Re: [PSUBS-MAILIST] Hello; Design; Materials; Thanks

[Ray Keefer <psubs2001@yahoo.com>]

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 control and slip passed that depth. 

"Brief dives to 60’" means nothing. If you think you might dive to 60' 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 times that. If you are paranoid then use even greater safety factors then 3 and 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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