Shocked by hull material catamaran

[nortonscove]

Originally Posted by leftbrainstuff

The oak versus reed analogy aligns well with how we engineer toughness, which is a measure of the ability to absorb energy. Objects that flex to be tough are lifed in terms of their fatigue life. When they reach their end of life they tend to fail catastrophically.

The dilemma is much more complex than toughness alone. Cost to manufacture tends to dominate and be obsessively minimized in this era of consumption, disposal and replacement. Life is measured in single digit years at best.

Strength of composites is rarely an issue when building composite structures. If we were to design for strength alone hulls would be even thinner. But thin, weight optimized structures pose huge issues at the interfaces. Stress gradients are extreme. This is why rudders, keels, etc, fall off some vessels. Sailboats have many complex interfaces and this is where we see problems arise.

In aerospace and motorsport we engineer these interfaces to have smooth stress gradients. We also monitor each and every load cycle. Any loss of traceability leads to scrapping of the component or repair to a proven specification.

The top echelons of sailing, like Americas cup vessels, are moving in this direction. The vast majority of sailboats have no fatigue monitoring and no proven repair specifications.

Interfaces include different materials, removable items and at changes of section and load transfer within composite structures.

Deflection tends to be the driving design parameter. This results in either more support, more thickness or both. A cheap core is a great way to increase bending stiffness. But what about the tradeoffs.

Durability, reliability and maintainability are rarely 'engineered' these days. Older vessels tend to outperform in terms of these 'ilities'. Not often by design but by accident.

A fiberglass hull that has not been subjected to manufacturing cost optimization, ie a thicker, more substantial hull will experience more gradual stress gradients. Removing and replacing components also produces less damage and fewer latent defects.

Clever marketing uses terms like lightness, sportiness, fastest and other 'weasel words' to sell the lowest cost to manufacture.

Time and success are the only determining factors needed in many cases. If there are a thousand boats having sailed a million miles without failure I really don't care for the after the fact engineering talk.

[Polux]

Originally Posted by Dockhead

Polux disagrees with me? How shocking! Why -- that's never happened before! ROTFLMAO.


I do agree that Oysters are generally well built, fantastically well built. But I think that the one that lost its keel is carp. The layup is extremely thin, and keels falling off is just -- well, we've discussed this a few times before -- totally unacceptable. I would not trust any other aspect of that particular design, once the designers made that kind of mistake.

"Built for speed" is the charitable interpretation. But I just don't believe it was built for cheapness. So that thin layup can only be for the sake of weight and speed. And they took it too far.

Oysters are built now the same way that one that lost the keel. The diference is that one, and their sister ships, were victims of a mistake in what regards engineering calculations.

Top boats are not built today like they were decades ago, with lots of unnecessary weight due to massive lamination, just in case, because they didn't know exactly were they could save weight and were they could not.

Boats were not engineered with aid of computer simulations and the work of structural engineers and composite engineers to maximize efficiency and design composites best suited to the the efforts with and adequate safety margin.

Last year I had the luck of having a patient engineer explaining to me the structure of a modern big yacht, an Ice 52 and even if you can tell on a cheap boat what is obviously made to save money, on a boat like an Oyster or a Ice yacht you cannot tell if the engineering was well done or not, unless you are a structures engineer and can have access to the calculations and to the profile of the materials used.

He was explaining to me, frame by frame, beam by beam how it was built and how much material and Eglass layers and carbon layers they had and it varied a lot depending the efforts that particular local was subject to. Ind the end every thing was completed vacuum laminated to the hull. Very complex and quite impossible to determine if that was very good, or poor at the naked eye.

But one thing I can tell you, if that boat was destroyed like that Oyster was, and the sandwiches come to pieces you would say that the boat is very poorly built because, weighting half than the Oyster, certainly the laminates, on average would be thinner than on that Oyster.

A new modern Oyster with about the same size of a Ice 52 (the 525) displaces 22 356 kg while a Ice 52 displaces 12 000kg.





The 525, a 2007 design was substituted by the Oyster 575 that weights 26 000kg.

The Ice 52 is a top performance cruiser and a light very well built boat, the Oyster 525/575 is a medium weight cruiser, certainly not designed for performance but to sail relatively well and to be a strong reliable boat.

And with this post I say goodbye to you and all till the next chair sailing season. Time to get ready for the real sailing season, the one with a boat and all

[robert sailor]

Originally Posted by nortonscove

Time and success are the only determining factors needed in many cases. If there are a thousand boats having sailed a million miles without failure I really don't care for the after the fact engineering talk.

So in your example if one of your boats sails a thousand miles (1000,000÷1000) it passes the test, pretty low bar in my opinion. Seriously though most boats sit around marinas for the bulk of their lives and only the tiniest number actually cross oceans in all sorts of weather so it's probably not the best way to judge a boat. When structural failures do occur the owners take the opinion that heck they built a thousand of this model conveniently forgetting the fact that 980 of them have had nothing but light use..in the aviation world it only takes one structural failure to cause everyone to rethink the design and build, boaters, not so much.

[Polux]

Originally Posted by Just Another Sa

For those who are actually interested in sandwich panel optimization, this link will contain the required math:
https://en.wikipedia.org/wiki/Sandwich_theory
For the best stiffness for a given weight, the core weight = 2/3 times panel weight, and both skins are 1/6 of panel weight. Said panel weight should not include weight of the glue film between the core and skin laminates. For example halve of a millimeter thick skins with 44 mm thick core. In reality I have never seen any hull panels dimensioned like that, all skins have been heavier and core thinner.
In reality panels are dimensioned as a compromise between bending strength of panel and point loading properties requiring somewhat thicker skins. Core density selected for required compressive properties for foams.

To replace solid laminate with a cored panel 2 times as thick and with the same weight results 6,85 (not 12) times the stiffness with 80 kg/m^3 foam and 1800 kg/m^3 laminates.
4 times as thick as a solid laminate results 33 (not 48) times stiffer with the same weight.
Both calculated using the math in the link provided above.

You mean, you are not an expert on the subject are using the wikipedia to make calculations and are saying this is wrong and your calculations right?



Sorry but I trust more on the one that posted that image on an article about foam cores (Foam Core Materials in the Marine Industry), he is an expert and knows of what he is talking about. The article is from Trevor Gundberg a Composite Materials Engineer that worked on DIAB and is now Director of Composites Engineering at Vectorply Corp.
Foam Core Materials in the Marine Industry

[nortonscove]

If a thousand of them do I assume they are successful at what they were designed to do. Fact is success leads to more success whereas as a single failure leads to drubbing by the Internet forum experts. I'm simply pointing out in misread metaphoric terms that no boat is perfect but most people feel safe sailing the one that best fits their needs that they can afford. Because my boat is massed produced and has been to Australia from the northwest atlantic I feel confident in its ability to transport me where I am going without having and engineer tell me so.

[robert sailor]

Originally Posted by nortonscove

If a thousand of them do I assume they are successful at what they were designed to do. Fact is success leads to more success whereas as a single failure leads to drubbing by the Internet forum experts. I'm simply pointing out in misread metaphoric terms that no boat is perfect but most people feel safe sailing the one that best fits their needs that they can afford. Because my boat is massed produced and has been to Australia from the northwest atlantic I feel confident in its ability to transport me where I am going without having and engineer tell me so.

I don't disagree with you generally and certainly structural failures are canon fodder for Internet junkies but it's also important to realize that many of the problems that come up on boats don't make it to the Internet.
Sounds like your happy with your choice and all is well, which it usually is, hope you have nothing but good times. R

[minaret]

When we built Schumacher's last design, "Cascadia", a 77' ultralight, it too had solid carbon skins exceeding 1" thickness in many places. And that's an "ultralight" which hits hull speeds in excess of 24 knots, designed by a legendary race designer.

[minaret]

For the record, as a guy who fixes broken boats for a living, I find it entertaining when these discussions focus heavily on grounding only as the source of damage. I see far more boats which have been hit by other boats or which have made contact with a dock, piling, or other stationary object at a bit too much speed. If you'd like a boat which doesn't have to be totally rebuilt if this occurs, stay well away from scantlings anything like this light. Or rely on your insurance to foot the bill, and make everyone else pay for it with high insurance prices...

[jimbunyard]

Originally Posted by minaret

When we built Schumacher's last design, "Cascadia", a 77' ultralight, it too had solid carbon skins exceeding 1" thickness in many places. And that's an "ultralight" which hits hull speeds in excess of 24 knots, designed by a legendary race designer.

Which, without much bulkheading and stringering, seems decidedly 'light' in a 77' boat...

[neilpride]

Its those 2 or 3 MM outer skin enough for Osmosis protection in the long run, i mean how thick is the gelcoat layer ??

[robert sailor]

Originally Posted by minaret

When we built Schumacher's last design, "Cascadia", a 77' ultralight, it too had solid carbon skins exceeding 1" thickness in many places. And that's an "ultralight" which hits hull speeds in excess of 24 knots, designed by a legendary race designer.

That boy was a master in his day, he designed some wonderful boats. I used to race in an Express 37 for a few years, great times back then.

[minaret]

Originally Posted by jimbunyard

Which, without much bulkheading and stringering, seems decidedly 'light' in a 77' boat...

Yes, and we are comparing it to the pics here of a 56' boat. Should there be THAT much difference in the scantlings?

[Just Another Sa]

Originally Posted by Polux

You mean, you are not an expert on the subject are using the wikipedia to make calculations and are saying this is wrong and your calculations right?



Sorry but I trust more on the one that posted that image on an article about foam cores (Foam Core Materials in the Marine Industry), he is an expert and knows of what he is talking about. The article is from Trevor Gundberg a Composite Materials Engineer that worked on DIAB and is now Director of Composites Engineering at Vectorply Corp.
Foam Core Materials in the Marine Industry

No, I'm saying I checked the math on wiki and found it to be correct. The same math is available in any book of structural composite engineering. Your picture includes obviously incorrect results, and any structural engineer will conform that, including Trevor Gundberg.

[Just Another Sa]

Originally Posted by Polux

You mean, you are not an expert on the subject are using the wikipedia to make calculations and are saying this is wrong and your calculations right?



Sorry but I trust more on the one that posted that image on an article about foam cores (Foam Core Materials in the Marine Industry), he is an expert and knows of what he is talking about. The article is from Trevor Gundberg a Composite Materials Engineer that worked on DIAB and is now Director of Composites Engineering at Vectorply Corp.
Foam Core Materials in the Marine Industry

How about this:
https://core.ac.uk/download/pdf/1332963.pdf
page 19/114 has the same case as your pic but with same skins, with the following results:
t = 1 2 4
bending stiffness strength = 1 7.0 37
bending strength = 1 3.5 9.2
weight = 1 1.03 1.06

As you see, strength does not remain the same, and that small increase in weight between the cored cases does not cause massive increase in strength from 3.5 into 9.2. In your pic strength is same 6 for both cored ones. How could reducing skin thickness from 50% of solid laminate into same total weight increase strength from 3.5 into 6?
That is an absurd claim.

http://www.diabgroup.com/~/media/Fil...1r2-locked.pdf
Figure 1.5 also contradicts your pic as well, if you trust DIAB more than a university.

[DumnMad]

Originally Posted by Just Another Sa

Your picture includes obviously incorrect results, and any structural engineer will conform that, including Trevor Gundberg.