Discussion in 'Laser Talk' started by moranatang, May 8, 2008.
How do u stop the daggerboard humming and do u have to sand the tiller blade asl well
My coach has said to have the trailing edge (aft) as square as can be, not pointy! Ive never sanded my blades so I wouldnt know!
Do your blades hum?
Slightly different take on this topic--is it useful to sand the trailing edge of the centerboard square even if it doesn't hum?
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.
Well with my new blades, they start to hum in about 15-20 reaching in a radial!
Well im quite unsure about this, have your blades ever hummed? If yes then I would probabally lightly sand them, but I am only 14 so who knows!
When my blades hum I know I'm going fast .
Now if they didn't hum would I go faster? If so is it that much faster?
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?
I dont think its a problem as majority of the fleet are having the same problem. If you can hike that much longer or call a big shift you can make even bigger gains
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.
Why do blades hum? .....Because they don't know the words.
Rob - what is the secret sauce to end the humming (and it better not be give them a lyrics sheet)?
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 have always filed the trailing edges to make them sharper.
What about narrowing the daggerboard slot with stick-on teflon or something of that sort?
And does the vibration really stop if you square off the aft edge of the daggerboard?
I just got my fourth Laser, and this is the first one where vibration is in my opinion, a problem. It starts up in winds of say 10 or 12 mph.
its illegal to narrow the daggerboard slot
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.
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