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.