Hi Guenther:
As seen in the attached screenie of the FS9 Aircraft SDK documentation on Effects, "waterspeed" refers to display of a specified water spray Effect when the aircraft velocity is at "higher" speeds; this is to be distinguished from a specified water spray Effect intended to be displayed when the aircraft velocity is at a comparatively "lower" speed.
IIUC, one can either map the same or a different Effect (*.Fx file) to be displayed when the aircraft velocity transitions from the lower speed range to a higher speed range.
I'm not sure where / how FS defines 'low' versus 'high' water "ground-roll" (water taxi) speed ranges, but I would speculate that it might be halfway between a speed from 0 to water take-off capability in KIAS.
BTW: One will hear a difference in sound file speed of the Wind and Water when specified WAV files are played as an aircraft's velocity varies.
This can be achieved by specifying certain parameters in the [FS9 install path]\Aircraft\[airplane name]\Sound\Sound.cfg file
ex:
[WIND_SOUND]
filename=c5wind2
minimum_volume=6000
maximum_volume=8500
minimum_rate=0.60
maximum_rate=0.90
minimum_speed=40.0
maximum_speed=120.0
...and:
[GROUND_ROLL2]
filename=LA-H2O_Bumps2
// filename=waterloop
flags=8
viewpoint=1
minimum_volume=8000
maximum_volume=10000
minimum_speed=15
maximum_speed=45
minimum_rate=0.25
maximum_rate=0.95
viewpoint=1
link=GROUND_ROLL3
[GROUND_ROLL3]
filename=LA-H2O_Bumps2
// filename=xwaterloop
flags=8
viewpoint=2
FYI: The latter edited "Ground_Roll" entries utilize a sound file I recorded in 16-bit WAV files during some real world flying I did in a Lake LA4-200 EP Amphibian aircraft several years ago with my colleague; the default "Waterloop" sound was substituted by my own custom WAV file.
PS: You could try substituting another Effect (*.Fx file) from the [FS9 install path]\Effect\ sub-folder such as "
fx_campfire.fx" or "
fx_ForestFire.fx" to see if you can better distinguish whether / when the Effect is being displayed (among the mist created by 'sprites' associated with the default waterspray Effect)... to test the above "waterspeed" scenario further.
If this test scenario works for you, it would interesting to know at what speed in KIAS the substituted "waterspeed" Effect is actually displayed, so I'd appreciate your being so kind as to share the test results with us back in this thread afterward.
Hope this info might help a bit more !
GaryGB