Hi there!

That's ultra offtopic for this kind of site, however the GOG community has proven itself many times as super reliable group of enthusiasts. And so I wonder if maybe I could find here some people who know how to calculate the minimum distance between two ships on a parallel course?

Do you need to know this minute? My dad is a licensed captain but he's not here right now.

No, anytime during next few days would be great. I'm researching some naval issues for my recent project and this particular calculation presented hardest challenge.

Is this something you nee to solve for your maths lesson or do you need people with real life experience?

If it's just an excercise in vectors, then I would disregard the curvature of earth as negligible and just calculate the edges of a right triangle (or two right triangles, depends on where the ships are on their trajectory). If it's experience you need, then hopefully someone will get back to you about that :)

I'd rather have something life-based. I'm writing a story and in spite of its rather light theme there are some certain issues that I'd love to have correct. The distance between ships (brig vs brig, brig vs sloop, line treasure ship vs sloop) is vital to the plot :)

I'll ask him when he gets back. TBH while he is out on the water a lot it has been a long time since he had to pass any kind of test so he may not immediately know.

It can be innacurate a little - I just wonder how people on the sea decide on what distance they are going to pass the other ship :)

My guess is this is a bigger issue when entering port or more strickly controlled and crowded shipping lanes / approaches than it is on open water but if anyone would know it'd be the licensed captain! I say wait for that answer!

The only thing I sail, is my fail boat.

Alas, I only had to pass the lake permit. I know virtually nothing about high sea regulations. :-(

[Edit: Oh, I thought it was about some minimum allowed distance.]

So, do you mean : distance x cosinus(90° - relative bearing) ?

It depends on what data you're starting with. I guess one has to, in order to reach the fuse box.

If you mean the distance between them at a specific instant (instead of the distance between their two paths), then it'd be with:
d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos(lon1-lon2))

Where obviously, ship 1 would be (lon1,lat1) and ship 2 would be (lon2,lat2).
I believe this formula is the great circle distance (i.e. it approximates the earth as a sphere instead of a flat plane).

That's actually really funny. XD I gotta remember that one.

Lol, I thought this meant how to calculate the distance on the spot, so I imagined using a rope between the boats..

Well, maybe you should specify the period during which your story is set, as the instruments used have varied in time

In the age of sail, Iguess one would have used knowledge / records to determine an estimate of the height of the other ship, then calculated, with a sextant, the distance ( the estimated height divided by the recorded angle = distance ); Successive measurements would have delivered a velocity differencial between the two ships. As sail ships are not that speedy, all of this would have been put on a chart. A compass would have been used to estimate the distance at future point in time

In the modern age, all of this would be done on screen, based on radar and gps technology

In the antiquity instrument were more primitive, but an anglemetre have could been used to that effect. ( devices known to have existed in ptolemaic times / roman period ) . But navigation was mostly coastal, so would ships have had such devices? Not a clue

GOOD point! Now a days it takes less than a second to look down and find out exactly how far everything is from you and from each other. Shit I even have a web page I go to here so I can follow the lake traffic in front of my house. A few weeks ago a freighter got stuck in the ice and I was able to monitor everything including distance depth and speed.