Vibration

I cruise my FS4372 out here on the left coast of Canada. When the boat really gets moving on a beam reach with a stiff wind, there is a vibration set up that resonates quite a hum through the whole hull. It feels like it could be coming from the rudder but since it resonates in the whole hull it could also be the centre board. it disappears as soon as speed drops to 'normal' cruising levels. Anyone experienced the same? Ideas on cause and gow to fix would be greatly appreciated.

Comments

At higher speed, the centerboards hum in both my former and new

At higher speed, the centerboards hum in both my former and new Scot, so don't wory about that. Do you feel the vibration throught the tiller? I do not, so maybe someone else will comment on that. FSSA Forum editor

The hum is most often in the rudder, but it can also be the cent

The hum is most often in the rudder, but it can also be the centerboard. It is caused by the way the trailing edge is shaped and is easily fixed. Take a fine file and work the trailing edge so that it is not square. If one side is slightly longer, the humming should stop. It would be best to do the rudder first since it is easier to manage.

I've noticed that hum too and all along I thought it was just "g

I've noticed that hum too and all along I thought it was just "good vibrations." Our cats purr when they're happy so there's no reason a Scot shouldn't hum when it's pleased!

The humming is indeed caused by vortex shedding from the trailin

The humming is indeed caused by vortex shedding from the trailing edge of the board. These links below give pretty piccies of vortex shedding:- http://homepage.ntlworld.com/joetapley/fvort.htm http://www.kevin.harkess.btinternet.co.uk/wisp_ch_2/wisp_ch_2.html http://www.ae.ic.ac.uk/research/rotorcraft/pubs/AHS2001.pdf Don't be concerned if they refer to air or other gas and not briney, as all fluids obey the same laws. A squared trailing edge and radiused trailing edge can both cause vortex shedding. In fact a sharp trailing edge can cause vortex shedding, but this requires a large angle of incidence which is avoided unless you sail almost sideways! The upstream shape of the body and where the water came from is largely irrelevant, vortices are caused by the two flows combining in the foil's wake. The frequency of the vortex shedding is a function of the speed, shape and size of the trailing edge. The quicker you go, the faster the vortices are shed. The wider the trailing edge, the slower the rate of vortex shedding (lower pitch), and the slower you need to go. Next time you're about to stir a cup of tea, don't stir but move the spoon in a straight line and look for vortices. Use both ends of the spoon. The humming noise is caused when the frequency of vortex shedding roughly matches one of the resonant frequencies of the board. These frequencies 'lock' together. This also explains why you only hear one or occasionally two frequencies at a given speed each. To reduce vortex shedding - reduce the width of the trailing edge or radius it. The vortices have little/nowhere to form before separating and drifting downstream. Thus vortices become small or non existent. To reduce humming - do above, or at least vary the width of the trailing edge. Tall chimneys either vary in width or have spiral 'spoilers' that prevent long vertical vortices being shed. Before the invention of these spoilers, they used to rock sideways and then fall over in a breeze of a given speed.

HarryC, If I run a file or sanding block down the trailing edge

HarryC, If I run a file or sanding block down the trailing edge to square off or angle off the trailing edge, is this allowed under the class rules? I'm asking about the rudder and the centerboard.

Can you please elaborate more on this subject? I am a bit confus

Can you please elaborate more on this subject? I am a bit confused. [url="http://www.hotels-all-over-the-world.com/portugal-hotels.html"]Portugal hotels [/url] - [url="http://gaming-online-poker-true.lavoa.com"]pai gow online poker[/url]