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Old 30-04-2007, 14:27   #1
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Boat: Pacific Seacraft Mariah 31
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re-bedding hardware on firberglass backed with plywood

Hi All,

I'm relatively new to boat maintenance and I have a question that may be somewhat naive.

I need to re-bed the stainless steel fitting for the hawse hole of our anchor locker. I've found a lot of information on rebedding hardware in cored decks, but our older boat just has a fiberglass deck backed with 1/2" plywood. For cored decks it seems like most people recommend removing some of the core material around the bolt holes and filling that area with epoxy to seal it up, and then bedding the fitting with some kind of sealant. Is the epoxy sealing necessary for plywood backed decks? Even though the deck isn't cored, I'm concerned about moisture getting into the plywood. Also does anyone have a suggestion for a sealant between stainless and fiberglass? I may want to remove the piece at some point so a permanent adhesive won't work.


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Old 30-04-2007, 17:50   #2
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I'm certainly no expert, but...

If I were in your deckshoes, I woud
  • Remove the fasteners
  • Remove the fitting
  • Remove old bedding compound with flat scraper
  • Clean with soap & water or solvent as necessary
  • Use drill to remove old bedding compound from holes
  • Allow any trapped moisture to evaporate, if necessary
  • Use countersink bit to slightly "flare" hole in fiberglass deck
  • Seal walls of cleaned hole with epoxy applied with Q-Tip
  • Mask area around foot print of deck fitting with quality tape
  • Apply quality bedding compound to area within masking tape
  • Insert fasteners through fitting
  • Insert fasteners part way through deck holes
  • Apply bedding around top portion of fasteners
  • Push fasteners & fitting snugly to deck
  • From inside hull - install backing plate, washers & nuts
  • Employ assistant to hold fasteners on deck without turning
  • Tighten nuts from inside until just snug
  • Go have a beer with your assistant
  • Tighten nuts until firm the following day
  • Remove masking tape
  • Done.
Backing Plates - depending on the job, I like to use stainless steel plates or a half inch piece of plastic cutting board (available at any grocery store) - traced from foot print of fitting and cut & drilled prior to installation. Sometimes I'll use fender washers (only) for light load applications. Don't use nylock nuts.

Using a countersink bit to "flair" the hole on deck tends effectively increases the sealing surface around the fastener and compresses the bedding compound into the threads when tightened.

Leaks rarely come back to bother me when I make this effort.

I prefer plastic cutting boards over plywood because it's cheap, readily available, non corrosive, non conductive, doesn't hold moisture, doesn't rot and tends to bend a little to take irregular shapes. And it's real easy to work with.

In closing, when making backing plates, I think it helps to drill the holes a bit oversized to provide a little room to wiggle the plate onto the fasteners.

Works for me.

To Life!


PS - after re-reading the specifics of your post... a backing plate on a hawse pipe may be un-necessary and regular flat washers may be the go. And I NEVER use 3M 5200 sealant on something I may want to remove at a later date. Have fun!

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Old 30-04-2007, 17:56   #3
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Aloha Han,
Kirk has it right. For your bedding I would use polysulfide, not polyurethane or silicone sealers.
Kind Regards,
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Old 30-04-2007, 19:34   #4
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3M 4200 would work well and allow you to remove the fitting in the future should you need to.
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Old 01-05-2007, 06:21   #5
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i agree with gallivanter's on everything accept the size of the backing plate dimensions. although this has nothing to do with your particular job at hand, backing plates should always have a wider surface area than the piece you are installing/ backing. the reason is you need to spread the load out further than the footprint of the on the piece of equipment so there are no localized stress points at mounting holes. if the backing plate is only the same size as the foot print of unit to be mounted you stand a far greater risk of pulling the unit and a piece of deck under load.
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Old 01-05-2007, 06:33   #6
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What Mike & Kirk said.
Note Kirk's line 8 - seal edges of FRG holes.
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Old 01-05-2007, 08:17   #7
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Thanks for the great replies. Kirk, your step by step directions are excellent, I'll print them out and have them next to me on deck when I do the job! Now as soon as it stops raining here, I can get started on this.

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