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On this page you will find details of some of the changes I have made to Circe. Modifications, upgrades, repairs.
All are fair game. If you want to make a contribution just let me know and I'll post it here.
The first thing you will see here is the rudder modification I just completed. One of the few bad things about
the P30 is the rudder head. Lots of people have tried to fix the original by using other materials. A bad design
well executed is still a bad design. I think I have been able to make a fundamental improvement. If you like it,
use it. If you don't, differences of opinion are always interesting.
I chose to make this change after years of trying to make the original design work. For those of yoou who aren't
familiar with it, here's a description.
The rudderhead fitting slips over the rudder shaft. A bolt passes through the rudderhead and the rudder shaft,
connecting the two. The main driving force is through this bolt, which passes through two clearance holes on its way
through the assembly. To deal with the slop that this created there is a vertical slit to allow the rudder head fitting
to clamp around the shaft when a transverse bolt is tightened. Sounds good, right?
Unfortunately there are a couple of problems. First of all, as you can see from the tapered slot in this photo,
the clamp slit doesn't go through the entire casting, from top to bottom. As a result, the casting clamps only at the
bottom, which amounts to no clamp at all.
The slop in the drilled holes for the main cross bolt puts a high compressive stress on the casting because there is
contact only at the tangent point. Over time, the result is the kind of damage you can see in this photo.
The fix I decided upon consists of match drilling and tapping for 4 bolts which pass through the casting and the
rudder shaft. The original fit between the casting and shaft is pretty good, so there is little clearance between the
two. The bolts both clamp them together and act as shear pins to carry the steering load.
In this picture you can see the pilot holes I drilled in my shop. With a machinists square I laid out four lines
45 degrees off the centerline. I then measured down about half way the flat area on the casting. After leveling
the casting in the vise, I used a hand drill with a bubble level on it to drill four pilot holes in the casting. I also
drilled and tapped a 5/16-24 hole for a clamping screw at the aft end to take a clamp bolt which holds the casting in place
on the rudder shaft while I complete the installation. With a little care you can make a nice, neat job. I drilled
each of the four holes separately but they were aligned well enough that I was able to pass a drill through the opposite holes.
It isn't really important that they be that well aligned because they are only pilot holes. You will drill through them
and rudderstock later, so the final hole will be perfectly aligned.
The final step is drilling and tapping in place. I decided to use 5/16-24 screws for several reasons. The
casting and rudder stock are both aboou 1/4 inch thick. The 5/16-24 bolt gives me about 6 threads of engagement and
almost one full diameter of thread. The rule of thumb for steel is that one diameter develops the full strength of the
fastener in steel, so I can almost break off the bolts before they will strip out the rudder stock.
First I jacked up the rudder to be sure it was in the full up position. Then I dropped the casting over the shaft
and clamped it in place with a bolt through the tapped hole. This way everything is tight and aligned as I drill and
tap the final holes.
Again, using a hand drill, I drilled out the holes through the shaft. A couple of cautions. Be sure to use
a SHARP drill. Stainless is tough and you don't want to break a drill. Second, drill through several times using
progressively larger drills until you get to the tap drill size. I did it in 2 steps and it wasn't enough. I would
go in 1/32 increments if I did it again.
Finally, tap through the holes and insert the bolts. Again, use a new tap and GO SLOWLY! Sometimes I was
only able to get 1/8 of a turn or less. Use lots of lubricant and back the tap out often to clear the chips.
I made provision for four bolts but, after two, the end result was so good I decided not to use the second set, for no
other reason that I had to turn the rudder around to do it.. I'll probably do them another time. Extra strength
is couldn't hurt.
I did the job out of the water. If you arrange something to be sure the rudder doesn't fall out you can do it in
the water.
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