Almost-A-SCAMP Progress Report #5B . . . .

[Charles Brennan]

More Centerboard/Rudder progress! 

Last report showed marking out the lines for routing in 11 lb of lead on each side of the centerboard foils.
Finally got to rout them out over the holiday weekend.
I MUST be making progress!! Look at all the sawdust I'm making!
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TONS of it!!
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I was pleased at how flush they fit.  Didn't rout out too much, or too little.
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Now, back to the rudder.  I had 3 pieces of ½" Douglas Fir marine plywood which is a little too thick for the designed spec.
Weighing pros and cons, I elected to thin one board aggressively rather than 3 boards slightly; that way if I royally screwed up I would only have to re-cut one board, not three.
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Having recently gotten a power planer, I ran it up and down, removing the outer plies on each side.
Worked good.  Glad I stopped periodically to measure, because I could have easily gotten carried away and removed too much.   
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Wow! Look at all the Progress on the floor!! 

A comparison of one side versus the middle, to show how much material was removed.
But it now measures exactly right!   
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Trying to put a NACA foil on a slab of plywood almost gave me screaming fits.
Trying to go down the whole length of one side proved to be as futile, as it was scary.
My biggest problem was that I had no way to use my reference foil gauge that I had made, unless the material was already removed and how could I measure it when material wasn't removed yet?!?   
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After some thought, I decided to only remove a small section of wood on each side.  Used one of two new tools I recently acquired: A Japanese Pull saw and a Shinto rasp.
Shinto rasp is a very cool tool, although you have to wonder at the mentality of the Japanese, to design two tools; one that has to be pulled and one that has to be pushed.
   GEEZE!! JUST PICK A DIRECTION AND GO WITH IT, GUYS!!!   

So I concentrated on a one rasp-width section (as shown, top of pic) and got it shaped until it roughly conformed to my foil gauge.
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Note the discrepancy between the penciled in line and the sharpie marker line.   
Apparently, I don't measure much better than I loft lines, but at least I caught it in time.  (Sigh.)   

Repeated the same process on the trailing edge side, which removes more material and is spread out over a longer distance across.
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Now that I had a comparative reference point in the wood, I was able to rough in to match the rasped out curve with the power planer all along the length, and smooth with the belt sander using a 36 grit belt while re-checking with the foil gauge, almost obsessively.
Was getting ready to blend in the bottom with the edges.
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Still have to do the other side, though.
Either that, or only be able to sail efficiently on one tack!   
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More sawdust!! PROGRESS!! 
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The rough shape (needs a lot of sanding with a palm sander).
Once I get the other side done, I will be able to see how much depth I have and where it's located, for adding the 2½ lb rudder  weight. 
Preferably, without some of the lead sticking out on one side or the other.   
There's a WHOLE LOT of  "shape to suit" and "locate to suit" and "length to suit" in these plans.
Clearly, John Welsford is a very experienced designer who already knew when he was herding cats.
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I was encouraged by  how similar it is to pics done by REAL Boat Builders.
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Still, a little more progress, (or at least, sawdust) every day!   
Charles Brennan

[Captain Kidd]

Good work!!

[Norm L.]

Amazing work Charles.

But considering the labor, those hours at your previous $ rate means you are getting close to completing a $7000 rudder.

[Timm R Oday25]

Charles , I'm not sure where you are buying your woodworking tools . I usuually end up at Wood Craft . I impulsively bought several Japanese pull saws . They are now my go to saw . Keep posting please , I'm enjoying watching someone else who actually has the time to do boat stuff.

[DBthal]

...........Japanese pull saws . They are now my go to saw.

2x - the best!

[Riley Smith]

Great job! Isn't it fun seeing all that wood turn to dust? Query....don't know nothing 'bout nothing at all but was wondering how the pin was engineered. I can't recall if it was advised or not in my case, but my cb pin was a stainless rod, and to keep the cb from getting all worn out, I inlet two stainless plates into the board (in addition to the lead counterweight); a sort of wear plate. Never had any trouble. Of course my cb is only rounded and not hydrodynamic and I'll go hang my head now 

[Charles Brennan]

Riley, I've seen your boat and there ain't nothing about it, to require hanging your head!

You didn't specify which pin.   
The centerboard uses a ½-inch stainless steel pin for the centerboard. In the sides of the centerboard trunk and the centerboard itself are ½-inch I.D. bronze bushings.
The original design had a 9 mm plywood stop block on the hull side and the cockpit side had a ½"-11 S-S bolt (with the threads cut off) epoxied through another piece of 9 mm plywood as shown in the pic below.
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I have NO intentions of using that method.   
Besides complaints about the trunk leaking, and/or screwing through the side of the  CB trunk into the inside of the trunk, as well as difficulties reaching into the water-ballast tank to unscrew the cap, there seems (to me, at least) no real good way to remove the CB pin in the field.  I can think of any number of scenarios, requiring unjamming sand, seaweed, rocks, and oyster shells, etc. from inside a stuck centerboard trunk.

My intent is to use ½" I.D. threaded bronze bushings and ¾" bronze pipe caps on each side.
Wrapping the threads with Teflon tape and using pipe caps, means they can be easily undone with pliers or a crescent wrench and the pin pushed (or punched) out from either side of the CB trunk.  The pin will simply be a ½" S-S bolt with the threads AND the head cut off, and with the ends rounded over.

The rudder pivot uses a 3/8" S-S bolt through 3/8" I.D. bronze bushings on the rudder itself and the same kind of bushings on the upper-half rudder case.  I am considering using bushings with shoulders on them for the rudder case, to keep the washers under the bolt from digging into the rudder case.  Finally, the bolt is held on with a S-S Nylock nut. Between the rudder and the rudder case, I will have either nylon fender washers or HDPE stock  (Mama loses ANOTHER cutting board!)    cut with a hole saw, depending on whatever thickness I need after I get this thing assembled.

Hope this clarifies,
Charles Brennan