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Thread: rudder discussions

  1. #61
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    There's rudder stuff on the history channel here. Punch Search if interested.
    338's clam shell rudder has just been reactivated.
    Basically the top third of the blade comes apart, held by a keyed channel on the post with three bolts. On the trailing edge the shell is held with 4 machine screws.

    The rudder post is silicon bronze, as are the 1/8" straps, as are the fastenings. as is the welding wire. The idea of course was to get all the metal parts the same to avoid galvanic action. That was fine until Bristol admitted to casting the shoe in manganese. I had a discussion with Bristol about my rudder - the upshot being that silicon bronze is too soft for the job. Bristol said they supplied Pearson with rudder stock in the Ariel days and it was manganese. Roger said that while made from manganese the rudder would last 150 years my silicone one was only good for fifty. Silicone is 98% copper.

    Hell, I attached the Bristol shoe to the rebuilt heel of 338's keel with peened over silicon rod and it seems to be showing some corrosion with crusty bright green weeps. The boat has been out of the water for more than two years and its showing signs of corrosion!!! It's obvious that there still is saltwater in the laminate in the aftend of the keel. But we do have two bronzes reacting. Out of the water! They're holding hands in the galvanic series.

    The take apart design (the idea is not to have to raise the boat) requires more metal I think than a straight welded rod and strap. I had to kind of double the strapping in the two-part clamshell area. A plain welded strap to the shaft design IMCO is a good alternative to having holes drilled in the rod for the bolts in the wood version. Altho there has been no problem with this design, I understand. except aging. With the 338 rudder I used a rigid closed cell expanded PVC foam (Divinycell) to fill the spaces. Setting it in with epoxy gell.

    I'm just about to do the glass work. But keeping the take apart option makes the glass work very difficult and takes away from the massive strength gained with sheathing the whole blade with glass around the rudder post. To be able to still take it apart the upper third would be split along the rod and, of course, split to the clam shell. I need a chunk of time to ruminate on the complexity to have it come out ok.

    Even so, I'm not happy with the small fastenings holding the design together.

    If you did not build your rudder out of polyester and urethane foam like the production boats (C'pete's survey report) but used PVC foam and epoxy, I think the rudder would be waterproof, taking in very little water, depending on the workmanship.

    [Weight wise, this is a heavy rudder. I think it will turn out to be much heavier than mahogany with a bronze shaft. I also think a recreation of the original rudder will enhance the value of the boat, while a composite or trick rudder might detract.
    On the other hand a bronze rudder post (rod, shaft) with welded bronze strap (rolled sheet) developed into an efficient grid that comes to a more pointy trailing edge than the woody - with hard closedcell foam, epoxy and frp (not carbon fiber which is too distant on the galvanic scale
    from bronze) - would be most desireable and nearly indistructable.]
    Last edited by ebb; 10-06-2003 at 07:37 PM.

  2. #62
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    Just want to add this:
    There are problems with the rudder I remember.
    Corrosion, galvanic action?, at the waterline IN the rudder tube. Manual, I think.

    And I think there was something similar happening to the bolts holding the pieces together in the lower half of the mahogany rudder, from some posts in the past. The ones which pass thru the shaft.

    Sacrificial zincs obviously play a big part in protecting the shoe and rudder. Has anybody a system that seems particularly efficient?

    IE zinc on or near the shoe. Zinc on the rudder. Are they wired? Are they interconnected. Are they independant of thru hulls ETC ETC.

  3. #63
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    On #76 we use a teardrop shaped zinc attached to the shoe. That protects the shoe and the lower rudder shaft. Another zinc is attached to the upper rudder shaft via half a jumper cable - one end has the zinc and goes into the water. The other end with the battery clamp grips the bolts holding the tiller head fitting to the upper rudder shaft. Both zincs last about four years.

  4. #64
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    Sep 2002
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    Alexandria, VA, boat in Deale, MD
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    Ebb-
    We must see pictures or a sketch of your rudder. I just cannot picture it.

    Bill-
    the teardrop anode: is it thru bolted in place of one of the broze nails/rivets that holds the shoe in place? is there one on both sides of the shoe (port and stbd)?
    -km
    aka, "sell out"
    S/V Beyond the Sea
    C&C 35 mkIII

  5. #65
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    We have some early photos of Ebb's rudder design. I'll post them after I find them.

    The zinc is not through bolted to the shoe, only fastened with machine screws using a couple of holes drilled on one side.

  6. #66
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    EBB'S RUDDER

    Photos of Ebb's new rudder mockup can be found on the Gallery forum in Ebb's Photo Gallery thread.

  7. #67
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    Sep 2002
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    Alexandria, VA, boat in Deale, MD
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    I got a call from my yard's carpenter about my rudder.

    He wanted to do the following:
    1. replace the two bronze shafts with a single stainless (or bronze) shaft with a plate welded edgewise along the length.
    2. laminate two pieces of marine plywood on either side of the plate and shape the rudder from that.
    3. coat the whole thing with a few layers of fiberglass.

    He claims that stainless up against the bronze shoe is not an electrolytic problem. I have my doubts.
    He also (after some nudging from me) realized that the install would include lifting the boat about 5' to put in this massive long rudder assembly.

    I told him to write up the estimate, but not start the work. I don't think i will like the result (neither the price, nor the methods).

    So, has anybody ever crafted an exact mahogany replacement?
    I found a place that has 2x12 honduran mahogany to piece together like the orginal.
    Does anybody know what the drift pins (between two panels) were made of? Were they mahogany drift pins or bronze. I am not talking about the bolts/screws that come from the rudder stock, but the pins between two panels.

    much gras-
    -km
    aka, "sell out"
    S/V Beyond the Sea
    C&C 35 mkIII

  8. #68
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    IMCO here.
    338 had a fiberglass rudder with s.s. shaft. It obviously had been on the boat awhile.
    I had to recast the rudder shoe (there is pulenty on That here! Type yer favorite werds into the 'search' option.) because there was galvanic corrosion on the side of the shoe the zinc was on. The side of the shoe was also crusted with zinc. So I don't what happened. It is entirely possible that the damage to the shoe occured befor the substitute rudder had been installed. I assumed it was the two different metals.

    Merely conjecture: but if Bristol Bronze, anyway, says the original rudder shaft was manganese bronze, my assumption is that the bolts or rod going thru the shaft holding the planks together were the more common silicon. Don't know that Pearson would have used manganese rod. Right? If there is a corrosion problem at the bolt and shaft juncture, it must be pretty unusual, as the bronze alloys are together on the galvanic scale.

    Others vocal on the site here have made rudders different from the original. IMHO if you have to depend on somebody else to make the rudder I would go as near as you can to the original design. No epoxy, no glass. Since it sounds like you have the OB version, a straight thru version of the shaft would make for a very strong rudder. After you give the carpenter the plans from the Manual I would ask to see a full scale drawing on mockup showing where the fastenings will go. If all-thread is decided on I certainly would thread it into the shaft. You'ld have the machinist do the threading in the shaft to match the rod.

    It is important that the keyway for the tiller head is exactly on line with the rudder blade. I found an (Edson, I think) tiller head that had the keyway on the opposite side of the original. So I had the machinist mill keyways fore and aft on the top of the shaft.

    The original rudder is still active on many A/Cs. Maybe no upgrade is needed for the traditionalist. Yes, use Honduras mahogany or Burmese teak.
    Last edited by ebb; 11-19-2003 at 09:33 AM.

  9. #69
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    Alexandria, VA, boat in Deale, MD
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    all thread

    I like your idea of threading the bolts directly into the shaft.

    We'll see if i can convince the carpenter to make a new one just like the old. my guess that my financier (the wife) will just want the cheapest method.
    -km
    aka, "sell out"
    S/V Beyond the Sea
    C&C 35 mkIII

  10. #70
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    Capt Mrgnstrn,
    The guy has to layout all the pieces befor putting the rudder together. All the measurements will be known, some people might be more comfortable using rod (more metal for your buck) and threading the ends only.

    Depending on the size of the rod, The threaded hole in the shaft could be blind, not all the way thru the shaft. Maybe this is a way of getting more protection for the fastening from the water. using 5200 to get a seal where the wood meets the metal shaft.

    I'm just noodling here, it would be great if there was feedback.

    In thinking about this 'natural' rudder: you wouldn't glue the pieces together if you had more than one plank - so you have to allow for the swelling of the wood - how much swelling do you allow for? Swelling could create a bow in the blade. Most of the wood rudders I casually see in the yard have this problem. It is my considered opinion (and I have been called on this) that to help avoid the bowing you make the rudder from pieces where you have reversed the grain. If it's cut from one narrow plank you flip the faces when laying out.

    But as usual, contradicting myself:
    You could 5200 the edges together as a kind of gasket that could possibly give against the clamping of the bolts and swelling of the wood. In other words: I might glue the pieces with say a fat 1/8" gasket of 5200 and not cinch it up with the nuts until it was set. There may be enough give in the rudder as a unit to allow swelling without getting the curve. And 5200 is still keeping the whole kabootle nicely together? Then you grind and sand the blade to final shape.
    Just an idea. But this could be a way of isolating the blade fastenings from possible galvanic action.

    Question authority (& tradition!)
    Last edited by ebb; 11-20-2003 at 01:20 PM.

  11. #71
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    Here is an example of a replacement rudder. This one came off of Commander # 199. Its covered with bottom paint and dried slime, but otherwise in reasonably good condition.
    Attached Images  

  12. #72
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    I don't have any construction details. It was made about 20-25 years ago. I'm not even too sure how the original rudder was lost. I remember hearing stories of a violent grounding in the Fire Island Inlet.

    The rudder is made up of two big slabs of wood. I filled the seperation between the boards with sealant at one point, which probably only made the boards seperate some more.
    Attached Images  

  13. #73
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    Five long pins secure the wood to the shaft.
    Attached Images  

  14. #74
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    The pins go right through the rudder shaft, which is straight, and solid bronze.

    There's a notch at the top.
    Attached Images  

  15. #75
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    A pin is formed at the bottom
    Attached Images  

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