RE: [PSUBS-MAILIST] Acrylic Dome

[Alec Smyth <Asmyth@changepoint.com>]

Jason,

 

The hull calculation spreadsheet is based on calculation of a cylinder, it should definitely not be used for stress calculations of hemispheres. There are formulas for hemispheres in various books, but I understand they're grossly innacurate in real life with most construction methods introducing deviations in thickness and sphericity that render the formulas pretty useless. Of course there are ways to build a pretty consistent acrylic sphere, but those are the expensive methods. As in prohibitively expensive for a PSUB.

 

I'm no expert, but what I've learned so far is that viewport calculations are more table-driven, based on heuristics, than formula driven. I've based mine strictly on the ASME publication "Pressure Vessels for Human Occupancy". Its pricey (about $140 if I remember right), but worth every penny.

 

cheers,

 

- Alec

-----Original Message-----
From: Jason Ness [mailto:nessjj@eckerd.edu]
Sent: Saturday, April 14, 2001 5:06 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Acrylic Dome

    I am new to the list, and I am still reading through all the archive information so I don't waste time with questions that have already been answered.  My question is about acrylic domes, I am trying to get an idea of a formula for hemisphere, and what the Young's Modulus, Poisson's Ratio, and Yield Stress values are for acrylic and possibly fiberglass, I know it would vary a great deal with fiberglass, but I was thinking multible layups of unidirectional cloth in epoxy.

    I am still trying to locate a copy of the elusive Manned Submersibles for my very own, but I wanted to here for those who have dry subs, what thickness and diameter they are using for what rated depths, the Kittredge subs use a hemisphere.

    One thought that I had after reading the archives and hearing many "sub stuck in the mud stories" I had an idea, it is probably over simplistic but why not run a high pressure hard line (split one off the line used to fill soft ballast tanks) to a point under the subs hull, then if you did get caught in "mud suction" you could squirt high pressure bubbles from under the sub to blast away the mud, this coupled with a little positive boyancy should free you in short order.  If anyone is interested I am designing a one person dry sub down here in Florida, the goal  (after working on Karl Stanley's monster yellow sub) light weight and manuverability, my initial calculations put it at just under 1000 lbs dry weight and a submerged displacement of 1700 lbs.  There is alot a intelligence and knowlege in this group  and I feel like the proverbial tadpole.

Jason Ness