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Hi T.C.
Below is a link to a free calculator for underwater
pressure vessels.
There is a manual you can download with it. You
have to install the sql server
first.
It is easy to use & will give you a good rough
idea as to thicknesses of material you need
to get you to certain depths. Also calculates your
weight & displacement.
This does not consider internal reinforcements.
There is an ABS hull calculator on the psubs site
that does this. However by differing lengths
of the hull & checking the crush depth it becomes obvious
where reinforcement should be. Again this is just a
tool to give you a rough idea of where you can go.
If you went ambient at that size it would take
roughly 5000 litres of air to equalize the hull at 33ft.
(a couple of 90 cu ft dive tanks)
With regard to your dimentions, its normal to stick
to cylindrical, spherical or conical shapes as they are the
most pressure resistant.
Just about all submersibles are steel. I don't know
anything about wood other than that it would be a lot more
unreliable than steel & more difficult to
calculate your crush depth.
In general there is a calculated crush depth that
in theory the sub should colapse at.
Then there is the test depth at wich it is tested
unmanned. Then an operating depth half of the test depth.
I would suggest you read through the free online
book "Manned Submersibles" on the Psubs site, it makes
for a great start. Others more experienced might
give you better direction.
All the best
Alan
----- Original Message -----
Sent: Friday, September 18, 2009 7:20
PM
Subject: [PSUBS-MAILIST] Hello; Design;
Materials; Thanks
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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