Hi Don. I was gone all day, and I see that Jim K. has pointed you in
the right direction. ABS is the first starting point.
On the thickness question, I would suggest making it as thick as you
can reasonably deal with for a couple of reasons.
First off, stronger is better, and when you run the calcs the
difference between 1/4 and 1/2 inch is quite substantial. The actual work
involved is really almost the same, and the material cost, although higher,
is a small percentage of the total cost. Like I said, if I was starting new,
I'd have used 1/2 inch.
The second thing is, to get the sub to dive, it's gotta be heavy. In my
case, that's going to mean almost 2000 lbs. of lead. It would have been
cheaper to use some of that weight as steel, rather than the lead. The extra
strength is just a bonus.
The stiffener design is more complicated in a saucer, but again, the
work involved is mostly the same. I'll be using 1/2 inch by 3 inch
stiffeners, but without the "T" portion. The "T" part is to prevent buckling
of the stiffener. I'll be using round stock between the ribs like a ladder
configuration. This is easier to fabricate than the "T" shape. Especially
when you consider that the saucer shape ribs can't be just rolled to round.
They are ovals, and must be made to fit individually rather than just making
a dozen rings all the same and welding them in. The ribs are all the same,
just not round. I'll make a pattern, cut the ribs from plate, and fit them
in. The round stock "ladder" bars can be cut to fit and welded in
after the ribs are all done. Although not quite as strong as the "T"
flange, the locations and spacing can be adjusted to nearly approximate the
same strength. They will also serve as attachment points, and handles. The
fabrication difficulty and time spent making the "T" shaped
ribs will be a lot less with the "ladder" method. Painting and paint
maintenance will also be easier.
The biggest down side to the saucer shape is the drag. With a straight
cylinder or "cigar " shape, it's pretty efficient. Not so with the saucer
shape. I'm trying to over come this with
sleek fairings.
On the plus side though, the draft is less, so the sub can be launched
in shallower water. Because these subs don't go very fast any way, the
difference in drag is small, and offset by the increased area available for
forward windows. Not to mention interior room. I've been inside a few
shapes, and find the "Flattened Sphere" the most comfortable. With the
cigar shape, there's a lot of interior space that you have to crawl to. With
the saucer shape, I can just reach over to everywhere. It's not crowded at
all, and for the same volume, nicer to sit in.
Again, every one's design is driven by what
their sub is used for. My primary use will be video, but I also want to do
some salvage. I plan on mounting a metal detector array under the sub, to
search the sandy bottom areas near my Florida home. With a grabber arm,
I may be able to find some stuff and pick it up, or attach a lift bag from
inside the sub. (Still working on that idea)
I've also made the sub modular, so different shaped
structures can be bolted on to the front and rear. I'm hoping to replace the
rear structure later with a larger section containing a diesel motor,
additional batteries, fuel tanks, and a gen set for charging while motoring
on the surface. Maybe even an on-board compressor.
This will also be a one atmosphere hull, but not connected to the main
pressure hull. Bolted on, with connecting thru-hulls for controls, but
access will be limited to the surface.
The alternative ( actually my original plan) was to have a
motor section that would stay on the surface while the small pressure hull
submerged. I think a pontoon boat could fill that role, and have enough deck
space for the required equipment and crew spaces. Plus it could act as a
float limiting the depth the sub could sink to in case of a system failure.
This of course would require a tether, which has it's own set of problems.
It is still possible to dive without the tether, but a tethered sub could
have some serious power supplied from above via a 220V line and hard wire
communications to the surface, and maybe even an air line. For now, I'll
keep it simple, get it working, and use it for a while to gain experience.
Usage will help me understand what works, and what changes I'll need. That's
why the modular design. The pressure hull itself is straight forward, and
everything else can be changed relatively easy by unbolting and
re-configuring.
Try building full size mock-ups with card board and wire.
Sit inside, cut holes for windows, change the shapes, locations of things,
and generally figure out what shape suits you best. I spent a long time
playing around with card board shapes, and it was a lot of fun, and almost
free. That was the beginning of my adventure, and really got me hooked on
the idea that I actually could build one of these. Its fun and really cheap.
Frank D.