Macgregor 65 Chain plates

Discussion in 'Sailboats' started by mac65, Apr 2, 2021.

  1. mac65
    Joined: Apr 2021
    Posts: 2
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    Location: Brisbane, Aus

    mac65 New Member

    Hi,
    I recently purchased a Macgregor 65, and I am in the process of replacing the rig. While I had the mast out, I thought that I would re-bed the chain plates. Problem is the way they were installed by the factory makes it near impossible to get them in and out.
    The bolts were glassed into the hull, such that they are like studs protruding from the side of the hull. At the deck, there is a plate which is welded to the chain plate to seal against the deck. This forms to constraints where you effectively have to bend the top plate so that you can get enough angle on the chain plate to get it off the bolts.
    While this works, I cant see any way to get them back in again, and get the top plate flat again and have it all seal.
    I would really like to replace the bolts, but I cant see any way to do it without messing up the side of the boat.
    I'm hoping that maybe some one here has been through this before and has found a solution.
    I have a few ideas, but most of them involve making new chain plates.
    Thanks,
    Chris
     
  2. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    So, I must ask if the bolts are accessible and can be replaced. I understand it sounds like a mounting with a corner.

    For an entirely different use, I had custom bolts made with an adhesive head in Metric size 16 because I misread the designer's print. But you can also purchase more standard sized adhesive head stainless bolts from McMaster Carr.

    It sounds to me like the bolts are the real matter and you could either rebed or simply replace the bolts.

    pictures may help unless someone has experience with the specific case

    if the bolts are accessible; then you would grind them out from the reverse; this is a bit scary though as you mustn't damage the hull in the process

    in my use; the bolts are bonded to a solid frp and then layers of glass are on top of the adhesive head, if yours is similar, the extra glass must also be removed and replaced; for example...my bolts are very buried so to speak, and two of the bolts in each hull are next to impossible to access; hope to never have to..

    if you don't have access, then avoid the desire to do the job as much as possible, or consider the work on as one bolt as needed basis
     
  3. Max J. Allen
    Joined: Apr 2021
    Posts: 1
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    Location: Redwood City CA USA

    Max J. Allen New Member

    We have a MacGregor 65 built in 1992. I have looked at taking my chainplates off for inspection but ran into the same conundrum as mac65. The only way I can imagine MacGregor assembled these would be to screw the bolt in last. We have put sufficient stress on the rig that some bolts heads are now showing through on the outside of the hull as stress cracks in the gelcoat - they must be just under the surface. I would assume MacGregor embedded a threaded stainless plate inside the hull glass for the bolts to thread into but I have no proof of that.

    One solution I was thinking of was to jam two nuts on the inside head of the bolt to back out the bolts and then pull the chainplates out through the deck.

    I'm considering adding outside backing plates and through-bolting in the future - scary having anything you can't inspect !

    Hope that helps !
     
  4. mac65
    Joined: Apr 2021
    Posts: 2
    Likes: 0, Points: 1
    Location: Brisbane, Aus

    mac65 New Member

    Thanks for the responses.

    Failguy, I get that its a bit hard to picture, I try to add some. The bolts are accessible, just the heads are hidden. I don't believe that they are glassed over, just filler.

    Max, mine's a '92 also. Im glad that you mentioned the cracking, it made me go and have a closer look at the hull. Pulling the first chain plate involved a lot of levering and hammering, which I can now see some cracks in the filler where the bolt heads are. Checking the others, I found a couple of other small cracks, really had to look for them.

    I had a bunch of different plans on how to deal with getting them out, but have now settled on backing them out as per Max's idea. Although I doubt I will have to do this again, I would like to make them serviceable, and not just replicate what is there now.

    My initial idea was to fabricate 316 threaded inserts bonded into the hull and then use bolts from inside. However I have also been looking at bonding the bolts into an epoxy plug instead. This has the advantage of not having to make all the inserts. Going of the west system guide they recommend a 0.25" increase in hole size for the epoxy plug.

    One thing that I am trying to work out is would the epoxy have sufficient compressive stress of the chain plate bolts. My initial thought was that it wouldn't, however on reflection, the GRP is taking that compression load now, and the epoxy should be stronger than the GRP, so I'm leaning towards it being OK.

    My other concern is getting sufficient tension on the bolts. If they are just bedded in the epoxy, there will be little tension on the bolt. The west system guide says using release agent will reduce the pullout strength by 4-10%, and recommends straight bonding. But as I said Im not sure about not being able to tension the bolt.

    So in summary, this is what I'm thinking of as the process;
    1 - Back the bolts out through the hull
    2 - Drill out the bolt hole to 1" (they are 5/8 bolts so its a bit more than 0.25" over size)
    3 - Put the chain plate in place with the bolts, with out washers and prepared with release agent
    4 - From outside the hull, fill the cavity with epoxy (west system recommends the high strength additive 404)
    5 - After curing, remove the bolt and replace the bolt, but with a washer to allow for clearance at the bottom of the hole while tightening
    6 - fair and paint

    Would be great to hear some thoughts, particularly from anyone who has experience with bonded fasteners in epoxy.

    Thanks,
    Chris
     

  5. fallguy
    Joined: Dec 2016
    Posts: 4,146
    Likes: 687, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Well, the hull per the Mac65 brochure is 1.25" thick there.

    If they inserted a nut or insert, drilling it out renders the insert junk.

    The reasons, per the Mac65 brochure for this method, was to avoid any leaks.

    I am a bit confused as to the plan here. I recommend you pause it until you have posted pictures and a few more people coin in here. It is a large boat and I am uncomfortable with your proposal unless I misunderstand. I hear no mention of a nut, so it sounds like the threads are doing the work.

    Be patient with forum members and post some pictures. If nothing else, it'll keep your post recent to have me curious.

    It does seem quite odd, Macgregor would not have had a maintenance plan here, so am nervous something is being overlooked.

    For example, if the cp is bolted to the hull and the head buried for ingress, then the head is to be dug out and refaired for maintenance... but only a guess from an amateur.

    also, those are really gorgeous boats...
     
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