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Wood Zeppelin
Joined: 09 Feb 2016
Posts: 310
City/Region: Seattle
State or Province: WA
C-Dory Year: 1997
C-Dory Model: 22 Angler
Vessel Name: C-Creature
Photos: Childhood Dream
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 Posted: Wed Aug 31, 2022 11:40 pm Post subject: |
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Epoxy Plugs:
Hey everyone-
I like the idea of the screws going into epoxy (or two-part polyurethane) plugs. This way, no screw penetrates into wood, and the interface between wood and fiberglass would be sealed off as well.
The previous screws were #10 x 3/4" long. #10 screws are approximately 1/8" in diameter. So I figured I'd drill 3/8" holes to have 1/8" of "meat" all around the screws. And, I'm concerned about drilling these holes too big...
MAIN QUESTION:
- There are a lot of these screws (about every 6") going into the underside of the chines. Would drilling all these holes create structural weakness?
Other questions:
- Does 3/8" sound good? What about 1/2". Should I keep them as small as possible or not worry about a larger hole?
- Since now screwing into tough epoxy/poly rather than wood, could the screws be shorter (and therefor the holes less deep!?)
Thanks in advance for all and any input!
_________________
James Salay - Real Estate Broker / Investor, Engineer, Artist, Fisherman, Canyoneer, Outdoor Enthusiast
Current boats:
1997 22' Angler - "C-Creature"
1988 16' Angler - "E-fishn-C" (Project boat)
1997 16' Cruiser - "Wet-a-Net"
Also:
14.5' Drift Boat - "Wood Zeppelin" |
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thataway
Joined: 02 Nov 2003
Posts: 20803
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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| Posted: Thu Sep 01, 2022 12:31 pm Post subject: |
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| Quote: | | - There are a lot of these screws (about every 6") going into the underside of the chines. Would drilling all these holes create structural weakness? |
Why in the World would anyone put screws into the boat's bottom core, underside of the chines every 6"?
Please post photos of where the screws are located.
You want to removed a thin rim of the core material, between the inner and outer fiberglass layers. You drill the holes big enough to get whatever you are using to remove the core with. I use a Dremel Tool, with about 1/4" bit, so a hole of 1/4 or slightly larger would be proper. Do not put in any larger hole than necessary.
_________________
Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
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Wood Zeppelin
Joined: 09 Feb 2016
Posts: 310
City/Region: Seattle
State or Province: WA
C-Dory Year: 1997
C-Dory Model: 22 Angler
Vessel Name: C-Creature
Photos: Childhood Dream
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| Posted: Thu Sep 01, 2022 7:16 pm Post subject: |
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This is a wood drift boat, with a fiberglass exterior layer only. AKA "fiberglass over wood". So there is no "core" or inner layer of glass.
I'll take some pics |
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thataway
Joined: 02 Nov 2003
Posts: 20803
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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| Posted: Fri Sep 02, 2022 12:15 am Post subject: |
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OK--I understand that it is a wooden boat with fiberglass over the bottom. So how are the screws now gripping the bottom wood? If you drill out the hole, then there no longer is the bevel for the flat head screw to hold the bottom in place.
So are you basically depending on the epoxy plug to hold the screw in the bottom planking (I assume plywood).
Are you going to glass over the screw head after it is in place?
I have never seen epoxy plugs used in this type of application. I would be reluctant to depend on just the epoxy plug in the bottom planking being good enough in adherence to hold the bottom screws in place. (hold the bottom in place.)
I looked at several of the drift boat builds using epoxy and glass--basically they were built as "stitch and glue", or glued bottom and then covered over with the glass--but no screws. if Screws were used they were counter sunk and then the hole plugged and sanded smooth before the glassing.
I guess if you were building a new bottom, you could do the epoxy plugs in the chine log--and then have a template that would allow placing the screws thru the bottom ply, counter sinking and then glassing over.
I have made a number of small boats--not drift boats specifically, but using the same techniques as used in drift boat building using epoxy resins, and then bottom glass covering. |
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Wood Zeppelin
Joined: 09 Feb 2016
Posts: 310
City/Region: Seattle
State or Province: WA
C-Dory Year: 1997
C-Dory Model: 22 Angler
Vessel Name: C-Creature
Photos: Childhood Dream
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| Posted: Thu Sep 08, 2022 1:43 pm Post subject: |
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| thataway wrote: | OK--I understand that it is a wooden boat with fiberglass over the bottom. So how are the screws now gripping the bottom wood? If you drill out the hole, then there no longer is the bevel for the flat head screw to hold the bottom in place.
So are you basically depending on the epoxy plug to hold the screw in the bottom planking (I assume plywood). |
Hi Bob,
No, not screwing on the bottom of the hull. This is for adding UHWM. Refer back to the original post for a full description.
The UHMW plastic sheet method is debated among drift boat people. On the one hand, it is superior abrasion resistance. On the other hand, attaching in to the bottom means screwing it in (adhesive bonding is to complex for me to get into, and has marginal results I hear.) If screwing it in to just a wooden hull, this may be simpler. Mine is glass over wood. I used sealant on the screws (which are countersunk into the UHMW and recessed a bit to avoid hitting rocks), worked well for many years.
UHWM has a higher rate of thermal expansion than the wood/glass combo. (Again, see the original post). This puts a lot of pressure on the screws. Eventually, one of the screws started to leak.
I have taken the UHMW sheet off, and I'm actually impressed! The one screw that leaked seems to have a widened screw hole, but all of the rest were fine! No sign of water intrusion where the glass/wood interface is cut by the screw hole. (I think I used 4200 sealant, or maybe Sikaflex). I don't know why the one screw leaked.
Instead of the UHWM I could add a layer of graphite impregnated glass or maybe "kelvar", but for various reasons I'm opting to stick with the UHMW for now.
With all that said, here's my question: The existing screw holes are about 1/8" (#8 screws were used). I could drill the over to say 3/8" and fill with epoxy or a 2-part polyurethane. I'm leaning towards Poly, because the right blend (durometer) can have enough flex the allow the screws some lateral movement, and enough toughness to hold the screws really well. I'm not sure if epoxy has as much flex and toughness as the Poly would(?) In addition, plugging the holes would seal off the wood, as well as the wood-glass interface in the hull bottom. Even if the screws wiggled loose, the water would not get past the plug that the screw was embedded in.
Although the plugs may allow some lateral movement to the screws, I don't want to use countersunk heads anymore. Instead, I'd (1) counterBORE the holes in the UHMW (2) drill the holes oversize and (3) and use truss-head screws. This way, I'd have "clearance holes" that would allow the UHMW to move under the wider screw heads..
I'm curious if:
- Anyone has experience with 2-parts poly vs epoxy in an application like this? Would it bond the both the wood and the epoxy-glass layer that's over the wood just as well?
- I assume the chine logs are not really a "Structural" member, and the bottom of the ribs are not critical (the top is), so drilling some 3/8" holes about 1/2" deep would not "weaken" anything structurally?
- does 3/8" seem like a reasonable size for a plug for a #8 (~1/8" major diameter) screw?
- The old screws were 5/8" long. I'm thinking a screw into the new plugs (rather than the wood) could be a little shorter, like 1/2"?
This may seems like "over-engineering", but I want to do it once and not again for as long as possible!
Any other thoughts anyone? |
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