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Screws into deck pulled out...

Discussion in 'Ask All Sailors' started by Allowishish, Nov 27, 2017. Add this thread to a FAQ

  1. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    Seriously... there is a bunch of banter over this topic and a bit of over-kill. I would have had this job done in less than afternoon with about $10 in hardware and literally 2 pumps or less of West epoxy. If I was in Colorado I would have fixed the O.P.'s boat on-site for the cost of beer and conversation, taken plenty of pics to illustrate how easy this task would be.
     


  2. SG

    SG

    Joined Feb 11, 2017
    608 posts, 80 likes
    J/Boat J/160
    US Annapolis
    Over drill the holes but don't penetrate farther than the bottom skin of fiberglass. Measure your depth. Fill will epoxy, let cure. Drill holes to depth and tap for bolt thread size; done

    As suggested above in previous posts: Why do you believe in epoxy in this application that tapping the screws instead of using a more conventional screw is a better approach?

    I'm not sure that you have a more durable and strong attachment in this application.
     


  3. Tom G P-21

    Tom G P-21

    Joined Aug 15, 2012
    293 posts, 13 likes
    Precision 21
    US Newburyport MA


  4. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    Because... I've done it in various applications. Cap Screws (the correct term for hex bolts) will have more threads per inch than a screw intended for wood. A stainless wood screw is weak, you can break it off easily. Wood screws are intended to go into wood, not fiberglass. The pilot hole you drill for wood is much smaller than what you would want for glass/epoxy. Wood fibers have much more room for compression and tightly grip the threads of wood screws, but when you use the same size pilot hole in fiberglass you run the real risk of severe binding and breaking the screw, even by hand. Cured epoxy takes and holds threads very well and is much stronger than you might think. See this article about thread repair using epoxy;
    https://www.westsystem.com/404-high-density/
    https://www.westsystem.com/instruction-2/epoxy-basics/bonding-fasteners-hardware/

    As I said before, I'm pretty sure the grommets on a dodger will be too small for 1/4" 20 cap screws. 3/16" will have 24 TPI (I believe), and that will have a good grip over a possibly short depth. We still need to hear from the OP on exactly how thick the cabin top is.
     


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  5. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    Stainless inserts I could go for... way better than many posts above for products that are just nickel plated from Home-Depot... However, these are still overkill and costly (considering the cost of the rivnuts plus the installation tool. Then you have the risk of fouling the threads with epoxy when installing. Yes, you can wax them but you risk cross-contamination and then you gotta clean the wax out... plus, they will still rust eventually and be a bear to remove. The WEST article claims 800 psi strength on threads cut into epoxy. The OP's Dodger will have grommets every 6 to 8 inches, why would you need more than that? Seriously, this is a $20 repair and this thread is going nuts on it (no pun intended).
     


  6. Allowishish

    Allowishish

    Joined Oct 30, 2017
    33 posts, 12 likes
    Catalina c 27
    Long Monday US Colorado Lake Pueblo
    well......


    that didn't go well. I used epoxy and fiber matt. but wasn't patient enough. looks like I have a mess to clean up at some point.

    Lesson learned... DO NOT RUSH!!! Be patient and use the right tools for the job. I will not make that mistake again.

    I think it is on solid at this point and will go back next weekend to "clean it up" and make it look presentable. Luckily it is pretty well hidden by the dodger.

    When I got there and removed the dodger I wanted to go a different route but was stubbornly set on getting it done that day... then rushed the job on top of it.



    The good news is that I did get the outboard throttle lever fixed and supports made/installed and a template cut for a larger berth.

    So I'm going to say 2 out of three isn't bad (only since I'm willing to admit I screwed up on the 3rd item and learn from it)
     


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  7. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    Whut? What did you need the fiber matt for? I am assuming the screws must have yanked up some laminate when they ripped out? How deep are the screw holes (thickness of deck)? I am pretty familiar with the C27 but I don't understand where these dodger screw holes are that you don't have access to the backs of them from inside the cabin. Try to post some pics if you can.
     


  8. Allowishish

    Allowishish

    Joined Oct 30, 2017
    33 posts, 12 likes
    Catalina c 27
    Long Monday US Colorado Lake Pueblo
    26F70A44-5264-41E0-AB74-8862F3746C81.jpeg I attempted to tape off the area to reduce the mess I knew I was going to make at this point.

    You can get to where the cabin top comes down but just outside the cabin top, where the holes are is not accessible.

    Like I said, I knew I was not doing it right and just wanted it done. Lesson learned. I attempted to use fiber mat to ‘thicken’ up the epoxy (it didn’t need it... I did not realize how sticky it was going to be so went ahead anyway)

    There is a list of what I should not have done. Possibly the worst part is that the previous owner probably would have been more than happy to come show me the right way... but I wanted to do it myself.

    All that said, we bought this boat to learn how to sail and learn how to work on boats. Before moving up to a larger cruiser. So I am learning.

    I know I won’t do that again.
     


  9. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    How much do they cost plus the installation tool vs. $0.00?
     


  10. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    2 pump of epoxy and 2 tablespoons of microfibers = $0.56
    Drill bits and taps you already have in your tool box = $0

    Still a stronger repair, can be reversed/repeated/repaired easily, will not rust.
     


  11. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    I agree its not a contest, but you seem pretty insistent...
    So tell me how 800 psi x 2 fasteners isn't enough? Have you paid attention to the OP's follow up posts and the pic he provided? Are you familiar with the Catalina 27? I agree with your comment that the best method is through bolted with backing washers/plates w/nuts, but if you saw the pic that was provided and the repeated statement that there is no through deck access then you would understand why the best method isn't possible. Also from the pic, and if you were familiar with the C27, you would know that the mounting depth of the area in depth is two inches or greater. I am VERY familiar with Catalina construction methods, and although from the initial post I wasn't sure as to what area the OP was talking about I am positive now from the pic he posted later... Also, if you read my initial comments, you'd see that I already suggested fiberglass rods (G10 to be specific).
    So, the only contest here is that you insist your method is better and none other is acceptable. You are wrong, and your although your suggested method is not bad it is just not ideal and it is more expensive in time and labor than is required for this application. Your Tartan 3800 has a much different Dodger than the C27 is equipped with, you should recognize that difference. You probably have an Iverson Dodger or something similar, judging by your description. Much tougher construction and designed with grab rails that need to be supported, so yeah fasteners in threaded resin might give you pause. What you are neglecting (in this application) there are two screws on each side... If WEST Systems testing claims 800 psi for each threaded fastener holds true you have 1600 psi for both, please call WEST and tell them they are wrong and that is insufficient. Again, look at the pic.... 'fairly thin' coachroof is not the issue here.
     


  12. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    "I consider threading some machine screws into some fairly-thin, threaded, reinforced resin to be a bogus means of attachment, just as bogus as the original (I assume) sheet metal or wood screws."
    I didn't put words in your mouth, those are your words I quoted above.
     


  13. SG

    SG

    Joined Feb 11, 2017
    608 posts, 80 likes
    J/Boat J/160
    US Annapolis
    What psi (pounds per square inch) have to do with this? Aside from other issues of how that measurement means anything by itself, I'm not sure what you'd do with it information? The screw is subject to simple withdrawl, torsional (bending and twisting) forces, and a number of other stresses. In addition the screw holes may be been subject to moisture with freeze-thaw cycle issues working on the fiberglass; and, maybe the hole was drilled in an imprecise way since "the beginning of its time". Who knows.

    We are WAY over complicating this situations: The poor guy had a dodger frame attachment hinge which came loose when either really leaned on -- or over time over worked the hole. If he want's to get back to "where he was", then there are simple, more complicated, and more complicated methods of dealing with this.

    If the dodger was fine for a number of years and someone really "bashed" into it, then I'd try a simply approach of resetting the screw. On the other end, if the issue is the inadequacy of the attachment for the purpose intended, then you can have a couple of custom attachment pieces fabricated with 4 spaced screws, not two and move on.

    I think I'd try the simple approach first if were me -- unless there was something odd about the circumstances.

    (I keep getting these email messages about "new post" on this subject.... ;^)))) )
     


  14. CloudDiver

    CloudDiver

    Joined Sep 8, 2014
    2,406 posts, 294 likes
    Catalina 22 Swing Keel
    US San Diego San Diego
    800 Psi is the rated strength of threads cut into epoxy resin for strength, as tested by WEST Systems and published in the articles I posted.
     


  15. jviss

    jviss

    Joined Feb 5, 2004
    2,117 posts, 142 likes
    Tartan 3800
    US Westborough Westport, MA
    You can "unwatch" the thread, see the top. That's what I'm doing right after this reply.
     


  16. SG

    SG

    Joined Feb 11, 2017
    608 posts, 80 likes
    J/Boat J/160
    US Annapolis
    What psi (pounds per square inch) have to do with this?
    ______________________
    800 Psi is the rated strength of threads cut into epoxy resin for strength, as tested by WEST Systems and published in the articles I posted.


    I don't mean to quibble. I think the observation that facts by themselves aren't always applicable or useful in understanding what's needed.

    The cited published fact means little per se. I respect West Systems, use their stuff, trust them, etc., etc. HOWEVER:
    • Is the cited psi capacity in tension, compression, or shear?
    • Does it mean that you take the projected area in square inches of the threads perpendicular to the long axis of the screw in one direction and measure it against "withdrawal" with an imposed load of x pounds?
    • How is the load applied? Slowly (like if you take the Superglue guy who is hanging from a helmet which has been attached to a square [inch] which he is gently hanging from) or like you snapped it with a sudden load?
    • Is the load applied torsional or just axial?
    • The factoid is only relative; and then maybe relevant or not (i.e. proportional with some safety factor)?
    How some fitting gets loaded-up and what the substrate is has a lot to do with whether the materials fail. Examples: mortar and bricks. Work great in compression -- work for shit in tension -- work okay in shear. (if you allow me to generalize.)

    Another example, more relevant: In the case of the dodger fitting let's talk about how the fitting is "challenged" and has to respond to forces. In the axis of the two screws that hold the fitting that the dodger is attached to things happen very differently if the load is limited to being in-line with the axis of the screws and the "hinge-pin" that fitting has with the dodger frame. Take the same fitting and bend the dodger framer from the side -- suddenly the "hinge-pin" ceases to just a point load and it becomes one where the frame of the dodger is acting to create a twisting, torsional element that is imparting very different forces. So an 100# load (for example) on the dodger isn't transferring 100# -- but the dodger frame becomes a lever that is twisting and bending the little screws in a very different way.

    The "speed" (actually acceleration or deceleration) of the load on the fitting is material. Example, for illustrative purposes, you can take 200 pounds and slowly load up the fitting -- but take 200 pounds and slam it onto the fitting and it just is completely different. Force exerted (or received) is a function of load and acceleration (i.e. time, rate of change of speed, etc.)

    If the loading is in a predictable directions and is not subject to dynamic changes, then deducing what is adequate is easier. (e.g., a picture frame hanger which is restraining a load very close to being only in shear will hold a __# item). But approximating what a person being thrown around by a pitching boat or tripping and catching themselves from falling forward, back, or sideways is a much different thing. ;^)))

    A seemingly simple dodger which (for example purposes) is strapped back and tightened down and fully secured is a different assembly than one that has it front wind rolled-up, it side curtains not in, or it's retraining lines not taught and running aft to make the sides, front, and top function light a stretched membrane.

    Anyway, I've OVER DISCUSSED THIS ISSUE WAYYY TOO MUCH. ;^))) I apologize. Hopefully JViss will have turned his thread alert off.
     


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  17. HMT2

    HMT2

    Joined Mar 20, 2014
    461 posts, 62 likes
    Hunter 31
    US Houston, Texas Shoreacres, TX
    +1 for CloudDiver. I had the same thing happen on my boat. At the bottom of the screw holes it opened up to a large gap between where the deck fiberglass stopped and the interior fiberglass started. So I drilled the holes to 1/2 inch dipped a 1/2 teak plug into epoxy and then pushed it into the half inch hole as deep as I could go without pushing the plug into the gap. I let that set and then filled the holes with West System epoxy mixed with some finely chopped fiberglass let it dry for a couple of days then re drilled and used some self tapping stainless screws. No problem. However, if you have any spreader bars or other means of tightening up your bimini ensure that it is not putting any upward preasure on your attachment points.
     


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  18. seadaddler

    seadaddler

    Joined Dec 19, 2006
    5,169 posts, 92 likes
    Hunter 36
    US Punta Gorda
    I have noticed since adding grab handles on my dodger that yes the screws have come loose and did repair with some expoy and next time they come loose will do more of better job after reading these posting and with the grab handles will need something stronger.
    Nick
     


  19. jibes138

    jibes138

    Joined Jan 27, 2008
    2,717 posts, 82 likes
    ODay 35
    US Beaufort, NC
    So a screw in epoxy can take an 800 "PSI" load??? Sounds great, let's see what we get when we figure it out on the back of a napkin. A 1/4-20 screw has an area of (0.25)^2 x 3.1415/4 = 0.049 square inches. What is really happening here is the square inches will be the area of the threads that are in the epoxy since the epoxy will most likely fail before the cross section of the screw breaks. For sake of argument let's assume 6 threads are fully engaged in the epoxy. From this chart http://www.carbidedepot.com/formulas-tap-standard.htm we see the minor diameter is 0.1887 so if we assume for simplicity the threads don't have clearance at the tip or the root the area of one thread is the area of the major diameter minus the area of the minor diameter. The latter is (0.1887)^2 x 3.1415/4 = 0.028 square inches.

    So one thread is 0.049 - 0.028 = 0.021 square inches.

    Going back to my assumption of 6 threads full engaged we get 0.021 x 6 = 0.126 square inches of thread in the epoxy. 800 PSI x 0.126 SI = 100.8 pounds in tension for the epoxy to fail. Given two screws it (the fitting) might hold up to 200 pounds in tension.

    Assuming someone grabbing the dodger to prevent a fall or falling into it will likely apply a severe bending moment to the fitting. A 100 pound person will grossly overload the fitting in this case. The medical examiner and forensic scientists should be able to figure out what went wrong during the accident investigation.

    Any of you mechanical engineers or professors feel free to critique my simplistic analysis.
     


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  20. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    588 posts, 147 likes
    O'Day 19
    US Littleton, NH Littleton, NH
    I think you are on to something, however, there is more support there than that single two screw base. If the load is lateral to the dodger, say from someone stepping onto the boat from the dock, force will be distributed across the arc of the dodger's main structure in compression to the opposite side by an unknown but significant percentage. If, instead, the boarder pulled, then both bases take the torsion with the near base being mostly in compression. The resistance of the dodger to being pulled out of shape will transfer much of that force from tension to sheering force across too both sides.
    If, you were pulling on the dodger from fore to aft because you were stepping over the combing to get from cockpit to foredeck, your force would get distributed to the forward supports and the main support would then be a fulcrum under compression. Again, the structure's resistance to being pulled out of shape would also transfer some, though a smaller percentage, to the opposite side as well. However, the canvas canopy would draw the opposite diagonal into support it also.
    While the exact proportions of force distribution is hard to predict without doing a thorough force diagram, it is, I think, safe to assume that any single two screw base would ever only take about 2/3 of the load, most likely closer to 1/2. The caveat is, over build, because you must always engineer to the extremes not the averages.
    - Will ("engineer wannabe", Dragonfly)
     


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