Stainless rudder stock needs replacing in foam core rudder?

Discussion in 'Fiberglass and Composite Boat Building' started by DennisRB, Dec 3, 2013.

  1. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Hey guys. I pulled the rudder from my 40 foot boat. It has crevice corrosion at the base of the shaft where it enters the rudder. So I need a new shaft or whole new rudder. I am looking here to seek opinions on the best course in action. :)

    Options are, cut apart the rudder and replace the SS shaft (or maybe go to a composite shaft), then glue the rudder back together ad re-laminate. If you suggest this method please explain the rough details of this suggestion. IE where is the best place to slice it up etc to make it easiest to get back together straight.

    Another option is to build a whole new rudder, possibly with composite shaft. Note my particular model of boat usually did come with a glass shaft and the fact that it is stainless is actually odd. I do fancy building a boat one day so this might be good project, however I do really want to get this out out sailing again soon.

    The rudder is foam and glass and does not appear to be water logged as no water came out of any holes I drilled in it. Some water did slowly drip out where the shaft goes into the rudder. But I even drilled holes around the shaft area from the rudder skins and no water came out, so the water must be fairly localized around the rudder post entry.

    It may be hard to see from the pics but it is quite big. Its a 2 person lift and the blade is 1140 x 860 x 118mm, and the post sticks out 930mm and is around 87mm tube 6mm thick.

    Any suggestions?

    Click for pics

    https://www.dropbox.com/s/6tlcndg93nmof42/IMG_2875 (Copy).JPG

    https://www.dropbox.com/s/lqfxdtdzi638z97/IMG_2876 (Copy).JPG

    https://www.dropbox.com/s/o74esp9f7jm8dly/IMG_2878 (Copy).JPG

    https://www.dropbox.com/s/oxbci2l0fgprj18/IMG_2877 (Copy).JPG
     
  2. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Dennis,
    I have never cut a rudder, just made new ones, but it may be possible if you slice it thru the centreline (offset say 8mm to allow for the web system that attaches to the rudder shaft). Maybe you can cut it with a blade from a mechanical metalworking saw, (the back and forth type). You will be say 16mm too thin then, but so what, you still need to make up a shaft and web, so copy what you have when you get it out (it was OK till now so it is still OK to make the same dimensions). Epoxy glue the two slabs back onto the web using filler and then simply fill in the gap when it has all gone off.
    Retape the outer edge all around and Voila, one new rudder.
    You MUST grind off all the gelcoat before the tape goes on, just grind down to the glass level carefully. I live in Brisbane if you want me to look at it.
    Regards, John
     
    1 person likes this.
  3. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    John we have met. :) Remember when that broker left us waiting for an hour to inspect Hotel Tango the Ben Lexen 40? You suggested there were better deals in the states. Well you were right of course and the boat we purchased was the same price as HT but is twice the boat. But I am well aware all 20 year old boats need maintenance like this and this is to be expected. Over all we are very happy with the boat.

    I think I might try and get the old rudder apart, if I butcher it I can always make a new one in the end. The boat builders at Monties say I should slice it around the edge and pull one skin off then dig the skeleton out then replace it, bog it up with epoxy and re sheath it. This rudder has a lot of small cosmetic blisters any way so a good grinding of the skin is in order anyway. The hull has zero blisters.

    The rudder is at Bray Park, which is out of your way a fair bit.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Make a casting of the exterior, before you take a saw to it. This can serve as a mold for reassembly or to female mold a new blade.
     
  5. michael pierzga
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    michael pierzga Senior Member

  6. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Thanks guys. Would I make the mold out of CSM and poly?

    The rudder is foss foam.
     
  7. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Anyway, I am still trying to decide on the best way to rip this rudder apart so that it can be salvaged. I want to be confident that when I do it I am doing right. I have been told several different ways.

    Skinning one side by removing the laminate, then digging down to the metal shaft and tabs. This sounds like it would end badly unless the skin is not well bonded?

    Chopping in from one side above the shaft and tabs. This should leave enough of the skin to fair over. Once again even if I can use a drill to feel out where the tabs are, it will still be pretty hard to rip the metal part out if its recessed down a hole I cut in the face of the rudder.

    Splitting the rudder in half with a sawzall so it comes apart in 2 halves. This should expose the tabbing and it will glue back together easily. The sawzall should be able to get around the tabbing by feel. Seems to have the least drawbacks.

    The prob is I have no idea what the tabbing might look like so as to choose the best method. If the tabs are just laying flat as compared the rudder face the sawzall method would be best for sure. But if any tabbing is perpendicular to this plane the rudder may not come apart.
     
  8. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Dennis,
    If I was doing this first I would template the outline & section profile at top,bottom & a couple in the middle....... then i'd carefully mark up the leading edge/centerline & about 50-80mm forward of the trailing edge up one side....... then I'd support & clamp it to a nice height..... then I look after my eyes, ears, lungs & skin... respirator, tyvecks, visor, muffs.... in a spot where the dust dosn't affect others... then I'd get my angle grinder... with a metal cut off disc & cut in, I'm soon gunna have an idea of what might be in there.... foam, bog, ply, water once I've cut as deep as possible & "found" the armature within I'll make a load of wedges out of hardwood & start them into the leading edge & gradually work along them... with a hammer!, then you'll find out how well it's made, maybe full of voids & a skin will pop off, or really well interfaced with probond or whatever in there then it might destruct to get apart.... no loss.. it's already RS. You might salvage the armature & fit a new stock, glue the skins back on & repair your cuts, you might use parts of the old stock as bearing faces with a composite shaft. Main thing is to have a go & put one back as much like the original specs as possible, you made the templates for this.
    Jeff.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I think trying to save the skins might be more trouble than it's worth. I would use a diamond blade in an angle grinder and run around the centerline, creating two halves. Of course, getting these to delaminate without breaking, will be the fun part. I'd try it, but if it fought too much, I'd just give up and burn off the core, to reveal the armature.

    This is the reason I'd mold it first. You can use poly, though I might be tempted to just use plaster, the process is the same in either case. I'd build a shallow couple of boxes and support the rudder inside, just off the bottom, then pour in the plaster, vibrating it down good. When cured, pop the rudder out and cast the other side. Naturally, you'll want a good wax job on the blade, so it pops out nice, maybe some PVA. With some trimming and internal adjustments, you can use these to make a new blade, when you get to that stage.

    All this said, this is a fairly complex set of skills, which should be evaluated, before you drop a bunch of cash into materials. It might be easier to have a local CNC shop mill you a blade blank, maybe two pieces, with knockouts for the armature.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Save the skins ?

    You must be kidding. Take some ply templates off the rudder profile ...tear the thing apart..investigate the stock engineering...rebuild.

    Shaping foam and skinning a rudder is a simple fast job.

    Dont overthink it ...dont cut corners
     
  11. waikikin
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    waikikin Senior Member

    I agree, it's unlikely to peel them off undamaged, but start gently & it might come. I like to use the metal cutoff wheel when I dive into the unknown, only a $4 blade & I have a 9" grinder(B carefull!) that goes fairly deep(in one workshop got nicknamed "the LAAZZOR beam...Austin Powers).
    On rebuilding that with out retaining the skins it would be just as well to build up off the armature, shape, glass & fair... it's not so big a thing to smooth.
    Jeff.
     
  12. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Thanks guys. I would prefer to just get the foam shaped at a CNC shop. Not because I don't like the idea of making a cast, but because this rudder is not fair anyway. I am going to the trouble of making a new rudder it has to be better than the old one :) Due it its elliptical shape I think it would be hard to do it myself accurately.

    But I have nothing to loose by trying to split it in half. If I succeed thats a lot less work and money, and if I dont there is nothing lost.

    I am having other people try and tell me my 87mm (3.5") X 6mm (1/4") wall tube is poor quality and it needs to be solid. But, its this big because a fiberglass shaft was usually deemed big enough. If it was solid it would weigh 190lbs or 86kg!
     
    Last edited: Dec 6, 2013
  13. abcdefg
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    abcdefg Junior Member

    Just build a complete new one if you are happy with how that one has held up over time. Take a bunch of measurements and templates of the planform and a few thickness etc.

    Tear the thing apart, and copy the stock and internal frame that is likely to be there and rebuild. You could add foam in two halves and using the join as a centreline/datum router a series of slots into the foam using a jig to get your shape. Then knock off the remaining foam and you have your shape. Router any grooves for glass overlaps. Any number of people here could give you section templates using a naca 00xx profile (myself included) which will work fine.

    Glass with multiple layers of biax/db and epoxy resin. Fair and paint.


    As to people telling you that the tube material is poor(er) quality....they be right. Tube material is likely to be 316. Solid stock can be bought in 2205 easily and a bunch of other alloys. Without knowing the dimensions of your rudder blade, it would be worth taking a look at the ORY (or ISO) rules for yacht rudders. It does to my eye look a little light on, but the numbers will tell you soon enough.
     
  14. PAR
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    PAR Yacht Designer/Builder

    A diamond blade in an angle grinder, works a whole lot better than a fiber cutoff wheel, with less dust too.

    Tubing will be fine, assuming the correct alloy, diameter and wall thickness for the loads, with the same being true of a composite armature and shaft. The folks talking to you about solid stock, don't have any clue in what they're talking about and should be ignored.
     

  15. abcdefg
    Joined: Mar 2011
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    abcdefg Junior Member

    Saying that people don't have any clue when they talk about solid stocks is a pretty big call when 99.99% of the worlds boats have them.

    Using a solid stock material allows you to machine and taper the stock both within the blade and above the bottom bearing to "satisfy the design loads" since maximum bending moment is at the bottom bearing and not at the ends. Hollow tube cannot do this. This also flows onto upper bearing selection, tillers and more....

    A solid stock is also stronger for a given diameter (obviously) which can be usefull for high aspect planforms where one might not wish to have an excessive chord thickness.

    Solid bar is readily available in a greater ranges of alloys. Most stronger than 316.

    Solid bar is less susceptible to corrosion,

    The downside to a solid stock is of course a little more weight...


    There are trade offs in everything, but saying those that suggest solid stocks "have no clue and should be ignored" is arrogant and incorrect.




    Considering that Dennis is not trying to redesign the entire system here, as I said just go with what you have, but a check of numbers is probably worth the effort...
     
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