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
- 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.
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.
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!