judy, this problem occurs only under auxiliary power. i think you're right on with " Balance is not your friend when the prop is pushing water at the rudder." having had an outboard on the last boat i'm used to the thrust being aft of the rudder. now we have an inboard and it's all adding up. sail plan and such all being accounted for, i do believe your suggestion to be the correct one. though i'm still a bit confused as to why the amount of thrust being pushed at the small percentage of the rudder forward of the post would grab instead of the larger percentage aft of the post. perhaps it's because the water moving over the forward portion is moving faster, due to prop thrust, and therefore producing more pressure than the amount, pressure and speed of the water passing over the hull when moving forward. if the boat could move as fast forward as the thrusted water moving aft then they should equalize. yes?
--- In [email protected], "Judith Blumhorst, DC" <drju...@...> wrote: > > More descriptive details please..... How does it behave under sail > power?  How does it handle under power? is the boat an inboard or > outboard? > > Take a look at this page: > http://www.blumhorst.com/catalina27/catalina-27-rudders.htm > > The C27 is a nicely mannered boat when the rig is properly tuned and good > sails that are properly trimmed.  I can sail my C27 with two fingers on > the tiller just a couple of inches to windward of the centerline, in winds > from 10 knots to 35 knots and higher gusts. (That's true before and after I > replaced the OEM barn door rudder) if I take the time to set the right sail > plan.  > > If the the tiller violently gets away from you under fully powered-up but not > overpowered sailplan, you either have an inadequately tuned rig or an > unbalanced sail plan. If you're consistently heeling more than 30 > degrees, the boat is carrying too much sail area  or the the sails > are over-trimmed, and you' can expect to feel the boat try to round up hard. >  Less likely but still possible, your boat is not sitting on her lines > fore and aft.   Or, possibly  your rudder is grossly asymetrical from one > side to the other, a defect that is emphasized when the maximum foil is too > far aft, like the OEM rudders.  > > Under power, it's a different story.  A little balance area on a rudder is > generally a good thing under sail, decreasing tug & load on the tiller, but > too much balance can cause problems when powering in forward with an > outboard. Balance is not your friend when the prop is pushing water at the > rudder. The prop wash from the inboard tends to push her off course when > I'm trying to go straight ahead under inboard power.  > > With the old OEM rudder, my C27 yawed strongly to port, and pulled very, > very strongly.  That's because of two factors - the balance area on the > rudder and an asymetry of the rudder foil. > > Backing is always a problem if you let the rudder get too far from > centerline. The longer the chord of the foil the longer the lever arm and > the harder it is to keep on course. > > Awaiting more info from you.... maybe it's something I've forgotten to > mention, > > Judy B > 1977 C27 TR #3459 inboard > Sailing San Francisco Bay area > > >  > > ________________________________ > From: RobAdkins <robadk...@...> > To: [email protected] > Sent: Mon, March 29, 2010 11:57:55 AM > Subject: [IC27A] a rudder with a mind of it's own > >  > hi all, > > upon first sailing my c27 i noticed the tiller can get away from me mighty > quickly if i'm not careful. this was not the case with my old columbia which > had a keel mounted rudder. i thought a bit, yes it did hurt, and after > drawing pictures in my head i've come to the conclusion that a small > percentage of the rudder, on my c27, is foreword of the rudder post. this > would explain it's violent tendencies to leap from my hand when executing a > sharp turn and it's equally violent resistance to coming back to center after > said turn is complete. i'm wondering if anyone has any clue as to why this > design "feature" exists. it does make the helm more responsive/sensitiv e > under sail but while under motor it is a definite hazard. any info would be > appreciated. thanks-rob >
