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Do EPO's make a HUGE difference?
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Author:  janek.w [ Tue Oct 12, 2010 9:40 pm ]
Post subject:  Do EPO's make a HUGE difference?
Just wondering, in which way to EPO rudders increase performance over the older white ones?
Author:  tchilds [ Tue Oct 12, 2010 9:56 pm ]
Post subject:  Re: Do EPO's make a HUGE difference?
They flex in the right ways to reduce cavitation and have a better foiling edge. Carbon fiber is neat stuff. It can be laid in ways that make it smart at adapting to varying loads in a favorable manner.

The floppy plastic rudders bend in all kinda directions including twisting a lot more than they should. In my opinion the EPO rudders are as significant a difference in performance as a sloppy rudder assembly versus a tight one.
Author:  MBounds [ Sun Oct 17, 2010 8:04 am ]
Post subject:  Re: Do EPO's make a HUGE difference?
They're also thicker. A thicker rudder is more stall tolerant (you can turn the rudder more before the flow separates).
Author:  Karl Brogger [ Sun Oct 17, 2010 8:22 am ]
Post subject:  Re: Do EPO's make a HUGE difference?
tchilds wrote:
They flex in the right ways to reduce cavitation and have a better foiling edge. Carbon fiber is neat stuff. It can be laid in ways that make it smart at adapting to varying loads in a favorable manner.


You can do that with fiberglass too.
Author:  MBounds [ Sun Oct 17, 2010 9:49 am ]
Post subject:  Re: Do EPO's make a HUGE difference?
tchilds wrote:
They flex in the right ways to reduce cavitation <snip>

The key is that they don't flex at all.

I can make a plastic rudder (Lexan from the '70s/'80s, PCG from the '90s or the current Nylon ones) bend under hand pressure.

You can't do that with EPOs or fiberglass rudders.

Plastic rudders are heavy, too. Original EPOs were so light, they had to change the class rules to allow them. Nobody ever thought a strong rudder could be built that weighed only 3 lbs.

BTW, technically the rudders ventilate, not cavitate.

Cavitation occurs when the pressure gradient around the rudder goes below the vapor pressure of the water, creating a water vapor bubble. These bubbles can collapse violently, eroding the surface underneath them. (Google "cavitation damage" to see how much of a problem it is on ships.)

Ventilation occurs when the pressure gradient around the rudder is lower than the ambient air pressure at the surface. Air is drawn down the side of the rudder, and since air is 1000 times less dense than water, the rudders "lose their grip."
Author:  tchilds [ Sun Oct 17, 2010 10:46 am ]
Post subject:  Re: Do EPO's make a HUGE difference?
Thanks for setting me straight. I've never even heard of ventilation before in that context. Glad someone finally got some facts out there!
Author:  ftlauderdale16 [ Fri Oct 29, 2010 3:16 pm ]
Post subject:  Re: Do EPO's make a HUGE difference?
I have just bought a new boat that has EPO2's on it, and right out of the gate they really do feel great. Sharp and responsive and they do seem to "hold on" longer before you're able to stall them. Absolutely no rudder hum so far... :D
Author:  DarekR [ Fri Oct 29, 2010 3:36 pm ]
Post subject:  Re: Do EPO's make a HUGE difference?
MBounds wrote:
Cavitation occurs when the pressure gradient around the rudder goes below the vapor pressure of the water, creating a water vapor bubble. These bubbles can collapse violently, eroding the surface underneath them. (Google "cavitation damage" to see how much of a problem it is on ships.)

Ventilation occurs when the pressure gradient around the rudder is lower than the ambient air pressure at the surface. Air is drawn down the side of the rudder, and since air is 1000 times less dense than water, the rudders "lose their grip."


Class dismissed! ;)
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