Cored Hull Underwater

[DDW]

Originally Posted by boatpoker

This is true however, very high performance boats such as Spirit of Canada with Nomex honeycomb core (I worked on this one) are painstakingly built to extreme standards. Not so production boats built by low skill itinerant labourers overseen by one or two guys who know what they are doing with an order to get that thing out of the mold real quick.

That is quite true. I said way up thread that a cored hull requires more care than most ordinary production builders can supply. Nevertheless we should not condemn a good material because of poor construction practices.

BruceK: I just googled "cored boat hull sinking". It returned 1,390,000 results. Among them you should find some of interest.

There are examples of cored sailboat hulls losing their keels, and in a few cases it was due to under engineered or poorly constructed cored structures. In most cases it is due to under engineered or poorly built keel structures, having nothing to do with core. Beneteau in particular has had a few lost keels, and those cases indicate weaknesses in engineering and construction, not necessarily core problems. Beneteau is not one of the production builders I would want to buy a cored boat from. They are poorly thought of in the sailboat world, sometimes derogatorily referred to as "Bendy Toys". They are considered a lower end or "value brand" there. Plenty of fans, and perhaps a good value for the money, but no one thinks they are the best examples of construction.

The 40.7 was built with a solid hull (in the failed area) and a bonded in "grid liner" consisting of stringers and floors. Like coring, this requires attention to detail when bonding in the liner; and like coring, it is more or less uninspectable once built. If incorrectly built, or subsequently damaged by grounding, you likely won't know it until it fails. The loss of the Cheeky Rafiki was probably due to that effect.

[IslandTractor]

Originally Posted by boatpoker

Never seen a J (any model) more than a few years old that did not have significant moisture in the hull. Attached are a couple of pages from a very typical J-boat survey

As a past owner of a J36 I can confirm that their balsa cored hulls were/are a big problem. I lost mine when the yard determined it was not safe enough to relaunch and I had two independent surveys to confirm their findings and assessment. I ended up selling for a pittance to someone who wanted to take the time to do the repair himself. Not an economical repair at a decent commercial yard.

[MichaelB1969]

Originally Posted by DDW

BruceK: I just googled "cored boat hull sinking". It returned 1,390,000 results. Among them you should find some of interest.

BTW, the inference here is that cored boat hulls sink a lot, but the Google search does not accurately support this inference because if you actually search for the exact phrase "cored boat hull sinking", it returns zero results. Not a single one.

A better related search strategy is one that contains the word "sinking" AND one of the following phrases:

"steel hull" 25,700 results
"fiberglass hull" 34,400 results
"solid hull" 7,460 results
"cored hull" 6,530 results
"cored fiberglass hull" 990 results

What does this all mean? Not much I'd argue.

That said, by searching these terms you will obviously find a lot of information. But the search volumes are meaningless in my opinion.

Mike

[MichaelB1969]

BTW, I am a 2014 ST44 owner (boat is for sale if anyone is interested) who researched this issue of cored vs. solid quite a bit prior to purchasing.

At the end of the day, I felt comfortable that the hull was strong and sound given their manufacturing process and the sheer volume of boats out there on (top of) the water. In their process, the balsa is cut into small rectangles, each of which ends up getting encapsulated in vacuum-infused resin thereby limiting the spread of any water damage that might occur if the hull were to be compromised.

Unlike smaller manufacturers, Beneteau has a huge R&D budget and engineering team along with 130 years of experience behind them. Given their massive volumes, any problems related to hull manufacturing or materials that led to boats sinking or other major problems would be WIDELY known at this point, and their reputation would suffer greatly. And a multi-billion dollar company would likely go under.

Yet every time I go out on SF Bay I see tons of Beneteaus, some quite old, with seemingly happy owners enjoying their time out on the water...cored hull and all.

Note: if anyone is interested in a 2014 ST44 with low-hours, check out https://www.denisonyachtsales.com/ya...fornia/6903722

[Rufus]

Originally Posted by sunchaser

That is a very good accident report. Well worth reading for those intending to do offshore sailing and racing.

The photo on page 53 of the report does look like coring was torn away...maybe the very small area where the keel bolts up is solid laminate. Clearly the bonded in "grid" is essential for hull rigidity. I found the report to be lacking a comprehensive engineering analysis and lab testing of the most probable failure sequences...a conclusive failure modes and effects analysis in the aviation world.

https://assets.publishing.service.go...ort_8_2015.pdf

[BandB]

Originally Posted by Slider70

QUESTION: Why does a "state of the art" boat get blisters?

.

I find that question interesting just because there are various good quality boats with certain regular issues. We didn't have the problem, but Sunseeker is notorious for after a few years in the sun a lot of spidering in the gelcoat. Nothing structural, just ugly. They claim it's because of temperatures and humidity during build but they have the problem solved. I had to ask then why Princess, also built in the UK didn't have the issue. They may really have the problem solved now and I hope so. But it was something they were doing wrong.

[BruceK]

Originally Posted by MichaelB1969

BTW, I am a 2014 ST44 owner (boat is for sale if anyone is interested) who researched this issue of cored vs. solid quite a bit prior to purchasing.
At the end of the day, I felt comfortable that the hull was strong and sound given their manufacturing process and the sheer volume of boats out there on (top of) the water.....

Thank you for posting. I found myself balancing similar considerations. My unresolved concern was how well each thru hull was sealed. That Beneteau had not managed to seal the bow cabin portlights was a concern.In many ways we really liked the boat, electing not to proceed was a tough decision.
The subject boat was an early one, 10 years older than yours. In 2005 Beneteau began injection moulding the hull builds, doubtless there were many other improvements between the respective build dates.
I wish you every success with your sale.

[gsholz]

I looked at one of Beneteau/Jenneau's Prestige 46 power boats at a recent boat show. Boat show special reduced from > $1M to 800k. I was not impressed. It felt there were many corners cut just below what you could see and touch. Every floor we walked on creaked and deflected like they used 3/8 inch ply. Most surprising was the bow thruster installation. The builder simply cut out a triangular wedge of the bow section below the water line, installed a small tube and then just caulked the tube/wedge back into the hull. No fiberglassing just caulk. I have never seen anything like that.

[MichaelB1969]

Originally Posted by BruceK

Thank you for posting. I found myself balancing similar considerations. My unresolved concern was how well each thru hull was sealed. That Beneteau had not managed to seal the bow cabin portlights was a concern.In many ways we really liked the boat, electing not to proceed was a tough decision.
The subject boat was an early one, 10 years older than yours. In 2005 Beneteau began injection moulding the hull builds, doubtless there were many other improvements between the respective build dates.
I wish you every success with your sale.

Thanks Bruce!

[sunchaser]

Originally Posted by gsholz

Most surprising was the bow thruster installation. The builder simply cut out a triangular wedge of the bow section below the water line, installed a small tube and then just caulked the tube/wedge back into the hull. No fiberglassing just caulk. I have never seen anything like that.

Caulking? There has to be more to the story. If not, that is a sure fire way to promote hull saturation or delamination.

[Jeff F]

Originally Posted by gsholz

Most surprising was the bow thruster installation. The builder simply cut out a triangular wedge of the bow section below the water line, installed a small tube and then just caulked the tube/wedge back into the hull. No fiberglassing just caulk. I have never seen anything like that.

I haven't looked in detail at the new STs, but the recent larger Beneteau sailboats have thrusters that live in a molded cavity in the hull. There are removable fairing assemblies for access. Looks like a really smart design. I suspect that's what you saw.

Here's deets on the sailboats: http://no-frills-sailing.com/bow-thr...e-in-the-hull/

[DDW]

Originally Posted by MichaelB1969

BTW, the inference here is that cored boat hulls sink a lot.....

No inference. the poster wanted information, there is a lot to be had. Cored boats are actually a bit less likely to sink, since the hulls are buoyant.

When I had my sailboat custom built I could have specified any construction. I specified cored, including below the waterline. But it must be done with due care, and I'll repeat that few production builders exercise sufficient care for me to be comfortable.

The fact that balsa is built up in small blocks does not prevent water channels between them that can run the length of the hull. This is easily provable by cutting one apart. Infused boats have a small chance of filling these with resin but usually don't achieve that. Hand laid up, no chance.

[gsholz]

Originally Posted by Jeff F

I haven't looked in detail at the new STs, but the recent larger Beneteau sailboats have thrusters that live in a molded cavity in the hull. There are removable fairing assemblies for access. Looks like a really smart design. I suspect that's what you saw.

Here's deets on the sailboats: Hole in the bow? A common misconception of Bow Thrusters. |

Yes, that is exactly what it looked like.

[Boat]

Originally Posted by BruceK

Thank you for posting. I found myself balancing similar considerations. My unresolved concern was how well each thru hull was sealed. That Beneteau had not managed to seal the bow cabin portlights was a concern.In many ways we really liked the boat, electing not to proceed was a tough decision.
The subject boat was an early one, 10 years older than yours. In 2005 Beneteau began injection moulding the hull builds, doubtless there were many other improvements between the respective build dates.
I wish you every success with your sale.

I tried to search this one and couldn't weed through the results. Can you elaborate a little or post a link?

In the bottom of my cereal box I found an injection molded hippopotamus. I can't make the jump from the hippo to the boat.

Here's one link:

https://www.cruisingworld.com/how-it...n-molded-decks


Guessing quality control could be far better with injection molding.


Does anyone make an injection molded one-piece core?

[JLD]

My concern with a cored hull, isn't sinking, its possible blistering and delamination. I think these concerns multiply for an older boat that spends most of its time in the water (maybe even full time). May be less of an issue for a newer boat or one that spends only part of the time in the water.

Jim

[smitty477]

Originally Posted by DDW

No inference. the poster wanted information, there is a lot to be had. Cored boats are actually a bit less likely to sink, since the hulls are buoyant.

When I had my sailboat custom built I could have specified any construction. I specified cored, including below the waterline. But it must be done with due care, and I'll repeat that few production builders exercise sufficient care for me to be comfortable.

The fact that balsa is built up in small blocks does not prevent water channels between them that can run the length of the hull. This is easily provable by cutting one apart. Infused boats have a small chance of filling these with resin but usually don't achieve that. Hand laid up, no chance.

I am not aware of any reasonable sized cored hull boats where the bouncy of the coring would come close to 'floating' the balance of the equipment and machinery.
They may very well sink slightly slower - I am sure it would not be measurable or relevant.

[DDW]

There are numerous cases of both powerboats and sailboats floating for months after capsize due to cored hulls. Monohull sailboats which lose their keel and flip, catamarans that flip. For example, the Beneteau 40.7 referred to above was found floating upside down and flooded several weeks after the capsize. Largest sailboat I'm aware of was an 80' that lost it's keel, was recovered in a couple of days and salvaged. Powerboat may depend on the specific model but certainly it happens. On my own sailboat, there is 900 sq ft of cored surface in the hull, 650 in the deck, and 1110 in the interior. That is enough to float the hull it if lost the 11,000 lb keel.

It isn't a big advantage, it will float very low in the water and likely be unsalvagable on recovery.

[Comodave]

The March 2019 issue of Boating magazine has an article about drying out a wet core. Interesting technique on how they dry out a wet core. It was expensive but cheaper than other methods maybe.