C28 re-propping

[TristenT]

I wanted to get a fresh and updated thread going for changing the propping for c28s. My goal is to get input from people who have changed there prop from the original 19x23 prop. I am getting ready to change up my prop this winter. After putting around 250hrs on the my c28 this season I have found the that the 19x23 prop is not well suited for how I run my boat with the loads, with a typical load for a trip I am constantly coming in several hundred rpm u see the minimum WOT range. When the boat is low on fuel empty on water and low on gear it hits the WOT rpm range well but that a rare occurrence. I spoke with Sharrow/Veem and smallest prop they will make is a 20” so that’s out for now. Iv heard good things about dropping to a 19x21 zero cup. Id be interested to hear any input if you have played with cupping at all as well.

 

[Automaticman865]

Ran into this problem back in 2012 when was new. could only hit 3300 when boat was fully loaded. Had Volvo on the boat with their vodia tool. All said and done the replacement prop was ordered by Cutwater directly with Acme. Here is the end result Acme prop #1906 19.00X21.00CR4B 1.50 .045 Prop, Mod prop to 40M -- Remove .030 Cup, to leave .015 Total .... Stamp 40M. I had the original prop modified by the local prop shop, 19X23 re pitched to 19X21 , added .015 cup.
All said and done the new prop is slightly faster than the re pitched prop, hitting 2600+ rpms at season launch and although i picked up more barnacles this year I was just shy of 3500 rpms at the end of season. I have been using Blue Water Barriershield paint as a base on the prop with a couple of light coats of cold galvanizing spray. I usually run about 2 gals/liter, 7.4 gal/hr 2650 rpm 13.6 knots.
Stuart

 

[TristenT]

Ran into this problem back in 2012 when was new. could only hit 3300 when boat was fully loaded. Had Volvo on the boat with their vodia tool. All said and done the replacement prop was ordered by Cutwater directly with Acme. Here is the end result Acme prop #1906 19.00X21.00CR4B 1.50 .045 Prop, Mod prop to 40M -- Remove .030 Cup, to leave .015 Total .... Stamp 40M. I had the original prop modified by the local prop shop, 19X23 re pitched to 19X21 , added .015 cup.
All said and done the new prop is slightly faster than the re pitched prop, hitting 2600+ rpms at season launch and although i picked up more barnacles this year I was just shy of 3500 rpms at the end of season. I have been using Blue Water Barriershield paint as a base on the prop with a couple of light coats of cold galvanizing spray. I usually run about 2 gals/liter, 7.4 gal/hr 2650 rpm 13.6 knots.
Stuart

Perfect that’s what I was looking for. Sounds like just a very small amount of cup is working well then with the 21 pitch. To clarify you re worked the original prop to be 21 pitch with .015 cup. And then bought a new prop that was 19x21 with .045 cup but had the cup reduced to .015 cup. Despite the two props metrics being the same the newer prop seems to do better? What is the stamp 40m?

Do you remember how these new props were doing cruising between 18-20 knots?

 

[Automaticman865]

Hi, the 40 m was on the original invoice from Acme that is all I know about that. I had run up the engine to 3500 and was getting in the ballpark 20-22 kts at ~13.7 gal/hr, engine oil at 70-73 psi, and turbo boost 26-28 psi.
I've included the link to Tony Athens and his discussion about engine longevity ~35 hp per liter and 2 gal/hr per liter...

Continuous Duty - A Different Perspective

Continuous Duty - A Different Perspective

www.sbmar.com