Myles,
You show concern that you will need a "substantial air reserve to blow
tanks of such size." Perhaps you should considering using pumps, or do
what the U-Boats did...blow it out with the diesel exhaust. This is
after you have broken surface, of course.
Unless I am mistaken (which has happend before!), it only takes a small
blast of air to bring a submerged boat to the surface, be it a one ton boat or
a 20 ton boat. Filling just 1-2% of your full hard tanks with air will
bring you up to the surface. Or at least the tip of your boat up to the
surface. The question then becomes one of getting rid of the other 98%
of the water in the tanks, in order to give you your full freeboard on the
surface. That means either (1) blowing with compressed air, (2) pumping
overboard, or (3) blowing it out with your diesel engines.
You are considering option #1. That takes a lot of air.
Option #2 takes more battery power but much, much less air. If I had to
choose between lots of extra air tanks and lots of extra batteries, I would
take the batteries. They have more uses than the air does. Option
#3 is not usually open to psubbers, as most don't have diesels. But if
you do, then you won't need extra air or extra batteries. An extra
advantage of this practice, according to WWII German accounts, it that the
oily exhaust coats the inside of the ballast tanks and reduces rust buildup
while on patrol.
Just a thought,
Doug Farrow
-----Original Message-----
From: Myles Hall
<myles.h@sasktel.net>
To: personal_submersibles@psubs.org
Sent:
Sat, 29 Oct 2005 16:54:42 -0600
Subject: Re: [PSUBS-MAILIST] Hard / soft
ballast tanks.
Bill,
Thanks for that.
I have been giving the design much
thought. Have drawn and redrawn a lot of plans.
My plan from the onset was to make
the sub U-boat -esque in that I wanted something long and lean, diesel
electric, with decent surface performance. I arrived at a length of 30'
max from tip to tail, being what I could feasibly transport. I have calculated
a pressure hull length of 10' x 36" which would be in the middle of the 30'
overall length. The two ends on either side, which would give the sub
some hydrodynamics, I was planning on making into for/aft soft ballast tanks
out of a fibreglass shape. The "saddle" tanks were going to be
compressed air reserviors (following the principle of having your bouyancy up
high). I figured I would need substantial air reserve to blow tanks of
such size. My bat pods will be mounted low in the floor within the
pressure hull but in their own sealed compartments for safety reasons.
The fuel cell will also be mounted low with vents and the filler cap accesible
fr! om the floor. All the while I am trying to design the sub with the
weight down low, and the bouyancy up high. ....then comes the variable
ballast tank. My design called for mounting it directly underneath the
pressure hull amidships in that I wanted to control just the one tank to
obtain neutral bouyancy. I was looking at the design of actual U-boats
which also have a similar tank directly underneath the control room
amidships. I was working under the assumption that with all the other
weight down low, as well as a weighted keel that will be under the tank, that
would be sufficient to keep the boat stable, both surface and submerged.
The primary function of this variable ballast tank is to compensate the weight
lost as a result of the diesel fuel consumption.
That's the basic premise from which
I'm working from.