Plotting an intercept course

[JAFO]

Heh.. Saw this thread, and immediately thought to myself, "any submariner worth his salt can plot an intercept!", and then, a few comments in, I find a reference to my favourite submarine simulation forum!

Originally Posted by SeanPatrick

The images I posted are from just such an app. It's called MoBo (short for maneuvering board) and the only place I know of to get it is the Subsim Radio Room Forums. It has a feature that will do the vector calculations for you. (I should have taken advantage of that.)

For those who wish to check the app out, finding the correct thread to download it from can be a bit tricky.. you can't use the forum's search facility unless you're registered and logged in, nor can you download it unless logged in.

But even if you are logged in, finding the download may not be simple, so once you've registered and logged in, these are the links you'll need:

The MoBo app itself:
https://www.subsim.com/radioroom/dow...do=file&id=648

The User Manual for MoBo (English):
https://www.subsim.com/radioroom/dow...do=file&id=649

The User Manual for MoBo (Spanish):
https://www.subsim.com/radioroom/dow...do=file&id=650

[requiem]

Originally Posted by rooiedirk

In general this done/needed to plot a course to an other vessel that does need help/assistance.
You can do the same in OpenCPN as you would do on paper.

1. Make a route from own ship to target. (blue)
2. Make a route from ownship in the opposite direction as the targets course with a distance of targets speed. (green)
3. Change the last waypoints props by adding a circle with a radius of your own speed/
4. make a route from last waypoint to the crossing of circle and the first route. (yellow)
5. The course of this last route is the course to steer for interception. 286 (if you are doing 5kn)

Took me a second, since this is a little different than I'd do on paper. I think it can be simplified a bit....

1. Plot a new route with the first waypoint corresponding to contact's true course and speed.
2. Place the second waypoint along a bearing corresponding to contact's bearing at the time of maneuver. Make the length nice and long.
3. Measure the bearing and distance to any point on 2nd leg of the route such that the distance to that point corresponds to a feasible speed. That's your intercept speed and direction.

You can even do this on basic tools like iSailor (see screenshot). Note that I scaled the speeds by half; 2.5 miles thus means 5 knots. Sorry Navionics, I tried, but the UI is just too dumbed down.

[SeanPatrick]

Originally Posted by JAFO

Heh.. Saw this thread, and immediately thought to myself, "any submariner worth his salt can plot an intercept!", and then, a few comments in, I find a reference to my favourite submarine simulation forum!

Yeah, you know: it didn't occur to me to mention the myriad other solutions and gadgets available over there to solve maneuvering problems. They really do have the market cornered on the subject.


I'm still [kind of] working on that intercept spreadsheet in between a seemingly never-ending list of home improvements. But rgleason and rooiedirk took the words out of my mouth when they said you could just plot it directly in OpenCPN.

[KeithMidgette]

Originally Posted by C420sailor

Time to dust off a maneuvering board!

Somewhere, an old surface warfare officer’s ears are burning.

Aye, me pack of MoBoards may be found in the Nav Table!!!!