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Marco Flamingo
Joined: 09 Jul 2015 Posts: 1155 City/Region: Seattle
State or Province: WA
C-Dory Year: 2004
C-Dory Model: 16 Cruiser
Vessel Name: Limpet
Photos: Limpet
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Posted: Mon Oct 23, 2017 7:20 pm Post subject: Cavitation burns |
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These showed up right after I put on my new prop, and never got any worse, so I just let it be. But I'm wondering if it might be the symptom of something I should correct. It's mostly just the paint that's missing, but the underlying aluminum is rough, so it must have taken (or is taking) some of the metal off.
[img]http://www.c-brats.com/modules.php?full=1&set_albumName=Limpet&id=102_0156&op=modload&name=gallery&file=index&include=view_photo.php[/img]
I still have never successfully placed a picture in a post on this site. That has to be a record. It's the last picture in the Limpet photo album.
Mark[/img] |
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Robert H. Wilkinson
Joined: 26 Jan 2011 Posts: 1235 City/Region: Port Ryerse
State or Province: ON
Vessel Name: Romakeme IV
Photos: Romakeme IV
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Posted: Mon Oct 23, 2017 7:54 pm Post subject: |
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_________________ Talk to me and I will listen-- but if its not about boats or fishing all I will hear is bla,bla,bla,yada,yada,zzzzzzzz |
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Da Nag
Joined: 24 Oct 2003 Posts: 2820 City/Region: Port Angeles
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 16 Angler
Vessel Name: Taco
Photos: <a>Da Boats</a>
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Posted: Mon Oct 23, 2017 9:34 pm Post subject: Re: Cavitation burns |
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Marco Flamingo wrote: | I still have never successfully placed a picture in a post on this site. That has to be a record. It's the last picture in the Limpet photo album. |
https://www.youtube.com/watch?v=IjPmIRvAPww _________________ Will, C-Brat Nerd |
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thataway
Joined: 02 Nov 2003 Posts: 20829 City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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Posted: Mon Oct 23, 2017 10:41 pm Post subject: Re: Cavitation burns |
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Marco Flamingo wrote: | These showed up right after I put on my new prop, and never got any worse, so I just let it be. But I'm wondering if it might be the symptom of something I should correct. It's mostly just the paint that's missing, but the underlying aluminum is rough, so it must have taken (or is taking) some of the metal off.
Mark |
Mark--the change you made is the new prop... What is the difference from the old prop? Several things involved--turbulence from a transducer ahead of the prop, different configuration (cupping or rake) in the prop, prop too high, running at constant RPM where the cavitation is worse.
Here is a quote from Tom Clarke (Whose opinion I greatly respect) on THT Quote: | "Let me straighten a few things out about cavitation and ventilation, which are two distinct phenomena.
Cavitation is NOT the formation of air bubbles. The bubbles formed are vacuums, or more precisely water vapor, not air. Cavitation bubbles are formed when the pressure is so low the water goes from the liquid phase to the vapor phase. Remember how water boils at lower temperatures at higher elevations? ....
The damage to a propeller blade occurs when these bubbles collapse actually eroding the stainless steel (or other metal) of the blade.
Ventilation is the sucking in of air from the surface or exhaust gases from the exhaust into the propeller and the dilution of the solidity of the water around the propeller with these gases."
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So will it eventually damage the blade? Yes. Is it doing any harm to the boat or engine? Most likely not.
What can be done? Change props. Take the prop to a really good Prop Scan Shop, and see if they can change the cup....but this will most likely cost more than another prop--down the line.
You might try running at different RPM's than you are most of the time now--higher or lower.
If the engine is performing correctly--I would not change the height. But in some cases that may help.
If there is anything close to the prop causing turbulence, that can be moved further outboard--consider that.
What is the WOT RPM and GPS speed?
Personally if the boat is reaching its rated RPM at WOT, then I might see if changing the trim of the motor makes significant difference--but probably run with it, and buy a new prop down the line...The next prop may be fine... _________________ Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
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Barry Rietz
Joined: 21 Jun 2006 Posts: 409 City/Region: Sierra Vista
State or Province: AZ
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Posted: Mon Oct 23, 2017 11:48 pm Post subject: Cavitation Burns |
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These props are cast from molten aluminum. The molten solution could have had some impureties that collected at the outer edge of that blade. Another possibility is the prop could have been removed from the tool before it was fully cured. Unless it occurs on the remaing blades, I would just keep an eye on it and not worry. _________________ Barry Rietz
N9DXC |
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