From Charles' report the jammed rudder was bent sideways and "forward" as I recall. The other one was "free wheeling"? There was no discussion of webbing or struts protruding through a busted rudder face? If the rudder had delaminated or split, I would have thought that would have produced some commentary.

SKIING: Since you seem dismissive of my analogy of the snow skis, in spite of the winter season here, LET's condisider the analogy of WATER SKIS accross a crossing wave pattern with a wind generated background. ;^)))

Take the rest of the analogy for snow skiing in that somewhat different medium. Oberservations are the same. Your thighs, needs, ankles, stomach, back, etc. are measuring different loadings which you are attempting to balance. Little is the same except in flat water, going straight. That combination of balancing stresses is because the forces are different you, as part of the system, are accomodating those. Even if you're rigid (and in balance), you are transfering, combining, or whever word you wish to apply to stabilize what are uneven forces. It is both dynamic and statically indeterminant, nothing is even because the forces acting both in concert are that way. I know you aren't comfortable with this, but it is so.

Statically indeterminant conditions happen all the time. Life is like that. What seems intiutive, isn't necessarily so. If you have a simple horizontal beam with three support: two on the each end and one in the middle. If you impose a load that is in the middle of the beam (over the middle support). What will the load be on each of the three supports? 1/3 of the load in the middle? (Not likely, and if so, not until things "moved" or yielded.) Now take the load and put on one side of the center support. How are the loads distributed between the three supports? Evenly? Almost surely never. Make the load non exactly vertical, or make the beam not exactly horizontal, etc. and the modelling is clearly unclear. This a static condition (Not a constantly changing dynamic one.) http://en.wikipedia.org/wiki/Statically_indeterminate

Simple supports (e.g., a horizontal beam supported at each end with a vertical load in the middle) aren't generally considered "statically indeterminant" They rarely occur in reality, they are mathematical abstactions that allow us to engineer things. All kinds of modelling and assumptions are made when designing complex structures. When you design a moving composite structure, with moving loads on it, in fluid (liquid and air mediums), and so forth you really are just doing your best to break the forces that the object experiences and exerts -- then adding all kinds of experience or safety factors. Which modelling make sense is part science and part "art". That's why they have test pilots and test planes.

There are some problems that are simpiler. I suggest that a monohull is simplier than a cat -- but it's not simple to understand what is really happening to each component in each condition until you build one, monitor a particular place or component, and begin loading it differently. Even then you have so many variables, that you can't monitor and model them all (or even most of them). In reality, experience and an "eye" have to govern. You can of course take a FAILED component and modify it to resist an observed failure.

I don't know why those rudders failed. For example, let's take the bent rudder: If there was a "stop" on the rudder inside the hull on the steering quadrant (or equivalent); and that stop had precluded the rudder from rotating too much so that a force was taken "broad-on" the rudder, would it have kept the post from bending? I don't thing you want the rudder to be at more than a 40 degree angle or so (but I haven't thought a lot about that). Certainly forces, including bending and torsion would much greater if rotation wasn't restricted. In simple bending, the size of the section makes a huge difference. These rudders aren't that deep but they are relatively "square" -- so you may have more torque as well well as imposing different bending.

Mark: As for your rudder post at 1.5" -- I believe that you should look at similar length and displacement weight power boats for guidance. I would look over the stops especially carefully. Can the be "jumped" or overcome? Do they have neopreme to provide some tempering of shock loads? etc. Some robust hydraulic steering systems can exert a lot of load -- and electro mechancial autopilot, usually not.

If there are sister ships of your boat which have successfully sailed without failure in conditions that you consider similar to what you'd want to feel comfortable with, then I wouldn't necessarily go replacing your rudders. As you know, you can't just turn around an put-in a 3" tube without changing the whole rudder foil, it's leading edge, it's interaction with the props, etc. Having it solid helps a bit (certainly there is no issue with inadequate wall thickness ;^))). You should look for signs of distress on a periodic basis when the boat is out of the water You can make some marks and check them periodically; e.g. have a vertical scribe line on each shaft where it's visible -- then see if it shows any sign of torsion distress; Mark the top of the rudder on the port and startboard side with a SMALL scribe line -- see if there is any sign of rotation of the post from hose marks; check the position of the streering and see that the rudders are aligned to match after marking the prior position when they are, etc.