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Cause cavitation?
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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sun Nov 08, 2009 9:13 pm    Post subject: Reply with quote

I considered the potential of a slot effect and water injection when I installed the Permatrims (especially in the Tom Cat--where the boat is run most of the time at 25 to 35 knots. Based on this, I did fill in completely with the 5200, so that there would be no water. If the motor was mounted too high--then the hydrofoil would be one cause of ventiallation. But some boats which have ventillation (common problem in single engine cats) seem to be improved with the Permatrim.
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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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Scuppers



Joined: 05 Sep 2020
Posts: 25
City/Region: Knotts Island
State or Province: NC
C-Dory Year: 2008
C-Dory Model: 19 Angler
Vessel Name: Scuppers
PostPosted: Sat Nov 21, 2020 8:24 am    Post subject: polish Reply with quote

what are you trying to accomplish by polishing a surface rainbow from your prop? I cannot find any info that indicates a prop improvement, based on prop life or performance. If it is indeed caused by cavitation, that issue will degrade performance, and should be addressed. But I think polishing discoloration off your prop is like putting tire black on your tires. What am I missing?
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Pressure busts pipes.
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NORO LIM



Joined: 24 Apr 2008
Posts: 875
City/Region: Olympia
State or Province: WA
C-Dory Year: 2006
C-Dory Model: 23 Venture
Vessel Name: NORO LIM (sold 12/12/14)
Photos: NORO LIM
PostPosted: Sat Nov 21, 2020 2:44 pm    Post subject: Re: polish Reply with quote

Scuppers wrote:
what are you trying to accomplish by polishing a surface rainbow from your prop? I cannot find any info that indicates a prop improvement, based on prop life or performance. If it is indeed caused by cavitation, that issue will degrade performance, and should be addressed. But I think polishing discoloration off your prop is like putting tire black on your tires. What am I missing?


Well, that advice was given almost ten years ago, so who knows what any of us were talking about in this thread back then. Laughing I for one am having enough trouble with whatever it was I said yesterday. I think the polishing suggestion was more of a diagnostic one than a cosmetic one, i.e. the OP indicated a one-time encounter with seaweed might have been the cause of the rainbow. Removing the rainbow and watching to see when and if it returned would be a good clue as to the cause of the rainbow. I'm sure some will chime in if I've missed the boat yet again. (Truth is, I miss the boat every day.)

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Bill, Formerly on NORO LIM
2001 CD 16, 2001-2006
2006 CC 23, 2006-2014
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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sat Nov 21, 2020 3:29 pm    Post subject: Reply with quote

I agree, Joe did a great presentation in 2009 and that still holds today.

Why did "Scuppers" bring up this old thread? I noted that he had a major prop issue where he could not get over 4000 RPM with a new SS 4 blade, 13.5 x 15 with an Etec 90. What was the outcome of the prop exchange, and is that related to possible cavitation??
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Scuppers



Joined: 05 Sep 2020
Posts: 25
City/Region: Knotts Island
State or Province: NC
C-Dory Year: 2008
C-Dory Model: 19 Angler
Vessel Name: Scuppers
PostPosted: Fri Nov 27, 2020 10:56 pm    Post subject: speaking of not looking at a date! Reply with quote

Lol, I could have sworn that was a current thread, you all get your chuckle in. I, too, have trouble with yesterday's news, much less, ten years old.

Anyway, to answer your question, after three swaps, I got the right prop, and I am very happy with performance, which I now understand is very much a function of boat, motor, load, and elevation and prop design. I will caution anyone to use this as a starting point.

I have a 4 blade Stainless Mach 4 Turning point, 14D x 13P, that gives me 5550 WOT on my 19 angler with a 90 ETEC BRP, medium loaded. I get a 28MPH cruise at 4400, which feels great. I have bennet trim tabs and use them a lot, and I have much improved stern lift. I boat in very shallow Currituck sound waters, and I have always liked stainless because the sand is rough on an aluminum prop.
Thanks for all the C-brat prop threads. I learned how to select one for the characteristics I wanted.
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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Fri Nov 27, 2020 11:01 pm    Post subject: Reply with quote

Scuppers, good to hear that you have your boat dialed in. Sounds like good economic cruise RPM.
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