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  #411  
Old 08-06-2013
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Re: Pros and cons of steel sailboats

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Originally Posted by bobperry View Post
Jon:
I like to think I have ears that good. I can hear my dogs fart.

lucky?
Sorry Bob, I could not resist it... I usually blame the dog too.
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Re: Pros and cons of steel sailboats

Mark:
"Brent, I hate to tell you but your math is extremely flawed."

Yeah but,,,you have to give him a B- for creativity.
While his math was wrong I found it entertaining.
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  #413  
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Re: Pros and cons of steel sailboats

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Originally Posted by bobperry View Post
Mark:
"Brent, I hate to tell you but your math is extremely flawed."

Yeah but,,,you have to give him a B- for creativity.
While his math was wrong I found it entertaining.
Hmm, none of my professors in any of my math classes would give me grades for creativity, well not good ones LOL. I will admit that his idea of how to multiply the length times the whatever and come up with the something times the square root of the thingy was just about the best example of the old saying "If you cannot dazzle them with your brilliance, baffle them with your BS" I have ever seen.
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Re: Pros and cons of steel sailboats

Bob- two evenings ago was sitting on my boat after wonderful daysail and a lovely dinner listening to BB and Eric singing and playing duets through a Boston acoustic system with a killer woofer watching a delightful 4y.o. dancing with my bride. The Henricks was pretty good as well.We're trying to brake him slowly as crew. Hopefully, he will be able to set the pole. Think even with gimbals no way to put an analogue system on the boat. Oh well.
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Re: Pros and cons of steel sailboats

So, wait, if I add up the lineal inches for every Brent boat that's ever been built, isn't that, like, in the billions?

Dang. Those are some strong boats.
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by bobperry View Post
Mark:
"Brent, I hate to tell you but your math is extremely flawed."

Yeah but,,,you have to give him a B- for creativity.
While his math was wrong I found it entertaining.
Some P.C. elementary teachers refer to a kid who can't spell as a "creative speller".

Wrong is wrong - period.
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Re: Pros and cons of steel sailboats

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 using engineering formulas. 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
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Last edited by Jeff_H; 08-06-2013 at 09:29 PM.
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Re: Pros and cons of steel sailboats

In an odd way some of Brents rants remind me of some of L. Francis's articles.If L. Francis had flipped his gull wing benz and suffered a traumatic brain injury.
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Re: Pros and cons of steel sailboats

Jeff:
I'm just jealous that you got to hang with those old guys. It must have been amazing. How old are you? 244? You don't look a day over 67.
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Brent Swain View Post
Mild steel is 60,000 PSI tensile and compression strength . That is 11250 per linear inch for 3/16th plate. Multiply that by the 96 inches in the side of one of my twin keels. 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?
Just saw two navy 100 footers in Heroit bay. 3/16th hull plate on 100 ft navy ships . And you say the same plate thickness is too light for a 36 foot pleasure boat? You say that a boat which could survive 16 days pounding in 8 to 12 ft surf on the west coast of the Baja, or pounding across 300 yards of Fijian coral reef in big surf, or colliding with a freighter, or hitting the sharp corner of a sunken barge at hull speed, all with minimal damage, is not strong enough? Now that's a stretch!
My hulls are all single thickness, 1/8th for the decks cabin, etc, 3/16th for the hull ,1/4 for the keel sides, and half inch for the keel bottom ( with 4500 lbs of lead ballast poured on top)
Layering steel is a big mistake, guaranteeing corrosion between the layers unless totally sealed.

A good whack with a sledge hammer and a centre punch on lower parts of keels, etc, where corrosion is most likely, is a good starting point on buying a steel boat. If it doesn't give, you have enough thickness there.
Structural failures of steel boats under 40 feet are extremely rare. Your "Invisible " fractures have zero chance of ever causing any problems in steel boats under 40 feet in their lifetimes.
How does such "invisibly fractured" steel compare in strength to a copper fastening in red cedar every six inches, or six inches of plastic?
Okay, let's address the math here....

First we need know that to figure the force of the impact, we are going to have to calculate the Impulse of Force, which is the force of the impact in PSI in this case over the period (length of time) of the impact. In order to know the force we have to know the weight, the speed and the size of the impact point, and to get the Impulse on that we need to know the duration.

From there it is a simple little calculus problem, and we can get it all done in just a few minutes. So, we figure that the length of one of Brent's keels is about 60 inches long by 6 inches wide at the point of contact. ( I tried to look up some of Brent's designs on sailboatdata.com like I do with Bob's or Roger Long's but I found this photo, and I am just kind of guessing on the actual length, at the end of the story it won't matter.

So we have a weight (per Brent) of 20,000 lbs
A hull impact area of 360 square inches maximum.
We will designate a forward hull speed of 10 knots which is 26.465 per sec
A downward force of 954417 N on the keel, and that is not a full calculation, but there are too few here who would understand the math to make it worth the effort.

So that translates to 214561.47 PSI

Score Fukushima Debris Field 1 BS hull Zero

In other words a full on 10 knot collision would poke a hole in your boat, and that force is the force that would occur along the entire 360 square inches, angle it slightly and it goes way up. I know my math is dirty on this because the formula I used was not the full formula, which gets to be fairly complex because I would have to estimate too many of the numbers. I used

Impact Force(F): 2 m vt

Which is really too simple. The actual formula for calculating keel impact force is longer and more complicated and I would have to calculate too much stuff after a very long day at work.

However for those interested the whole formula is here....

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