Re: Questions to Jon Shawl

[shawl@torchlake.com (Jonathan Shawl)]

STEVE McColman wrote:

> I went to your website and saw your submarine.  It was very similar to
> the submarine I am designing except my submarine has an extra set of
> ballast tanks at the back.  I figure you have 480 pounds in batteries at
> the back of your sub and I was wondering how your submarine stays level
> with your ballast tanks being at the very front?

The ballast tanks don't lift the batteries. First keep in mind no one was in
the sub when some of the photos where taken. It is sitting higher than it
would be if  it where ready to dive. When ready to dive no part of the hull
or ballast tanks are out of the water and the sub sits level. The ballast
tanks normally only lift the conning tower out of the water when they are
air filled. The ballast tanks only make up for the lost displacement of the
conning tower when surfaced. If the conning tower was located in the center
so would the ballast tanks. As far as having all the batteries all in the
back,... well it is the front of the sub that is about 500 lbs heavier
because of the added submerged displacement in the front due to the conning
tower. What you don't see in the photos is a 300+ pound iron emergency drop
weight that is centered directly under the conning tower on the bottom of
the sub, 5- 100 lb lead weights under the very front end and another about
1000 lbs of custom shaped lead weights under the floor in the front. The
skids on the bottom are about 600 lbs of upside down RR rail. I will have to
dig out my figures to be sure but I think there is more ballast weight than
sub weight.

> I also have some other questions about your sub.
>
> 1.  Does your main prop cavitate being so close to the hull?

Only when chasing mermaids. :-)No. It is geared down 10 to 1 and turns slow.
1.5 hp won't make a prop that size cavitate. It is a 22" prop. about 18"
from the hull. Props don't cavitate as easy under the pressure of a dive,
even if I had more horse power.

> 2.  How do you latch your hatch shut?

With one hand. :-)A single latch in the front and a hold down adjustment on
the hinge makes a tight seal. After diving under, the water holds it shut
with a total pressure of about 500 lbs for every 2 feet of depth.
In the past, I thought I would have some fun, and to see the passengers
reaction to me trying to get out under water, I would unlatch the hatch and
push on it at about 6 feet of water depth over the hatch. The hatch has
never opened, but I never got any laughs either. No one thought I had sense
of humor they just thought I was cruel. I would not recommend anyone trying
this!

> 3.  What kind of seal did you use for your main shaft?  Is it a
> mechanical ceramic seal?

Yes, and a rubber lip seal inside with a pressure sensor plumbed into the
space between the seals, then if the mechanical seal leaks you can tell
before it to late to surface.

> 4.  Do you have any problems launching your sub from that trailer?

No if the ramp is a good one. It's about the same as a 4500 lb boat. Push it
off and winch it up.

> How deep does the water need to be to float it?

about 48"

> 5.  Are you neutrally boayant when your ballast tanks are completely
> flooded?

Yes, but that depends on who is along for the ride and what they had for
lunch. I have about 100 lbs of removable trim, lead weights of different
sizes, to get it close to a  neutral trim line. I have a mark on the hull I
trim to when surfaced.
Remember to include a pressure proof trim tank in your design.
Keep in mind A sub hull can shrink all over about the thickness of the paint
when cooled down and put under pressure.
This could amount to about 10 to 15 lbs of lost displacement during a dive
on my sub.
You know you have to take on a small amount of weight after each time you
surface to adjust for the lost weight of the compressed air that was used
when you blew the ballast tanks. I have a 40 lb trim ballast tank that
remains sealed, but can be adjusted during the dive, it is needed for these
reasons.
Did any one out there think of this when in the design stages of there sub?
You have to figure your trim tank size for your own sub design or you just
might not be able to stay off the bottom to move around once you get there.


> I'm sure a lot of people on this website would like to know the answers
> to these questions too.

When I get the time I will add them to my sub site also. FAQ page.

Jon Shawl
http://www.nwcis.com/submarine/