submerged navigation turn circles

[GenXGamer]

ok...
so I've been doing some circles in the uboot to figure out turn radius for speed in knots.
The equation looks linear regardless of ballast level or depth.


radius=knots*55/3

This is a rough estimate for only 30 degree turns. I have to figure out adding rudder angle into the equation.


Handy for drawing the turn circle when predicting the path of the submerged sub during a turn.

also, full 360 degree turn at 30 degree rudder is 4 minutes.
that comes to 1 min per 90 degrees.
or 20 seconds every 30 degrees.


I assume that the rudder values are "degrees per 20 seconds"


hope this helps fellow navigators....now if only we can get the crew to keep us properly informed on contact bearing/distance and when steady and controlled turns will begin.

:)

[EmptyK]

Isn't the rudder value just the angle of the rudder?

[GenXGamer]

maybe, but what I'm more concerned with as a navigator is how long it takes to make a circle and what that radius is for various speeds.

[Valen]

Turn full circles at whatever rudder angle and speed/RPM you wish to test, and time the lap with the compas. Then calculate the circumference of the circle based on the speed indicated and time of the lap. (good chance the odometer matches that) From that radius should follow by dividing by 2 pi.

[Soda]

I'm using this equation to calculate the chord:
chordlength = 2*Odometer/Radians(turn_in_degree)*Sin(Radians(turn_in_degree)/2)

This is the chord for turn circle.

[Go_Rongor]

Originally posted by TK-421:

I assume that the rudder values are "degrees per 20 seconds"

Don't. Because they're not.
Rudder effectivity is heavily relying on speed and water density (=depth, temperature...)...

[GenXGamer]

this is what i've measured with rudder setting to speed: (each value tested twice)


at 7 knots

rudder time to turn 90deg
5 4:54
10 2:34
20 1:16
35 0:56



10 knots

10 1:46
20 0:56
35 0:56



18 knots

5 2:03 - 2:05
10 1:02 - 1:03
20 0:56
35 0:55 - 0:56



the turn speed is dramatically affected at lower speeds and lower rudder settings.
but when speed and rudder increase, turn speed reaches a limit of about 56 seconds.

these measurements were taken at surface with diesel.
I waited to reach speed before measuring.

last time I did this test i did not notice a difference in times underwater an various depth.
I would expect the greatest effect on water pressure within the first 33 feet (first atmosphere) as the ratio is highest. the deeper I would go the ratio gets smaller for ever atmosphere. (this is why we feel most pressure change when diving to 33 feet and most at risk of getting decompression sickness coming up to quick at that depth when scuba diving)

regardless..going to give a time test at 1 atmosphere (aprox 10 meters per atmosphere) and then again about 100 meters down

[GenXGamer]

1 atmosphere (10 meters) 7.5 knots.....35 rudder = 0:56 seconds per 90 degrees

~100 atmospheres (100 meters) 7.5 knots, 35 rudder = 0:56 seconds per 90 degrees

depth has no effect on full rudder and full electric speed