Quote:
Originally Posted by TorpX
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.
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oh yes TorpX ...this formula is the correct one !
have in mind this: the angle that is named as 'AoB' in this formula is NOT trully the Aob but a 'compromised' angle that is very close to AoB.these angle as so close that 'allow' to this formula to give 'acceptable' results for target's speed
(for those that interested)...the 100% correct formula is :
a) length in meters and time in sec :
u(t) = 1,944 x [length/time] + u(b) x [sin(Abg)/sin(lb-Abg)]
b) length in feets and time in sec :
u(t) = 0,593 x [length/time] + u(b) x [sin(Abg)/sin(lb-Abg)]
where,
u(t)= target's speed
u(b)= u-boat's speed
Abg= bearing angle
lb= target's course angle relative to own course
ps:@TorpX:if there is interest in this theme i can give you the proof of the above formula
ps2:try the back side of attack disc ...it allows you with these data to get target's speed without having to use a digital calculator ! i believe that they did it that way back then.
bye