Re: [PSUBS-MAILIST] How much drop weight?

[Ian Roxborough <irox@ix.netcom.com>]

On Sat, 15 Nov 2003 06:57:25 -0600
David Buchner <buchner@wcta.net> wrote:

> DJACKSON99@aol.com wrote:
> > I suppose if you were near the bottom, you could use your drop weight 
> > as an anchor , and control or even stop your accent.
> 
> This seems like such a good idea, that everybody ought to have one. I 
> don't know why it hasn't occurred to me before --

Ropes and similar long stringy type things are often considered very
hazardous to the 'health' of a submarine.  I've heard many people say
the two greatest dangers to a submarine are fire and ropes.  This is
probably the reason it's not popular.  It does sound neat though, for
a while I was into the idea of attaching a rope to the drop weights
so the could be recovered after they where used.

Consider the type of circumstances you will dropping your drop weight.
Should your submarine make it's ascent in a none upright position,
there would be in danger of snagging the rope on some other part of
your submarine, or even worse, should the submarine roll as it's freed
from what ever reason the drop weight was dropped, then it would be
well tangled up in the drop weight line.

I think the incremental drop weight is the best way to solve the 
ascent problem for ambient pressure.  You could even have a hopper
of small lead balls which you could let out at any rate you wanted.
But I'm also liking the idea of making the lead weights shaped like
dounuts, then threading them on to a bar which can be moved in away
that will allow the lead dounuts to fall off the end one by one.
You could even thread the dounuts and bar, so all you have to do it
turn it and the weights drop off (I'd probably be a little worried
that the threads would get clogged and the drop weights won't drop).

> all the times I've 
> tried to imagine just what a chaotic mess it would be, pulling the pins 
> on that big weight and hoping the whole thing doesn't rocket to the 
> surface, leap out of the water, and get stuck in a tree.

A funny image there.  But if I had just had to use my drop weights to
get to the surface, I would be happy to be inthe tree... ;-)

You can start by calculating what are the minimum and maximum ascent
rates that you would want to see in an emergency situation.  Remember
to take into account any flooding that you might be dealing with.
With the min and max ascent speed you could estimate what type of
force that would been need to move the sub at the speed you need.
If you drop a 50lb drop weigth, you've got 50lb of up force.

That kind of brings up the terminal velocity of the sub floating
to the surface.  I think that the terminal velocity of a sub
in water could be calculated by using a scale model and the
deep end of a swimming pool (time it's ascent for different know
depths).  Sounds like a nice science fair project...

Ian.