Newbie - Hello Everyone

Discussion in 'Boat and Accessory Building' started by rookiebuilder, May 30, 2009.

  1. rookiebuilder

    rookiebuilder Paddler

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    Yes I do.

    Great call, I just haven't gotten that far yet.

    Yes, I plan to add those bumps.

    This is a GREAT idea! So I plan on incorporating something along these lines.

    I know you have mentioned this previously. I assure you your suggestion hasn't fallen on deaf ears. I am working on those form, I just didn't have them in the layout yet.

    Thanks Mick! You speak from a context of one who has built a kayak or two... :wink:
     
  2. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    You probably don't want to cut those spacers from the same material as your panels -- you'll need the space to only be about 1/8 inch for the gasket. If you have more thickness, your hatches will end up being recessed once the gasket material compresses a bit.

    *****
     
  3. mick_allen

    mick_allen Paddler & Moderator

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    Just to be sure of what i/m trying to get at here:

    If the hatch edge was the same as the seam edge, a tight strap going over the flush hatch and then sloping down the 2 side panel's slopes will put a downwards force vector on the hatch. In other words the hatch lid IS the bump. The force component will be the sine of the angle that the panel slopes away from the flat. (Heresy here, but if you shape your hatch so that the edges curl up slightly, the downward edge vector will help to put even force over the whole hatch mating surface.)

    If you build a hatch that is internal to the flat top panel, the same tight strap will put NO downward vector on that hatch and you HAVE to use bumps.

    So, at this stage you still have a choice of approach - especially tempting as the panel seam is so close to the hatch edge as drawn.
     
  4. rookiebuilder

    rookiebuilder Paddler

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    Yes Mick, I'm sorry I didn't comment more precisely. I do get your point. It makes sense. :wink: I don't have any issue with the bumps though. And for some reason, I don't want to make the seam of the hatch coincident with the panel seam (I can't think of any real argument, :? it's just one of those things I'd rather not do). :cool
     
  5. rookiebuilder

    rookiebuilder Paddler

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    Sorry, I didn't see this post until now. :oops:

    Here is a cross section of how I plan to make the hatch seals. I am really anal about having the hatches watertight. I will also make the gaskets from a sheet of closed cell neoprene so there is no seam.
    [​IMG]
     
  6. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    Hmmm... the problem that I see with your design is that there is no room for the lid to get extra compression as the neoprene gasket compresses over time, which will compromise the seal. I wonder if a hollow sealed gasket would work better for this design?

    Looking at your design gives me an idea though -- instead of the stop, use an additional gasket that is attached to the hatch lid. This could reduce the amount of compression (or at least slow down the time for the compression to occur) as well as provide an additional barrier for water to work around. This would be similar to the method that Ted Moores (of Bear Mountain Boats) uses, with the exception that the hatch lid is flush with the deck as opposed to Ted's method of using a hatch "lip" on top of the deck and hatch (which I find aesthetically unappealling).

    I have to think about this a bit more...
     
  7. DarenN

    DarenN Paddler

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    Hey Mick;
    will you please bring up the exterior water channel idea that we have talked about. it's your idea, so............
     
  8. rookiebuilder

    rookiebuilder Paddler

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    So are you saying that the neoprene will take a set, and therefore will no longer get compressed enough to seal?

    If so, this is where I have made a different assumption. I assume that if it does take a set, there will still be sufficient compression remaining to still provide a seal. The reason for only compressing in the center of the gasket is to allow there to be uncompressed gasket on the inside and outside to give support and help with spring-back (well, at least that's my theory... :wink: )
     
  9. mick_allen

    mick_allen Paddler & Moderator

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    Your approach is fine.
    The use of the stops will force equal pressure on the gasket all around the perimeter. It will also control over-compression of the gasket.

    If you use the approach that Dan suggests (which is also equally fine), make the upper narrow compression gasket the same thickness as the lower so that the end compression is at 50% of the total to equal the stop height.

    That way also allows the neoprene to not get too compressed.

    (I would not worry at all about cutting a narrow pce of neoprene and gluing it together rather than sacrificing a larger sheet. All you have to do is to cut an angled joint (say 6:1) so that there is a large glue area - the neoprene will also be glued to the flange so that there is hardly any movement)

    .
     
  10. Roy222

    Roy222 Paddler

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    hatches

    Rok,
    I think the Material Reduction Engineers ( cost/weight cutters - if are forced to work with these people you know what I mean) will delete the 2 stops. You will just need a foam seal about 50% thicker then the gap.
    The gap between the hatch and the hull needs to be a lot wider and you need to leave space to seal the end grain with epoxy. If you don't plan to use Marine Plywood you need to double seal the edges. Any pin hole leak will ruin the appearance of the outer show surface. Non Marine Plywood will have small gap or splits in the layers. If exposed to water these very small splits will suck water in. The glue will then discolor the show surface. Consider wrapping the hatch edge with glass. You might consider using internal bungee cords to hold down the hatches.
    Build time:
    That is a lot of panels to wire, glue, fillet, and glass together in 70 hours.
    Then there is glassing, sanding, and fill coats. If you want to do more then slap on a few coats of varnish plan another 3 weeks.
    You could shorten the varnish time using HVLP spray gun. The trick: mask off areas, along the seams, that give you a straight shot. You will never see the mask over lap on the seems. Divide the work into 3 surfaces: deck, sides, and bottom. If you are good you might only have to lite sand before the last coat. Sears sells a HVLP gun that will work with a standard compressor for about $109.


    Roy
     
  11. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    Yes. I've found that over time, the gaskets do compress and as they compress, you'll get less positive contact with the hatch.

    The gaskets on my Coho are currently in need of replacement (after less than a year and a half) as there is no "memory" left anymore -- the neoprene gaskets are now completely flat and offer no expansion at all -- and they now leak. In your case, I think the stopper will cause the gasket to become ineffective much sooner.

    *****
     
  12. rookiebuilder

    rookiebuilder Paddler

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    Hmmmm... I'll have to think more on this. :? There must be a way. This problem must have been solved by someone already. The concern I have is that as the gasket ages, it will allow the hatch to go beyond flush with the deck (which is why I included the stop)... :? I'll look into it. :shock:

    When looking through the build journal for Dan's Enterprise, it doesn't appear that the edges of the plywood panels are beveled (the same with Maddie's Magic and the Coho). This leaves a larger gap on the outside of the joint but it makes it easier to know the profile of each bulkhead.

    I have seen other journals where the edges are beveled. Am I missing something or are there two different schools of thought here?? :?
     
  13. woodensoul

    woodensoul Paddler

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    Re: hatches

    I have not had good success with HVLP and varnish. It will depend on the varnish you use. It's generally a bit thick to spray with anything but a conventional system. Having said this the issue with varnish is not so much the application, but the drying times and the number of coats. You need 6 to 8 coats and you need to do the boat in halves (top half and bottom half). So that is 12 to 14 applications. You need to allow some drying time between coats (some folks on the site have experience with reducing these times). If you do 1 coat in 24 hours it takes 12 to 14 days, if you do 2 coats...

    For fast drying I have used auto clear coats. It does work with HVLP and it flashes in 15 minutes, so you can build up 3 coats pretty quick. However it contains isocyanites which will kill you if you do not use a fresh air breathing system when applying it...
     
  14. woodensoul

    woodensoul Paddler

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    *12 to 16. no math skills this morning... :oops:
     
  15. Tootsall

    Tootsall Paddler

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    In the instructions, Pygmy does have you bevel the edges of the panels #4 and #5 (on the Coho) where they meet at the sheer line. It appears that stitch and glue "requires" that there be a bit of a gap so that you can subsequently fill the open side of the gap with the filler which they say is required for strength. Those particular two panels meet at an extreme angle that, were it not for the bevelling, would mean a particularly thick "pinstripe".
     
  16. Tootsall

    Tootsall Paddler

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    Oh, the second reason for having a "pinstripe" of filler between panels: if it were not for this line of filler, when you start sanding the boat down, you'd most likely either have very "sharp" (and easily damaged) lines at each joint or when you round them off a bit you'd cut through the top veneer of the plywood exposing the (lighter colour) center veneer.
     
  17. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    Are you referring to the bevelled panel edges at the sheer?

    *****
     
  18. rookiebuilder

    rookiebuilder Paddler

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    I wasn't specifically referring to any particular edges. It hadn't dawned on me that there may be a need to bevel some but not others. Tootsall answered my question in spite of my ambiguity. :wink:
     
  19. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    Oh, I thought you were still referring to the hatches.

    The only edges that Pygmy suggests bevelling are the edges along the sheer (for the reasons that Tootsall mentions).

    *****
     
  20. mick_allen

    mick_allen Paddler & Moderator

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    referring to a hard overcompression stop:
    Neoprene gasket material is not a solid piece of rubber - it consists of many, many closed air cells within a matrix of the solid material. The large volume of air cells is what allows the gasket to compress so much and so readily.

    If (like in many hatches), there is not an over compression stop - prolonged high compresssion or very high compression can burst the air cells causing the material to be unable to spring back to it's original volume. That's when the 'set' happens and you see kayakers tightening and tightening their hatches over time.

    To reduce (I don't think eliminate is so likely) this possibility, it makes sense to limit the amount of over compression (this is just aircelled neoprene here) of the material by the use of a stop. I would guess that the limit whould be around 50% for normal wetsuit neoprene and maybe about 60-70% for the high stretch neoprene that has become available in the last 8 or 9 years.

    If one is concerned about not being able to recognize overcompression while using hard stops, a possible reaction is to use a combo gasket of a hard neoprene for the stop and aircell neoprene as shown for the main gasket. Solid neoprene is quite hard and yet will compress a little bit.

    Under consistent pressure over use - at first most of the load will be taken by the aircell neoprene and minimal on the hard; then much farther down the road of high use, the aircell will perform more poorly, but the 2ndary stop of hard neoprene will be able to slow down water intrusion.

    Quite frankly I don't see this as much of an issue either way, because one will notice the progressive failure of the original gasket in either case.

    Some of the other important issues are:
    • -how stiff is the lid?
      -how stiff is the flange/deck? (this is not a trivial issue for some kayaks)
      -how well the does the lid mate with the stop all around with no down pressure
      -how much does a non-mating lid have to deflect in order to finally mate all around with the stop.
      -where
    • does the lid have to deform to mate with the stop in relation to where the 'bumps' (or high compession areas) are. (they should coincide for equal pressure all around the perimeter

    anyway, some considerations.
    .