7 ms·
Ha! I love the "Masthead Light" option - that reminds me of a story. When you are sailing at night you take bearings of lights you see with a hand-bearing comp
by nickcw 5y ago
Ha! I love the "Masthead Light" option - that reminds me of a story.
When you are sailing at night you take bearings of lights you see with a hand-bearing compass. This is a device you look through and it tells you the magnetic bearing of the object you have lined up in the cross hairs. If you see a light that you can't identify then you take bearings on it over the course of a few minutes, and you remind yourself of the sailing motto, "If the bearing does not change, a collision will occur".
I was on a night sail in the Mediterranean with one of my younger cousins who came down below in a panic to report we were on a collision course as the bearing of the light she had spotted was not changing.
I think she could have done with this flow chart, because it turned out to be Venus :-)
- _Microft 5y agoIf someone wants to know more about why such a situation would eventually result in a collision, look for the term "Constant bearing, decreasing range", e.g. in Wikipedia: https://en.wikipedia.org/wiki/Constant_bearing,_decreasing_range https://en.wikipedia.org/wiki/Constant_bearing,_decreasing_r...
- henvic 5y agoInteresting. Thanks for the reference.
- jedimastert 5y agoIt did make me stop and think for a second. Like it totally makes sense, but I don't think I would have come up with that rule on my own for whatever reason. Of course, I don't do much in the way of sailing...
- pontifier 5y agoThere was a big scrolling marquis sign at ground level near a road I used to drive on frequently. At a certain point the letters had that "constant bearing" property. If I wasn't paying too much attention I would just get the feeling that ~something~ was coming fast at me from the side and would hit me. I would have to fight my instinct to swerve away and consciously reassure myself that it was just the sign that I saw.
- thewakalix 5y ago> collision with Venus It’s a reasonable concern! …if you’ve installed a Silmaril on your ship.
- Galxeagle 5y agoIf it makes her feel better, professional pilots make the same mistake! https://www.news.com.au/breaking-news/air-canada-pilot-mistook-venus-for-aircraft-plunged-plane-toward-atlantic/news-story/12d337c75606a36b658995f12bf4743d https://www.news.com.au/breaking-news/air-canada-pilot-misto...
- jhgb 5y ago> and you remind yourself of the sailing motto, "If the bearing does not change, a collision will occur". It's also the anti-aircraft-missile's proportional guidance motto. (Being from a landlocked country, it doesn't surprise me that I learned about it from anti-aircraft missiles first.)
- wahern 5y agoIt's also an innate (or at least universally acquired) mental heuristic. IIRC, there are experiments showing that if, say, a baseball player can't readily make use of a fixed background by which to gauge and maintain a constant bearing viz-a-viz the object to be caught when positioning themself, their success rate plummets. Searching for "Outfielder Problem" should bring up some interesting literature.
- gue-ni 5y agoIsn't this how the early AIM-9s worked?
- jhgb 5y agoIt's pretty much how most modern missiles work, as far as I can tell, and it's very natural to use it on missiles with passive guidance in particular (as opposed to for example missiles with control guidance, the oldest of which used beam riding). Maybe some super-advanced ones calculate optimal trajectories of some sort but that requires more storage, more computing power, and perhaps even a way of estimating distance, whereas proportional guidance only requires angles.
- h00k 5y agoMariner here, I've been in a similar situation on the Great Lakes (US). Absolutely the first thing I thought of.