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Attaching flag to fiberglass without through bolts.

Giro

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Jul 23, 2019
62
MacGregor MacGregor 25 Monterey
Hello:
I need some advise on what the best and strongest way to attach a metal base (stainless steel or chrome plated brass) to a fiberglass surface without using through bolts. There is little to no potential room to access the undersurface to attach lock washers and nuts to bolts or even a backplate to increase the strength of the base to be used for the teak wood flagpole. I’m wondering if there might be a type of stainless steel toggle bolt that could be used for such an application. If that might not be possible, would it be a bad idea to use simple screws and some additional epoxy glue to secure the base in this process? Any advise would be appreciated.
Giro
 

Ward H

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Nov 7, 2011
3,092
Catalina 30 Mk II Barnegat, NJ
An alternate method is to use a rail clamp flag pole mount.
This would be less destructive to your fiberglass.

Where are you mounting the base?
 
  • Like
Likes: Justin_NSA
Jan 11, 2014
7,727
Sabre 362 113 Fair Haven, NY
Self-tapping screws with a little sealant, like 3M 4000UV. Or a rail mount flag pole.
 

capta

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Jun 4, 2009
4,291
Pearson 530 Admiralty Bay, Bequia SVG
How about a small block on the backstay and a flag halyard through it?
 
Jan 7, 2011
2,825
Oday 322 East Chicago, IN
You could glass an aluminum plate in the area you want to mount the flag base, and drill and tap holes for your bolts.

Or mount a wood block with some thickened epoxy and screw your flag base to the wood block.
 

Giro

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Jul 23, 2019
62
MacGregor MacGregor 25 Monterey
I want to thank you all for your suggestions. Since each of your ideas make good sense, now I’ll have to decide which application will be the most appropriate for the exact location on the taffrail. The suggestion regarding placement on the stern rail is a good and logical one, but I think that for my boat I should attach it directly to the fiberglass. I know that we should try to avoid drilling holes in our boats hulls, but three small screws are probably not going to be too bad.
Again, thank you all.
 
May 24, 2004
6,765
CC 30 South Florida
Why don't you attach the base to the stern pulpit? I'm not opposed to drilling holes on the fiberglass but on the pulpit tubing it will be a much stronger mount.
 
May 17, 2004
3,421
Beneteau Oceanis 37 LE Havre de Grace
If the surface is cored it would probably be good to overdrill the holes, fill with thickened epoxy, then screw into that. That will keep any water leaks out of the core.

@dlochner has suggested a process in the past for leaving a waxed bolt in the epoxy then backing it out once cured, leaving behind tapped holes. I wonder if this could be an application for that process?
 
Jan 11, 2014
7,727
Sabre 362 113 Fair Haven, NY
@dlochner has suggested a process in the past for leaving a waxed bolt in the epoxy then backing it out once cured, leaving behind tapped holes. I wonder if this could be an application for that process?
I borrowed the idea from West System Epoxy. It is in their manual. :)

No need to overthink this project. There will be very little stress on the flag pole, so backing plates and through bolting is unnecessary. If that area of the deck is cored, then drilling over sized holes and filling with epoxy would be a good idea. Otherwise short self-tapping screws will do just fine. A sealant with moderate adhesive properties, like 3M 4000UV would work well. This sealant has UV protection so it doesn't turn brown.

Avoid at all costs Silicone sealant and 5200. Both are poor choices for this application for opposite reasons. 5200 is an adhesive, not a sealant and silicone is too weak and gets into the gelcoat and prevents future sealants or paint from adhering to the hull.
 

Joe

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Jun 1, 2004
7,410
Catalina 27 Mission Bay, San Diego
If you're mounting it on the deck, it will most likely have a wood core beneath the thin layered fiberglass. A test hole can answer the question. You'll want self tapping or wood screws long enough to anchor into the core. You'll also want to use the proper sealant. A polysulfide works well, such as Life-Caulk (not Life Seal) Lots of folks here swear by butyl tape. Definitely not 5200 or silicone. The load shouldn't be too great unless you're using the flag pole for something besides holding the flag.
 
Feb 5, 2009
251
Gloucester 20 Kanawha River, Winfield, WV
I needed some u-bolts on my transom to accommodate a split-backstay modification. There was no way to get into the backing space, so I made a way. Not entirely elegant and might be more trouble than it's worth for what you're doing, but it's another option to throw on the pile.

boot2.jpg
 

Giro

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Jul 23, 2019
62
MacGregor MacGregor 25 Monterey
I do not believe that the portion of the deck where I want it has a core so I believe that the tap screw method is probably the best way to proceed. Thank you all.