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  #11  
Old 05-22-2015
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Absolute Kaos Absolute Kaos is offline
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FYI The Rudder on AK and on Hurricane (ex Oxygen) have a 2" SS rudder shaft and they are basically the rudder that was designed for Karma. Although the bottom section is a little more rounded than the sharper edge that Karma's rudder had. We tried a couple of rudders with the Fiber glass shafts but broke two of them.. Thus went SS... Certainly as J says best thing we have ever done to the boat.. The Original one that John made for AK ended up with a water egress issue so we built a mold and produce what is currently on AK, Oxygen and the Dash in Kelowna.. I still have the molds out at Strait Marine and they have the correct layup schedule to make another one if needed.
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  #12  
Old 05-22-2015
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Quote:
Originally Posted by Absolute Kaos View Post
FYI The Rudder on AK and on Hurricane (ex Oxygen) have a 2" SS rudder shaft and they are basically the rudder that was designed for Karma. Although the bottom section is a little more rounded than the sharper edge that Karma's rudder had. We tried a couple of rudders with the Fiber glass shafts but broke two of them.. Thus went SS... Certainly as J says best thing we have ever done to the boat.. The Original one that John made for AK ended up with a water egress issue so we built a mold and produce what is currently on AK, Oxygen and the Dash in Kelowna.. I still have the molds out at Strait Marine and they have the correct layup schedule to make another one if needed.
thanks for the info AK. I'm curious if you can tell me what the failure mode of the shafts were: shear, bending, torsion or something else? Was it the same both times?

Maybe a better question is what action caused the failures: hitting an object, heeling, torquing the tiller?

Last edited by guar; 05-23-2015 at 01:09 AM.
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  #13  
Old 05-24-2015
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Both broke off right at the lower bearing.. I think the 2" shaft was just not up to the challenge when loaded up..
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  #14  
Old 05-31-2015
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Originally Posted by Absolute Kaos View Post
Both broke off right at the lower bearing.. I think the 2" shaft was just not up to the challenge when loaded up..
I went through ABS 1994 rudder calcs and 2" dia is on the thin side for a larger blade. Even with a SS shaft - it should be closer to 2.5" (2.48 to be exact).

For Epoxy/Glass and alum (which have similar allowable stress), you need to have about 3" dia for a round shaft section. For a square section you could get by with 2.5"

I noticed on the Jefa Rudder site they have some rudder specs posted . For the RUD34 which has a similar area and planform to the modified Dashes, they list a dia. of 88 mm or 3.46" for the alum rudder stock, although I suspect they designed them on the conservative aside.
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