Well, I finally got out for this season's shakedown cruise which was great except I'm noticing a fair amount of hum from the daggerboard and/or rudder on the starboard side.

I'm not aware of needing to reshape the trailing edge of these foils like one would do on a Hobie to reduce hum, but maybe it's needed?
There's about 1/8" of play total between the tiller cross-bar and tillers. Could this be part of my problem?

Any ideas to remedy this would be appreciated.

Thanks.

I get some cavitation (sp?) in my boards when I get above about 8 knots of boat speed (that is a guess because I don't have a GPS to judge speed). The board just kind of hum. I like it because it lets me know I am staying at speed. I think the easiest way to get rid of it would be to put some indoor/outdoor carpet in the daggerboard wells at the front and back of the well. Just a little piece to hold the front and the back of the board stable would probably fix the problem.

Rob V.
Panama City
Nacra 5.2

I don't know the daggerboard slot arrangement on the 5.2. but do you have anything to 'isolate' the board from the hull. I mean something like a carpet or felt or neoprene liner or gasket at the bottom of the slot?

The reason I ask is that on my Stealth I have just lost the thin piece of short bristle material from the bottom of my port board case. Result - I now have hum when I didn't before.

I fully expect that when I find a suitable replacement, silence at speed will return

Tim,

That's a tough one - some great suggestions have been made above but I think you will find that the solution will lie somewhere in what you originally suggested - fairing the boards or reshaping the trailing edge. I can't speak from experience because I struggled to get my 6.0NA to be quiet (my 5.2 sang loudly too - but I never tried to fix it). I reshaped the trailing edge of the boards to no avail. After consultation with a lot of different people, my next task was going to be to look for "hollows" in the profile of the board and fix those if any existed. The way it was explained to me: take a straight edge and place it along the board (or rudder) vertically. Look for hollow spots as you slide the straight edge fore and aft. These concavities - particularly if they are uneven, apparently can cause the singing. Try filling those up maybe?

Don't take all the play out of the tiller/tiller cross bar connection. If you do, you will not be able to tack. (I did it once).Swing the rudders side to side and watch the connection get tight and lose. The NACRA is not a real 3 axis connection and depends on play to make up the difference. About a 1/16" of play is needed.

It is normally the trailing edge that causes hum. Make sure everything is smooth and square.

Thanks everyone for your suggestions.
I'll try them and post the results.

Status Report:

I purchased some "Board Carpet" from Annopolis Performance Sailing for 1.85/ft. It's 1" wide 1/4" thick with adhesive backing. I only needed about 1" to 2" per side to tighten up the daggerboard play.
This reduced the hum by maybe 60% of what it was.
It's almost tolerable now.

However, I'll probably end up smoothing the trailing edges of both boards and rudders in the fall.

I also tightend up my tiller extension a bit which also helped the helm response.

Question:
On starboard tack I'm getting slight weather helm (good) but on port tack I'm getting a little leeward helm. I noticed that my port tiller arm has been dented inward from the inboard side by maybe 1/4". Could this be the reason for the leeward helm on port tack?

Thanks,

Tim