3 ms·

Someone I know is a hydrographer who charts our local waters and it’s incredible to see how many wrecks they pick up in their multi beam data. Some are very cle

Someone I know is a hydrographer who charts our local waters and it’s incredible to see how many wrecks they pick up in their multi beam data. Some are very clearly ships, others less obviously; you kind of develop a knack for picking that signal out of the noise. Apart from ships, there are also the odd aircrafts here and there. Those are far less common from what I’ve seen. I’d estimate the bays around our city have several dozen wrecks combined. The main harbour has had some removed over the years, but there are around a dozen fairly small and boring wrecks and 3 which recreational divers frequently check out. A little further out and you can actually find an entire barge that lit on fire and sank with like 100 crushed cars on it. So weird. Maybe not all that shocking though, considering one lit on fire with a pile of cars on it just 5 years ago (though it didn’t sink). It’s a real mess down there.

13of40 3y ago
Not sure how many are still there, since I read that the State of Washington had a campaign about cleaning up derelicts a few years back, but the canals just north of where US Route 2 crosses the Snohomish river by Everett used to have a ton of derelict and sunken boats. I think there are some back-alley marine works up the canal to the east that might be the source of it. I skipped work one day several years ago and took my little boat up that canal to look at a half sunken wooden tugboat (that doesn't seem to be there anymore) and actually saw a derelict motorboat hull, upside down, with its inboard motor removed, just floating down toward the sea. The cops were there at the dock when I landed, trying to figure out if it had flipped in an accident or something.
martin_a 3y ago
Is there an "easy" way to do this mapping with local lakes and ponds? Without disturbing/hurting fish and other wildlife?
- LeifCarrotson 3y ago
  Not really, the "easy" way is to hook up an enormously expensive multi-beam sonar to a surface vessel. A more difficult but inexpensive way to start would be to take a single-channel Ping2 transducer: https://bluerobotics.com/store/sensors-sonars-cameras/sonar/ping-sonar-r2-rp/ https://bluerobotics.com/store/sensors-sonars-cameras/sonar/... and hook it up to a pan/tilt system and datalogger. Low-power sonar shouldn't hurt fish. At only 0.2W, even with a 10ms pulse width increasing the instantaneous power output to 20W, that ultrasound pulse is probably not even perceptible to fish. Lots of studies have shown that "fish finders" are not perceptible to fish, and humans typically can't hear them either. On the other hand, military sonar can have power levels of many kilowatts and sound pressure levels that are literally off the charts, generating forces of 235 dB that cannot be replicated in air at atmospheric pressure. These are known to kill whales, dolphins, and other wildlife! They are even powerful enough to kill or maim humans who happen to be swimming too close to the ship or submarine; navies will use this to deter/repel boarders when docked in potentially hostile locations.

13of40 3y ago

Not sure how many are still there, since I read that the State of Washington had a campaign about cleaning up derelicts a few years back, but the canals just north of where US Route 2 crosses the Snohomish river by Everett used to have a ton of derelict and sunken boats. I think there are some back-alley marine works up the canal to the east that might be the source of it. I skipped work one day several years ago and took my little boat up that canal to look at a half sunken wooden tugboat (that doesn't seem to be there anymore) and actually saw a derelict motorboat hull, upside down, with its inboard motor removed, just floating down toward the sea. The cops were there at the dock when I landed, trying to figure out if it had flipped in an accident or something.

martin_a 3y ago

Is there an "easy" way to do this mapping with local lakes and ponds? Without disturbing/hurting fish and other wildlife?

LeifCarrotson 3y ago
Not really, the "easy" way is to hook up an enormously expensive multi-beam sonar to a surface vessel. A more difficult but inexpensive way to start would be to take a single-channel Ping2 transducer: https://bluerobotics.com/store/sensors-sonars-cameras/sonar/ping-sonar-r2-rp/ https://bluerobotics.com/store/sensors-sonars-cameras/sonar/... and hook it up to a pan/tilt system and datalogger. Low-power sonar shouldn't hurt fish. At only 0.2W, even with a 10ms pulse width increasing the instantaneous power output to 20W, that ultrasound pulse is probably not even perceptible to fish. Lots of studies have shown that "fish finders" are not perceptible to fish, and humans typically can't hear them either. On the other hand, military sonar can have power levels of many kilowatts and sound pressure levels that are literally off the charts, generating forces of 235 dB that cannot be replicated in air at atmospheric pressure. These are known to kill whales, dolphins, and other wildlife! They are even powerful enough to kill or maim humans who happen to be swimming too close to the ship or submarine; navies will use this to deter/repel boarders when docked in potentially hostile locations.