Originally Posted by Brent Swain
You claim that a batten out in the open ,attached to nothing behaves the same as a longitudinal welded and contained inside a steel hull, and you accuse me of failing to understand basic engineering principles ? I have explained the principles time and time again , but each time it goes right over your head. So I'll try one more time , not for Mike , ( he'll never get it) but for other readers. When you weld a longitudinal to a flat plate, then curve the plate, it puts the longitudinal under compression, the inside becoming shorter than the outside . No, increased outward pressure doesn't reduce the ability for it to resist inward pressure. When you put pressure on the hull, and longitudinal , from the outside, the only way it can give, is for the ends to move along the plate, to which it is welded. You have suggested that it bulges outwards, which would require small angle iron compressed on end, to stretch several feet of 3/16th plate at 11,250 lbs per linear inch tensile strength. The ends are fully supported by the plate they are welded to, and the curves, which they in turn maintain.. To do that, it would have to diagonally stretch 3/16h plate, with a tensile strength of 11, 250 lbs per linear inch, 3 ft of it in the topsides.
The other is for the longitudinals to buckle. With a weld every 4 inches which has more metal than the cross section of the longitudinal, you would have to bend it in 4 inch increments, in a span of 4 inches, supported by the ends, which continue to be supported by big welds a quarter way up the leg of the angle . You would also have to twist the 3/8th by 1 inch angles . So give us your estimate of what it would take to bend the inside flange of 3/8th by 1 inch angle in a 4 inch span, then the leg, 5/8th by 3/8th angle again in a 4 inch span, held to the plate by a weld halfway up the leg. Not by direct pressure, but by pressure at 90 degrees to the direction of the bend. Add to that the support of the rest of the angle, far beyond the bends.
Or perhaps you could explain how you get pressure on the end of an angle, to stretch 3/16th plate , 3 or more feet of it, at a tensile strength of 11,250 lbs per linear inch.
Span is the amount of curve it takes to support the angle ,which in turn supports the curve. It is not an angle standing alone, attached to nothing, which you imply, as I point out above.
I remember the Joshua style boats, which Moitessier, Patrick Van God, and others, proved beyond all reasonable doubt. They had only transverse frames, which looked like 2 inch by 1/4 inch flatbar frames, ..........................
Give a man enough rope !
What I indicated was that if your proposed revolutionary theory was valid then it’s applicable to a simple beam too. All I did was show you a comparison between two beams, one bent within it’s elastic limit as in your building method and one that was formed with no pre stress whatsoever.
Under load the beam with the ‘Brent pre stress arc’ was less able to withstand a point load. All you were supposed to take away from that is that your structural argument is a fallacy. It’s as valid for a beam section as it is for a hull structure when considering local panel loads.
The other situation which is far stronger is for the inner structure to be in tension rather than either neutral or compression. That is otherwise known as a ‘pre-tensioned’. That’s stronger again. Your method puts the pre-tensioned bit in pre compression, what that means is that it assists the arc in straightening out rather than resisting it. Your arguments are inside out, and simply wrong. You were claiming all over the place that it was a structural arch but that was also shown to be a complete fallacy.
So again your 36 footers are apparently strong enough but they dent easily and with large dents under relatively low level impacts than they should, so they are not tough in that regard. But for everyone’s sake, before you start promoting 60 foot versions of your boat, go ask anyone with a bit of real structural knowledge. Try and find anyone other than you that thinks this is a valid argument. Even load test a structure yourself.
Importantly and sounding like a broken record ….Your method doesn’t make your boats stronger, it makes them weaker than they could be and more prone to large denting from point load. For real strength the plate should become a diaphragm under load so that it is in tension and that takes adequate framing.
And again: You just don’t understand buckling at all it’s got nothing to do with tensile or compressive material properties nor the tripping of the stiffeners, it’s about ‘snap-through’ instability of the hull.
As for denting 5 or 6mm plate with either a sledge or a pick next to a frame you are deluded if you think you could put a hole in a hull with either. And as I said where are these properly framed boats that holed so easily? They are just in your imagination, it’s just not a valid observation.
I also said grillage can yield before the plate ruptures which is why Gringo didn’t have any holes in her plate. Gringo was also extensively transversely framed. And you use the Gringo example for your own ends at times so she is a good example of how transverse framing keeps the plate in place so it can take stress rather than simply buckling under a far lower load which takes far less energy and is far more catastrophic.
Now lets look at rotating keels into the hull once again. This is a significant issue, you know very well there were more boats built to your own design than the tall tale with an unnamed boat, unnamed owner, and variable location.
It shows that your presumed strength from curvature didn’t exist and that the supporting plate buckled easily in low speed collisions. It’s a good example of intuition being wrong, no different to your intuition that your design could scale frameless to 60 feet. When in reality anything much over 40 feet would be inadequate to meet any sensible offshore design head requirements, and would be significantly prone to grounding damage.
As for Lawyers telling you your designs are safe; lets presume for a minute that is true, and the Lawyer actually said that, (which I doubt with your record). What do you think that lawyer would say if you were the designer of a 60 foot design that just killed it’s crew and that expert professional witnesses were testifying that they had told you that your design was inadequate, and that your understanding of structures was abysmal ?
All the tall tales of incredible strength tend to ignore that fact that most of the boats involved were not built to your design but had more transverse framing. For example the NW passage boat you use for vindication had both thicker plate and extensive transverses not in your plans. In fact I’d suggest that most of the BS boats built have significantly more framing than shown in your plans.
Then you have the temerity to compare other designers plate first then frame construction method with your design and pretend it vindicates your design methodology. And now Joshua !
Bernard Moitessier’s “Joshua” that you mention had deep floors (transverses) and closely spaced transverse frames from the floor to the deck beam which were fully ‘fixed’ at both ends tied into floors and deck beams ( end fixity of 1 ). So you are way off likening Joshua to your designs or saying she had minimal framing she was a very strong design.
The fact is that you made dangerous assumptions in the presumed strength of your construction method. Those assumptions are wrong. I've asked you before and I'll never get an answer becsaue you simply don't know....What head of water do you think would collapse the fore-part of your 36 footer ? How about a 60 footer ? Why is this important? Do you know?
Your stability arguments are also hype, your small steel designs are on the tender side and the best estimate of AVS is closer to 135 degrees than the 180 you initially touted. That’s just a by product of using steel for small boats.