The blade people (and hydro experts) I have talked to like to see either a sharp trailing edge (which is impossible to maintain on the Laser) or sharp edges between side and back, either square or beveled. Very similar to ice skates and snow ski edge thinking.
IMHO the blade hum is a vibration under the boat, (like a flapping leech on top of the boat). It absorbs energy and reduces speed. Think of it this way....A race car going down the track picks up a tire vibration that starts at 190 mph. There is a car right beside it with no vibration and thus is easier to handle and accelarate for the driver and easier to control.
So what do you think is faster. Smooth and quiet or vibrating and loud?
Everyone in my fleet has worked with their blades to stop them from humming.
When I go to big events I do not discuss blade hum with anyone. Of all the things we discuss about the boats blade hum is not one of them. So I assume everyone has fixed theirs, but I don't know for sure.
My guide to fast foils:-
1. Ensure the foils are not warped or twisted
2. Fill or polish out all dents, scratches and be super super critical around the leading edge radius, super critical in front one third of chord, critical over remainder. Make sure that the leading edge radius is just that - no steps or flash lines.
3. Sand a square flat at the trailing edge that should not be any more than 3mm wide. Sharp corners are best.
4. Wet and dry finish starting with say 400 grit>600>800>1000>1200>cutting polish>polish and try to get to as close as possible glass finish.
5. Inspect after every race and keep them that way.
Foils are just as important as sails and don't cost much to maintain - just time!!!
I'm not sold on the idea that the harmonics produced by the CB affect speed significantly. How about someone run a speed test and compare a "hummer" with a "non-hummer"? I mean are we talking the difference between going .00000001 knot faster without hum? Or is it a bigger difference that would dramatically improve results? Or is it placebo effect: no hum, feels faster? We can guess and hypothesize all we want, but I think the truth will only be found out with actual OTW speed tests comparing the situatons. My CB is trim and filed with 3mm squared sharp edge and I still get humming sometimes. I tend to fly on reaches (when the humming might happen). I think it's more about boat handling and weight rather than a hum or not, but then again the experimentation is really the best way to find out what's really affected.