30' cruising catamaran repair log

Discussion in 'Boatbuilding' started by jdory, Aug 7, 2015.

  1. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Catching up here. In August I worked a bit on fairing the cabin sides on the exterior.. still might have some touch up work depending on what standards I decide on. Not going to be a mirror finish.
     

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  2. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Kurt had me worried about the net attachment when using pvc pipe glued onto the hulls when he talked about the forces at the corners that can pull out an eye pad. So I took the extra precaution of adding some uni fiberglass (culled from some triaxial I have on hand) at the ends to help resist peel forces. Soaked the uni in epoxy and threaded it through holes in the boat around the ends of the channel, and wrapped around.
     

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  3. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    September got some more outside fairing and some new primer to some areas where I had done some modifications.
     

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  4. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Still in September, glued up some G-10 fiberglass backing pads for 2 winches, and got the interior mostly painted. Still need to treat the floors with something - probably a clear varnish with some non-skid. And the bench sides will probably get paint when I'm done figuring out how to make a folding step to get into the bunks. The bench is a bit high for an easy climb in.
     

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  5. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    For batteries, I'm hoping to afford lithium. Maybe get a lead battery for starting, or something. To be determined. But to accommodate a lithium pack, I made a shelf in the starboard bench. Don't have a picture at the moment of it.. still need to finish it. Probably just start off with a starting battery and won't have to worry about lights in the summer up here , where it doesn't get dark. This was October I got to working on it. Also did some varnishing of various interior hatch covers. Screwed that up a bit - made some newbie mistakes and had to scrape some off.. haven't fixed 'em yet.
     

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  6. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Did a bit of travel for seeing some family and friends in October. Then in November, began the boom project on an old strongback I had in stock from building a kayak back in the nineties. The plan was to set up removable stations to define the form, cover them with 2 layers of 3mm luan mahogany plywood, with 1mm of carbon uni on four corners inside and out, and reinforced with 17 oz. biaxial fiberglass on the outside corners. Whole outside to be covered with 1mm carbon. I've also covered the inside with 6 oz. cloth to give some wear and weather resistance - not sure I'll paint it yet on inside. Corners are made up of sitka spruce I had left over from stringers. I vacuum bagged the carbon on, as well as the top plywd skins that aren't yet glued on so I have access to installing the sheave boxes.

    Sheave boxes will be made of G-10 fiberglass. I think I am going to make them removable in case of some kind of needed maintenance. Currently working on that. Boxes are assembled for most part - but thinking of doing some more reinforcing when I have their final shape. I have so far just glued on a bottom for the sheave cheeks using epoxy thickened with Cab-O-Sil and micro balloons - with chopped fiberglass for structure - on the roughened up G-10. I used a 36 grit sanding disk in my grinder to rough them up where the epoxy goes.
     

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  7. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    First image is vacuum bagging the top. I used shims to force the curve down onto the shape, after reinstalling the stations to help give shape. Also included are installing some cloth inside and the sheave box images which brings me up to current (the wood inside the sheave boxes are just temporary spacers to maintain correct widths):
     

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  8. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Today I may make the cutouts in the boom for the sheave boxes, then I can final shape the boxes. Otherwise, two images - one from my boat shed last week and the other looking out over the partially frozen Bering Sea (Norton Sound) just before noon, which more and more is having a hard time freezing. Happy New Year!!
     

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  9. Rohde.Soda
    Joined: Oct 2018
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    Location: Northern Ca

    Rohde.Soda New Member

    Awesome! Thanks for posting all that. If it isn't too much hassle, I'd love to keep up to date with your progress going fwd. You're doing a lot of things that align w/ my own project.

    The boom especially intrigues me. I have a dream of building a composite "park avenue" style boom. Ideally from a set of plans, but unsure how attainable (or affordable) those would be.

    How exactly will those sheave boxes load? I assume all the load wont be on a shear glue joint?

    Edit: Also, I think your 30 footer has about the same elbow room (or more) in the hulls as our 37 footer!
     
  10. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    I bought the plans for this boat from Kurt Hughes in Seattle. As a designer, he is invested in his designs and wants to see them succeed as it helps his business. So when I asked him about the feasibility of building a boom, he gave me a really good price on some drawings. The drawings leave some things to the imagination, and as he is a busy guy and the fact I hardly had to pay for these drawings, I hate to bug him about details. One of those details is exactly what you mention - how to mount the boxes to resist loads. I did ask, and got some vague answer that didn't help. If you approached a designer for plans - the more you provide in info on the boat the easier and cheaper for them to do a design. For instance, the weight of the boat and size, wetted area, deck hardware layout, square footage and dimension of mainsail, and whatever else might be helpful. I would write/call some designers and just feel them out. Don't know if you're on facebook but there's a helpful group or two there - the Multihull Appreciation Society.. that might steer you in the right direction - though I hate to steer anyone to facebook.

    So partly why I'm making these boxes removable is in case I need to re-engineer them due to poor mounting or whatever reason. Might be stronger just permanently fixed in place. I'm hoping to rely on butting the sheave cheeks against the body of the boom - where they exit the boom. That will have a small bit of biaxial on the body to resist crushing. The base of boxes, where they rest against the body of the boom - I'm going to set them into thickened epoxy with a release agent (probably plastic wrap) so they have a firm base that will help the machine screws (with nuts) resist too much shear. The 1/2" pins for the sheaves will exit either side of the boom. Where they exit, I'll build up some reinforcement there with either a few layers of a couple square inches of biaxial, or perhaps a bit of plywood/biaxial. That pin, plus butting the ends of cheeks against body, I hope will be enough. I am also considering a second pin through the boxes opposite side of loads, a bit lower than the sheaves and through the boom body, to help reduce load on sheave pin. But not sure if I will. I can't think of any other way to do it - happy for ideas.

    Wasn't going to post this pic of boom with cut-in boxes until I shaped the boxes where they exit to avoid confusing anyone. They run wild at present but will get trimmed down. But thought now it might help see what I'm doing.
     

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  11. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Here's shaped boxes.
     

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  12. Rohde.Soda
    Joined: Oct 2018
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    Location: Northern Ca

    Rohde.Soda New Member

    What you described is about the best option I could think of. That basically leaves you with a perfect socket to fit the boxes into. That way the pins are more or less "keepers" than actually taking significant load.

    What do you estimate this boom will weigh in at?
     
  13. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    I just weighed all the parts at 46 lbs. Still need to add carbon fiber and some biax reinforcement, plus a bit of fairing and paint, so hopefully under 50 or thereabouts. Oh, and I didn't include some rails to catch the sail and hold off lazy Jack's, so they will weigh a couple pounds probably.
     

  14. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Senior Member

    Got the carbon blind coves done.. so just a few more little things before gluing on the top. Not real happy with the area of carbon where it will bond to the top - a bit wavy which means more thickened epoxy.. and perhaps not that great of bond, but it got a good bond on sides and corner wood. Outside will also get carbon fiber and some biaxial tape at the corners. Should be stout.
     

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