Hull flex on modern production boats

[TheThunderbird]

I went for heavy displacement.

I would never buy a modern boat.

Slow, but no regrets.

Ah, yes, doors close smoothly after 30years (journey by Carlini - Rimini, say he's like the Italian Cherubini of the US)

[bsurvey]

the entire interior of THAT boat is built like a separate hull so it will all move around if it is properly bound to the interior of the hull.


most boats use tab bonding of the interior joinery to the actual hull itself.


beneteau and jeannu is this same type of cheap construction to which they over charge you for its a poor type of construction.


if you get a hole in the hull you will never find it due to the liner.


by a real boat the keel won't fall off, they never corrected the wekness in the last keel bolt

[Pitchondesign]

I have only two data points, the only two boats I have owned. The first was a 1982 Morgan OI 51. It weighed 48,000 pounds, and had a cored hull. It has been characterized as a bomb shelter on a keel. In the roughest conditions, there were no creeks, noises, or any signs of flexing anywhere. The downside was it didn't sail very well. My current boat is a 1990 Beneteau Oceanis 50. This boat is 28,000 pounds, a full 20,000 pounds lighter. It has a solid hull, and flexes in conditions that the Morgan wouldn't notice. However, fiberglass can flex. Just look a snow skis, which are fiberglass, move and flex. It seems that fiberglass can safely flex to a considerable degree. The noise of the flexing is there, but doesn't seem to be a safety issue, just annoying. My current, considerably lighter boat, is way more fun to sail, and way faster.

[Cheechako]

Originally Posted by Dave Humphreys

Most Benetaus are not cored hulls (the 474 is definitely not cored) and they are built with a rigid internal stringer floor system that insures stiffness. It is more likely that the boat you were on was damaged at some point. Was this a rental fleet boat? If so, who knows what abuse it has experienced. If a properly maintained and surveyed 474 interests you, have no fear!

Well at least I learned something today! I thought all Benes were core at this point. This 2014 video shows full coring the hull by Bene (go to minute 1:38) but this video is for their power boats as well as sail boats, so who knows? Some views show stringers inside the cored hull.

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

[SteveSadler]

I worked on older wood boats for Windjammer Cruises and yes they creaked and groaned all day long. My own production boats didn't hardly make those sounds, but some. Our 2007 Jeanneau 49ds not a peep.
I suggest looking at the glassed in bulkheads for cracks.

[double u]

there is one surefire method to disillusion anybody about the rigidity of their boat:
1. slacken off backstay
2. string a thin line from pulpit to pushpit, put constant tension on it (either with a rubber or a weight) & have the line just touch the side of the mast
3. put mark on mast where line touches
4. crank up your backstay as much as you dare
5. cry about the distance the line is now higher than the mark

[boatpoker]

Originally Posted by a64pilot

However they can be a real asset, when I was buying a high volume production Boat, it was the owners group that told me exactly what to look for, and what the fix was. I looked, found it which shocked the owner cause he didn’t know about the oil canning. Without the owners group telling me, unlikely I would have found it, and the Surveyor missed it too.
Who goes around pushing hard on the exterior hulls of boats they are looking to purchase?

After (unintentionally) flexing the hull by hand on a Hanse about 1/2" some years back I now test all. I have since found it on other Hanse, Dufour and one Lagoon model. The Lagoon was a production flaw, The H & D were .... well just they way they were built.

[boatman61]

Originally Posted by double u

there is one surefire method to disillusion anybody about the rigidity of their boat:
1. slacken off backstay
2. string a thin line from pulpit to pushpit, put constant tension on it (either with a rubber or a weight) & have the line just touch the side of the mast
3. put mark on mast where line touches
4. crank up your backstay as much as you dare
5. cry about the distance the line is now higher than the mark

Ahh.!!! The famous Banana Effect.

[boatpoker]

I've previously posted this link on another thread but I think it is germane to this discussion. A number of years back I found this full liner boat with a liner that never was fully bonded to the hull. It is extremely difficult to detect before things start to go wrong. I have had a slightly more skeptical view of the modern full liner construction ever since.

Liner Bonding Failure

[Dockhead]

Originally Posted by boatpoker

I've previously posted this link on another thread but I think it is germane to this discussion. A number of years back I found this full liner boat with a liner that never was fully bonded to the hull. It is extremely difficult to detect before things start to go wrong. I have had a slightly more skeptical view of the modern full liner construction ever since.

Liner Bonding Failure

The only benefit of a hull liner is to allow assembly line mass production of the interior fitout elements. The downsides however are many, especially as the boat ages. Stick built boats are more expensive to build but are surely worth it if you can possibly afford it, especially if you are buying used or planning to keep the boat long term. If you plan to buy new and sell off after a few years, I guess it might be OK, but do many people really buy and sell boats like that?

[double u]

Originally Posted by boatman61

Ahh.!!! The famous Banana Effect.

...in this test & even our Pouvreau 11.30 did banana, & she was full of framing, T-stringers, floors, frames, you name it, she had it, all welded up & in french aluminium & never leaving us in the least doubt that upwind our brains would start dripping out of our ears before she'd succumb. there was no groaning to be heard until conditions were so wild that the cacophony of the smashing upwind would have drowned any groaning outout

[double u]

"...if you can possibly afford it..." - the crux of the matter...

[Polux]

Originally Posted by Cheechako

Well at least I learned something today! I thought all Benes were core at this point. This 2014 video shows full coring the hull by Bene (go to minute 1:38) but this video is for their power boats as well as sail boats, so who knows? Some views show stringers inside the cored hull.

That is a bad piece of journalism (the movie) and it is not your fault you have been induced in error.

This are the specs regarding hull most benes have. This is a 2018 48ft, so already a big boat:

• Monolithic hull design in polyester
• Monolithic structural inner moulding bonded to the hull
• Injection moulded deck in glass fiber/balsa sandwich, covered with

http://www.beneteau.com/sites/defaul...N_LIGHT_en.pdf

Note that contrary that on appear on the movie that shows a motor boat hull being infused, the sailboats have not the hull infused but only the decks that are cored.

[Polux]

Originally Posted by Dockhead

The only benefit of a hull liner is to allow assembly line mass production of the interior fitout elements. The downsides however are many, especially as the boat ages. Stick built boats are more expensive to build but are surely worth it if you can possibly afford it, especially if you are buying used or planning to keep the boat long term. If you plan to buy new and sell off after a few years, I guess it might be OK, but do many people really buy and sell boats like that?

I agree that there are downsides namely those that boatpoker says but there are also many advantages that in what regards inexpensive boats vastly superaste the disadvantages (that's why mass production boats are built that way).

The all thing can be built outside the boat, the big size can contribute to a better rigidity and for a good distribution of the loads and if well built the large surface will provide a very large surface for the bonding agent dispensing expensive lamination.



The state of the art in what regards those grids have to do with having slots where the bulkheads are put in as well as furniture (and bonded), contributing to a better fixation and contribute to a much better overall rigidity.



Of course, the problem is if a repair have to be made due to a grounding. Than it would be very costly to take everything out to repair the structure. I have a friend with a recent Beneteau (40ft) that after a strong grounding (on a rock) that apparently had no consequences had to pay (the insurance paid most of it) 30 000 euro for a decent repair.



That on an old boat would mean probably a ditched boat. Not different than what happens on modern cars when something bends the chassis or the main structural part. Then the price of replacing the chassis and the work to take the car apartar and mounting it again is so big that if it is not a recent one the car is ditched.

Above the photos are form French boars, Benetau, Dufour and Jeanneau. The German ones also use a stucture made out of the boat, but a different one, more of a grid:

[Dockhead]

Originally Posted by Polux

I agree that there are downsides namely those that boatpoker says but there are also many advantages that in what regards inexpensive boats vastly superaste the disadvantages (that's why mass production boats are built that way).

The all thing can be built outside the boat, the big size can contribute to a better rigidity and for a good distribution of the loads and if well built the large surface will provide a very large surface for the bonding agent dispensing expensive lamination.



The state of the art in what regards those grids have to do with having slots where the bulkheads are put in as well as furniture (and bonded), contributing to a better fixation and contribute to a much better overall rigidity.



Of course, the problem is if a repair have to be made due to a grounding. Than it would be very costly to take everything out to repair the structure. I have a friend with a recent Beneteau (40ft) that after a strong grounding (on a rock) that apparently had no consequences had to pay (the insurance paid most of it) 30 000 euro for a decent repair.



That on an old boat would mean probably a ditched boat. Not different than what happens on modern cars when something bends the chassis or the main structural part. Then the price of replacing the chassis and the work to take the car apartar and mounting it again is so big that if it is not a recent one the car is ditched.

Above the photos are form French boars, Benetau, Dufour and Jeanneau. The German ones also use a stucture made out of the boat, but a different one, more of a grid:

That all seems to make sense, more or less, to me, especially the analogy to cars. There is no question that it is far more efficient and therefore cheaper to build boat this way. But the problem is that while cars are used and then scrapped without ever having structural repairs done to them -- the idea of a "major refit" just doesn't apply to a non-collector car -- boats have normally much longer useful lives which may include some rewiring or replumbing and possibly some hull or keel repairs. A glued-in grid and full hull liner makes any such work vastly more expensive and indeed uneconomic in many cases -- so boats built that way are essentially disposable, destined to a much shorter useful life before scrapping, compared to a normal stick built boat.

Is that OK? Is that justified by a much lower acquisition price? Well, if we start to use boats like cars, buying, using for a while, then throwing them away like something disposable, then probably it does make sense. All I can say is that I have never used boats like that myself. I have never bought a boat new (so far) and have never kept one less than 10 years. I would not personally be comfortable with not being able to reach the plumbing or wiring, or to repair the hull economically in case of damage. I had an accident last year with a fishing boat which probably would have totalled my boat if I had had a full hull liner -- in the event, the inside of the hull was easily reachable after taking apart some of the furniture, and the repair was not too expensive.