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Thread: Need trick to seal chainplate deck joint

  1. #36
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by Henning 4148 View Post
    Thanks for all the ideas, keep them coming!

    If cedar wedges set in Jefferie's marine glue work, I would not mind. In any case, it is an interesting idea to use the swelling of wood to seal the joint. I am beyond the point where I would say, that the solution must be beautifull - I need a solution that works to stop the damage the leak is doing to the boat.
    I still think that considering the movement in both directions a flexible boot clamped to the grp deck and lashed around the shroud iron on a bed of sealant goop is the only reliable solution.
    It really is quite difficult to build an ugly wooden boat.

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  2. #37
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    Default Re: Need trick to seal chainplate deck joint

    Boats leak. Nothing you can do. What you can do is mitigate the damage. The holes in the deck need to be protected from water ingress that will rot your deck core.. Trim the holes nice and clean. Soak the ply edges with CPES until it wont take any more. Block up the holes from the underside and fill the void with thickened epoxy. I like chopped strand. Recut the holes for the chain plates with a fairly tight fit leaving enough room for your goop of choice, say 1/8" all around.
    You need a backing plate below and a cover plate above to encapsulate said goop. The inside one can be a nice piece of teak or mahogany, stainless, whatever. The exposed one on deck is best in stainless and should be a tight fit around the chainplate. Scuff up the chainplate with some 80 grit emery so the goop has something to stick to. A quick swab with some denatured alchohol to decontaminate just prior to putting on the goop.
    Fill the void with goop and smush down the cover plate; screw it to the deck. When the goop is cured trim all the excess with a sharp knife. Of course you masked off the deck first....
    This is one of the few places where 4200 or 5200 has a place on a boat.

  3. #38
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    Default Re: Need trick to seal chainplate deck joint

    What goop will stay stuck when distorted a distance equal to half of its thickness?
    It really is quite difficult to build an ugly wooden boat.

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  4. #39
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    Default Re: Need trick to seal chainplate deck joint

    Unless Im reading it wrong the OP said the horizontal travel was .5 mm, roughly 1/32"?

  5. #40
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by willin woodworks View Post
    Unless Im reading it wrong the OP said the horizontal travel was .5 mm, roughly 1/32"?
    Yep - but vertical is 1.5mm - that's too much for 5200.
    "If it ain't broke, you're not trying." - Red Green

  6. #41
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    Default Re: Need trick to seal chainplate deck joint

    butyl rubber sealant (commonly and inexpensively available as "gutter and flashing sealant" at home improvement store) is the thing to use, though it is messy because it stays gooey for a long time.

    The diagram in #6 comes close, but the shape of the sealant cavity is a problem.

    Ideally, you want the cross-section of the sealant to be kinda sideways-hourglass-shaped.... fat where it meets the chainplate and the deck, thinner in the span between. Kinda opposite the usual big-goober-of-goo profile.
    You want it fat where it meets the chainplate and deck for maximum adhesive-surface, and then thin in the middle so that it doesn't resist the flex as the components move.
    No adversary is worse than bad advice.

  7. #42
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    Default Re: Need trick to seal chainplate deck joint

    What about different chain plates with different mounting and location? Maybe this design is just wrong to begin with? Not an inexpensive change but perhaps what is required.

  8. #43
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by Peerie Maa View Post
    What goop will stay stuck when distorted a distance equal to half of its thickness?
    No goop can do that in a poorly designed joint.

    The question lacks sufficient detail. The gap width and aspect ratio of the sealant is important. If by thickness you mean the depth perpendicular to a wide enough gap, some low durometer, high strength silicone, PU, butyl/terpolymer, or polysulfide sealants can be configured to tolerate the motion. If the gap filled by the sealant is narrower than the depth of the sealant, it will fail. Softer sealants can usually tolerate a lower aspect ratio than harder ones.

    The problem is to design a formed in place elastomeric gasket around a fixed size object with a specified range of motion. The gap width and gasket thickness are not defined. There is an escutcheon that can clamp a gasket to the top surface of the deck, so the gasket can be thin. A thin gasket clamped to the deck would need to have a spacer to maintain some thickness during cure.
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  9. #44
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by MN Dave View Post
    No goop can do that in a poorly designed joint.

    The question lacks sufficient detail. The gap width and aspect ratio of the sealant is important. If by thickness you mean the depth perpendicular to a wide enough gap, some low durometer, high strength silicone, PU, butyl/terpolymer, or polysulfide sealants can be configured to tolerate the motion. If the gap filled by the sealant is narrower than the depth of the sealant, it will fail. Softer sealants can usually tolerate a lower aspect ratio than harder ones.

    The problem is to design a formed in place elastomeric gasket around a fixed size object with a specified range of motion. The gap width and gasket thickness are not defined. There is an escutcheon that can clamp a gasket to the top surface of the deck, so the gasket can be thin. A thin gasket clamped to the deck would need to have a spacer to maintain some thickness during cure.
    Alternatively, follow the KISS principle. Make a rubber boot.
    It really is quite difficult to build an ugly wooden boat.

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  10. #45
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    Default Re: Need trick to seal chainplate deck joint

    I hesitate to enter the fray again, having failed to read the original post correctly ... but I assume now that the shroudplate (and associated knee structure) is not in fact moving, but that the deck itself is flexing around a substantially immovable shroudplate?

    While that is a somewhat alien concept, assuming again that it was a design intention (even though I think flawed), then I would say that the only reasonable solution is a rubber boot - like a mini mast collar, as suggested by Nick and others. Most mastics are designed to accept lateral shrinkage and stretching, rather than vertical or sheer stresses.

    if it could be done without creating a hard spot – that is if the deck in general does not flex that much – then I would seriously consider linking the deck to the shroudplate knee so it doesn't move in relation to the shroudplate – but without some design information and photos of the set-up it is hard to second guess this.

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  11. #46
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    Default Re: Need trick to seal chainplate deck joint

    Perhaps some sort of distorted low durometer, fat o-ring sandwiched between a couple of plates? That would both seal and allow the deck to "oilcan"

    (I dislike inboard chainplates for all of these reasons. It may make sense on a race boat where the jib must come in that extra few inches, until it hits the spreaders maybe, but it always seemed problematic especially on a wood vessel where the "leak" will eventually compromise the structure)

  12. #47
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    Default Re: Need trick to seal chainplate deck joint

    Thanks for all the input!

    I will have a discussion with my boatyard this afternoon. They were also thinking about fastening the plate to the deck as well as to the knee to make sealing easier, but it will create a hard spot under the deck which can lead to cracks and it is going to change the flow and distribution of forces in a hard to foresee way which can lead to overloading somewhere, again leading to new additional damage.

  13. #48
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    Default Re: Need trick to seal chainplate deck joint

    I should add that, if you choose to use the cedar wedge and Jefferies Marine Glue method of sealing chain plates, a long athwartships copper wire rivet on the fore and aft sides of the chain plates is a way to prevent splitting of the covering board when the rigging takes a shock load. The idea of using this method has been around for hundreds of years! Back when this method was devised, there was no 5200 or other products around to confuse the issue. The wedges themselves can be made of slash grained Eastern white or Alaska Yellow cedar. The slash grain provides the greatest amount of swelling of the cedar that has been driven using a wooden block against the wedge and a hammer to drive it. I learned this trick back in 1952 while I worked for Carl Chapman Boat works as an apprentice while I was still in high school. I was impressed to find that Larry Pardey, later, used the same method on his boats as well. This method is most effective when decks are sloshed down with seawater at least once a week. The wedges swell and the marine glue is merely an added bit of insurance. The wedging works best on teak covering boards that are left bare and merely scrubbed along with the teak or cedar decks.
    Jay

  14. #49
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by Henning 4148 View Post
    Yes, the boat is fglass. The movements are my estimation of the flex the deck might have here against the knee, which is bonded to the hull but by design has a gap of 1 or 2 cm to the deck. So, the designer wanted to decouple hull and deck here, probably to avoid a hard spot with resulting cracks in the gel coat. Fglass boats flex ... When a wave hits the side of the boat, there will be some flex, in case of solid water on deck, there will be some flex, ... ... The knee is approx. 1/2 metres behind the main bulkhead. The design or similar designs are also used on wooden boats as shown in above pictures. It is a cause for upset on many boats, wooden and fglass. And there must be a solution that works. A boot is a good idea. Thank you for your ideas and input!

    J's - I did look at the disassembled main bulkhead of a small J yesterday. The chainplates are attached to this main bulkhead, the deck sealing is similar, it had started to leak, the bulkhead rotted and has been taken out now ...
    Jay, with all due respect for your expertise, you are discussing a different boat entirely.
    Quote Originally Posted by Jay Greer View Post
    I should add that, if you choose to use the cedar wedge and Jefferies Marine Glue method of sealing chain plates, a long athwartships copper wire rivet on the fore and aft sides of the chain plates is a way to prevent splitting of the covering board when the rigging takes a shock load. The idea of using this method has been around for hundreds of years! Back when this method was devised, there was no 5200 or other products around to confuse the issue. The wedges themselves can be made of slash grained Eastern white or Alaska Yellow cedar. The slash grain provides the greatest amount of swelling of the cedar that has been driven using a wooden block against the wedge and a hammer to drive it. I learned this trick back in 1952 while I worked for Carl Chapman Boat works as an apprentice while I was still in high school. I was impressed to find that Larry Pardey, later, used the same method on his boats as well. This method is most effective when decks are sloshed down with seawater at least once a week. The wedges swell and the marine glue is merely an added bit of insurance. The wedging works best on teak covering boards that are left bare and merely scrubbed along with the teak or cedar decks.
    Jay
    It really is quite difficult to build an ugly wooden boat.

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  15. #50
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    Default Re: Need trick to seal chainplate deck joint

    Quote Originally Posted by Henning 4148 View Post
    Thanks for all the input!

    I will have a discussion with my boatyard this afternoon. They were also thinking about fastening the plate to the deck as well as to the knee to make sealing easier, but it will create a hard spot under the deck which can lead to cracks and it is going to change the flow and distribution of forces in a hard to foresee way which can lead to overloading somewhere, again leading to new additional damage.
    Agreed, you don't want to create a hard spot. The deck was designed to move with respect to the chain plate and any attempt to prevent that is likely to cause problems.

    I posted links to two sites that described this repair in some detail. The link to Three Fools is more detailed. The Simson ISR 70-02 sealant recommended in the ocean Navigator site in 2011 appears to have been replaced by Simson ISR 70-03, which appears not to need the primer. I don't know if those repairs were designed to accommodate as much motion as you have.

    I am not disagreeing with Nick that the most reliable solution is some kind of boot. I am just trying to say that the gap needs to be wide enough to allow for the sealant to accommodate the relative motion between the deck and chain plate. If the total range of motion is 2mm x 1 mm, it adds up to 1.7mm, so my guess based on a Sikaflex tech data sheet would be a 3mm gap and a sealant thickness between 2 and 3 mm. If your boatyard thinks that I am mistaken, they might be correct. I can't see trying to control the sealant thickness under the deck trim plate, so the sealant thickness will be controlled in the gap. The sketch below is what I was thinking with a 1mm grid.

    There was a good link to the use of butyl tape in there. https://www.sailnet.com/forums/gear-...utyl-tape.html
    sketch.jpg

    Edit: not worth bumping and buried here for lack of a better place to store it for future reference --
    We argue ad nauseam about the value of marine ply that costs several times as much as exterior ply. We happily live with the crevice corrosion problems associated with 304 and 316 stainless. We will pay twice as much for 316 which is not twice as corrosion resistant. Why don't we consider stronger, much more corrosion resistant alloys for critical items such as chainplates when the cost ratio is similar to plywood and a tiny fraction of the overall cost of a boat? Alloy 2205 is much more resistant to pitting and Alloy 625 is virtually immune, and both are twice as strong as 304 and 316. McMaster prices for 12x24x1/4" plate 304: $126, 316: $226, 2205: $352, Inconel 625: $874.
    Last edited by MN Dave; 05-01-2019 at 01:02 PM.
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  16. #51
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    Default

    Just pondering this last night, I was thinking that there are various rubber boots to keep water and dust out if hydraulic control levers on various machines. They must be pretty tough and UV stable. The top might fit around the lower part of your rigging screws, and at the bottom you'd need some sort of fabricated base plate.

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  17. #52
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    Default Re: Need trick to seal chainplate deck joint

    Well bunch I can see that I am guilty of skimming the posts and not realizing that this is not a traditional built wooden boat!
    I will retire now, and let my dog lick the egg off of my face!
    Jay

  18. #53
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    Default Re: Need trick to seal chainplate deck joint

    These are generally used for outboard engine rigging. They come up to 4-1/2" diameter.Screen Shot 2019-04-24 at 2.12.54 AM.jpg
    There are two kinds of boaters: those who have run aground, and those who lie about it.

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