Pros and cons of steel sailboats - Page 49 - SailNet Community
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post #481 of 5317 Old 08-10-2013
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Re: Pros and cons of steel sailboats

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Originally Posted by Razcar View Post
2: Steel, like the others, requires it's own considerations respective to maintenance, construction abilities of it's owner, hull dynamics, etc. It's not the easiest thing to sort through for a hobby builder, but doable to a certain degree by a tenacious amateur (s.v. seeker comes to mind).
If you think Seeker is an "amateur" - you're kidding yourself. Oh...and..

213. Used fiberglass boats are the best possible way to for the 99% to realize their dreams of cruising affordably.
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post #482 of 5317 Old 08-10-2013
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Re: Pros and cons of steel sailboats

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Actually BS was saying that his keel could take a 1.8 million PSI impact, go back and read it, if that is not what you get out of it then maybe I am wrong, but it sure looked like that was his contention. Also he is taking the linear shear maximum tensile strength and calling it the tensile strength of his hull. That is entirely incorrect. The way he is calculating it his hull would not only meet but exceed the requirements for an armored hull, but we both know that 3/16 " mild steel is not armor plate. .
His exact statement is below. He clearly is talking only about the keel itself and describing the total force based on strength. Nothing to do with the hull. He is also not saying the keel can sustain a million pound impact, just giving an indication of strength. Numbers seem correct as TS*Area. Weather it is A36, 1018 or some other alloyed steel seems inconsequential in the discussion. Seems to me his point about sheer-tensile is referring to the point about buckling that Jeff is talking about. Not that shear strength is some how the same as tensile strength.

Quote:
1.08 million pounds per side, times two, means 3.6 million pounds per keel, if you only hit one keel at a time. Sheer and tensile are the same at that point, as you are not talking about a sharp edge. Still not wooden boat numbers, nor plastic boat numbers. To buckle, plate has to buckles both ways, inward and outward . Kind of hard to for it to buckle inwards, if they have 4500 lbs of lead cast inside.
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post #483 of 5317 Old 08-10-2013
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Re: Pros and cons of steel sailboats

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The way that I am getting the KE figure for the impact on a solid substance ( Fukushima Debris and submerged cargo containers have been mentioned repeatedly as the potential impact sources) is a formula used to calculate the impact of a hull on a fixed and solid object such as a bridge. It figures in the weight of the boat, the forward momentum of the boat, the downward momentum of the boat, the weight of the water pushing along in concert with the boat and the duration of the impact as well as a few other little variables. I got the formula from an engineering text that is specifically focussed on just this type of impact on bridges by ships and boats.
And you say that reduces to this formula from your previous post?

Quote:
Impact Force(F): 2 m vt
It seems the above formula is missing something as it does not result in units of force. Now a divide sign between v and t would give units of force.

Quote:
Your math is good, but it is not going to excuse a point loaded keel impact on concrete from causing damage.
This whole discussion about impact damage fails miserably because no one is setting the conditions for the type of impact. I pointed out the conditions in my discussion. And any calculation about the merits of a steel boat must include a comparison to a wooden boat or fiberglass boat to be useful. My discussion applies to either type.

And of course a sailboat is radically different than any other boat in that up to 40% of the mass of the boat may be in the keel. This means weight distribution is going to be incredibly important in any discussion of keel impact.

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

Guide Specifications and Commentary for Vessel Collision Design of Highway ... - Aashto - Google Books
Your discussion about the impact force might be more persuasive if you point out what particular page of the book supported your assertions. To suggest the readers have to read the whole book does not make sense.
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post #484 of 5317 Old 08-10-2013
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Re: Pros and cons of steel sailboats

Not sure what this math excersize is trying to prove. There are a lot of variables with groundings and collisions. I'll sit and wait until the variables are included if we are going to be realstic here. I think I'll have a long wait. We know steel is strong. But if you are just having fun with numbers carry on. I'm enjoying the back and forth.
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Re: Pros and cons of steel sailboats

Looksd like the same numbers that show a shoal draft lead is better than a deep draft iron from a righting movement issue, or a fin is not as good as a full at times. There is another thread with similar numbers that don't always include EVERY possible issues with in a certain fact. Seen it on other forums too, where some take numbers one way, make it work for them, but when someone shows that one should also include this variable in the numbers, they go haywire.

LOTS of that going on in this thread now.

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Re: Pros and cons of steel sailboats

"Looksd like the same numbers that show a shoal draft lead is better than a deep draft iron from a righting movement issue, or a fin is not as good as a full at times."

Lots of variables there Marty. I would not say either of those things without some qualifiers. Remember that stability is about more than just the ballast. You would have to do the comparison fairly using the same hull for each type of keel and ballast material. But then it wouldn't be very realistic.

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Re: Pros and cons of steel sailboats

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Originally Posted by smackdaddy View Post
If you think Seeker is an "amateur" - you're kidding yourself. Oh...and..

213. Used fiberglass boats are the best possible way to for the 99% to realize their dreams of cruising affordably.
Both wonderful opinions.

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Re: Pros and cons of steel sailboats

Bob,
I would agree with you on that, ie where one has to have the same hull etc. BUT< one still sees folks trying to do numbers with out certain elements in the total equation, and things do not add up as they should in the end, to get to a point one wants to see vs how it will REALLY be!

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Re: Pros and cons of steel sailboats

Marty:
At some stage you have to make the numbers relevant to your design task. If you can't do that you are just playing with yourself.

But lots of people like numbers challenges for numbers sake and I can understand the fun of the mathematical quest and challenge. But after hours of discussion I don't want to look at a number and say, "Fine, now what?"

I almost always start a calculation with a guess. My guesses are pretty darn close and if my caluation is not close to my guess I have to look hard at the calculation. I've had a lot of practice guessing (see the "Mr. Perry" thread on the General Interest forum).

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Re: Pros and cons of steel sailboats

Bob,

While I do not know boat numbers etc, I do understand to a degree other numbers, Yes, doing numbers to do numbers is not a good thing. On the other hand, to know the correct numbers for the task at hand.....that is good to know, or understand.

I had to build a block wall for a client a number of years ago, I know the wall block and design needed to be beyond the general spec. Bid the job and got it per the way the I thought it should be, based on other numbers added. Glad I did, as a few months later the nisqually quake hit. I had it designed then built it with some earthquake added material. Glad I did that. Meanwhile the $100K/30K lb motor home that was parked 3' away from teh wall was fine etc. If it had been built as one person bid it, the wall and MH would have been behind the yard in a collapsed heap!!

Another job, and engineer designed a wall using a different wall block than I typically use. Even got it passed the city inspectors and approved by there DOT folks. I looked at it and said it would not work, put in a different design and got it approved, and built accordingly. This wall had Metro buses running 5' from it, with a concrete sidewalk above it, the wall block in this situation was not designed to hold this type of both static and active load on it. Neither wall block design was in all honesty, but one had to know that one needed other reinforcement to make it work.

Hence why I believe with all math issues one has to have ALL the factors built in, not just some of them!

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