Laminating a Rudder's Trailing Edge...WTF?!?

Discussion in 'Fiberglass and Composite Boat Building' started by CatBuilder, Sep 22, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Third time is a charm!

    I've tried laminating my rudder's trailing edge twice now. Both times failed.

    The rudder calls for 2 layers of 6oz (200? gsm) cloth on a trailing edge that is cut off at an angle to reduce rudder hum.

    Here's what happens...

    Infusion or Bagging: You always end up with a wrinkle in the cloth under all the peel ply and stuff that you can't see. Since it's just 2 layers of 6oz cloth, the fiberglass is destroyed with any repair and you are back to the beginning again.

    Hand Lamination: The cloth rises up off the trailing edge no matter what you do. The transition is too sharp and glass won't stick.

    Varied meeting arrangements:

    Meet two pieces together, following the rudder's foil section to a point aft of the trailing edge: That leaves a very narrow, continuous thing to grind off, but when you do, you are left with something not waterproof.

    Wrap it around the trailing edge: Glass won't stick. It pulls off this sharp transition.

    What do I do?! How did you laminate your rudder's trailing edge??
  2. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Ive only ever built simple...two guys and a grinder rudders . the rudder skin had no glass tape overlapping the trailing edge. The skin of the rudder wrapped around the leading edge then was bonded to itself at the trailing edge. The trailing edge was trimmed off with a saw and that was it. never a problem.
    If you want a taped trailing edge you would need a minimum of one half inch radius on the trailing edge so the fabric would bend around..then with bog fill in the trailing edge.
  3. Tim B
    Joined: Jan 2003
    Posts: 1,438
    Likes: 59, Points: 0, Legacy Rep: 841
    Location: Southern England

    Tim B Senior Member

    Meet the skins at the trailing edge and continue each skin a short distance aft. Infuse/Bag etc. then cut the trailing edge to the correct profile, ensuring that you ONLY cut away the laminate (the last bit (1/8" or 1/4" or so, I'm guessing) should be laminate) of the trailing edge, not the core. Sand and coat with resin, then finish as you wish.

    I have been looking into Vac bagging recently, looks like a good system. The model aircraft lot seem to have the process down to a pretty fine art.
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 494, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The trailing edge has to be done in two stages; the first is to get the fabric down, which requires a substantial radius so the material can lay down around the corner. It's likely you'll need to do each side separately in this regard or puckering and wrinkles will develop. The second phase of the job is to bulk out the trailing edge with thickened epoxy, to provide something to grind down, so you're not just cutting fibers as you proceed. This part doesn't need to be bagged or infused, just butter the trailing edge with peanut butter viscosity, structurally reinforced goo and roughly shape (proud) with a knife or applicator. When this cures, take a grinder to the hardened trailing edge, without worry you're cutting through the fibers. The result leaves you with a hardened trailing edge that covers the fabrics.
  5. CatBuilder

    CatBuilder Previous Member

    Great advice, guys. Thanks.

    PAR: That method is exactly the same one my designer suggests. You guys are in agreement on how to do this. He just answered this question as well. Thanks for the great post.

    I had thought it wasn't right to have thickened epoxy outside the laminate in the kind of quantity you need to give the trailing edge a shape. Never realize you could use it as a piece of structure.

    Learn something new every day.
  6. Steve W
    Joined: Jul 2004
    Posts: 1,834
    Likes: 72, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    I dont wrap the glass around the trailing edge but rather use a strip of G10 let into the core and then run the glass wild and trim it off when its set,there is plenty of faying surface for the epoxy to bond to on the sides of the G10 as its such a long angle.
  7. rwatson
    Joined: Aug 2007
    Posts: 5,952
    Likes: 339, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    ... or you could use Peel Ply.

    Make sure you have at least 12 inches of peel ply for each side of the rudder. Apply the cloth, wet out, and pull both sides of the peel ply tight, and smooth out the wrinkles.

    You may even need to get some tape to keep the tension on the peelply, and this will force the glass onto the sharp transition.
  8. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 256, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

  9. nrg
    Joined: Sep 2011
    Posts: 15
    Likes: 1, Points: 0, Legacy Rep: 26
    Location: V.A.

    nrg Junior Member

    Skip the glass, round your edges with some 80 grit and microbubble some west brothers on there. Your wife is wrong you CAN fix everything with epoxy.
  10. CatBuilder

    CatBuilder Previous Member

    Ha ha ha! :D

    That's a good one.

    The rudders are now done. I ended up rounding the trailing edge, then using the 6oz cloth. It stuck no problem with the rounded (yet still fine) edge.

    Next step is to use some bog (colloidal silica and microballoons) to make that sharp, but staggered trailing edge to reduce rudder hum.

    Thanks for the input here. The thread was very helpful.
  11. tunnels

    tunnels Previous Member

    Next step is to use some bog (colloidal silica and microballoons) to make that sharp, but staggered trailing edge to reduce rudder hum.

    Colloidal silica this ito thicken and microballoons is a filler , Neither of those has any strength and will last a long as it takes to wipe it on the edge . You need to add micro fibres to the mix so it will stay together for at lest untill it is painted !!.
    Remember if it hasent got glass mixed in it,it will break for sure !!. :confused:

    Polyester resin or Vinylester or Epoxy Resin is just resin it breaks!!! but add glass or some other fibre and it becomes vertually indistructable !!!!
  12. CatBuilder

    CatBuilder Previous Member

    Ok, I give up. Can anyone explain this chart to me, then?

    Where is that guy from West System that posts on here?


    What am I reading wrong on the third row down?

    I see that is for "smoothness and strength." Well, don't I want the trailing edge of my rudder to be smooth and strong? It also shows Colloidal silica as being the 2nd best adhesive quality filler (it is 2nd to left on chart) and the best overall filler getting a minimum of 3 stars in every category, except fairing, which makes sense because it doesn't sand.

    I've been mixing microballoons with it in varying amounts to do various things. If I need something really strong, it's mostly silica. If I need something to fill in foam core gaps, it's a little bit of silica and mostly microballoons. If I need to fair something, mostly microballoons again. When I need strength (and thixotropic characteristics), I add more colloidal silica.

    And... what if it has a glass face, like putting glass on a cove joint?

    Not saying anyone is wrong (including PAR, who I got into a bit of an argument about this with), but why is there no definitive answer for this stuff?

    And... what would anyone here consider "structural bog" to be?

    It's specified in my plans here and there. I keep asking my designer but he never answers that one.
  13. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 256, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I think tunnels has been a bit too harsh on colloidal silica. It is true that glass fiber fillers increase the strength of the thickened resin, but in this particular case one has to consider that your goal is not to create a structural part but just to form a volume of resin strong enough to allow a grinding to a desired shape. So imho the colloidal silica is ok for this usage.

    The best thing would be imho to create a small specimen made of epoxy thickened with colloidal silica bonded to an epoxy-covered board and grinded to the shape of your trailing edge. Then hit it, bend it and do whatever necessary to assess how resistant it actually is - considering the real-life working conditions it will be exposed to, of course.

  14. CatBuilder

    CatBuilder Previous Member

    Thanks for the input, Daiquiri. I am thankful for any posts helping with this issue. This issue has dogged me for a long time now. Every time I think I have it figured out, somebody comes along and says my boat will fall apart. It's a bit nerve wracking.

    What about a structural cove/fillet where you have a colloidal silica and microballoon mixture, but have some biaxial tape over it as well?

    This type of fillet is something common in my boat. My bulkheads, including structural beams, are held in this way. I have also used the same type of fillet (with the glass outside of it) for some internals on my rudder.

    Is this correct?

    Below are the finished rudders. I rounded the trailing edge a little bit and put on the 2 layers of very thin (6oz) cloth. They just need a little exterior fairing, the trailing edge installed and the tops mated/bogged to the hull underside shape for a nearly zero gap between rudder and hull.

    Also, I added pictures of one of them under infusion, for those interested in infusing rudders.

    Attached Files:

  15. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 256, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    They look good and the trailing edge appears to have sufficiently small radius from here. It will not have a significant effect on the generation of lift, and will likely even reduce the probability to hear your rudder "singing".
    So I would cut further philosophical discussions here... Just put them on your boat and try them out. I'm pretty sure they will do fine just the way they are. You will always be in time to correct small issues later, if you find any.
Similar Threads
  1. Scuff
  2. Tungsten
  3. KD8NPB
  4. andysailor
  5. Cjmac
  6. Cjmac
  7. Cjmac
  8. andysailor
  9. fallguy
  10. burke
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.