cacluating ship speed manually

TorpX · 04-29-11, 12:24 AM

OK, you guys were right. Note to self- CHECK YOUR WORK!

I did some quick geometry to figure this out.
The formula I posted earlier is incorrect.

This is the correct formula:

Vt = .59 Tl / t + Vs * (sin Abg / sin Aob)
where:
Vt is target speed, in knots

Tl is target length, in feet

t is time, in seconds

Abg is bearing angle, in degrees

Aob is angle on the bow, degrees

Vs is sub speed, knots

Note that I define Abg as bearing angle, not relative target bearing. This is because the sine of angles between 180 and 360 deg. are negative and will give the wrong answer. If the relative target bearing is between 180 and 360, the "bearing angle" must be measured from the bow going counter-clockwise. Note also, that at relative target bearings of 0 or 180 deg., the last term becomes 0, and one need not know the Aob. The same goes for a sub that is not moving. Similerly, if the sub is on a parallel course, the ratio (sin Abg / sin Aob) becomes 1.

Also, as before, if viewing the port side of the target from port side of the sub, or starboard side of target form starboard side of sub, then subtract the sub speed. (This would mean you are heading in opposite direction of target.)

Well, I think I got it right this time. I did a numerical test case and it checked out.

One more thing; I would not try to use this for targets at a very sharp aspect, that is at Aob angles near 0 or 180 deg. This would make it very difficult the time the transit. I believe Don Reed mentioned this also. If anybody uses this, in game, please let me know how it works.

04-29-11, 12:24 AM	#10
TorpX Silent Hunter Join Date: Sep 2010 Posts: 3,975 Downloads: 153 Uploads: 11	OK, you guys were right. Note to self- CHECK YOUR WORK! I did some quick geometry to figure this out. The formula I posted earlier is incorrect. This is the correct formula: Vt = .59 Tl / t + Vs * (sin Abg / sin Aob) where: Vt is target speed, in knots Tl is target length, in feet t is time, in seconds Abg is bearing angle, in degrees Aob is angle on the bow, degrees Vs is sub speed, knots Note that I define Abg as bearing angle, not relative target bearing. This is because the sine of angles between 180 and 360 deg. are negative and will give the wrong answer. If the relative target bearing is between 180 and 360, the "bearing angle" must be measured from the bow going counter-clockwise. Note also, that at relative target bearings of 0 or 180 deg., the last term becomes 0, and one need not know the Aob. The same goes for a sub that is not moving. Similerly, if the sub is on a parallel course, the ratio (sin Abg / sin Aob) becomes 1. Also, as before, if viewing the port side of the target from port side of the sub, or starboard side of target form starboard side of sub, then subtract the sub speed. (This would mean you are heading in opposite direction of target.) Well, I think I got it right this time. I did a numerical test case and it checked out. One more thing; I would not try to use this for targets at a very sharp aspect, that is at Aob angles near 0 or 180 deg. This would make it very difficult the time the transit. I believe Don Reed mentioned this also. If anybody uses this, in game, please let me know how it works.