12’ catamaran tender

Discussion in 'Fiberglass and Composite Boat Building' started by Jolly Mon, May 30, 2021.

  1. Jolly Mon
    Joined: Jun 2019
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    Location: East Coast, USA

    Jolly Mon Junior Member

    A year or so I asked the group about building a catamaran dinghy, layup schedules etc. attached is a picture of the boat completed. It’s carbon over pvc core for most except for outer hull sides carbon only. 150 lbs. Splashing her tomorrow.

    upload_2021-5-30_18-20-10.jpeg
     
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  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    She does look very impressive Jolly Mon! A lot of hard work has gone into that build.

    Is the outer hull sides laminate just single skin carbon (and with no glass at all)?

    Please do post some more photos of her, including the sea trial tomorrow if you will be going out on a run to test her out.
    What size O/B motor will you be installing?
    And what sort of configuration will the deck / cockpit area be arranged in - or will it be like a RHIB, with just some seating on the side decks?
     
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  3. Jolly Mon
    Joined: Jun 2019
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    Jolly Mon Junior Member

    the outer sides are 4 layers of 9 0z warp carbon/epoxy. No glass.
    We did 2 early sea trials to mark water line and look for water rising up lower unit. Put a pod in front of lower unit to deflect water, worked well.
    Two people and a 4hp Yamaha top speed 8 mph. The Tohatsu 20 hp schedule for Tuesday delivery.
     
  4. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Looks gorgeous!
     
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  5. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Was this done from a purchased design?
     
  6. Jolly Mon
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    Location: East Coast, USA

    Jolly Mon Junior Member

    No, this was my own design.
     
  7. Jolly Mon
    Joined: Jun 2019
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    Location: East Coast, USA

    Jolly Mon Junior Member

    Launching this boat went well enough but 3 things surfaced that we hadn’t seen before now. The first was the stainless sheet metal wrapped over the transom was glued with 3M 5200 and the quickset version. After 3 days the outboard motor clamps squeezed uncured 5200 out of the joint. The quickset is supposed to cure in 24 hours, frustrating. The second item is the lifting points for pulling the tender up on the davits/radar arch on our sailboat. I drilled holes in the tunnel top and reinforced the holes with carbon/epoxy washers. The tunnel top is a better location for centering the boat in the radar arch. Then I passed dynema line thru the hole with an estar knot on the bottom. However when not in tension the line settles on a simple knot allowing water to geyser up providing an unexpected bidet effect if you sit in the wrong spot . Trying to figure out the best way to plug these 4 holes. Last item is the blunt, plumb bows are producing spray that we didn’t see earlier. The heavier outboard that’s coming today may be enough to trim the bow up to be less of an issue. Otherwise I was thinking of bending some Aztec, pvc on to act as spray/lift rails.
     

    Attached Files:

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  8. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Seems very heavy, especially for primarily carbon laminate.
     
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  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I wasn't, but since you did, I also thought it came out a bit heavy, would have hoped for 100#.

    It seems like 36 oz of carbon is a bit much.

    How did you arrive at the layup? Then did you use seam tapes as well? And the hullsides are only carbon, no core, or did I misread?

    Is the core 12mm?

    It is a sharp looking boat. Perhaps fairing and other things added weight as well.
     
  10. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    I understand the desire to not be critical, but many people come here for examples of what can be done.
    Both positive and negative outcomes provide lessons for future design/build of boats.
     
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  11. Jolly Mon
    Joined: Jun 2019
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    Jolly Mon Junior Member

    What would be your comparison?
     
  12. Jolly Mon
    Joined: Jun 2019
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    Jolly Mon Junior Member

    Hey Fallguy,
    The outer hull sides are solid carbon epoxy, no core. They’re 4 layers of 9 oz. I did a layup of 3 and didn’t like it. Just didnt seem stiff enough for the span. Now that it’s put together I’m very happy with the outer hull sides. All the joints used a filet of epoxy/cabosil covered by a layer of carbon tabbing. The rest of the boat besides the hull outer sides used a 3/8” core except the transom uses coosa for core.

    Originally I was targeting a 100 lbs or less however one thing leads to another and here we are. Looking at it now I can honestly say I’m glad it’s 150 lbs. a 12’ cat with 6’ beam weighing only 100 lbs would be a kite
     
  13. fallguy
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    fallguy Senior Member

    I have plans for a foam sandwich dinghy 10' that come in at 65#...now, 12 vs 10 is certainly not linear, but I think 100-110 would have been achieveable..
     
  14. fallguy
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    fallguy Senior Member

    what did you do for laminate over the core?
     

  15. Jolly Mon
    Joined: Jun 2019
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    Jolly Mon Junior Member

    2 layers of 9 oz each side. 50/50 cloth resin ration hand layup of course
     
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