Glassing in a shaft log

Discussion in 'Fiberglass and Composite Boat Building' started by LMB, Nov 28, 2010.

  1. LMB
    Joined: Nov 2008
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    Location: North Carolina

    LMB Junior Member

    I'm finsihing up the structural rebuild of an early 80's Ski Supreme. It's similar in style and size to a Ski Nautique, I guess about 18'. Anyway the owner complained of water leaking in at the shaft log for the propellor shaft. After grinding into the area, it looks like it was bedded down into bedding compound or something similar and then glassed over. The bedding has become brittle and is no longer bonding the shaft log in. I'm open to suggestions on the best repair. I typically mix my own putties for similar applications but wonder if a true bedding compound is better here.
     
  2. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    I would use a filled Epoxy system to get the shrinkage @ nil,West 404 filler would be one choice.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I'll second the hard mount that War Whoop recommends as well, though I'd likely use a mixture of 403, 404 and 406. The 403 (milled fibers) to improve the "glue" aspect, the 404 to harden the mixture and the 406 as needed to control viscosity. Work neatly as you're not going to want to sand this mixture when cured.
     
  4. LMB
    Joined: Nov 2008
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    Location: North Carolina

    LMB Junior Member

    Yeah, this is one of those situations where I was leaning on an epoxy mix. The only other issue is whether to completely remove the shaft log. That's the only way I can remove all of the old compound and get the best bond. It will also mean going to some lengths to make sure the alignment doesn't get off though. The alternative would be to "just" grind out and rebond around the perimeter of the log. Working on one side at a time the log would never move from it's original position and the bond would "probably" be sufficient.

    You know, the thing is I don't usually proceed with methods described by "just" and "probably", but I don't want to unnecessarily open up a can of worms here either. The owner will be installing the engine later so I've only got the strut to work with. I appreciate any insight or assurances here.
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's a tough call not being able to see what you're up against, how much difference between the shaft and tube diameters, any mis-alignment, how much bedding was used, how this bedding was applied, etc. If alignment is an issue a simple jig to insure holding the inside of the tube in it's current location could be arranged. Something temporally glued to the hull (hot glue gun or something easy to remove) that can be disassembled while you remove the tube and clean out the bore, then reassemble so the tube can be epoxied in place in it's proper location.

    Also upon thinking about it, I'd recommend using West System's new product G-Flex for this job. It's higher elongation properties will be beneficial in this application. What is the tube made off?
     
  6. mark775

    mark775 Guest

    LMB, The reason they used putty before is they probabaly did the glassing in poly. The thing is bronze? Epoxy bonds to clean bronze. Poly barely does - hence, the putty. Somewhere, I'm sure you can find some shear tests of glued substrates, including bronze. The test will show something on the order of gawdawful strong with a suitable epoxy (G-flex). Taper (grind) the area around it, minimize your epoxy putty, I think you can get a maximum glass to resin ratio using a cloth for this repair. A twill is good and drapable for this, lovely to work with but any cloth you have, really (How far out you taper on the hull will be more of a deciding factor of ultimate strength than what glass you use - I mean don't taper just 3"). Don't need to taper so much on the inside because you can build up.
    Check the alignment of the points you do have. If it's wrong after this repair, it's your fault in their eyes!
     
  7. LMB
    Joined: Nov 2008
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    LMB Junior Member

    Thanks PAR and Mark, you are both echoing my thoughts. I almost mentioned the G-flex. I like the properties but having used it in the past my biggest complaint is that it is so tacky/goey it can be difficult to spread and shape. I have used it mixed with the regular 105 to get a compromise on working qualities, so thats a consideration as well. Setting up a simple jig should solve the alignment equation and head off any future problems. A little more trouble now will save some headaches down the road. Mark echoed my concern that after the repair it's my problem no matter how screwed up it was before hand.
     
  8. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    The local shaft log cutless bearing technique over here is to use good practice, ....say Gflex as you suggest...and install an over sized shaft log tube. Then the engine guys come...bring everything into perfect alignment..and then the Cutlass bearing is installed in the oversized shaft log tube with " Chocfast ". Alignment is critical, no matter what material or technique you use to seat the shaft log cutless bearing . Chocfast is not an adhesive, its a bedding compound.
     
  9. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The shaft log is there to keep water out only. It holds the stuffing boz. Since it is not a structural element, you can just fiberglass around the base from the inside and outside. It is easier if you take the shaft off and then tape around the edge.
     

  10. mark775

    mark775 Guest

    Gonzo... oh, nevermind. Have a good day.
     
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