Dean, you mentioned that your drop weight was not very big and the
front was a little light.
It started me thinking about the size of my planned drop weight. I've
read about a lot of subs and there doesn't seem to be a lot of commonality
in percentage of drop weight used for the various sizes of psubs.
I remember the little video about towing the Delta sub and during the
submerged part of the video they said it had a 40 pound weight that could be
dropped.
Other subs had drop weights that ranged up to 400 pounds.
I wonder if there's a danger in having too big a drop weight. Can it
cause problems when it's released?
An advantage to a large drop weight would be that when dropped the
sub would have more buoyancy and be able to "tear free" from a minor
entanglement like the kelp we have around here.
The disadvantage could be a too rapid ascent and maybe some instability
once you reached the surface.
Both of these could be quite dangerous.
The surface instability may not be that critical because at least
you're back up where you can be reached by the surface crew and a line can
be attached to the sub.
The uncontrolled ascent rate is the thing that I was worrying
about.
I had planned on a pretty large drop weight. More like 750 pounds. The
drop weight mechanism is designed in a keel shape, and has a bunch of wheel
rollers so I can roll the sub around when it's on the floor in the shop, and
when launching the sub it can roll on and off the trailer.
The actual lead weights will be shaped to fit inside the steel keel
form and bolted in. The total weight can then be adjusted by adding/removing
weights but the steel keel mechanism itself weighs about 250 pounds.
The total lead ballast needed to sink the sub is going to be close to
1800 pounds. Most of this is bolted to the floor inside with some of it on a
sliding mechanism to adjust trim angle.
These are rough numbers at this point of the build and my float test
will determine exactly how much is actually needed depending on what all I
put into the interior of the sub.
Adding a passenger, equipment, and later improvements like a
manipulator arm or whatever can be compensated with the underfloor
weights.
In the model testing I did the sub wobbled during ascent when it
was simulated dropping the weight but it stayed level and fairly stable on
the surface. It's the wobbling when coming up that concerns me.
Anybody got any thoughts on this?
Frank D.