New hull to deck joint inboard flange

Discussion in 'Fiberglass and Composite Boat Building' started by farmerRob, Jan 9, 2022.

  1. farmerRob
    Joined: Jan 2021
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    Location: Olympia WA

    farmerRob Junior Member

    Hi all,
    I’m working on a kit boat I recently acquired and have been grappling with the best way to do the hull do deck joint. The kit came off the molds in the early 80’s and was never completed, it’s been sitting by on a trailer in storage. The kit has a standard cored fiberglass deck and the hull had an inboard flange. The plans recommend the standard -bed the flange in 5200, pop on a toe rail and bolt it every 4”. I know the hull to deck joint is a common source of consternation and repair for folks and I’m trying to figure out a better more permanent way since I have the opportunity. Originally I though, just glass it over however and while I plan to glass the underside i am hesitant grind into the gel coat on the hull topsides to glass over the top since it’s all new and nice and I don’t think I could fair it well without bringing in professional help. To complicate matters I really want to add a bulwark or high toe rails. So after much back and forth and research on what others have done and looking at different ideas I’m not really sure which direction to head. My thinking right now is to, bed deck to hull in 5200 or thickened epoxy, glass the underside, and then just do hardwood toe rail which would be through bolted with bronze fasteners to spec and then maybe expoxy / xynole fabric over the rail and paint? Then just fabricate metal bulwark fittings ala pardey style. Thoughts on if this type of toe rail system would be more ”permanent” and less fraught with long term issues? Better solutions/ideas? Bite the bullet and glass the outside? Thanks all in advance!
     
  2. kapnD
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    kapnD Senior Member

    Photos, and/or drawings?
    Don’t neglect to grind the areas to be bonded, or it won’t stay stuck for long.
     
  3. farmerRob
    Joined: Jan 2021
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    farmerRob Junior Member

    Here’s a drawing of the recommended hull to deck bonding from the plans.

    91E4FBA7-019E-4FBD-8BBF-9029935BF721.jpeg
     
  4. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    It's possible to do a first class job just as drawn, it's just a lot of detail work. First you put the deck on the hull dry and draw the exact toerail position. This is so you can cut the deck to that exact profile (maybe this has already been done). Then you drill the holes for the screws. If the deck is cored in that area, you need to overdrill, epoxy fill and redrill. Now you mark the hullflange with two lines, one following the exact deck profile, and the next outboard, marking the edge of the toerail. When sanding the hull flange you need to remove all gelcoat up to the first line, and not sand farther then the second.
    Next is glueing the deck to the hull, using thickened epoxy, plexus, or a polyester structural putty. Use short waxed machine screws and washers to apply pressure, and make sure that everything is taped well. Remove as much squeezeout as possible remove tape, clean the edge of the joint (all this when the adhesive is still soft). After everything is cured, remove bolts and countersink the deck holes. Grind and glass the inside joint.
    Toerail installation is with an elastomeric compound of your choice and screws. It's adhesive properties are up to you, they range from strong (5200) to none (butyl tape). If you choose to follow the drawing you need to make sure the toerail profile is properly glued to the batten covering the deck edge before you screw it down for good. Another option is to machine the toerail directly with the step. If you want to use a metal toerail you will have to figure out the installation beforehand, since it might affect your deck glueing operations.
     
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  5. fallguy
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    fallguy Senior Member

    Epoxy is more permanent.

    You don't show the core, but the core cannot be bolted if it is a light core or it'll crush.

    But.

    The reason the hull to deck seam causes consternation is it is generally a requirement to remove the cap for transom repairs.

    The 5200 bond is a good way to do it, 5200 will not cure very fast, so don't tax the joint for at least a week or two.

    ps. @Rumars and I cross posts; he went into great detail for you and you can follow his post; he really laid out the details well
     
  6. farmerRob
    Joined: Jan 2021
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    farmerRob Junior Member

    Thanks for the insight rumors and fallout. I wasn’t as specific as I should have been in my original post, the flange is all glass on both deck and hull, the core starts farther in. I’m just debating what to do as I read everywhere that folks have to pull the rails and mess with the hull flange due to leaks in a lot of craft
    That have the exact design as mine. Maybe I’m being too picky as a lot of those are after 20-30 years of service, but then again maybe there’s a better way?? What do you guys think of doing the epoxy and xynole over the hardwood toerail to help isolate/ reduce the expansion/contraction cycling of the bare wood which I think is why a lot of the seals in the area of the rails start to leak through?

     
  7. fallguy
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    fallguy Senior Member

    Well, from my inexperienced perspective, but builder knowledge; using epoxy would result in making the replacement of the teak toerail in 20 years rather difficult. The bolts could end up bonded in, unless you are careful.

    I am 55 years old and figure anything on my boat in 20 years that'll need replacement I am probably on the hook for; Lord willing. So, I always plan for replacing parts like a toerail. And for that reason, I'd prefer to bond the hull to deck in a fashion that allows the toerail to be replaced.

    On my build, anywhere bolts were subjected to bonding in with epoxy, I waxed and removed them after about 12 hours of cure time. Then let the cure finish and reinstalled them. It is perhaps the only way I differ from Rumars great advice.

    My boat, I'd use epoxy for the hull to deck joint, pull the bolts the next morning and give it a few days to cure and I'd use 3M 4200 for the toerail bonding, but my boat is white. I like butyl an awful lot and if you are bright finishing the teak; it is a lot less mess, but you can get a teak colored sika or other sealants and also use great care sealing down the toerail. I only offer the alternatives because the 3m is only white and may look horrid.

    I do have some teak on my boat and sealing with teak colored sikaflex iirc. I can look for the product if you like in the morning.
     
  8. fallguy
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    fallguy Senior Member

    By the way, using the teak is what provides the opportunity for leaks.

    Teak is oily and bonds poorly to lots of stuff. Prepping the teak using acetone can help, but the toerail seam requires maintenance. The leaks around the bolts is due to the wood drying and seams around the bolts opening and lack of due care. The flange seam sealed with 5200 will almost be impossible to get water through done right. As builder, you can make sure to avoid skimping, but 5200 is really expensive, too, and a couple of small 1/8" beads are probably not enough...
     
  9. Rumars
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    Rumars Senior Member

    You have two issues there, one is the hull deck joint, the second one the toerail.

    As great as 5200 is, it won't stay flexible forever. If the hull deck joint is sealed with 5200 or similar, eventually water will find a way in, the twisting of the hull breaks the aging sealant. That's why it's better to rigidly glue it with epoxy or similar. Glassing the outside is not a requirement, the bonding area is probably sufficient as it is, plus you plan to glass the inside anyway. The mechanical fasteners have no role anymore in this joint, they are there just for the toerail.

    The toerail has its own problems. Any toerail (or other fitting), wood or metal, that is bolted on can leak trough the bolts. That's why you need to chamfer the holes so that the sealant can make an O-ring around the fastener. How long the seal lasts is unknown, there is no hard rule. But, the important thing is that the toerail can be rebedded independently of the hull deck joint, just like you would rebed a cleat when needed.
    If you want to not have this potential problem of leaking fasteners the toerail has to be either glued on, or be integral to the deck. Reliably glueing a big chunk of wood or metal to the deck is problematic, so the realistic option is an integral toerail. If you want one of those forget the xynole over hardwood idea. Make the toerail out of foam and put fiberglass over it. Using polyester you can then gelcoat over the whole affair and blend it in. If foam is to expensive use a softwood that plays well with epoxy as a core, WRC or AYC, but that means you will have to paint it, and the transition to gelcoat will be visible. But, regardless if foam or wood core, it still means you have to grind off the molded gelcoat, then fair and refinish, just as if you would be glassing the outside of the hull deck joint. How much work that is depends on your expectations, "factory perfect" is very different from "workboat finish".
     
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  10. farmerRob
    Joined: Jan 2021
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    Location: Olympia WA

    farmerRob Junior Member

    Thanks Rumars. Perhaps my assumption was that if I only epoxy the joint and glassed the inside it would still be prudent to put in the mechanical fasteners hence the toe rail by necessity. So if mechanical fasteners are NOT necessary I would just epoxy the hull/deck joint, glass the inside, fair the outside flange seam with thickened epoxy and then do bulwarks attached up off the decks on heavy metal brackets spaced at say every 3-4 feet, fewer holes through the deck and no toerail joints/seams to swell and leak. Does that jive with what you are thinking?
     
  11. Rumars
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    Rumars Senior Member

    That you can not do, epoxy requires paint over it. Either live with the step, or you are right back at grinding, fairing and painting.

    As for bulwarks on brackets, you can do that if you like, but 3-4ft between them means a heavy bulwark on top, are you sure the deck laminate can stand up to that?
     
  12. wet feet
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    wet feet Senior Member

    One topic that hasn't been addressed is the number of people who will present for the attachment of the deck.It matters because if Plexus is chosen the builder would need enough helpers to apply the adhesive and then lower the deck into position before the cure begins.Working short handed would very likely rule it out.The drawing of the bonding amused me as it only appears to extend a tiny distance onto the underside of the hull flange and every instance I have seen inevitably spread over pretty much the whole of the surface.

    My choice would be to drop the deck onto a generous bedding of butyl rubber-from a tube rather than the tape form-and use a few bolts to hold it in place while the bonding is done in sections.With a good number of sections bonded,remove the bolts and bond the rest.Then add the teak toerail,which again I would bed on butyl rubber from a tube.I'd also look at a radius on the top corners of the toerail.Incidentally,the fasteners may need the shanks liberally coated with mastic as machine screws have a built in helical leak path all the way along the thread if you don't. If anybody doubts the durability of the concept,it was common in the late 1970's/early 1980's and a couple of years ago I saw an example that was 38 years old and still holding up.
     
  13. farmerRob
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    farmerRob Junior Member

    Rumars- so are you saying you would space bulwark supports closer together to spread out the load on the deck?

    wet feet- you bring up a really good point, I hadn’t thought much about the actual physical process on the day the work gets done, so it would be prudent that whichever route I go I definitely need to plan for the labor component as needed. The drawing is pretty accurate to the layup crews execution on the hull side, the flange comes in about 6 inches or so all the way around. The deck on the other hand is a bit oversized at the edges and will need to be trimmed back to be in line with the hull in spots..
     
  14. Rumars
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    Rumars Senior Member

    Bulwarks are heavy by design, with wide space brackets you must make them even heavier to maintain rigidity. When a wave hits them all that force is transmitted to a few points (prepare large backing plates). I would rather have lighter bulwarks with more supports instead of sailing with a 4x4 as a rail. Yours is no wooden boat, with clamp and shelf to take all those loads.
    But for real, unless the boat was designed with them, I would not use bulwarks, a good toerail with tall stanchions and, if desired, netting over the lifelines is lighter, has less problems with waves and is just as secure (if not more, few small vessels have bulwarks as high as the usual stanchion). I don't know how big a boat and what design you are building, but I have a feeling it's not a 50ft schooner.
     

  15. farmerRob
    Joined: Jan 2021
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    farmerRob Junior Member

    That makes sense, its not just about static loads but expected dynamic forces at sea. For bulwarks I was planing teak boards about 3/4” thick fastened to the mounts for total height of 8” -9” off the decks total wood 8” high per side and the lifeline stantioms would come out of the bulwark brackets (as mentioned similar to the Pardey design from their books) The boat is pretty stout for her size, it’s an Allegra 24, various specs I have show 6000-6500
    Displacement. I say it was a kit but really it’s just the deck and hull and a random assortment of some of the design details. The guy I acquired this hull from actually acquired the original molds from the designer and was going to start production. This was going to be his boat. Long story short life got in the way and he had this stored for the past 35 years+ or so. The paperwork I got is a lot of random marketing material, some old correspondence between the designer and the gent I bought the boat from and then as mentioned a random collection some of the details for the craft.
     
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