Catamaran dinghy 10-11' long

Discussion in 'Multihulls' started by Boatguy30, May 9, 2015.

  1. saltdragon
    Joined: Oct 2014
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    Location: UK

    saltdragon Junior Member

    Boatguy, thanks, for some reason I'd skipped that page, found the link. Mark Gumprecht designs are interesting,and his carpentry looks superb.
     
  2. Boatguy30
    Joined: Dec 2011
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    Location: St Augustine, FL

    Boatguy30 Senior Member

    Making some progress

    Weather has been good, so no issues working without a cover. Now also have both hulls glassed. Plan to weigh it tomorrow to get an idea of where I'm at. I doubt I'll be able to keep the finished boat under 50kg, especially since I've added some bouyancy foam under the false floors and aft under the swim steps.
     

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  3. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

  4. Boatguy30
    Joined: Dec 2011
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    Location: St Augustine, FL

    Boatguy30 Senior Member

    Nice looking little dink. Certainly better than other 8' designs.
     
  5. Boatguy30
    Joined: Dec 2011
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    Location: St Augustine, FL

    Boatguy30 Senior Member

    almost done

    So I nearly have her done. Just the interior/deck paint and hatches and a few padeyes. Weight has gotten away from me and will be close to 165lbs. Good thing I used 4mm! But it is a pretty big boat. Fits nicely on the arch.
     

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  6. Boatguy30
    Joined: Dec 2011
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    Location: St Augustine, FL

    Boatguy30 Senior Member

    A few more trying the 3.5 to save overall weight. Boat is super stable and I have run thru some pretty big wakes on the intercoastal and not shipped any water. Only run it at full load briefly in a ton of current.

    I should point out I have a scale and I would be tempted to say its much lighter as my wife and I can easily move it. Last weight was actually 150 but that was before hull paint and the hatches weigh close to 4lbs each.

    I'm a technocrat, so don't try to peddle the fantasy weights others claim.

    The 3.5 weighs 28lbs and a light 2 stroke 6 hp about 52 plus tank of course. So we'll see if its worthwhile. My neighbor with that 4hp also happens to have a 6hp I can test with.
     

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  7. Boatguy30
    Joined: Dec 2011
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    Location: St Augustine, FL

    Boatguy30 Senior Member

    Success (sort of)

    So the dinghy goes well at full load close to 700 lb total and 9 knots with this 4 horse I bought for $100 in Georgetown, Exuma. The main issue with the dink is the weigh (170lb) and length at 11.5'. I have some ideas about a 10' different hull shape and lower weight but hopefully nearly as easily driven.

    Will get back to you when I return home in April.
     

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  8. sailhand
    Joined: Jan 2017
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    Location: australia

    sailhand Junior Member

    nice work, Im from Australia and inflatables make up about 50% at least of our tenders. there are not too many cats used for tenders. we have only had heavy cat dinghys in the past with some of the newer kit ones even heavier than the old chopper gun molded cat dinghys which is beyond ridiculous, its just plain stupid. I have an 11'6" dinghy that weighs 45 kilos, 100lb, and it planes quite well with a three hp yamaha. I think the cats are better suited as tenders, they are easier to push in displacement mode with heavy loads and easy to row at a reasonable speed. weight is a problem when building and I resin infused mine to keep the weight down, it has made the hulls really tough though so it was worth it. I made mine self draining with one big flat floor and it is fantastic, no more bailing for me, it also makes for a lighter dinghy without all the decks, hatches etc. its not for everyone though, some people just love inflatables and the spartan decks and big open spaces of my dinghy dont appeal to everyone. anyway good luck with your project Im sure you will be happy with a little cat for a tender they are great. they are especially good for fishing!!!!
     

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  9. Goliat
    Joined: Feb 2017
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    Location: Poland

    Goliat Junior Member

    Hi, can you say something more about construction of this nice little boat? What is plywood thickness in it and how much epoxy fiberglass covers the hull, cause 84 pounds is very impressive, even hard to believe that almost 10 foot boat is so light. I'm constructing something similar to your mini-cat and my goal is to keep weight under 120 pounds for 10 footer. So any additional info from you will be great.
     
  10. sailhand
    Joined: Jan 2017
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    Location: australia

    sailhand Junior Member

    hi Goliat my dinghy weighs about a 100lb with the wheels out, check out my other posts for a video or go to
    https://www.youtube.com/watch?v=SA6cDk2Imb0
    the boat has no wood at all it is pvc foam and the hulls themselves are resin infused in a female mold and glassed to the "punt" made out of foam. the bridgedeck is 15mm and the sides are 10mm with various laminates on the foam. It is mostly 400gm2 double bias knitted glass (45,45). Do you have any pics of your cat dinghy or plans to post so we can see what you are building.
     
  11. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    It's constructed from 2 4mm and 1 6mm sheets of fir marine ply (and the scrap wouldn't fill your pockets). It is glassed both sides with 6oz cloth set in epoxy. The bows are stuffed with a few plastic 20oz pop bottles and foam poured. The aft flotation is a couple Styrofoam blocks that happened to be in the dumpster when I built it. They were supposed to be temporary (shrug). The floors are now planked with pink construction foam and some cabinet deadpanel skin, then glassed with 9oz. The edges of the beveled floor are heavily reinforced with scrap glass to form a strong flange to stop the weak foam from being ground up along the edges. That's the second go round for the floor, I used low density polyurethane foam without any ply skin the first time (pictured above) and it gave up after a couple years of hard use. The bow deck nose has also been reinforced with a layer of 1708 for running out anchor chain. The motor pad is a bit fussy because I built it up from scrap high density Divinycell bits. So it is 6mm, some foam, 6mm transom, some more foam, and another 6mm ply sheet. The rubrail was about 1" wide from scrap 17mm okume ply, but a 1x2 would have served just as well. It should have been a bit stiffer, maybe 1.5"

    There are some more pics scattered around, I'll try to find the links.

    http://www.boatdesign.net/forums/materials/laminating-polystyrene-ply-55053.html#post765747
    http://www.boatdesign.net/forums/boat-design/teotwawki-boat-42752-2.html#post548067
    http://www.boatdesign.net/forums/boat-building/fillet-question-40974.html#post509620
     
  12. Goliat
    Joined: Feb 2017
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    Location: Poland

    Goliat Junior Member

    That's great low-budget cat dinghy. I'm looking to build something similar for lake fishing, but it must be foldable for transport/storage.
    More photos will be very helpfull.
     
  13. frenette
    Joined: May 2011
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    Location: Southern California

    frenette Junior Member

    Why fold it? In this size the cat in the 10' to 12' length would normally be about 60" wide opened up. If you're motoring it not sailing real wide isn't so great.
     

  14. Goliat
    Joined: Feb 2017
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    Location: Poland

    Goliat Junior Member

    It should fit in car trunk. And right now it will fit in any combi car with folded backseat. Of course most of the time it will be transported on roofrack, but i don't like to drive with package on roof, so it is additional option.
    Here is a screen of a 3d model. Work is in progress, i must put there additional reinforcements and support for the middle, folding bench
     

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