Commander #256 (Ceili)

[ebb]

Chance,
I messed with the 'keelpost' of A338.
Naturally found the back end of the boat unsymetrical and hollow - so filled & faired it straight - and fattened it up. Worked the cove with sanding sleeves until the gelcoat was gone.
Was influenced by the original scantlings in the same set of Alberg drawings - I believe the keel is two inches wide at the cove where the rudder is mounted. Total, that includes the 1/4" flats on either side of the cove.
Spent too much time and epoxy fairing this socalled keelpost area and making it even and straight from where it leaves the bottom of the hull down to the heel fitting.

I was shocked that Alberg showed a fatter rudder in the plan view of the heel fitting. He shows an 1 1/2" shaft. It meant that the beautiful mahogany and bronze rudder Pearson choose to use - because it was thinner by half, ONE INCH wide rather tham 2"...had to be mounted further inboard.
When we make a simple paper model of the as built 'hinge' effect, the 1" wide rudder swings perfectly.
When we fatten the thickness of the rudder and use the same bearing in the heel fitting, it becomes obvious that either the cove of the keelpost has to be carved back to much less of a cove. Or the fatter rudder itself has to have its radius carved into more of an oval shape to get the swing needed. The swing neeeded matches the swing we have in the cockpit with the tiller.
Can't be anything less. And might have to be more, close as we can get to 80 degrees, which we can't do of course because of what we have. But we need that radical angle to ease the rudder out of its tube and past the heelfitting when we drop it. And when we put it back in.

Made various 1" dowel and doorskin models of failed rudder ideas. Kept one model so to try the fatness of the finished rudder. I'm on the hard so I can't put the work-in-progress rudder in for test fitting. Have to still use the mock-up when pasteing the final bronze and foam rudder together. The rudder is on my next to do list.

It's easy enough to make a cardboard rep of what you have and using the heelfitting on your boat and the cove in the keel.... figure out how the rudder will swing within the parameters.
Not talking about making a 3D rudder model, just making a 2D cardboard model of the swing on the flat of the keel fitting. Draw the heel fitting exactly as you have it. cut the original 1" wide rudder and with a push pin see how it actually swung on the heel.
Then cut and paste to see what you have to do to make your new rudder scantlings do what the 1" wide rudder could do.

The new rudder isn't going to perform exactly like a copy of an original one. Fattening the rudder at the keelpost comes with a price. We're assuming the rudder that came with the boat worked pretty good but wasn't hydrodynamic enough for sme fools. A beautiful rudder but it had no foil and came to a big fat round trailing edge. We can work in the foil and narrow the trailing edge but the price will be that the flow of water off the keel onto the nice new fat rudder is going to go over (or into) the space we have to leave at the rudder shaft for the rudder to swing properly.
It can be done but it's a compromis.

Have seen thin fairing strips added to the edge of a straight keel like ours that projected over most of the width of the relief space carved into the rudder....in an attempt to add back the hydrodynamic. It's not much, it's do-able. Have to use bronze* gauge sheet metal. And it's another time consuming thing. Do we have to dap the strips into the keel? What are the strips made of? How do we fasten them on? Maybe we're causing more turbulance than solving it?


How fat your rudder... is how it works out for your app. Looks like Alberg was happy enough with a step from the two inch wide keel to a 1 1/2" wide rudder shaft (that never happened.) In our case, if we have to modify the new rudder, it sure would be easier to add a modicum of thickness (with closed cell pvc foam, perhaps) than to grind it away.
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* no bronze available but half hard copper in gauge sizes is available from on-line metals. There are also plastic sheet like mdr nylon or maybe garolite that would prevail under water.