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
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