[C320-list] High pitch whining (singing) noise from shaft above 2800

[jbrown5093 at yahoo.com]

I saw a good example of harmonics with blades going through the water watching the America's Cup trials. The Swiss boat's foils really screamed above 20 knots. 

Jim Brown

Sent from my iPad

> On Jun 19, 2017, at 6:09 PM, jbrown5093 at yahoo.com wrote:
> 
> The singing is from harmonics off of the sharp prop edges.  Happens with both 2 blade and 3 bladed fixed props and is just at the rpm you mentioned and which I use a lot. Sounds bogus I know but my yard was well aware of the noise and cured it on the next haul out by slightly  rounding the prop leading edge with some sandpaper.  I would not worry about it until you are hauled. 
> 
> Jim Brown.   Desafinado 973
> 
> Sent from my iPad
> 
>> On Jun 19, 2017, at 4:51 PM, danny jensen <danny at jensenshouse.com> wrote:
>> 
>> I have hull 972 with new shaft,strut  and stuffing box about 4 years ago.
>> Cutlass was replaced about 5 years ago.
>> 
>> When I run above 2800 the singing starts.  Then at 3100 it stops.
>> 
>> I've got GFO standard packing and the noise is not coming from stuffing
>> box. Only happens in gear. It Didin't sound like if was from transmission.
>> 
>> If the prop hits a chunk of kelp, this fixes the problem for a while and I
>> don't hear any singing.
>> 
>> Any clues?
>> 
>> Danny
>> #972
>