Propspeed meet Singing Prop

[Hydraulicjump]

Picked up my boat from the yard a few weeks ago and headed back to my slip in Elliott Bay. When I slowed down I heard the sound of a banshee in the vicinity of my PSS shaft seal. I immediately blamed the yard, of course, but could not for the life of me figure out what was going on. This was not the sound of a cutlass bearing, that is for sure. Then this last week we headed north to Canada for the 4th (my earlier post asking if Lake Union was a good place to watch fireworks from convinced me to get out of town). The soprano aria only occurred between 1000 and 1200 rpms (single prop). Fortunately, while hiking on Stuart Island of all places I ran into Van Helker of Helmsman Trawlers. I described the haunted boat sounds and he asked two questions: 1) have you done any work in the yard (yes) and 2) did you perhaps put Propspeed or something like it on the prop (bingo).

In an internet search I am not the first to experience this. And I am embarrassed for having never paid attention to it, but it is quite common. And the physics is both complex and not all that well understood. The additional layer of Propspeed is just enough to start shedding vortices at the edge of the prop that then set up a nice loud harmonic. Most of the veterans on this forum who know so much more about this can weigh in, but I am stuck. Short of hauling the boat and having a shop remove the Propspeed, or at least smooth the edges, I think I learn to live with it until I haul the boat again for something else.

Just a heads up I guess. Happy 4th to you all, even if you are on Lake Union in the scrum telling yourself that you really do like people and crowds and knuckleheads in boats.

Jeff

 

[Delta Riverat]

Stay safe and have fun!

Fourth of July knuckleheads are some of the worst. Too much beer, too loud mufflers and too loud music.

"Can you hear me now"

But all should quiet down after they get off the water and back to work, there will be peace until Labor Day -

 

[klee wyck]

Not to worry. I get this every time I apply new prop speed. It usually only affects a narrow band of the rpm range which I avoid for awhile, and then it goes away mostly after 6-12 months.

 

[luna]

If you want to eliminate it from happening again, try filing a 20º bevel on the backside of all of your prop blades for about 1/4 of the length of the edge of the business end of each prop blade.
Yes, this will go through the Propspeed finish, that you may then chose (or not) to restore once you have finished with the filing.

Here is a reasonable explanation. https://neprop.com/wp-content/uploads/2017/07/anti-sing-edge-instructions.pdf

Once done it should not be needed to do it again. My bevels are about 12 years old and still work just fine, the props are silent. I filed the bevel ( 4 blade, 33"props.) as I'm no good with a grinder. Took about 30 min. per prop.

Good luck with the filing, or in the meantime, just sing along with the props.

 

[Hydraulicjump]

Thanks. These are great recommendations. I am not due for bottom paint for another three years (did a double coat this time) and my patience with a file is not particularly strong. I can only see disaster with a grinder, so I think I will sit on this for a bit and every time the singing starts I will think of Madeline Kahn in that great scene from Young Frankenstein “Oh Sweet Mystery of Life at Last I’ve Found You”. Not appropriate to put in a link here, although those of us who remember this classic will know exactly what I mean.

Ha! Happy 4th from Ladysmith BC

 

[O C Diver]

This happens when the propeller is sanded or sand blasted to clean the surface. Basically the leading edge and the outer radius are tapered to a fine edge. The simple solution is to take a flat file parallel to the edge and take the edge off. It takes very little to correct the problem. Having delt with this twice, after the prop is cleaned, I check the edge and flatten it if necessary before they paint.

I did it the first time while cleaning the boat bottom on scuba. Probably took less than 5 minutes.

Ted