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  #421  
Old 08-06-2013
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Re: Pros and cons of steel sailboats

Starling Burgess Little Dipper.

Great book about her by Richard Baum, By The Wind.One of the many books I read when I should have been studying math.
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  #422  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Jeff_H View Post
Mark,

I'm not sure that Brent's math is as wrong as you may be suggesting. My assumption is that Brent is using something like an A572 which is a high-strength low alloy steel which has better corrosion properties and more strength than A36 which you mentioned, and which has a tensile yield strength in the 60,000 psi range.

Brent said,"That is 11,250 lbs per linear inch for 3/16th plate. Multiply that by the 96 inches in the side of one of my twin keels." And in that regard, something like A572-60 that was 3/16 thick would have a tensile yield strength around 11,250 lbs per linear inch. (60,000*3/16= 11,250) His arithmetic is essentually correct.

The problem is one of how the is applying that math relative to proper engineering principles contained in Brent's metaphoric description of:
"That is 1.08 million pounds per side, times four keels sides.
How are you going to break that with a boat under 20,000 lbs?"


This metaphor assumes that the loads are shared by both keels equally and that the loads are solely in tension. Neither is likely to be present or likely to relate to the actual failure mode of the keel.

The more probable failure modes for a frameless keel connection would more likely be some mix of buckling of the keel sides in compression (skinny column failure), sheer where the keel sides try to cut through the hull plate (as you noted in your comments), or bending of the hull skin perhaps coupled with lamellar tearing near where the hull meets the keel since the hull plate would be in bending due to the large lever arm formed by the depth of the keel and the narrower width of the keel root being resisted in bending by comparably thin plate.

But beyond that I also want to touch on Brent's Herreshoff reference.

I am not sure that its clear which Herreshoff Brent is referring to, but by and large all of the Herreshoffs were consumate engineers. Nat Herreshoff and Herreshoff Manufacturing developed their own formulas for many of the calculations involved in properly engineering a boat. At a time when boats were 'engineered' by rules of thumb, Nat did his own scientific research and developed his own formulas based on his research. And he used these formulas to design some of the most sohisticatedly engineered designs in that era. He later boiled those down into his own set of widely used rules of thumb, but these were heavily based on proper engineering based methodologies.

L. Francis began his carreer working with Nat as a designer at Herreshoff Manufacturing but did the majority of his apprenticeship working beside Starling Burgess and Frank Payne at Burgess, Swasey & Paine in Boston. Burgess was one of the most creative, multi-discipline, engineering-oriented designer/ inventors of his day. Burgess was a brilliant mathematician who was able to do high level scientific research, then develop mathematic equations to explain the observations and ultimately literally wrote the book on a wide range of early 20th aeronautical engineering applications.

In yacht design, Burgess literally developed sophisticated formulas that replaced the crude rules of thumb which preceeded his time. Starling Burgess working with Glenn Curtiss was key to the design of the first successful seaplane (only a few years after the Wright Bros first flight), he designed three America's Cup winning defenders, he designed the first successful aluminum masts, he designed many of Buckminster Fuller's so called Dymaxion inventions (car and house being most notable), (and designed 'Little Dipper' for Bucky, one of the most beautiful little cutters of all time), as a kid in the late 1800's he designed one of the first light weight machine guns, he also is thought to have possibly/probably designed the Times New Roman font, wrote poetry, and novels, and produced world class paintings.

And L. Francis learned his trade at Starling's side and along side of Frank Payne as well. And Frank Payne was no slouch either when it came to sophisticated engineering. There was nothing even slightly shoddy about L. Francis's math or engineering skills.

But of all the Herreshoffs', L. Francis would be the only one that I could imagine who might write negative comments about engineering formula. I can imagine that since L. Francis was known for writing things that he thought sounded good and doing just the opposite. (Like advising adult sailors that they had an obligation to take children sailing and teach them the ways of the sea, when L. Francis notoriously hated kids and hated being around them.) So, if L. Francis was dismissive of the crude formulae of the day, it was only because he and his close life long friends, Starling and Frank, were beyond the quick and dirty engineering methods that he decried.

Sidney Dewolf Herreshoff was a graduate from MIT in engineering. 'nuf said. He used the numbers. Halsey Herrshoff has an undergraduate degree from Webb Instutute and a masters from MIT, I have to figure that he uses the numbers as well.

Please, lets try to keep the historic references close to what is actually known about these people.

Jeff
Jeff, my view on this came out of the formula for calculating bridge impact or impact on structures, as well as knowing that Brent said "mild steel" and looking at a photo of a BS boat, I can see the steel in it looks pretty ugly, and the whole thing looks pretty cheap. The problem with Brent's calculations are multiple, but the main one is that he is not working with the whole picture, his 1.8 million PSI calculation is not going to work out like it seems it might. First you have to remember that he may or may not be working with the steel you mention, my guess is that he is not, simply because it would be expensive, and his costs that he has quoted were dirt cheap. The second is that the 3/16 is on edge, now that might seem like you could multiply things out and come up with a higher number, but if I am remembering right you should not do that, because of point loading. I think, and I may be wrong, that you would actually be increasing the shear load on the hull by having the edge being like a knife or a metal shear...

The real issue is the impact forces being way above what he thinks they will be, somewhere on the upside of 250,000 psi or more, and probably a lot more, I hate to admit it but I have such a headache right now that I cannot do the math without a blackboard and chalk. You might look here and see if you can do it for us, the formula is right here. I was trying to read over it again, and I will get back to it, but the force is going to be far more than you would think.

Guide Specifications and Commentary for Vessel Collision Design of Highway ... - Aashto - Google Books

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Last edited by tdw; 08-06-2013 at 10:12 PM. Reason: Reduced Image Size
  #423  
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Re: Pros and cons of steel sailboats

Nice boat.
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  #424  
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Re: Pros and cons of steel sailboats

She's a beaut.
  #425  
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Re: Pros and cons of steel sailboats

Do any of those boats actually float or sail? Or are they just always banging on hard stuff?
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  #426  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by smackdaddy View Post
Do any of those boats actually float or sail? Or are they just always banging on hard stuff?

I think there were some of the photos that were floating, but of course I could not see the keel on those.


I just keep going over the stress loads on that keel at impact, the question in my mind is why is the hull not thicker, especially in light of the fact that the boat is frameless, the impact stress is going to be high, especially since as I understand it from Brent's earlier post that the keel is filled solid with lead. My thinking is that this would make the keel a little too rigid, meaning that it would concentrate the point loads on the thin hull plating which should be far thicker than 3/16" along the keel area for the entire length of the boat.


I am still trying to get my head around the way this design is supposed to look, and why it would not have a thicker plate in this critical area. My instincts tell me the design is flawed on several levels, and only good fortune and the short length of the vessels has prevented issues that would show up if there were more than 50 of them built and actually sailing. I know that in some cases as much as 1/16" of that 3/16" hull thickness will be lost to corrosion, and even though the owner might paint on the hull coating thick as can be, which I also think is a poor design idea, heavy coating should not be considered a part of the vessels normal hull conditions. It should be coated appropriately, and done very well, but not put on extremely thick because thick hull paint will actually not last as long as properly applied coating will last. The paint that is super thick as Brent has described will actually be subject to damage due to the weight of the coating itself pulling the coating loose from the steel.

So, a thicker hull along the keel load areas for the length of the boat with frames to spread the moment. A hollow keel with heavy walled pipe to reinforce the leading and trailing edges, and lead or cast iron bulb at the base. A very well prepared and properly coated hull with a better finish and proper thickness of ablative hull paint for the bottom, and you are starting to get a better boat, but you still do not need to grind it on reefs, crash it into cargo ships, or any of the other abusive treatment Brent's clients seem prone to do so often.

As I read Brent's answer one more time I see he thickened up his keel to 1/4" in his last post, but I am still thinking that is very thin for the keel area. I do agree with Jeff H about columnar failure being an issue with the frameless design, make that boat 50' long and you have a boat with huge issues hogging and sagging, and you would have to stiffen it with a lot of bar stock welded longitudinally and frame it to keep it from warping the deck upwards and downwards like an accordion bellows, I guess you could use that for ventilation, the boat that breathes. When you factor in the mast weight flexing one way, the keel weight flexing it the other way, this design is going to beat the everliving crap out of you in short period waves.
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  #427  
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Re: Pros and cons of steel sailboats

sorry about making the page fat, it was Brent's boat picture that did it.
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Re: Pros and cons of steel sailboats

If I post one more maybe that will move us
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by jak3b View Post
Starling Burgess Little Dipper.

Great book about her by Richard Baum, By The Wind.One of the many books I read when I should have been studying math.
Those are nice photos, I was studying math when I should have been reading, and reading when I should have been studying History, and well I did not get much sleep in college, 22 hours a semester plus a full time job.
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Re: Pros and cons of steel sailboats

My dad and I read 'By The Wind' when my dad and I were learning to sail and I was a kid. It shaped my whole view of sailing and voyaging under sail. To this day I think of Baum's stories pretty often. Around 10 years ago I reread the book again and happened to notice that Baum mentioned where he lived in the foreword to the book. On a whim I looked him up on line and called the phone number. His daughter answered the phone. Richard Baum had died shortly before and they had sold the house and were cleaning out. The marriage to Lucy did not last but he sailed for most of his life. Little Dipper was owned by a curator at Mystic Seaport for a while and I spoke to him for a bit when she was for sale. By then she had an engine again.

Jeff
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