Frank,
One
of the issues that has to be considered with using a very large drop weight is
how will the hull float after dropping. Vance can verify but I seem to
remember that one of the Perry boats would float upside down once the weights
were dropped. Don’t really think this will be an issue with your
hull.
Dean
has done a great job with his video clips. Looking at his freeboard and
guessing at the volume of his conning tower with the cylinder extension aft to
equal ~3 ft.3, he only has about 189 lbs. of reserve buoyancy…not
much. From what he has previously stated, he was planning on adding
further buoyancy materials to help rectify this matter. I am guessing
that he is going to have to add a substantial amount to get a safe reserve
buoyancy capability and still have a sizeable drop weight. Looking
forward to the presentation on syntactic foam at this year’s
Conference.
R/Jay
Resepectfully,
Jay K.
Jeffries
Andros
Is., Bahamas
Save the
whales, collect the whole set.
From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
ShellyDalg@aol.com
Sent: Tuesday, September 15, 2009 11:53
AM
To: personal_submersibles@psubs.org
Subject: Re:
[PSUBS-MAILIST] Drop Weights
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?