vibration in rudder under sail?

[puddlejockey]

Hi guys;

I'm getting a vibration...more like a throbbing, in the rudder of my H27 while under sail, that never seemed to be there before. I haven't changed the tuning or made any functional changes to the boat, and it does NOT seem to happen under power.
any thoughts?

Thanks!

Jim

 

[JoyRide28]

Could it be your prop spinning?? You can check by putting the transmission in reverse (engine off, under sail). If the vibration stops immediately then you've got your cause.

Some people advocate always putting it in reverse while under sail to stop vibration and (in theory) reduce wear and tear on the tranny... I'm really not convinced one way or the other...

 

[RichH]

Early Hunter 27 rudders easily cavitate or 'suck air' when the top of the rudder is exposed and is partly out of the water. If this happened during a 'heavy helm' (weather helm or skid to leeward) event and the boat heeled over - then what you feel may be the beginning of a rudder cavitation and these may be the warning signs that youre about to totally lose control of the boat by its rudder. The H27 shoal draft is especially prone to 'sudden' loss of rudder control when 'pressed' and is heeling.

If so, the Rx is to remove that 'heavy helm' by better sail SHAPING, better Sail trim, proper rig/shroud tensions, etc. … so that the turbulence wake coming off the stern of the boat is no more than about 3-4° from the boat's centerline (an almost 'neutral' or almost 'dead fish' helm). If your boat is prone to 'weather helm', suggest you do something about it, or keep your companion way boards in place during 'heavy weather', etc. in case that rudder 'loses its bite' because its sucking air down along side of it.

Also a rudder that has lost is stiffness or a rudder with a sharp leading edge can experience this. Next time out of the water, pull sideways on the bottom of the rudder and see if the rudder is 'bowing' due the side forces applied.

 

[Johnb]

When I was sailiing dinghys the solution was to sharpen the trailing edge of the rudder and or center board. That eliminates the vortices that are shed and result in the vibrations.

 

[rufus1138]

we have a problem lately in pensacola bay of getting a "shudder" like that, its jelly fish, really freaks you out first time it happens lol.

 

[Eddie7045]

I understand the feeling there. I had an Ericson

that sailed really sweet but I noticed a slight vibration when I was on a long tack. The next time that I had it hauled out I asked the owner of the yard about it. He checked it out and said that they do replace a nylon sleeve on rudder shafts but that mine had less play than some brand new boats that he has gotten ready to put in the water. I chalked it up to one of those things that is always just over the rainbow and got accustom to it.i did feel a lot better about it after I had it checked out.

 

[puddlejockey]

Thanks, all, for the responses!
Rich, your answer certainly seems like it may be the culprit at least partially, since the last few times I've noticed it we've been at a slight to moderate heel- 10-15 degrees.
sadly, I thought I was getting pretty good at sail trim....until I bought the chart.

Now it's obvious to me that I just don't know enough to understand what I don't know....