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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.
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