Need help with a fin box

Discussion in 'Surfing' started by Walnuts, Dec 11, 2019.

  1. Walnuts

    Walnuts Active Member

    103
    46
    Mar 25, 2018
    Long Beach, NY
    4DFA1276-4899-4098-A64F-8FE2D1B1A134.jpeg 7A65924B-3911-45D8-91A1-FA7832DED625.jpeg AC3B28B9-5EF5-48CA-B837-227B1277221C.jpeg Bought a Bunger board at a garage sale locally. Think it’s from the late 60s, single fin. Had some major repair work that was needed and had done professionally.

    Long story short, tried to replace the fin with something more modern (Greenough 4a, and found the base of the fin is too thin for the box. Looks like a standard longboard box to me but who knows. The end result is the fin slides around in the box and won’t stay in place even if screwed tight.

    Any suggestions on how to fix this (outside box replacement). See pix below of the fin it came with and the box. .
     
  2. Ricksurfin

    Ricksurfin Well-Known Member

    1,036
    1,467
    Jun 9, 2019
    San Clemente, CA
    I’d try another fin before I did anything. My guess is it’s that fin. It looks to me to be a molded fin, and I’d try a nice fiberglass one.
     
  3. Walnuts

    Walnuts Active Member

    103
    46
    Mar 25, 2018
    Long Beach, NY
    Good idea. The board is a 6’8 but I would assume the width would be the same as the 9” fin I have in my longboard. I’ll report back.
     
  4. Ricksurfin

    Ricksurfin Well-Known Member

    1,036
    1,467
    Jun 9, 2019
    San Clemente, CA
    If it slides with the screw tightened, it sounds like a problem with the tab depth. If it tightened where it wouldn’t slide but was loose side to side, then it would seem like more of a problem with thickness of fin. Also, examine box closely to make sure it isn’t cracked.
     
  5. Walnuts

    Walnuts Active Member

    103
    46
    Mar 25, 2018
    Long Beach, NY
    tried with a second fin and same result. Screw tightens all the way and looks like it’s short enough that it’s not something with box depth. Also, when tightened the fin does remain loose side to side. And slides front to back when fully tightened.
     
  6. garagefull

    garagefull Well-Known Member

    411
    264
    Feb 22, 2004
    Santa Cruz
    Try a fin made by Fins Unlimited if you have one. Seems to me that FU fins have a little thicker base, and maybe a slight taper in thickness from top to bottom. So they kind of wedge down into the box. Or put some tape on the side of the base of your fin to make it thicker. That works most of the time but not always.
     
  7. SeniorGrom

    SeniorGrom Well-Known Member

    3,035
    1,821
    Mar 20, 2012
    USA New Jersey

    I agree. The fin screw really has nothing to do with tightening the fin. NEVER try to ‘tighten’ a fin with the screw! Something will give and you won’t be happy with the result. Sides of the fin are what tighten it in the box and as Jim Phillips has told us, the FU box sides are tapered. Either the fin base isn’t thick enough or the box slot is too wide. I would scuff the sides of the fin base and add glass & resin. Shape with 60 or 80 grit on a block til properly hand fit (trial and trial, over & over being patient). Just adding business cards or tape to the fin base is bogus but I have done it in a pinch.

    Also: The fin does appear to be a molded lexan material and who knows if it can be modified.
     
    Last edited: Dec 11, 2019
  8. garagefull

    garagefull Well-Known Member

    411
    264
    Feb 22, 2004
    Santa Cruz
    One more thing, don’t try to mess with that molded Lexan fin. Resin won’t stick to it anyway. Those fins are kind of rare, and actually work well with the very thick foil. If you’re not into that Lexan fin, I’d be happy to trade you a fiberglass fin of your choice for it.
     
    DJR likes this.
  9. shapewright

    shapewright Well-Known Member

    884
    658
    Aug 6, 2006
    USA California
    The bottom of the tab is too thick vertically, the plate makes contact with it before the base of the fin hits the bottom of the box.
    This prevents the plate from hitting the top edge of the slot it slides in, this is what pulls the fin to the bottom of the box
     
    DJR, Chilly Willy and Ricksurfin like this.
  10. Ricksurfin

    Ricksurfin Well-Known Member

    1,036
    1,467
    Jun 9, 2019
    San Clemente, CA
    Yep, I’ve had that problem when the glasser doesn’t set the box deep enough and the sander has to remove a lot of it. If that’s the case no fin will work properly unless you shave the bottom of the tab some.
     

Share This Page