Early autopilots, the motivation
Check out this recent entry in Maine Boats, Homes & Harbors great series of retro ads. It dimly reminded me of autopilots on the old fishing boats I spend time around in Gloucester, Mass., back in the late 70’s. Some were still using strange schemes to derive electrical signals from a tradition card-in-fluid compass, like a light shining through a hole in the edge of the card to a series of photo-electric cells arrayed in a circle beneath. The Photo-Electric Pilot didn’t make it to the Internet, but I did come across this amazing bit of related marine electronics history:
In 1926, Wood Freeman was salmon trolling along the Pacific Northwest Coast when a boom broke loose, struck him, broke his jaw in three places and knocked out his teeth. Unable to remain standing, he lay on the galley table for three days and steered the vessel home with his feet while watching the ship’s compass in a mirror balanced on his chest.
During his recovery, Wood -- an experienced mining engineer and college chemistry professor -- began designing a reliable automatic steering system. Popular but unreliable techniques of the day included steady sails, sea anchors and fishing lead on a trailing line connected to the tiller. Wood continued commercial fishing while working to perfect his steering system. He experimented with magnetic compasses and various ways to detect course error (including fluid conductivity, photoelectric sensors and mechanical pick-off) before determining the best available detection method: fine wires with physical contact on the compass card itself. In 1934, he installed and operated his first production unit, the Metal Marine Pilot Model 1, on the commercial fishing vessel Jean."
You can learn more at WoodFreeman. Meanwhile, I’m off to San Diego for the NMEA Conference. Write if there’s something particular I should look into at Thursday’s exhibit, and especially if you have questions about DSC and AIS for Ghassen Khalek of the FCC (meeting announced here). I’ve got a couple of interesting boat trips lined up to. Westward ho!
> if you have questions about DSC and AIS for Ghassen Khalek of the FCC
The DSC's MMSI seems not very well thought out. I've read a couple of articles about bogus MMSI information popping up. Why wasn't a more stable method of assigning MMSIs chosen (and I come from a a aviation and computer network background, so when I see something like this I just shake my head, because we don't have the same problem with Ethernet MAC addresses or DME equipment in aircraft)... and just so I'm not poking people with a stick, if I had to design the MMSI assignment system, it would have started with a manufacturer ID prefix and then serialization by the manufacturer of the remainder of the ID. The FCC/Coast Guard/BoatUS/whomever would be responsible for making the *association* between the physical layer ID and the vessel identification.
I'm also curious to know of anyone has done any real world technical analysis of the Self-Organized Time Division Multiple Access SOTDMA (particularly with respect to vessel density; the DME system is limited to ~100 aircraft) used by AIS and how the algorithm differs across implementations and what GP&C Systems International AB (the single patent holder) is doing to insure quality control across the wide range of implementations.