RAOBF and speed calculation

kraszus · 03-28-21, 04:29 AM

I've watched a few tutorials on RAOBF usage and it seems to me that most measure speed using the scope, ship length and time taken for ship to pass through centreline. However, none of the tutorials I've seen take into account the AOB of the ship. For example, surely a ship with an AOB of 45 will pass through the scope more quickly than a ship with AOB 90 at same range? Thus giving an incorrect speed.

So is it the case that RAOBF speed calculation is only accurate when target ship has AOB 90?

Or, more likely, I have failed to understand something?

kapuhy · 03-28-21, 05:29 AM

Quote:

Originally Posted by kraszus

surely a ship with an AOB of 45 will pass through the scope more quickly than a ship with AOB 90 at same range?

No it won't - and in this lies the beauty of this method:

In this example, two captains are calculating speed of the ship. Kaleun A is at more or less 90 AOB, Kaleun B at much narrower angle. Both place centerline of their scopes at bow of the target and wait until ship passes its entire length as seen through the scope.

As you can see, while distance traveled by the ship will appear shorter for Kaleun B, the apparent movement of the ship will be slower for B as well. For both observers, ship will take the same time to cover known distance (ship's own length in this case).

Thus, you can use this method to calculate speed at any AOB other than 0.

kraszus · 03-28-21, 07:09 AM

Thanks Kapuhy...that makes sense now.

Compans57 · 04-17-21, 02:18 PM

Can someone tell me if you end the time measurement when the stern of the ship reaches the inner or outer edge of the vertical?

les green01 · 04-17-21, 09:30 PM

Quote:

Originally Posted by Compans57

Can someone tell me if you end the time measurement when the stern of the ship reaches the inner or outer edge of the vertical?

i always use the outer but has small the vertical is i wouldnt think it matter much

Compans57 · 04-18-21, 12:07 AM

Quote:

Originally Posted by les green01

i always use the outer but has small the vertical is i wouldnt think it matter much

It depends on how slow the ship is going and how far away. It can be the matter of several seconds sometimes.

Also, is it best to round numbers 'up'. ie 4.56 works out as 5 knots?

les green01 · 04-18-21, 08:23 PM

let say 4.5 i round up below .5 i round down i know you use the electric eels a lot on the description does it show the speed of them at 28kts or 30kts for you

03-28-21, 04:29 AM	#1
kraszus Mate Join Date: Jun 2005 Location: Ireland Posts: 53 Downloads: 370 Uploads: 0	RAOBF and speed calculation I've watched a few tutorials on RAOBF usage and it seems to me that most measure speed using the scope, ship length and time taken for ship to pass through centreline. However, none of the tutorials I've seen take into account the AOB of the ship. For example, surely a ship with an AOB of 45 will pass through the scope more quickly than a ship with AOB 90 at same range? Thus giving an incorrect speed. So is it the case that RAOBF speed calculation is only accurate when target ship has AOB 90? Or, more likely, I have failed to understand something?

04-18-21, 08:23 PM	#7
les green01 Seasoned Skipper Join Date: Jan 2002 Location: Freeman Missouri Posts: 1,784 Downloads: 1405 Uploads: 0	let say 4.5 i round up below .5 i round down i know you use the electric eels a lot on the description does it show the speed of them at 28kts or 30kts for you __________________ I'll tell you what bravery really is. Bravery is just determination to do a job that you know has to be done. Audie Murphy Last edited by les green01; 04-18-21 at 09:37 PM.

03-28-21, 07:09 AM	#3
kraszus Mate Join Date: Jun 2005 Location: Ireland Posts: 53 Downloads: 370 Uploads: 0	Thanks Kapuhy...that makes sense now.

04-17-21, 02:18 PM	#4
Compans57 Officer Join Date: Apr 2020 Posts: 245 Downloads: 77 Uploads: 0	Can someone tell me if you end the time measurement when the stern of the ship reaches the inner or outer edge of the vertical?