Humming Foils Help Required!

Thread starter #1
Hi all,
Recently, when out sailing in moderately strong winds, i have noticed a humming sound when planing. The sounds seems to have two 'frequencies' which appears to depend on how fast the boat is travelling. Originally i thought the sound was due to the bow being out of the water and the wind whistling between the hull and the water (stupid idea i now have realised :p).

On doing some research in my copy of the Rya Laser Handbook and on the web, i now believe the sound is due to either the foils being misaligned or due to the trailing edge of the centre board not being very straight. The problem i now face is that i do not know which of the possible causes is to blame and once i determine which issue is causing the humming how to go about fixing it.

Any ideas? All help big or small appreciated :D (the sound nearly drove me mad last night so time has come to fix it!)

Cheers
 
#2
You should be able to see by eye if your foils are straight or not. If they are warped along the trailing edge you can warm them up so the edge becomes flexible and straighten them yourself. My foils have been straightened this way over an electric hob but a hair dryer might work too.
 
#3
i should assume this is your firs time sailing a laser in plaining conditions as all lasers make a humming noise when plaining and yes the frequencies will deffer depending on boat speed all lasers humm because of the bad fit between the daggerboard and the hull also when plaining water is thrusted up the rear of the slot and is also forced between the centerboard one side greater thant the other making it move to the weaker side then the reverse happens and it moves really fast ever so slightly if youre plaining and get ur hand onthe daggerboard youll feel this, theres nothing you can do about it! (assuming your daggerboard is strainght and hydrodynamically equal) although being on a broard reach the board is pushed to leeward making it hydrodynamically wrong.


dont worry about it go ssailing on the plain and have some fun!!!
 
#4
All Lasers do not hum, as prev mentioned it's an issue with blade shape and/or blade alignment. Reasonably easy to fix.

If you have access to another set of blades (borrow a friend's that don't hum), you can also try those to help you determine if it's the daggerboard or rudder or both :-( that need to be fixed
 
#7
This is caused by the shape of the dagger board. And it is difficult to avoid.
Would the dagger board have a different shape, for example, a width of 30 cm at the top and 20 cm at the bottom, it would be more difficult to bring in resonance.

So, in my opinion, there is no solution, except for buying a jig saw and reshape your dagger board.:eek:
 
#8
Every time I have a foil that hums I straighten them and then rub the trailing edge down with sand paper (only about 10 sec either side). They never hum then!
 
#9
Sail more dead down with your centerboard up and you will find most of the humming goes away.

i should assume this is your firs time sailing a laser in plaining conditions as all lasers make a humming noise when plaining and yes the frequencies will deffer depending on boat speed all lasers humm because of the bad fit between the daggerboard and the hull also when plaining water is thrusted up the rear of the slot and is also forced between the centerboard one side greater thant the other making it move to the weaker side then the reverse happens and it moves really fast ever so slightly if youre plaining and get ur hand onthe daggerboard youll feel this, theres nothing you can do about it! (assuming your daggerboard is strainght and hydrodynamically equal) although being on a broard reach the board is pushed to leeward making it hydrodynamically wrong.


dont worry about it go ssailing on the plain and have some fun!!!
 
Thread starter #10
Hi all, thanks for the advice

i should assume this is your firs time sailing a laser in plaining conditions as all lasers make a humming noise when plaining.
This wasn't the first time i had heard the hum when plaining but it did seem louder than usual last time, that said some of the gusts pretty fierce. I don't think i the sound is as prominant on all lasers as when i sailed a different laser (a tatty heavily used beach boat) in similar conditions i didn't hear the 'humming'. That said though, thank you for your thoughts.



You should be able to see by eye if your foils are straight or not. If they are warped along the trailing edge you can warm them up so the edge becomes flexible and straighten them yourself. My foils have been straightened this way over an electric hob but a hair dryer might work too.
On closer inspection i have noticed that the trailing edge of my centerboard is considerably warped so i now know what i have to fix. Thankfully my rudder is fine.


Sail more dead down with your centerboard up and you will find most of the humming goes away.
surely by doing this i wouldn't make the mark rounding and also would go slower? please correct me if i am being thick though :D
 
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