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Re: [PSUBS-MAILIST] Me



John, I have a couple of questions for you:

1) How is it that you have already determined the required thickness of your pressure hull, whilst simultaneously conceding that you have not "designed the stern section", and thus have no possible means of calculating buckling failure modes?

2) You mention searching for electric motors that will allow your vessel to do 8 knots.  As required propulsive power is a function of your vessel's displacement, form drag, surface drag and propulsor efficiency (the latter being strongly dependent on stern hull profile), and you have apparently finalized none of these design elements, what criteria are you using for motor selection?

If you understand the problems posed by the above questions, then you can understand why responses to your questions are rife with skepticism.  As an engineering student, I presume you have the ability to understand the concepts involved in submarine design; however, a little knowledge is a dangerous thing, and your post leads one to believe that, as of right now, you have VERY little knowledge of the subject from which to start.

The Busby book that Jon mentions is a good place to start.  You need to develop some background knowledge in order to develop your design criteria.  You need to define your requirements first, and then design to them.  Otherwise you are, as Jon aptly described, "putting the cart before the horse".  I would suggest that you forget about the acrylic book for now, but definitely download the ABS guides - these are free downloads.  While personal subs are not generally classed or certified, the ABS rules are a generally accepted community guideline for 1 atm sub design, and serve as a good basis for discussion surrounding particular design objectives.

Nobody wants to discourage you; however you do need to realize that you may not be prepared for this undertaking - yet.  Join PSubs, and read through the available information - particularly the mailing list archives.  There is a great wealth of information buried in there, and generally it is a good idea to read whatever you can find in the archives about a topic before posting questions to the list.

Good luck.

- Sean

PS - Jon, I didn't realize that I couldn't adequately explain elastic instability in fifteen attempts.  Must be why I'm not a teacher.  Perhaps a sketch would have helped?


On 26/10/2010 8:18 PM, Jon Wallace wrote:

If you want people on this list to spend their time solving issues for your project, learn to be more open about yourself and what you are trying to accomplish.  Be willing to state your goal over and over again as necessary.  Be willing to state details over and over again as necessary.  Most people won't open up if you don't open up.  Given your experience, the project you have described to us is analogous to you asking NASA engineering how to build a Saturn-V rocket without any experience of having even lit a bottle rocket.  There's a certain amount of self-education you need to do before people are going to take your project seriously enough to invest their own time into.  You can't get around it, no matter how many times you promise to do the legwork after the fact, which most of us recognize as putting the cart before the horse.  As a student without the $200,000 you say you need for your project and without the support you say you need for your project; NOW is the time to "read up" on books like MANNED SUBMERSIBLES by Busby, HANDBOOK OF ACRYLICS by Stachiw, and ABS documents such as RULES FOR UNDERWATER VEHICLES and STEEL VESSEL RULES.  Go through the PSUBS site and read the various standards and guidelines, scan the archives for some of your questions.  There will be plenty of time for resolving specific details about your sub later.  If you find the material boring or consider it a waste of time at this point, then in my opinion you don't have the fortitude, determination, or perseverance you'll require to build a sub safely.  That's not necessarily a bad thing, but you'll need to wait until you can accumulate much more money so you can hire someone to build the sub for you, or perhaps purchase a vessel ready to go.

When you find you are blocked, instead of saying "I can't understand the ABS spreadsheet calculator, can someone do it for me", try instead, "I've been looking at the ABS spreadsheet calculator and don't understand Line #27.  Can someone explain to me what circumferential lobes are?"  Go a step further and convince us that you've read the STEEL VESSEL RULES before asking your question.  Nobody is going to think you are stupid because you don't understand a particular concept or term after reading it.  Most of us are wearing the same shoes you are.  At the Vancouver convention in 2009 I must have asked Sean to explain elastic stability and lobes to me, about fifteen times.  I spent the better part of six months this year researching and reading hull opening reinforcement in ABS docs on internet material, then discussing my findings with various people on the list.  If that makes me stupid for not understanding the material the first time I asked or read about it, then hey, someone nominate me for the stupid award this year.

Understand that the majority of people associated with PSUBS have direct experience with small subs (10-15 feet length) and you are describing a very large sub.  While the concepts are the same for any size sub in many instances, there are going to be particular issues that are unique to a sub the size you desire which many of us are not going to be able to help you with.  Carsten Standfuss is likely the most experienced "amateur" in the world in regards to large home-built subs of the size you have set your mind on.  He's already responded to some of your questions, so listen to him.  When he says to read something, read it.  When he tells you $200,000 is not enough money for the project you are describing, accept it.  He is already well into a project the size you are describing, is well respected in the PSUBS community, and can lead you in the right direction if you are willing to heed the advice of someone who knows what they are talking about.

Don't get discouraged by your professors looking at you like a crazy man.  Get use to it because there are lots of people who look at all of us that way.  You are dealing with a very specialized industry that is not well understood, even by many learned men.  When I was trying to understand the "F" factor for hull opening reinforcement I discovered there are very few structural or mechanical engineers that have experience with pressure vessels.  Willing to pay for services, I literally contacted every structural and mechanical firm in NH and not one of them had any experience with ASME BPVC (pressure vessel code).  I was finally directed to a firm in Portland Maine who knew the code and were able to answer my questions (see Colby Engineering link on main web site page).  You're in the world of pressure vessels now, which appears to be a specialized industry.  It's not that the structural/mechanical engineers out in the world can't understand the topic, but the majority of them are concentrating on bridges, roads, and skyscrapers for which there is likely much more of a market than catering to pressure vessel design.  If you do your homework and educate yourself on submarine design, you'll know more about pressure hulls than your professors and can surely teach them a thing or two.

I'm not trying to slam you and you're free to proceed as you see fit.  However I think if you step back and take a different approach you'll have a much more satisfying experience with this group.  Save up $35 and join the group as a member, you won't regret it.  You don't need to own a submarine to attend our annual conferences and you'll get much satisfaction talking to experienced people face-to-face at our meetings.

Jon



On 10/26/2010 6:57 PM, Firebolt wrote:
Ok, since the whole galaxy (lie) insists on knowing my plans I will say them and only once.
I am a student, my age is of no importance as long as one day I build a Submarine (to me that is, I am not a kid). I have friends that will help and so I have a team.
Right now the sub is only in design stage and will be like that until I have the money and the support. I am trying to make the boat simple as possible so
I have taken out some features I had said on my last posts. The sub will be for exploration, researching and wreck diving. I will try  to keep inside a budget of 200000 USD.
I am studying electrical engineering and computer science and some physics. I still have some problems like "How to design the stern section of the sub" "How to install a shaft and propeller (and not let lots of water in)" "Control dive plane or move them" And Other problems.
The reason why I am doing this now is because I want to get a head start and not waist a lot of time or at least have an idea of what to do. This is about the only place where I can receive help. I ask my instructors about pressure hulls and I end up telling them it’s a sub and they look at me like I'm a crazy man. I have searched half the internet of electric motors that can give me speeds of 8 knots and I find little kids toys(exaggeration). I assure everyone I will research a lot lot lot more, even though some of these concepts are somewhat confusing (abs hull sheet).
I will say that I am determined to do this, if I ever do build the sub and your ages are not 100 I would very much like to meet everyone in a Psub meeting.
I am not mad it just my way of saying things, just don’t comment on my stupidity.
 
Current sub dimensions: length 56 ft, diameter 7 ft height 15 ft wall thickness 1/2 inch and 42 ft cylinder part. I may change the total length to 50 ft I don’t know how much space the stern section needs yet. I am planning on having x type rudders and dive planes also 5 blades for a prop. 
 
 
Thank you very much.
 
 
John