Hi TC,
I think the reason people don't design for shallower depth is because
if you are going to the bother of making a pressure resistant hull
for a 1atm
its not much more trouble to go a bit thicker with the metal &
hence deeper.
Given the overall cost of building a sub, going a bit thicker in
the metal is a
comparably small amount.
There is an article on fiberglass in the frequently asked
questions on the Psub site.
As said previous, you've got to go a lot thicker with fiberglass
than metal & hence
the subs displacement is more & you end up heavier, also its a lot
more expensive
& you really have to know what you are doing when laying it up.
Fiberglass has strong characteristics in tension but not in
compresion, & is only strong
in the direction of the fibers.
Maybe fiberglass on a small sub but the size you are talking about
would be a huge cost.
Then you have to buy extra lead to sink as you don't have the
inherent heavyness of steel.
Regards Alan
----- Original Message ----- From: "T.C." <tc.craig@gmail.com>
To: <personal_submersibles@psubs.org>
Cc: <personal_submersibles@psubs.org>
Sent: Saturday, September 19, 2009 12:31 PM
Subject: Re: [PSUBS-MAILIST] Hello; Design; Materials; Thanks
Dear Sirs;
First, let me thank everyone for the thoughtful and detailed
responses. You've given me a wealth of information. Thank you.
After digesting these responses, and reading my original post, it has
become obviouse that I failed to clearly communicate my design and
its
intentions as well as the quality of my previous research.
I guess this is what you get when you assume engineers will read
between the lines...:)
1. This will be a 1 atmosphere submarine. I will consider an ambient
if the operational design makes more 'sense'.
2. 25' in length (pressure hull)
6.5' in r^2
2.5-4' draught when surfaced. Though clearly this is volume/
displacment dependent.
3. Operational depth 20' - 50' with excursions into 60'. Crush depth
at 90' -100'. Most operations will be I'm a total atmospheric
pressure
of 1.5 - 3.
I
Might also consider a shallower crush depth and operate in 1-2 ATM
waters.
My point in mentioning WWI designs, monitors, and David boats was to
communicate the spirit of the design.
I'm aware that David boats "smack" of drug running craft. So do
single
engine Cessnas and go-fast speed boats, but that doesn't mean I
wouldn't become a pilot, or built a boat at 80mph.
I will not comprise my design for a losing war on drugs. I will
declare my flag (US), and allow them to board. But what I will not
do,
is sacrice the legitimate freedom to design a boat of my choosing.
Motorcycles are tough to see. So, like a motorcyle, I will attempt to
make myself as "bright" as possible. Though I do hear the all or
nothing surface argument, and it makes good sense.
My goal is light "cruising" capability and mostly on the surface. My
operations will be resticted to navigatable waterways, bays, and to
near coastal operations.
Finally, I appreciate the hull calculators and the ambient facts,
these will not go to waste. I am still considering fiberglass for
inland work. Ive thought about designing to 250' and if the economics
make sense, I might do that.
Basiclly, I wanted to get a better grasp of the full materials at my
disposal given the pressures I'd be facing.
Steve, I don't know why people aren't designing for shallower depths.
It seems more accesable using cheaper materials and decent integrity
given it's operational range.
Sent from my iPhone
On Sep 18, 2009, ts at 12:57 PM, Ray Keefer <psubs2001@yahoo.com>
wrote:
Hi TC,
What is the intended purpose of your submersible? Where do you
plan to operate? David boats smack close to current drug subs
and I suggest you stay away from them.
You said your vision was for a WWI (which means also WWII Fleet
Type) profile. For the overall size of:
L: 25’
B: 6.5’
D: 2.5 - 4’
I would expect a pressure hull of about 20' long. Using the 2.5'
diameter that would be an internal volume of 98 cubic feet ( L x
pi x r^2 ). Using the weight of sea water at 64.0 lb/ft^3 this
pressure hull would deplace 6,283 pounds of water. If you use
the 4' diameter the weight goes to 16,084 pounds or 8 tons of
displacement. Are you ready to trailer or move multiple tons of
submersible?
Your operational depths of 30’ – 50’ is fine. Though the
shallower the depth the easier it is, even temporarily, to loose
c on trol and slip passed that depth.
"Brief dives to 60’" means nothing. If you think you might dive
to 6 0' build that sub to withstand 60'. Actually if you plan to
go to 60 ' then design the sub to go 3 times that and test it
to 2 ti mes that . If you are paranoid then use even greater saf
ety factor s then 3 an d 2.
Dry-ambients have a couple of issues.
1. The interior volume must be pressurized to ambeint pressure.
The larger the internal volume the more air that takes. While a
20' long and 2.5' diameter hull is only 98 cubic feet, that is
more then the volume of one 80 cu ft scuba tank at fill at sea
level. Once you go to 32 feet deep the amount of compressed air
you will need will double because ambient pressure will double.
So just to get to 32 feet you are talking four scuba tanks. If
you go deeper you will need more tanks. If you repeatedly
descend and ascend then even more air will be used upon each
decent.
You must keep the air bubble volume small to keep air usage
small. The best you can do is just enough space for your body.
Semi-wet or Semi-dry ambients typically have just enough air
volume for the operators head.
2. Pressure compenstation
As you ascend or decend the air space must be compensated as the
same rate as the depth pressure the sub is currently at. Else a
pressure differential on the hull may split the hull open. Not a
good event.
Rapid changes in depth require bigger values.
3. Escape
A sealed ambient can be dangerous if it starts sinking
uncontrollably. You must design a way to get out before it
decends lower then 150'. I'll not degress in to physiological
issues of compressed air breathing at depth. I HIGHLY RECOMMEND
YOU TAKE SCUBA DIVING CLASSES.
The best material for an ambient is fiber glass. Metal hulls are
typically used on One Atmoshpere (1 ATM) subs. Wood hulls are
typically NOT used for any submersibles since finding the
quality woods of the past is most unlikely. Plus the skills for
such boat building wood working no longer exist.
"The vessel will conduct itself primarily in semi-submerged/ low-
profile condition"
Why? That is a collision hazard. Plus the drug sub motive of
operation is going to attract attention. When you are on the
surface, be on the surface. When you are diving, you are
submerged. There is no advantage to operating with decks awashed.
"The nature of these requirements clearly points to a dry-ambient
submersible but I wish avoid the dry-ambient for the reasons of
decompression."
The only way to avoid decompression is to build a 1 ATM pressure
vessel. In which case why limit yourself to a mere 60' depth. 250'
doesn't cost that much money considering how much effort and
time you will put into the project.
For a 1 ATM hull be prepared to learn welding and machining. You
will also spend money on acquiring those tools or farming out
the work. Expect to spend $25,000 to $35,000 on a small sub.
Your dimentions are not those of a small sub so you will be
paying more.
You need to have a clearer idea of what you want to have once
you are finished before you can go further. I suggest acquiring
and reading the following books:
Title Author
-------------------------------------
----------------------------------------------
Acrylic Plastic Viewports Stachiw, Jerry D. Design
Concepts in Submarine Design Burcher&Rydill
I Found Israel's Atom Bomb Factory Kittredge, George William
Manned Submersibles Busby, R. Frank
Submarine Design Gabler, Ulrich
ABS: Rules for Building and Classing American Bureau of
Shipping & Affiliated Companies
Underwater Vehicles, Systems , and
Hyperbaric Facilities
Of course you can join our discussion group and ask questions. I
suggest you read at least one of those books first to allow you
to ask informed questions of the group. The guys are very
helpful but they do not like designing subs for the uninitiated.
Regards,
Ray
--- On Fri, 9/18/09, T.C. Craig <tc.craig@gmail.com> wrote:
From: T.C. Craig <tc.craig@gmail.com>
Subject: [PSUBS-MAILIST] Hello; Design; Materials; Thanks
To: personal_submersibles@psubs.org
Date: Friday, September 18, 2009, 12:20 AM
Dear Sirs;
First, let me say hello and thank you in advance for
your
time.
I’m considering building a submersible with the
following
characteristics.
L: 25’
B: 6.5’
D: 2.5 - 4’
Operational depth 30’ – 50’
Brief dives to 60’
The vessel will conduct itself primarily in
semi-submerged/
low-profile condition (aside from the conning tower stacks
etc.), showing full
freeboard only in harbor, or as dictated by
necessity. At the desire of the operator, the
vessel can
make brief, excursion dives up to the aforementioned
depths.
The exact depths are yet undecided.
In other words, I’m looking to build a
David-boat/Monitor
type vessel capable of excursions to a designed depth,
mostly 1.5 to 3
atmospheres with extended submerged endurance.
Early-early WWI submersibles were treated (and
designed) as
surface-craft with limited submersible capability.
I would like to mimic this design
concept.
The nature of these requirements clearly points to a
dry-ambient
submersible but I wish avoid the dry-ambient for the
reasons of decompression. Even at thirty
feet, there are no-decomp limits,
and I would like to avoid these issues if possible.
Although I’ve considered limiting dive depths
to 20’, in which case ambient would make sense.
Materials:
Some pre/post-Victorian vessels were made of thick
wooden
planks, metal sheathing, riveted construction, and included
deadlights and scuttle-glass
portholes. Many of these vessels were
capable
of greater depths than I am now proposing.
What are some today’s hull materials that could
give me the same
performance more cheaply?
Why not consider steel/fiber/carbon/etc. reinforced
plastics,
or wood, given the limited design parameters. Indeed 60
psig is large, but it
seems a trifle to many of today’s resources.
Far older and more poorly designed submersibles
dropped past 70’ with
materials of lesser quality – and lived to tell the
tale.
Would it be folly to sink 5’ in a hull made of 3”
wood? What
about10 feet? or 25? At what depth does wood betray you to
the abyss?
What about 5/16” steel? Would I be
called an engineering marvel for using 5/16”
in a vessel designed to dive 5’ feet?
Personally, I suspect that most industrial strength
materials will bring you safely back from a depth of
<33’ – even those of mediocre
design. Informally, it appears that most
shallow
water (1.5 – 2 atm) accidents related to
through-hull/porthole failure, as well
as entanglement and swamped with decks awash.
Hull
failure due to pressure buckling appears to be a rare event
in shallow waters.
I could be wrong, of course.
Ultimately, I suppose I’m looking for
design/hull-materials
advice given the operational characteristics I’ve already
mentioned.
Thank you all for you time and I look forward to a
response.
TC
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