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

["ronleonard@shaw.ca" <ronleonard@shaw.ca>]

I would add that though there is little differential pressure across the hull of an ambient sub, the hull still requires great strength from the roof to the base. The sub's ballast is likely carried on the bottom of the sub, and the air inside the sub is lifting against the roof of the sub, in opposition to the ballast. The hull needs to be strong enough to withstand this stress. 

Ron

On 09-18-2009, at 1:33 PM, Jay K. Jeffries wrote:

TC,

Some people here are confused as an ambient sub does not need the hull strength of a 1-atm submersible.  For an ambient the pressure is equal on both sides of the hull.  In the past, most ambients have been constructed from fiber glassed wood while later commercial ambient hulls are usually GRP (glass-reinforced plastic, i.e. fiber glass).  While there is much to be learned in Stachiw’s book on viewports, this is overkill once again for ambients as there is not much (if any) pressure across the viewports.  Due to minimal pressure differentials across the hull surfaces, an ambient sub can be configured in just about any shape that you might want since it does not have to be extra strong to resist the pressure at depth.  Ambient subs are not worried about crush depth but are concerned with decompression issues for the occupants and pressure trauma from rapid or deep pressure transients.  As Ray noted, the volume of pressurized air that needs to be carried to maintain ambient air spaces within one of these hulls can be excessive.  There are some articles in old Popular Mechanics or Popular Science magazines from the 60s and 70s that have plans for ambient subs and these will give you an idea as to what is involved in making a successful ambient sub.  You may find copies of these articles of the web for free.  Do note that a pressure housing will be necessary for a battery compartment and your motors.  Also depending on your design, you may need shaft seals for your propulsion and maneuvering motors.

 

There has been so much focus here on 1-atms. subs here on the PSUB site that we forget some of the engineering features of an ambient sub.

R/Jay

 

 

Resepectfully,

Jay K. Jeffries

Andros Is., Bahamas

 

Save the whales, collect the whole set.

 

 

 

 

 

----- Original Message -----

From: T.C. Craig

To: personal_submersibles@psubs.org

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