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Re: [PSUBS-MAILIST] Wet-sub propulsion stability and X-tail
Jon,
Is it so necessary to go so fast on the surface? if you have a separate
motor, then all of your efficiency requirements are different.
If you DO have a separate petrol motor, you can just (more sedately)
motor out on the petrol motor, dive, look at cool stuff and motor around
with the electric motor, surface and drive back home on the petrol motor.
This might be less practical if you intend to dive to a site that is a
large fraction of (or multiples of) an hour away from the shore, but
otherwise, I can't say that I see a great deal of benifit (given all the
caveats you have outlined) in having a high-speed surface boat that
turns into a low-speed sub.
If you dont need to hydroplane, and all your questions are solved!
EM.
Jonathan Huntoon wrote:
Hello Everyone,
I have been an avid reader of the psubs website for quite sometime. My
purpose in this email is two fold. First, I have decided to join the
mailing list, and I thought I would make my formal introduction. I
currently a college student and I have been interested in submersibles
since my senior year of High School. I undertook an ambitious project
to build a one-man wet submersible. Using trolling motors, batteries,
plywood and PVC, I created what many considered a death trap, but it
worked! Due to problems with electrical insulation, the system only
performed admirably in fresh water, going 5 or 6 knots. I vowed, that
if I ever had the time, money, and inclination, that I would go back
and try building another wet sub, correcting all the problems with the
first design.
My second purpose in this email is to ask a few questions. I have done
my best to go back and read all the topics applicable to my situation.
I found very little information however, on my specific questions. I
think the best thing to do would be to give everyone a little
background into my new project, in hopes of giving you a picture of my
ideas. I am majoring in engineering, and I have experience in CAD. So
someday I can attach some design pictures.
I case you haven’t figured out by this point, I have decided to make a
new submersible. I was comforted to know I was not alone in my
efforts. Most people couldn’t believe I made my first sub, so I
thought they would not be surprised when I started another. I was
wrong (It is difficult sometimes when everyone thinks you’re
completely nuts).
I have made every effort in my new sub to follow hydrodynamics. As I
mentioned before my sub is a wet sub, it will hold two people. The sub
design is 14’ long and 4’ diameter at the widest point, which is 5’6”
down the length. The sub follows a tear drop contour and is as
hydro-dynamically sound as I can make it and still keep the project
manageable.
I wanted to make my project unique, and so I decided to try to come up
with one solution to the age old question of sub endurance and speed.
Because my vehicle is a wet sub, the driver must wear SCUBA gear to
operate it. Therefore it is not practical to drive the vehicle out to
the dive site. I wanted a way to quickly get the sub to the dive site,
dive down, surface, and then quickly drive the vehicle home. As I am
sure you all know the ideal hydrodynamic shape underwater performs
very poorly on the surface. As waves pile up on the hull, the vehicle
looses all efficiency. I asked myself how to fix this many times, and
the solution seemed to be staring me in the face. One of the
advantages that wet subs have is their weight. I can make my hull out
of fiberglass. What would happen if I added enough power to the
vehicle to get the whole hull to hydroplane out of the water? The way
the sub is contoured it might work.
I have designed my sub to (hopefully) hold a 40HP e-start outboard
motor. When the sub is on the surface, the outboard will propel the
entire sub out of the water at a high rate of speed. I can drain the
hull and close it making it a surface boat. Underwater I will withdraw
the outboard into the hull and store it in a pressure compensated
compartment. This minimizes flooding issues with the motor, and
eliminates the hull protrusion.
When I was faced with the obstacle of how I would steer my
submersible, I immediately drawn to the cruciform arrangement. I am a
big proponent of the KISS principle. Underwater steering can be
accomplished with the cruciform, but when the sub is hydroplaning the
tail presents a problem. Even if I extend the tail through some means
so that a section of the rudder is underwater, when the boat travels
at high speed there could be a real instability. Realistically the
hull could be completely out of the water. I was originally only going
to have the motor stationary, but even if I rigged it to turn a
little, is there a danger of the sub getting out of control? I have
seen too many movies of those high speed boats flipping out of control
and hurting people. I know I am inside the sub, but it can still hurt
me it flips at 30+ mph.
I decided a way I might combat this instability it to use an X-tail.
Some navies around the world have opted for the tail because it gives
25% tighter turns. I like it because I am considering using a piston
to extend the lower fins of the X into the water when the sub is at
high speed, effectively giving me 3 points of a stable tripod. Does
this idea sound crazy? I could turn the sub, but also adjust the hull
pitch up and down.
My last question is if anyone has experience dealing with X tail
control systems. Due to the complexity, I would need all four fins to
be actuated separately. I would need joystick control, and some sort
of motor control that could take my stick position and turn it into
the proper fin position. The trick is the forces off the fins are
additive, so all four fins need to work together.
I realize this is a long email, but I look forward to reading anyone’s
insights on the matter.
Best Regards,
Jonathan Huntoon
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