Even on day light ? At bright condition how we can get silky feel on sea/lake/river etc ….so normally we will use a big stop of ND and in the market have few well known

1.  B+W/Schneider 10 stops filter (nd1000x) (10 stops)

2. Lee Filter Big Stopper (10 stops)

3. Hoya400 (9 stops)

At daylight (Malaysia), even with smallest aperture & lowest ISO … we still will get something 1/400-1/100… e.g. even with 1/100 we will never get the silky effect

and this was shoot early morning where already bright enough to fail you to make silky wave…by using the “Lee filter – Big Stopper” I shoot with exif below

# Exposure Time (1 / Shutter Speed) = 116/1 second ===> 116 second
# Lens F-Number / F-Stop = 11/1 ===> ƒ/11
# ISO Speed Ratings = 200
# Original Date/Time = 2010:12:18 07:26:43

or with sun still on the horizon, I still able to make the shutter to 20s to create the silky as exif below sharing

5dm2 + 1635@18mm + Lee Big Stopper + Lee .9s GND
# Exposure Time (1 / Shutter Speed) = 20/1 second ===> 20 second
# Lens F-Number / F-Stop = 9/1 ===> ƒ/9
# ISO Speed Ratings = 100

previous share on this super ND with some compare among Big Stopper vs Schneider

http://liewwk-macro.blogspot.com/2010/11/my-gear-10-stops-nd-filters-b-w-nd100.html

and for those interest on Schneider – nd1000x (which give you 10 stops) and I have few on my hand brand new and few free to click link below

http://liewwkphoto.com/blog/?p=386