Realistic scantilings

Terms may not be clear

M&M Ovenden, MikeJohns, Brent

I've had discussions with our esteemed "virtual colleague" in other venues and do admit the Brent can be a bit less than willing to agree to any other point of view- separate from his own.

However, I noticed a few items that may be unimportant but wanted to remark to Mike about them so that these points are addressed in his great "theory of metal structures for the non-engineer" post.

One item Brent keeps mentioning is how the longitudinals inside the hull are in compression which he alleges is a very significant factor in the stiffness of these hulls- and that results from how the longs are installed.

Before the flat half hull shape is pulled up and even before the 'dart' amidships is drawn in, Brent welds the longs to the hull plate- flat. This is a bit different than adding them after by plating over them since they're welded flat to a flat sheet.

So when these longs are welded to the hull first, then the hull half is drawn in at the midships 'dart' and finally pulled to the centerline to meet the other half- well that does seem to compress the longs in a way that is unique to this method.

Sprung around ring frames they're in tension and that may relieve when welded to the hull. If they were added to a hull after the hull were tacked up, they'd still seem to be in tension along the outer edge anyway - but here they seem to be compressed by the curve of the plate after they're welded to that plate- while flat.

I'm not defending Brent's poor manners, they're posted for all to see, and I've mentioned to him in the past that his anecdotal accounts are meaningful only if someone is the exact circumstance- but I did want to say that his idea of compressing the longs probably comes from the sequence in which they are added in this method of construction.

Now, are they 'magical-longitudinals' as a result? No, I'm not saying they are but I wanted to note this in case Mike is willing to reflect on the effect of this sequence of assembly; good, bad, or no effect from deforming the hull with the longs already on the panels when you pull them into their half hull shape?

Mike, if you have time, I'd surely appreciate any continuation of your remarks which have been very informative and I've enjoyed greatly.

Thanks for the explanations you've provided.

Cheers,
kmorin

 

KMorin

Thanks for explaining that, initially the inner will be under some compression and at least something is clear,I can see some of Brent's reasoning now.

However this pre compression is only induced within the member itself from internal stresses and it does not increase with external load as in an arch but shifts quickly into tension (and of course in makes no difference to shear ). The pre-stress will add local stiffness, but very little in the way of global strength when you consider once again both the element thicknesses and the relative radius of curvature.

By way of basic illustration:
If you made a beam on the flat with the longitudinal stiffener and add the plating with width of 15 times its thickness as a flange over the length of the beam (vessel length ?) and then draped it over a formwork representing the vessels side. After affixing the stern end, I suspect a 5 year old could pull it into shape without too much effort . In reality this is the level of pre-tension added strength from the longitudinal that needs to be overcome before it acts as a normal beam................virtually zilch.

The longs are helping fair the plating curvature and acting as local stiffeners but they are not global strength members.

To be significant the longitudinals would need to be both large in section and without any transverses they would need to be very well supported (from tripping).

Structural collapse is a lot more complex than this and there are other factors at work which are more of a concern with a semi stiffened monocoque without any transverse support. Suffice it to say that I am very skeptical that larger vessels will have sufficient global hull strength built to this method. ( Brent was talking in another thread of up to 50 feet). I would stick to mid 30's with his designs.


Cheers

 

They only go from compression to tension when the arc disappears and the surface becomes flat.
50 ft origami boats have endured a lot of torture tests, with no structural problems whatever.
It is always amusing when someone states that something that has been working well for decades , and many torture tests " Won't Work".
Brent

 

Brent
The surfaces are fully restrained by adjacent elements. All that is required is for the locally applied force to be greater than the relatively low local pre-stress and then you are immediately back in conventional failure analysis.
Neither the curvature nor the level of pre-stress is enough to count as structurally significant relative to the types and magnitudes of applied loads and forces that we actually design to.

I would be very wary of a 50 foot hull If they really have been designed and built the same way. It is possible that their design strength will be well below accepted standards.

Anecdotal escapades are not a good basis for vindicating a design. If a designer wants to argue a different and specific construction method it is always up to the designer to prove the point with a proper analysis.

The idea of existing scantling rules is that they have been modified over time to take all this into account through both refinement of structural requirement and a detailed analysis of failures. If you vary from these methods you should have more than personal viewpoints to support your arguments, in other-words you should be able to show by detailed analysis that you have an argument worthy of consideration.

 

Tens of thousands of miles in some of the roughest waters on the planet is a very thorough analasis, far more thorough than mathematical theories. The sea has a way of finding the fatal laws in your theories ,quickly , and their naivete.
For safety I'll take the sea torture test over your mathematical theories any day.
Brent

 

and why argue further

 

I have far more than personal viewpoints . I have over 200 boats built to my designs that have sailed all over the world , many times in extreme conditions and which have survived many torture tests that would have quickly and easily destroyed many boats that your numbers rate structuraly sound. Few , if any owners would want anything else. They rarely come up for sale.
If there is a weak point , hundreds of thousands of ocean miles will definitly find them , which is not neccesarily the case with your math.
Mathematicians have approved the space shuttle . How many of them have we lost ,percentage wise.
Your calculations say that most fibreglas boats are structurally sound and most approval agencies like Lloyds, ABS , etc aggree. So lets take a Lloyds or ABS approved fibreglass boat and have a demolition derby against one of my unapproved origami boats and see who wins.I wouldn't bet on the approved boat. So much for the credibility of their theories.
Brent

 

Brent,
I'm no naval architect, far from it, but this has become ridiculous - you even go as far as using something that looks very much like the McDonald's argument (an explanation will follow).

Really? Yes, one might think that on the surface, but the reality is, that many boats and boat types have sailed 100s of thousands of miles, with nothing happening. Until disaster struck and the people injured, killed and lost. All because of a flawed design that eventually opened up for disaster.

Sorry, but with that argument, an open boat could be argued to be great for arctic sailing.

Funny, I prefer both.
Think about this (as an example): You can sail quite a lot in a boat that is build out of plaster, has quite a lot of initital stability, yet when encountering a certain type of sea state and wind force, it will roll (degree of vanishing stability, I think it's called in english?). Now, to makes matters worse, there's a hell of big hatch, set to starboard, so when it heels 80 degrees to starboard, water will enter, making the turn around even faster.
Now, the "designer" used the same argumentation that you do: Namely, that maths sucks, and science is no better than pocket theories, and so he didn't calculate how that extra weight would influence the stability, nor when the boat would roll, nor did he take into account that he would need to make a means to get out of the boat.

Now, such boats exists, and what you're doing, by way of "argumentation", is saying that we don't need anyone to calculate these matters. Because, as you imply, science and calculations can be wrong, thus everything calculated is useless.

First of all, hundreds of thousands of miles have been sailed in less than ideal boats. You're simply spewing anecdotal "evidence".
Hell, Joshua Slocums spray was anything but a seaworthy vessel, but by your argumentation it must be a boat whose "qualities" is to be copied.

Secondly, your point about your designs rarely coming up for sale, and therefore they must be seaworthy, is using statistics as the devil reads the bible. There can be numerous reasons for why your boats rarely come up for sale (how do you even know, btw? Those boats can be sold without you knowing, and without being advertised, for all you know). One of the reasons might be that circumnavigator boats people build themselves rarely are sold off. Or that the boats themselves won't fetch a good enough price. Or numerous other reasons. Besides, them not being sold is just a claim on your part, evidently to support the notion (by you making a logical leap) that they thus must be seaworthy.

Third, the McDonald's argument: Many people eat at McDonald's so it must be healthy, wholesome food. Now, compare that to: "Many people have build my boats (200), thus it must be a seaworthy design". Now, go a take a look at a bayliner or a sea ray. They must be many times more seaworthy than your design, if we're to follow your argumentation.

Read my example above.

Show me to a place that will state that it was because of poor math the shuttles were lost. Do that, and then you might have a far fetched point. However, even if you could (you can't), it wouldn't prove that math and scietific theories are flawed, even though you wish it so.

Ah, yes, because a demolition derby will certainly prove anything. Besides, it's a free suggestion, well known in the political world. The reason being that you know full well that a demolition derby will never happen, and so does the reader, and because of that, you somehow think you have "proved" your boats are perfectly seaworthy. "because otherwise, the opponent would have agreed to the derby". It's a logical fallacy, and even worse, it's intellectual dishonesty.

Now, you might conclude that I'm against not following "the rules" – that I'm against thinking out of the box. Well, I'm not. What I'm saying is that if one has to break proven rules and go against established facts, math and science, one better be able to argue one's case. If not, you're simply not trustworthy intellectually.

In fact, the argumentation reminds me of the creationists' ditto, who simply denies science is fact based, and if they can find one scientific fact that is later proved to be wrong, then all science must be wrong. And that, Brent, is simply honest ignorance (in the best sense of the word) or intellectual dishonesty.

 

Pick ax, sledge hammer, torture test, fiberglass boat....that triggered a little souvenir from last summer I thought of sharing. I'm not quite sure it fits on this thread so I posted it in materials. I wasn't really trying to make a point, just share an experience.
But if there was a point to be made it would be that a well built fiberglass boat could surprise the most hard core steel lovers, I was surprised myself by a not so well built composite hull.
Yes, Brent I realize that a sound steel boat can make a lot of damage to a fiberglass boat.

http://boatdesign.net/forums/showthread.php?p=203512#post203512

On an other note. Their seem to often be confusion on the reason being of construction rules, regulations as scantlings or approved welding rod, metal grades.... Those rules are not saying that nothing else will work, they're providing a solid base to guaranty quality. As previously mentioned those rules were established over time and based on experience ( not 200 boats.... just a few more over history). Numbers have come in play only recently. They have greatly improved our capability to translate experience from older technology to new ideas. Numbers are only a language used to clearly compare and describe physical properties. The numbers complement real life experimentation by greatly reducing the need for destructive test to find the material and structure limits. Real life situation still teaches a lot. When an accident happens, the situation gets analyzed and translated into numbers to improve regulations. The numbers don't stop evolution or new ideas. Number crunchers would become useless if there were no new ideas to crunch numbers on. Presented properly with a good argumentation a new idea can lead to a new standard.

Murielle

 

Yes, you start with mathematical calculations, then apply experience and logic , letting experience and logic overule when the two disaggree.
When math says a boat won't survive pounding across 300 feet of coral in a 12 foot swell or pounding 16 days in 8 ft surf on a west coast Baja beach or bashing thru the NW pasage in a single season, and survive hurrcane force winds in open ocean, yet boats repeatedly do with no damage, then your math is definitly wrong.

 

Had a a big response typed up and got cut of again. SOB.

A demolition derby will definitly prove which boat is the tougher one, beyond all reasonable doubt. Are you suggesting that in a demolition derby, that the boat which breaks up and leaves the other relatively undamaged is not neccessarily the weaker one , if your math decrees it to be so. That is self delusional. Of course such a demolition derby will never happen, because anyone with a fibreglass boat knows he won't stand a chance , thus conceding my arguement. All he has is theory, which he doesn't trust enough to put to a real test.
My boats that have sold , were all sold for far more than the owners had invested in them. Several 36 footers have sold for over $100,000 , and even roughly finished ones sell for around $65,000, still many times what their owners had in them. They all pass survey with flying colours , and several have been built under the watchful eye of well respected surveyors. The coast guard have admired and praised my boats, calling one the best built boat they had ever seen.
When people started building boats out of steel, all they had to go by were wooden boatbuilding traditions , which they became hidebound in, and have been ever since. Thus the formulas they came up with were arrived at on the assumption that the boat would be built using dinosaur wooden boatbuilding methods, methods that were developed for dealing with a material that only had real strength in one dirtecton ,and overal shape was less relevant than in a monocoque material. Thus they have held back steel boatbuilding, ignoring the many advantages steel construction has to offer. This is why one off steel boats are so expensive and time consuming and thus not more common.
I have hit origami hulls as hard as I could with the biggest sledge hammer I could find without dammaging anything. Been there, done that, many times.
Space shuttle ? Did they not use mathematical calculations to determine that the foam would never fall off the fuel tank and damage the shuttle? Did they never use math to determine that the O rings on the booster would never fail? If not, why not, given the huge amount of mathematical resources the space industy has ,and the predominant belief that math can determine every eventuality? Numbers must always withstand the test of logic, or become meaningless.
McDonalds? Go see the movie "Supersize Me". The proof is out here , like the poroof that origami boats are sound. Those who choose to ignore the evidence are suffering , just like those who ignore the well proven success of origami boatbuilding, and hire someone to waste their time and money on outdated building methods, and end up giving up years of cruising to pay for such wastefullness, or someone elses playtime.
My niece was learning to read . Her father was passing a McDonalds. She read the sign, turned to her father and asked "What does 10 billion survived mean?".
Brent

 

Funny, logic is deduction, and by definition applied math in the simplest of ways. All you do, is use some anecdote as "evidence" and then use conjecture to apply to all. As I have mentioned earlier, by your logic (as in deduction/reduction), any anecdote will do to prove things are perfectly safe.

See above: By your "logic", it's perfectly safe falling out a five floor apartment window, because the anecdotal evidence is there. Me, I think that's cutting it a bit too close.

Did you contact Jeff about this issue? You really should. Otherwise, type it first in textedit (or notepad, depending on your platform), then copy/paste it here.

Depends – are the boats rammed in the same position? Are some "overbuild"? Are some made especially for this demolition derby? Are some basically unmaneuvrable, and thus more susceptile to be rammed and on and on. There are many variables. Further, when we're talking about your designs, did you calculate the vanishing stability on them and is that available? How about flex? Did you calculate that? Too much flexing would mean it would be much weaker after a 100.000 miles, all things considering. You so want a demolition derby, even after I pointed out why that is nothing but rhetorics in order to convince the less than brilliant out there (yes, yes, it's a joke, alright – I'm not full of myself. It's just that when even I can see through empty claims, everyone ought to be able to).

See above. Even now, you have made nothing but unfounded claims. Even the rhetorical demolition derby-winner is just conjecture. We haven't held one, but in your argumentation yours will come out the winner naturally.

See above. You know what is self delusional? It's self delusional claiming that some design and method you thought up is by definition better than "old school methods. Especially seen in the light that although you claim as much, you have provided no proof, no valid arguments, no nothing. Except, of course, your anecdotal evidence. Fifth floor drop-out, anyone?

Oh, haha, this is rich! That is the exact logical fallacy I warned about, how one would only put forth the demolition-suggestion, if used like this! Excellent! You just proved the point, that it's mere rhetoric, a logical fallacy, a strawman:

Now, okay, to follow your reasoning:
I have a very small strip plank open boat. It's five and half meter long, plus a two meter bow sprit. I will gladly put this to the test. Now, provide with your toughest build design, and we'll have a demolition derby on our own. What's that? You aren't willing to pay for the trip to Denmark, not to mention the transportation of the boat? Surely that means your boat is far inferior to mine …

Great to see you continue this Erasmus Montanus-route (Mother cannot fly, a rock cannot fly, ergo: mother is a rock).

Still naught by claims from your part. Claims you have yet to make into valid arguments.

Oh, man, this really shows how ridiculous your argumentation is! You actually think you can argue that everything build today is built like that because engineers still think they're building in wood? And that, by extention, you're the great saviour, having come up with this "radical new method and thinking"? Come now, you cannot be that full of yourself, and at the same time be that ignorant.

I have tried the same on a "fake" side of epoxy strip-plank (don't want to screw up the paint job) What's your point?

No. They used math, and then they tested the thing. But as you know, crap things happen when people butt in. In this instance, the surface was either not very well prepared, or they had a crap batch of glue. Just like each and every other of your anecdotal evidence, this doesn't prove that math can be disregarded in any way, form or fashion.

No, they certainly did not. Noone used math to prove that anything would never fail! What the hell are you trying to say with such a horrendously stupid strawman argument? Where do you get you information from? Do you know what "applied maths" are?
The O-ring failed, not because of poor math, but because no-one told anyone needing to know that the material used for the rings had been changed.

Okay, first of all, you need to read up on the failures of the space shuttles. Secondly, you need to hone your skills when it comes to deduction, and make damn sure you're not using logical fallacies and therefore do all those leaps of logic you do constantly.
Thirdly,

You really don't get it, do you? I don't need to see that film in order to realise that McDonalds isn't a wholesome diet. That's my point exactly. The "McDonald's argument" is a way of showing people, why their logic is flawed, because everyone can relate to McD. It's a parallel for crying out loud. Just like my Sea Ray-example was a parallel. I could have said "You know what, there are sold more in walmart than any other chain, thus the best quality must come from there", or "Sea Ray and Bayliner sells the more boats than any custom builder, therefore they must be much better quality than any and every custom builder out there"<-- THAT, Brent, is "The McDonald's argument". It has naught, zero, zilch, to do with McDonald's.I'm amazed you didn't even get that.

Ah, yes, you're the saviour of the boat building industri …
Seriously, though, even though the term "anecdotal evidence" contains the word "evidence", it doesn't mean it's anything but "anecdotal", and anecdotal evidence really is just anecdotal.

I could build a bath tub with a lid and a stick and propably sell it too. That doesn't mean a well calculated hull, with proven scantlings and build methods is inferiour to my bath tub or in any way obsolete. It just proves that there are idjits out there willing to buy into anything, as long as someone is just making claims often enough: Hence christianity, judaism, islam, scientology, Jehovas Witnesses and any and every other sect out there. The number of people buying into unfounded claims doesn't mean the claims are suddenly founded.

Yes, very apt when it comes to McD. You seem to forget, though, that I pointed out that _you_ used the McD-argument to prove _your_ boats were sound … In effect, you could then say that very thing about your boats

 

Origami's Features

DanishBagger, MikeJohns, M&M Ovenden, Brent, all

I've given up some time past trying to hold the Brent to logic, as he's not so inclined. So I don't spend too much time over the noise but I do listen for any good information under the roar. Looking for nuggets among the less valuable rocks, so to speak.

The one aspect of origami that interests me is the shape issue compared to the other method of building.

As a function of the method of hull surface forming all the shapes ahead of the middle 1/4 of the hull and all the sections aft are more or less conic so the waterlines have to be much more straight than convex.

Given this severe (in my opinion) shape limitation, will there be a gain or loss to the same LOA/Displacement& B/L ratio hull's performance?

My sense is that the more fully convex curved shapes will have a dryer deck, perhaps not enough to notice? [As a non-sailing boater, I rejected the origami limits to power boat hulls although I use a vaguely similar method of construction.] I also sense that hulls with a more full waterline plan view curve will have a more rapid bow pitch in a swell, and that might be so slight a shape difference not to have any net effect?

Are there aspects of the method's legacy plate developments that are beneficial or detrimental to performance of a sailboat?

Cheers,

 

I feel somewhat obliged to reply, since you mentioned my name. First, no less, ha ha.
The thing is, I'm not a naval architect, nor a "seasoned" boat builder by any stretc of the imagination, but the way I see it, is that the way Brent is building (disregarding the utter lack of analysis and calculation) is that when build like that, the boat is gaining strength only from the form, meaning a hull too long, thus making the hull sides flattish will make his "design" loose a lot of rigidity and gain a lot a flex (which you don't want, of course). Further, the problem with the methods Brent's using, there's a somewhat set limit to how the hull can look, since it relies on hull-form almost exclusively (anyone who actually knows about this stuff, please reply and correct).

Speaking of hull-form: all things equal, a smaller hull will inherently be stronger than a bigger one (less flex because of less surface etc).
I think it was Murielle, who argued that a boat of 50 foot, built with Brent's methods wouldn't have the structural rigidity as the smaller design, and for all I can see, it seems about right, because at those lengths the plates are more or less flat, leading to flex, leading to fatigue. Well, that's how I read it, anyways, and if I misunderstood it, it's still pure logic. The convex shape is what makes an egg strong, after all.

Now, trying to answer your question about a dry ride the best I can as a pure amateur: I don't think one can say that a certain building method will give a dryer ride than some other method. It has to depend on design and basic hull-form, freeboard, speed, flare, flam, whether the boat is prone to hobby-horsing, have a slender stem and so on.

Now, would I go as far as far as warn against Brent's designs? Yes, I actually would. Not the building methods as such, but the very designs. The reason being, that if you go by something from him, he's indirectly admitted to having his customers check to see if his boats are seaworthy, and he has not calculated how well they do if knocked down. Those things has to matter if you're going to encounter harsh weather.

Please take the above with a grain of salt

 

I said it before and will say it again....

Firstly, if the numbers of boat plans Brent mentioned have indeed being sold / built, one must ask why?
And herein, according to my humble logic, lies the fact at whom it is aimed in the first place; people who want a build a boat, have limited or no steel working skills at all, knows nothing about hull lines as such and wants it pronto pronto. People prepared to pull a hull together with sledge hammers, chainblocks and what else that comes to mind.

Should you present to this "group" of people a set of chines/multi chine, or radius chine, round bilge or origami plans, what would they pick? Even more so if they can be convinced by some questionable facts and figures by someone.
I had seen photos of origami boat being "assembled" and the whole exercise reminded me of hillbillies at work - no offense meant to anyone.

But back to the spirit of this topic - realistic scantlings; when I do a design, I supply my client with proper scantlings and as is the case with the 43ft gaff schooner on my drawing board currently, I showed my client my calculations and explained it to him in person how it was derived at and the dynamics involved. These calcs are based on scantling rules and recommendations that are proven and adapted over times. This gave my client (and myself) a sense of security to know the numbers and specs were not thumb sucked. With that goes proper stability calcs and graphs to name but a few.

Question, as seen with the arguments and logic from Brent, does he supply the same to his client, and if so, how did he derive at the numbers:?: