Pygmy double- Recessed rear Coaming modification?

Discussion in 'Boat and Accessory Building' started by Rick_M, Sep 17, 2012.

  1. Rick_M

    Rick_M Paddler

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    Hi. I am building a Pygmy Osprey double and I want to make the rear coaming like Pygmy's Choho (or like boat). IE get rid of the rear cockpit peaks.

    I would like to think, that someone out here as done this already, and if yes, can you provide me with a sketch of your modification and the amount of plywood I will need?

    Thanks a bunch
    Rick McK
    Seattle WA
     
  2. mick_allen

    mick_allen Paddler & Moderator

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    Am I reading you correctly that you wish to drop the rears of both cockpits? If so, would you contemplate a continuous lowered region that includes both cockpits or solely a drop at the rear of each?

    [​IMG]

    And third question is, do you wish to drop them to the 1st deck chine height or the gunwale ht. (The 1st deck chine ht still looks fairly high).

    Conceptually though, the approach is very straightforward: the rear coaming is desired to be on a flat level region while the rest of the deck is left as before. So if the level region originates from the 1st deck chine, there will be a simple long triangular 'ramp wall' remaining between the 2 surfaces. Ramps, or stairs, or level changes are the most basic resolutions between 2 regular surfaces, so a simple answer is to wire up the shape and then cut wherever you wish the ramp edge to be. Push down the region you wish to be flat and level, remove the tiny bit of overlap at the centreline that would stop that area to be level, restitch that - and then make a 'filler wall' between the 2 surfaces with a couple of scraps of doorskin or leftover plywood. ( I would use pcs cut out of the bulkheads as the material would match - trace and make other blkhds out of scrap or doorskin).

    It's a simple approach, and you can get as fancy as you wish with curves, slopes, angle changes, etc for the filler area between the 2 surfaces.
    Your main issue remaining is that the coaming approach using plywood spacers between the deck and coaming will fight against the flat surface - so use more pieces, or thinner laminates or just use a full laid up glass coaming (say pted black).

    On the build series you can see the process on a Bear Mountain Magic:
    http://www.westcoastpaddler.com/building/displayimage.php?album=17&pos=87
    [​IMG]

    You can see a simple curve with a simple slope was initially drawn between the 2 surfaces, but any shape could be used: a straight line, with vertical rise would be the most simple of course - I believe in this case a more gentle curve was chosen so that the filler piece wouldn't have to curve as much. Note in the drawing that Dan was contemplating having part of the filler piece come to the edge of the deck chine (the two curves do not touch). For conceptual and aesthetic simplicity, I would make the two curves touch just at the end so that the panels can be laid out with more ease on the build and the ramp panel lines resolve to a point or intersection .
    anyway, ideas.
     
  3. Rick_M

    Rick_M Paddler

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    Mick. thanks for the questions and photos.

    Yes, I want to lower the rear of both cockpits and lower the coaming(s) closer to the shear line. I would guess that I need to "watch" the size of the coaming to be sure as it gets wider it doesn't get too big for my skirts.

    Like you suggest I am planning on making a triangular section like your bear Mt, to make the caoming flat meet the ridge tops.

    I may lower the top of the center section by placing a flat panel to remove the peak between the cockpits, but I have not decided yet.
     
  4. mick_allen

    mick_allen Paddler & Moderator

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    1)It's more complex to drop to the sheerline but way easier to the deckchine.
    2)If you make the sharp ends of the triangles at the deckchine come to a point, then the coamings automatically stay essentially identical in size.
    3)Do not use a flat panel to lower the peak between the cockpits as: a)the design becomes less aesthetically coordinated as the now nonexistent centreline and inc. number of deckpanels clashes with the rest of the boat. b) Its 100x more simple to just take about 1/8" off the ctr of each peak panel and lower it - that way thereby preserving all the concerns in a).

    The process to use would be to initially stitch all the deck panels together on the hull as if to build in the normal way but leaving off all plywood coaming risers. Add extra stitches beween the front of the front coaming and say 1' back of the rear coaming for the 1st deck chine and the centreline, but make sure all these stitches are just loose enough to allow the panels to change angle slightly. Lay scrap paper on the panel at the rear of the rear coaming and markup with a thick pen line where you think you wish the deck panel to be cut for the rearmost cutline. Where you mark this will be determined by whether you wish a vertical transition or a sloped one. Make sure there will be at least 1" gap between the outer coaming edge and the beginning of the transition upward to the deck and also think about having enough space for your body to lay back.
    -Take a deep breath, have a beer, take a break, maybe mark up the front ckpt a little, come back the next day and then make the rearmost cuts on each side only (1 cut on each side).
    -Then undo any stitches between the rear ckpt opening and the cut you made, push down the panels flat by overlapping them one over the other.
    -draw a light line on the lowermost overlapped panel using the upper panel as a guide and then lift the upper panel and remark the lower panel with a line that is halfway between the line you originally drew and the edge of the panel. Measure where this line is and draw an identical one on the other panel and then plane or cut the panels to this line. Now stitch panels together on the centre line and they will be flat (you may have to temporarily glue/stitch a pc of scrap on the underside to keep this flat).
    -Get some cardboard and make a template for the triangular filler piece. As the existing panels are vertically cut, you can mock up any slope you wish (the under cut on the lower panels can be made later)
    -Measure how high (from the 1st deckchine) the deckpeak is behind the rearmost cockpit, and using string or made up templates or careful measurement, derive the panel widths required at the front of the rear ckpt and the rear of the front ckpt. The offset will probably be very small - say 1/8" or thereabouts. Maybe mock it up with a couple of sticks to be sure and then cut the centrelines as with the rear ckpit rear. Stitch up.
    - then repeat the front ckpt recess the same as the rear.
    -make coaming upstands in multi-pces so they will conform to the more radical curvatures or lay up a glass coaming (use 8-10 lyrs equiv of 6 oz)


    If you use simple triangles the result will be something like this:
     

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  5. Rick_M

    Rick_M Paddler

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    Mick. THANK YOU :) Your advice is GREAT. Your process is clear, and I like the "look" of the triangular sloping sections vs the curved ones on the Coho, and your Bear Mt.

    From your suggestions once I have the hull done, and the deck wired together I will be able to "see" the best way to make the modification sections. Yes I like your idea on the center section (not flat) another idea I have is to lower the peak by making a cut on each side of the center line (say 2" ) that will produce a another break line to make a more "rounded" section. I will decide once I have the deck on and sit in it for awhile to determine how I like the "look and feel" of it.

    Thank you for the drawing as this really helps me wrap my head around what to do.

    One more question: Different topic

    How did you apply the Polyurethane to your Bear Mt? Can it be applied via roller & foam brush? Or does one have to spray it. If spray what type of equipment is required? I have painted cars so I know how to spray ,but I don't have the tools anymore. Can you direct me to a thread about this?

    Thanks a bunch

    Rick McK
    Seattle
     
  6. mick_allen

    mick_allen Paddler & Moderator

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    Firstly, the Bear Mountain Magic was built by Maddie Millsip just a short while ago, when she was still in high school! Her father, Dan, assisted with his huge depth of building knowledge and I would have to reread that building section to remember how he gets the finishes that he typically creates. (I just helped out with cockpit drop and deck advice plus dimensions)
    **

    Secondly yes, the deck needs to be initially wired to the hull or in such a state (say using formers and spacers) that it keeps exactly the correct topview profiles and 1st deckpanel angle(s) during the surgery. It would be a little annoying to cut the panels too much so that a gap is required to be filled or the deck is glued up too narrow, heh heh. So just be careful and make a good, firm setup first. Then markup the rear ckpt and make the first single cut (on ea side).

    and thirdly,
    -the triangular drop pieces are shown to try and clearly demonstrate the issue. But I agree, it actually works here better than I originally presumed ( I would have intially drawn curves that reflect the ckpt curves). Part of the reason it works so well is the simplicity and lack of confusion that helps the following concern:
    -I would strongly urge you to not change the panelization of the centre section. A double's shape is chopped up enough that further unrelated shape treatments will make the composition busy. There is an interesting rhythm of 'deck ckpt deck ckpt deck' that should be maintained here and the mentioned simple drops help to not distract from this.

    Here's my original preconception:


    So I think your original thought to keep the simple triangular risers is not bad at all in comparison with this latter view. And the other feature that becomes glaringly apparent is your other thought to drop the centre deck section down to match the height of the rear deck so that both drops are equal in height - makes strong visual sense.
    -mick
     

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  7. Roy222

    Roy222 Paddler

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    Another approach would be the way the Redfish King achieves a lower back opening. Achieving a fair side view line for the cut out would take some work.
    In the end you would have a mini hybrid deck.
    Be sure to check foot room for the rear paddler in any design. You might contact Pygmy and ask for their input. Pygmy has just developed a new line with "layback roll" rear decks.

    http://www.redfishkayak.com/king.htm


    Roy
     
  8. mick_allen

    mick_allen Paddler & Moderator

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    Roy’s pointed out other ways to make the drop. Making the long curve is a little complicated, but there are several conceptually similar but simple approaches. The front ckpt of this third image shows the basic idea where the drop is at 90deg to the boat form rather than vertical or sloped. The rear ckpt shows this horizontal drop in a less basic segmented transition . And the front ckpt of the 4th image shows a smooth transition as if you had a little extra deckply.

    As the main ckpt deck panels split on the centreline, to maintain visual consistency these triangular, segmented or curved transitions should split on the centrline also – but it seems contradictory to split this shape ( you can see how the segments look odd without the split, but probably would look busy with it!). Whichever way is chosen becomes jarring. If you do decide to use say, the segmented approach it would make the most sense visually to make strips from the ply so that the material, finish and appearance is similar – altho counterintuitive, keep the grain running longitudinally with the boat (make all the pces out of one larger pc so the grain runs from one to the other) to coordinate with the rest of the panel.


    And lastly the rear ckpt of the fourth image shows a facetted vertical drop that is similar in approach to the first and second images in the previous post, where the curve is pieced out.

    This facetted approach also seems to work fairly well as it also integrates nicely with the basic angular shaping of the whole boat. So my preference would be the simple angle drop(1st image), the just discussed facetted drop(ie the rear ckpt in the 4th image), and finally the curved drop(2nd image).

    As you can now guess, there are an infinite number of geometries to perform these level transitions – and one confronts them all in the various shapes and resolutions that are met.
     

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  9. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    I've modified a rear coaming as well as built and paddled a Pygmy Double for several years.

    Firstly, you don't want the coaming to go all the way to the sheer -- many times while paddling the boat fully loaded the water came extremely close to the shear -- as has been suggested, keeping the coaming minimum height within the top deck panel is wise.

    I also did the modification on a Bear Mountain (yes, it was Maddie's boat but I did the mods on it). Mick was a huge help in lowering the front deck on that boat (in fact, I doubt that I could have done as good a job as I did without his help).

    Lowering the rear coaming was pretty easy -- didn't take much figuring out and the final mod turned out really well. Basically, I did the coaming modification nearly identically to the Coho (which I also have). Regardless of which "style" of lowered coaming you use, the modification on the Pygmy Double is an excellent idea -- the stock rear coaming is way, way too high -- even for a larger person. The high coaming was a royal pain as it tends to push up your PFD at the back. After doing Maddie's Bear Mountain modification I thought that if I ever built another Pygmy Double (which is an excellent boat, btw) that I would not do so without lowering the rear of the cockpit and getting rid of the "peak".

    Good luck with your modification -- it takes a bit of courage to alter the design of a kit boat but in this case it's not really a huge mod and I'm sure you'll be happier with the changes.
     
  10. Rick_M

    Rick_M Paddler

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    Mick. Thanks for the advise. I am just getting ready to make my cuts in the plywood (after making a cardboard mock-up). I am going to make it look like the image #1 as this has flat place to place the paddle behind the coaming. I will knock off the sharp corner and add some extra fiberglass to the intersection where the triangle meets the chime as this point will suffer some wear and tear from the paddle shaft when bracing upon entering and exiting the boat.

    Do you have any recommendations or thoughts on:

    Should I put a layer of glass over the top of the coaming lip, so the glass goes from the inside of the cockpit all the way around to the deck? I have seen this done by wedging rolled up paper towels under the lip to hold the glass in place.

    Thanks
    Rick
     
  11. mick_allen

    mick_allen Paddler & Moderator

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    In any of the cases below, running continuous glass from the inside deck, around the coaming, to outside deck, - and expect it to have any visual success - would be an exercise in futile despair and frustration, heh heh. If something like this process is desired it is best/easiest to do it in pieces or steps or maybe only from coaming top to inside if the block method is used:

    The rear of the coaming obviously gets lots of stress mainly from sitting on it when entering. I don't know your coaming approach, but if it is using wide plywood blocking like the typical pygmy approach you will have to be careful (ie use thinner lams) so that it will conform to the new warping deck shape. And the large glue surfaces of the blocking and wider coaming lip will give quite a bit of structural support to this area after everything is glued up. I also assume you'll be putting in a bulkhead below the coaming (to reduce ckpt volume and give vertical coaming support - for both coamings) as well as possibly coaming(and backbrace) side supports. This all will give a fair bit of support to this area.
    It would also make some sense to use your scrap glass to lay in a couple of lyrs below the recess pieces.

    If you plan on the built-up coaming, I would run the glass from coaming top to inside, let set up, remove form, fillet decktop to coaming upstand, glass one lyr from deck top to upstand. This also assumes a bulkhead immediately below the coaming upstand. This is most important in this approach as the plywood deck edge gets more linear edge stress from the thinner vertical coaming upstand versus the block approach (but saves space, weight, and bulkiness).

    Good luck on your process. Take time to make both coaming drops as much the same as you can (even tho' the dimensions are different) and this will end up being a cool project that all of us can get lots of hints from.

    Be very careful with the corners of all the triangular bits so that they don't get damaged when trial fitting. Plan so that big pieces get put in place first (therefore moved the least) and then the more easily moved and shifted small pieces are placed last. Before gluing up, step back and look at the big picture so that deck and ends fair into the piece as a whole.

    And show us some pics of this early process - sounds like the best part!

    ps - During a different conversation Dan pointed out that a central compartment (a shaped one that protrudes back between the rear paddlers legs) would really make a lot of sense: reduces the huge connected cockpit volume and the bulkhead would give required coaming rear support. And as the front paddler is usually small, to move the very front bulkhead rearward far as likely useable. One could also protrude this one backward to cover all eventualities.
     
  12. Rick_M

    Rick_M Paddler

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    I am now ready to glue the seams with everything wired in place. :)

    My first try (cardboard) was to make a rounded coaming deck and a rounded upper deck. The geometry did not work as I would need to steam a compound curve into the plywood, and I think it would determinate in the process.

    The second try (cardboard) was to match the image in Mitch's first post above. This proved to be great and easy to do. I made a long enough flat behind the coaming to place a paddle shaft (entry and exit).


    I lowered the coaming to the shear line and it was fairly easy. I made the space behind the coaming to be about 2.75" and the sloped wall about 2.5" back. I made supports for the deck and the peak (2x2 hot glued in place). I let the deck overlap and then cut the center to match. Fitting the triangle pieces was time consuming, and they don't ling up exactly (they are within 1/16-1/8") I am sure it will look fine.









    After gluing the deck I will probably add a doubler plate across the deck flat and then when I glass the underside I will put a layer of glass to reinforce it all. I will also be putting a bulkhead behind both cockpits. Rear for the sealed hatch compartment, front to provide a small behind the seat storage place. This will give the flat plenty of support.

    A question: Do I need the doubler plate if I put in a bulkhead that supports the flat section?

    Another question: I want to make mesh holder in the cockpit to put light stuff in up under the peak. How can I attach some fittings (to attach the netting to) without making through holes? My current idea is to screw a strap eye to a small piece of wood and epoxy it to the underside. What do you think about this?

    Does anyone have suggestions on the size and shape of the holder I should make?

    Thanks for the advice as the mod was easy with everyone's' good ideas.


    Rick McK
    Seattle
     

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  13. eriktheviking

    eriktheviking Paddler

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    I would suggest making some epoxy+ fiberglass tabs that you can epoxy in under the deck. You could buy them <http://www.clcboats.com/shop/products/boat-gear/rope-and-cordage/carbon-eyestrap.html> but they are easy enough to make on a form. Since yours will be invisible you can make them out of fiberglass only rather than with some layers of carbon fibre cloth. If you want them to be black, then mix some graphite or toner in the epoxy. One Ocean's builders pages has some suggestions also <http://www.oneoceankayaks.com/Wshophtm/carb_hooks1.htm>. Epoxying them in place would be strong enough for your purpose.
     
  14. Rick_M

    Rick_M Paddler

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    Thanks for the idea. Yes they would be easy to make as I can make a form and make a long strip of them then cut it into strips.
     
  15. mick_allen

    mick_allen Paddler & Moderator

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    Hey, you rock! I just love the photos of what you're doing. Now you're the pro.

    some of your questions:
    - a curved drop may have meant preshaping the plywood piece that goes in. If the desired curvature was tight, bending by means of steam, heatgun , or thinning would be necessary. If the curvature was really tight, thinning or segmental piecing might be necessary as in 'pic4 rear'.
    -you probably don't need a doubler plate behind the coamings if you put a bulkhead directly below, but as there is a seam down the centre you should probably seam it with 2" glass and then put 2 lyrs of glass on that lower area. If it was me, I'd seam it, put a 2" wide doubler from side to side, with a 1:3 taper to the stern (to allow glass to lay), and glass the underside flat with the 2 lyrs, and then the bulkhead immediately below the coaming riser.

    Eric's loop making suggestion is bang on. Another is to glue (aquaseal) small pces of velcro so entanglement entraption is minimized - then if the netting is actually a bag, it can be dismounted if desired. Another is to buy bag/gear rings that tie the floatation and gear inside expedition and ww canoes. My personal prejudice is netting bags should be localized and small to minimize tangling and that larger bags should be smooth. ( I have nasty visions of someone in multi buckle sandals pushing their feet into a tightly meshed bagged cockpit and then having difficulty exiting after flipping over)

    In any case maybe mount some of these loops or rings on the rear of the bulkhead behind the front ckpt and maybe some ways back along the centre bottom. That way you can place and restrain gear in the massive central area - maybe even to between the rear paddler's legs.

    Fixing the large pieces in place and then just making the little triangular pieces fit is exactly the way to go, and I'm glad to hear that it is just a matter of a little time and small errors. Just relaxing a stitch here and there in the large pces may help make those tiny 1/16" differences essentially disappear. It's more difficult in your case, but the more you do this the quicker and easier it becomes.

    I'm a little concerned about the rear of the front ckpt not aligning but as you've been so careful everywhere else I presume it's working ok too. It all looks really fine and am glad to hear it was so straight forward.

    You rule!
     
  16. Rick_M

    Rick_M Paddler

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    Mick. Thanks, I could not have done it without your advise and guidance.

    To be sure everything lined up I used a long straight edge down the center, and I made a bunch of reference marks on the hull and deck before I cut it so the lengths would stay correct. I did the rear cockpit second and it went fast and easy using the front and a pattern and scrap of plywood as an angle guide for the peak angle.

    I am thinking I will fit, and glue the rear cockpit bulkheads before I glue the deck on, then all I will need to do is to glue the tops to the deck after the deck is on.

    Good points about the mesh netting. I am now thinking of making a drybag with a waterproof zipper that will use plastic clips to hold it to the underside of the deck.





    I can get all the fasteners and fabric from Seattle Fabrics (they also do mail order). This something I can work on after I get the boat on the water. :) After I finish it I will see if I need to make a secure drybag storage between my legs for extra gear.

    This boat is replacing a Skana double which is almost 20" longer and has a center hatch. When my wife and I do extend trips we fill up the Skana. So I figure I will have a dry bag between my feet with this boat.

    Thanks a bunch

    Rick McK
    Seattle WA
     

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  17. Tootsall

    Tootsall Paddler

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    When I built my first Coho I put the bulkheads in the way you suggest: fitting them as well as I could to the hull and fastening them in, then fitting the deck to both the hull and the bulkheads. Talk about a fiddly job! I really thought it would be easier but it took forever to get everything fitted just right.

    On the second I did the bulkheads the way the instructions suggest: putting them in after the deck is glued down. It went way quicker and easier.