plywood failed at the bond joint. Those are some of the things to watch out for.

[Breaking Waves]

This is from a Beneteau brochure - its a few years old (and they have mostly stupped using the teak toerail). But it suggests they at least used to use a 'custom polyurethane', which if I remember correctly was a 2-part formulation (not 1-part like 5200). The 2-parts tend to have better properties than 1-part, especially in long term elasticity retention. Clamped with screws and occasional thru bolts by way of specific hardware (like the cleats)





If I was contemplating Benateau structural considerations - I would read this report on the loss of Cheeki Rafiki, and the investigation they did on the detached hull liner.

[Dr. D]

Yeah, so don’t run your boat aground four or five times without a thorough inspection. And if you do, get the repairs done according to the manufacturer. Right, got it. Oh, and don’t sail into a tropical storm.

RIP for those aboard.

[Breaking Waves]

Hmmm - did you read the conclusions?

Originally Posted by Dr. D

Yeah, so don’t run your boat aground four or five times without

"A skipper’s perception that the force of a particular grounding is insufficient to raise concern does not necessarily mean that significant damage has not occurred to the keel and/or the vessel’s structure."

They inspected a number of other Beneteau's and the majority had some level of matrix detachment which none of the owners were aware of. Some which may have been caused by upwind slamming and NOT groundings.

a thorough inspection. And if you do,

"It is difficult to readily identify areas where a matrix detachment has occurred in GRP yachts manufactured with a matrix bonded to the hull. This is especially the case where the keel is not removed prior to inspection and where floors have been layed up between frames. "

"False indications may be obtained when hammer testing to identify matrix
detachment,"

Most surveyors would miss this damage, even if looking for it unless they removed the keel or undertook destructive testing, which many owners would not want.

get the repairs done according to the manufacturer. Right, got it. Oh, and

"There is currently no industry-wide guidance on appropriate methods for identifying matrix detachment and conducting repairs, or on the circumstances that would necessitate keel removal."

don’t sail into a tropical storm.

Right, you go on a passage, you get what you get

This is not a trivial issue. It is something which should be high on the mind of anyone buying a used boat with this construction.

I see you have a Beneteau. I am not attacking Beneteau. This construction is used by other brands also. But it is most certainly something to be quite aware of when you consider your boat's structure. Even what you may perceive as a very light grounding or upwind slamming into waves, probably requires you to drop the keel, and do a rather comprehensive inspection of the pan which may require some destruction of the interior.

[Dr. D]

Originally Posted by Breaking Waves

This is not a trivial issue. It is something which should be high on the mind of anyone buying a used boat with this construction.

Absolutely agree. Add to that what is the boat designed for (racing in this case) and how was it used (racing in this case). OTOH, no matter what an owner or a broker say about how a boat was used one can never be sure.

[Jim Cate]

Originally Posted by Dr. D

Absolutely agree. Add to that what is the boat designed for (racing in this case) and how was it used (racing in this case). OTOH, no matter what an owner or a broker say about how a boat was used one can never be sure.

And this is why I personally will never own a boat built with this sort of structure. The idea of requiring difficult and expensive diagnostics every time the boat runs aground or drives to weather in hard conditions is totally unacceptable, for those events are part of an actively cruised (or just sailed for that matter) vessel's life.

Jim

[Davo1404]

Originally Posted by Jim Cate

And this is why I personally will never own a boat built with this sort of structure. The idea of requiring difficult and expensive diagnostics every time the boat runs aground or drives to weather in hard conditions is totally unacceptable, for those events are part of an actively cruised (or just sailed for that matter) vessel's life.

Jim

Exactly. Really was surprised when we arrived in Savusavu after 14 hours of bashing to windward to be asked by 2 Benetau owners that had done the same passage why we weren't drying things out that had got wet from leaking hatches. These yachts were only a few years old. Our good old 1972 Lidgard yacht was dry as a bone. One of the owners we became friends with & followed with interest as he spent days resealing leaking hatches.

[Breaking Waves]

^^ I can't condemn Beneteau and the others for this structural approach. It is cost-efficient. And if the tolerances are tight and the surface prep excellent it can be quite good. Unfortunately, excellent tolerances and surface prep adds costs, and the mass builders end up doing 'just good enough'. I have seen one of these pans with variable 12 - 20mm gaps to the hull.

The buyers just need to understand what they are buying, what its true limitations are, and what they need to be aware of. Unfortunately, they are mostly sold a dream and not hard cold engineering.

I get the strong sense in their writing (in the initial report and two follow-ups they did) that the MAIB investigators were conflicted. They clearly were concerned about the construction technique but Beneteau convinced them it was totally appropriate for how 95% of their boats were typically used (there are matrix bond failures but they do not have life-threatening consequences for the vast majority of situations/users).

[Dr. D]

OK, I'd like to turn around the course this thread has taken.


What sailboats are currently manufactured following a process that guarantees structural soundness in all seas, allow ready determination of any damage, and can be repaired if damage is found?


And I do mean currently manufactured.

[Breaking Waves]

Originally Posted by Dr. D

What sailboats are currently manufactured following a process that guarantees structural soundness in all seas, allow ready determination of any damage, and can be repaired if damage is found?


And I do mean currently manufactured.

"Guarantee in all seas" is a pretty harsh standard, but

well, aluminum.

but you probably mean mass-produced grp boats. And I would suggest OutBound is pretty decent (for a competitive price). There are certainly others.

At the high end, monocoque pre-preg carbon/kevlar is about as good as it can possibly get. like at Persico Even fewer issues than aluminum (if done correctly, which requires serious skills), and as strong and light as physics currently allows.

[BenBowSirocco]

I have worked in boat repair and construction for over a decade and while I would readily admit- I have a LOT to learn. I have spent enough time around boats to know a glued hull to deck joint is standard and has been for decades. In my experience this is usually done with stainless screws and slow cure 5200. Methacrylate (Plexus) is far to expensive (and stiff) to be used in this way.

The point to remember, as stated by others, is that 95% of boats do not get sailed or used readily, or even often. Weekends around the buoys in the bay or a once a year race offshore is a boat used hard and based on my experience maintained enough only to keep is usable.

Delamination of structures in a boat SHOULD be unacceptable for anyone, especially someone who lives a world sailing lifestyle. Damage resulting from mild grounding- unacceptable. Damage resulting from hard sailing... unbelievably irresponsible. But people keep on buying them because people are (seemingly) cheap. (Walmart anyone?)

These are exactly the reasons why it seems common that many passionate lifestyle sailors go full custom or semi-custom. Or they tend to hyper customize a good production design to meet their needs, which usually involves much fiberglass added. What they are doing with their boats and what they expect from their boats is NOT what a manufacturer is building boats for. That market is far to small. Precisely why there are still independent designers and custom builders who make a good living.

I understand the criticism of this new boat. But its exactly what they customer asked for.

[sandy stone]

Originally Posted by Breaking Waves

I get the strong sense in their writing (in the initial report and two follow-ups they did) that the MAIB investigators were conflicted. They clearly were concerned about the construction technique but Beneteau convinced them it was totally appropriate for how 95% of their boats were typically used (there are matrix bond failures but they do not have life-threatening consequences for the vast majority of situations/users).

I got a slightly different impression after reading the report. It seemed to me the investigators were completely satisfied with the engineering by the Farr design team, and the construction and testing by Beneteau (destructive strength testing of sample glue joints off the production line). The big concern, mentioned above, was the difficulty of detecting and repairing damage after a grounding. Remember, this is on a purpose-designed ocean racing boat (that finished 1-2 in the Sydney-Hobart race), so engineering margins were probably stretched a little more that they would be on a mom-and-pop coastal cruiser.


Full disclosure - I own a mid-80's Beneteau First, and I doubt any boat has a stronger hull to deck joint (or shroud attachment, as far as that goes). I'm sure things have evolved over some 35 years.