170 Rumble Question...

[BlueRunner]

I've noticed that my 170 rumbles, vibrates, groans or moans when the breeze freshens and the boat accelerates through around 4.2-4.5 MPH. As soon as it reaches around 4.5 MPH and above, the noise ceases. I suspect it's some kind of flutter in the center board, but I don't feel anything when I touch the top of the board.

If nothing else, it's a good warning to start paying close attention to the mainsail sheet. Do other 170's "groan" around this speed? I'm wondering if I should be concerned about the center board pivot?

For those who may wonder, the speeds above are from my GPS.

 

[capejt]

Sometimes they just make noise

Your story reminds me of my days racing Hobie Cats. There you get going fast enough and the rudders develop a hum that turns into a higher pitch buzz as speed increases. I just accepted it as part of the "speed" package. It sort of adds to the adrenelin at times. I wouldn't worry about it, but if it annoys you I suppose you could put spacers in (maybe a series of washers or something) to make the centerboard pivot a bit more "rigid".

 

[BlueRunner]

Re: Sometimes they just make noise

It doesn't annoy me and like I mentioned, I DO grab the mainsheet for quick release if lee rail goes below my personal limit. The fastest I've seen the boat go is 6.1 MPH just briefly. Maybe the noise is just something tightening up. Wouldn't even surprise me if it was a shroud line.

I've seen similar noises on my fishing boat down rigger lines when the line starts to hum.

 

[esterhazyinoz]

I experienced the same moans and groans when I raced my 21 foot daysailer, particularly on a reach or run with the spinnaker flying. Haven't had it on my H15 yet as I have only sailed in light winds so far. I suspect it is a function of the forces that are in play on the rigging and flow across the centreboard.