Rudder Woes

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  • 07 Jun 2020 13:02
    Reply # 9020494 on 9010389
    ......I discovered that much of the rudder stock was rotten due to fresh water penetration. Fortunately the rudder had very substantial teak cheeks either side of the rudder stock, through riveted. It was obviously those which held the rudder together. In my case water had gotten in where the fiberglass had worn through at the point where the tiller fitted into the stock. So it is all about keeping the fresh water out. And of course if the rudder is then fiberglassed the water is not able to dry out. Almost better not to fiberglass a solid rudder. When I built the new rudder I glued a plywood cap over the end grain of the timber.

    I'm glad you brought this up. This makes two of us at least who have had the same experience. We serve as a bad example for our members. By "bad example", I mean ,an example that teaches. 

    Before I forget, Gougeon recommends fiberglass over Douglas Fir to prevent surface checking.

    The tiller was fitted to the rudder was very tight. No Chafe. That leaves the bolt holes as possible entry way. I would use the Gougeon method of drilling oversize, sealing and plugging with thickened epoxy for redrilling to bolt size next time.

    About corners. Yes, there is the danger of over sanding. There is also the danger of stress concentration. I can't say often enough, as wonderfu as wood epxy construction is, you must pay close attention to inside and outside corners. They MUST be rounded and carefully covered with glass, if using glass. Fillers can be used after for cosmetic adjustments.

    In their article, mentioned elsewhere, Gougeons don't like plywood for cantilevered rudders and centerboards because ply is not as fatigue resistant as solid wood. It's also more vulnerable to getting wet because water can migrate so easily along the grain.

    I am no expert on moisture meters but a have a simple one. I drilled multiple little holes through the fiberglass cover of Hobbit's rudder, spaced to receive the pins on my meter. I did this in a grid fashion and marked the moisture % readings at each location. It gives me a partial picture of what's underneath. One could draw a "hydrographical" map of the moisture. LOL. 

    I will probably drill 3/8" holes through the rudder (plugged later) in a staggered grid and bake it in the sun to extract moisture. If I had a suitable vacuum pump, I'd use that. Don't laugh, this method, using a far more sophisticated procedure, is used to extract un-catalyzed liquids from fiberglass hulls with osmosis problems.

  • 06 Jun 2020 15:23
    Reply # 9018991 on 9009568

    Anther article from the Goueon Brothers: How to Build Rudders and Centerboards

    https://www.epoxyworks.com/index.php/how-to-build-rudders-centerboards/

  • 06 Jun 2020 15:16
    Reply # 9018985 on 9009568

    The Gougeon Brothers have an article on this subject entitled Applying Fiberglass Cloth and Tape.

    https://www.westsystem.com/instruction-2/epoxy-basics/applying-woven-cloth-tape/

    They describe my method, the dry method and Arne's method, the wet method. They have a third combining elements of both.

    So they all work. I think I learned about the dry method from West  in the late 70's.

  • 05 Jun 2020 05:09
    Reply # 9016486 on 9015657
    Anonymous wrote:
    Anonymous wrote:

    I wonder if thI noticed he had a hardwood cap at the very top, covering the end grain of the plywood. Where did the water get in? Hard to say. Through the rudder/tiller connection bolt holes? A crack in the hard edge of the rudder head?

    Any bolt holes are probably best  treated with the popular West System method where you drill the hole oversize, paint the hole with unthickened epoxy, then fill the hole with thickened epoxy, then when cured re-drill the smaller holes leaving a solid ring of thickened epoxy around the hole.

    I think Arne has a good point, I'd also wet the wood out until it will absorb no more and let it start to cure first.  If you are worried about the glass sticking to the tacky epoxy you can wet the glass out on a sheet of plastic and transfer it to the rudder wet.  Peel off the plastic sheet after the glass is on the rudder.  Use thick plastic like vapour barrier to make life easier.

    If you sand the epoxy at all after it cures you expose fibreglass strands that water will want to wick along.  At a microscopic scale the fibreglass does not wet out completely.  Your final coat of epoxy really shouldn't be sanded.  Thus if you sand, you need another coat of epoxy at the end.  Amerlock or InterProtect 2000E are much easier as a final epoxy coat compared to West Systems.  Apply the antifouling while the epoxy is still green and there is no sanding needed.

    Or, at least, that's how I'd do it.

  • 05 Jun 2020 00:57
    Reply # 9016113 on 9015657
    Jim wrote:

    I noticed he had a hardwood cap at the very top, covering the end grain of the plywood. Where did the water get in? Hard to say. Through the rudder/tiller connection bolt holes? A crack in the hard edge of the rudder head?

    Going without glass on solid wood, that's an interesting approach.

    I have learned through long years of experience that corners of any glassed timber structure is one place where moisture can easily get into the timber substrate. This is because when sanding the fiberglass layer it is very easy to sand through a rounded corner, so I try very hard to do minimal sanding on corners.

    With regard to the use of glass over solid wood or plywood. I personally think that the only thing that glass does is to provide abrasion resistance, necessary especially on hulls. I have built numerous plywood structures such as solid dodgers and dinghies which have not been glassed, just several coats of resin, and these structures have been as long lasting as the glassed structures I have built, or owned. 

  • 04 Jun 2020 20:40
    Reply # 9015657 on 9015456
    Anonymous wrote:

    I wonder if the problems with glassed plywood can stem from the glass-fibre wicking away the resin from the plywood during glassing.

    When I fitted a ‘fore skeg’ to Johanna, around 2003 or 2004, I did not glass it. I therefore took extra care to coat it all round before installing it. I paid particular attention to the raw edges and to make sure every void was filled. When I sold Johanna, ten years later, there was no sign of that the skeg had sucked any water.

    I therefore think that one should first coat any plywood as if it were not to be glassed, and then glass it, when the epoxy have almost hardened.
    It can’t hurt...

    Arne


    I approached this problem in a different way. When I glass a piece of wood, I lay the glass on the dry wood and position it as best I can. I then apply resin in one spot and begin, with a rubber window squeegee,  to push the resin through the cloth and away from that spot in all directions. Soon, you will see milky patches which indicate that resin is being stolen from the cloth. So, I put more resin there , sweeping the resin back and forth until the whiteness disappears. Before I finish, I make sure the cloth pattern shows through evenly, everywhere. I know that the cloth is hard up against the wood and there is no puddling of resin. I would be afraid to wait for the first coat to get tacky. That would make it more difficult to even out the cloth. The wet cloth is easy to move enough to get out wrinkles and better position the edges. I think the milky test is a good indication of satisfactory resin penetration.

    O found a multitude of milky patches on HOBBIT. I doubt he used the squeegee method. If not, it would be safe to assume it wasn't used on the rudder either.

    I noticed he had a hardwood cap at the very top, covering the end grain of the plywood. Where did the water get in? Hard to say. Through the rudder/tiller connection bolt holes? A crack in the hard edge of the rudder head?

    Going without glass on solid wood, that's an interesting approach.

  • 04 Jun 2020 18:57
    Reply # 9015456 on 9009568
    Anonymous member (Administrator)

    I wonder if the problems with glassed plywood can stem from the glass-fibre wicking away the resin from the plywood during glassing.

    When I fitted a ‘fore skeg’ onto Johanna, around 2003 or 2004 (made of 2 x 15mm plywood), I did not glass it. I therefore took extra care to coat it all round before installing it. I paid particular attention to the raw edges and to make sure every void was filled. When I sold Johanna, ten years later, there was no sign of that the skeg had sucked any water.

    I therefore think that one should first coat any plywood as if it were not to be glassed, and then glass it, when the epoxy have almost hardened.
    It can’t hurt...

    Arne


    Last modified: 04 Jun 2020 21:42 | Anonymous member (Administrator)
  • 04 Jun 2020 15:45
    Reply # 9014826 on 9012519
    You probably already know this, but if you haven't begun work, I've found the end grain seals much better if you can get the part hot before applying epoxy.  For something as big as a rudder, the only choice might be to start work late on a sunny afternoon.  I've put small parts in an oven.  I've even been known to build a tent with a heater.  The trick is to work quickly once it is out of the oven and cooling.  End grain always absorbs a lot of epoxy, but starting at 40 or 45C, it is pretty amazing how much epoxy it will absorb as it cools over 30 minutes and draws the epoxy in.  I just keep applying epoxy until it will take no more.  This is too much trouble for most parts, but I like the trick for special bits
    I didn't know this. Very interesting. I'll keep this in mind next time I encounter this situation. Thanks.
  • 03 Jun 2020 17:23
    Reply # 9012519 on 9009568

    It sounds like you mostly have your problem solved for now Jim. 

    You probably already know this, but if you haven't begun work, I've found the end grain seals much better if you can get the part hot before applying epoxy.  For something as big as a rudder, the only choice might be to start work late on a sunny afternoon.  I've put small parts in an oven.  I've even been known to build a tent with a heater.  The trick is to work quickly once it is out of the oven and cooling.  End grain always absorbs a lot of epoxy, but starting at 40 or 45C, it is pretty amazing how much epoxy it will absorb as it cools over 30 minutes and draws the epoxy in.  I just keep applying epoxy until it will take no more.  This is too much trouble for most parts, but I like the trick for special bits.

    I once had to rebuild a foam-fibreglass rudder that had failed from water intrusion causing the stainless reinforcement to separate from the rudder stock.  I felt the cause had been that the epoxy really doesn't seal well to the stainless rudder stock, which is a location of very high stress.  When I re-assembled it, I left a generous chamfer in the fibreglass around rudder stock that could be filled with polyurethane sealant.  As far as I know there was no further trouble.

    Given your metal working skills, a better solution might be to build an all metal rudder.  The Origamiboats crowd do this in much the same way as David mentioned for tortured plywood.  There are variations, but a pipe for the leading edge a larger pipe (if steel) or rod (if aluminum) for the point of maximum thickness, along with welding the perimeter is all it would take.  If built in steel, welding machines are now tiny, readily available and cheap (can often be bought used and sold for the same price after the job) for DIY.  If built in aluminum, anyone could do the part cutting and fit-up with woodworking tools and then take it to a shop to have welded.  As you know much of the cost/time in metal work is the fit-up, if you are only paying for welding the cost should be reasonable.  Done this way and pressure tested, you should have a forever rudder.  I think I have slightly more detailed instructions for the rudder that I could dig up if you like.  

  • 02 Jun 2020 21:56
    Reply # 9010389 on 9009568

    I had a similar problem with the rudder on 'Footprints'. Not that long after having completed two ocean crossings I discovered that much of the rudder stock was rotten due to fresh water penetration. Fortunately the rudder had very substantial teak cheeks either side of the rudder stock, through riveted. It was obviously those which held the rudder together. In my case water had gotten in where the fiberglass had worn through at the point where the tiller fitted into the stock. So it is all about keeping the fresh water out. And of course if the rudder is then fiberglassed the water is not able to dry out. Almost better not to fiberglass a solid rudder. When I built the new rudder I glued a plywood cap over the end grain of the timber.

    Having just built the rudders for my new catamaran out of tortured plywood construction which automatically provides the foil shape and makes for a very light rudder, I now think this is a preferable method of rudder construction, if the rudder can be engineered to suit the boat. 

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