On Thu, 27 Nov 2003 17:08:42 GMT, Rick
wrote:

Larry W4CSC wrote:

Your DEC/VAX reminded me of her station keeping system which had a
PDP-8 mini tending 4 sonar pingers shot into the bottom over her work
site. It was tape programmed, as I remembered.

Instant flashback! In the late 70's we used a PDP-8 for submersible
tracking by laying an acoustic transponder array, calibrating its
position in UTM's and then tracking another acoustic transponder mounted
on the vehicle. The runs were recorded in real time on a pen plotter.

That's about how SEACON station keeping worked. When the current
dragged the barge off the center of the pinger, the sensor array
noticed the pinger drifting and the PDP-8 moved the constantly-running
propulsion controls so it would remain over the target pinger until
its battery went dead, when they shot down another pinger.

The barge had a huge crane on an elevated track along port and
starboard gunwales that went from the stern to the stack, even over
this big "garage" with an aft-facing rollup door. The deck inside the
garage and aft towards the stern could be removed by the crane so
divers and equipment could be lowered straight down into the abyss,
keeping the waves off it and allowing large loads to be lowered from
the deck without listing the barge. It was a beautiful arrangement.

Her only problem was she went 6 knots, in any direction, but only 6
knots wide open. They towed her to her work location with a long line
and seagoing tugboat so she'd arrive before everyone on board
retired...(c;

It's quite a sight to see her turn perfectly on her central vertical
axis, without the current pulling her away in the process. The old
PDP-8 did a good job, I suppose.

That was about 1980ish. Wonder where she is now?



The PDP was tape programmed. Remember the nightmare of dropping a roll
on the deck? We used to make corrections and enter new parameters by
using the front panel switches which took hours sometimes. Incredibly
primitive by today's standards but that system replaced a Decca unit,
Omega, a surveyor and hours of post processing.

Rick


Larry W4CSC

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