Hobie/J24 Trimaran Conversion

Discussion in 'Multihulls' started by Delane, Apr 17, 2005.

  1. Boat Design Net Moderator
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  2. Delane
    Joined: Apr 2005
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    Delane Senior Member

    Tri Conversion (Phase 2)

    Well here we go!

    In the planing stages of determining materials, construction method and dimensions for the soon to be added hump section for the Vaka. Yes, I'm effectively going to change the shape of the Vaka by adding the equivalent of another Ama under the Vaka thus changing everything, and hopefully for the better. In the end I intend to achieve a dryer, faster boat with minimum added weight. Initial thoughts are to construct in a (U) shape blumb on both ends thus taking out the rocker in the hull. Studying Canoe building methods now which I hope will prove helpful for my endeavor. Considering using either one of the following materials for the formers (sheet FRP, epoxy coated ply, thick surfboard foam, aluminum ) and would appreciate some suggestions there. Also haven't decided which material to sheet with (thin ply or foam ) before glassing up. Thanks in advance for any help!
     
  3. harrygee
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    harrygee Junior Member

    Hi Delane

    The work on your modification might be easier with the hull inverted or you could make a mould, using cheap junk ply faired with plaster or cornice cement. Then you could make a bolt-on conversion, which could be bolt-off if it's a flop.
    Taking out all the rocker, as it appears on your profile, will make it a bit reluctant to tack.
    I can understand your comments about the wet ride; my own soling conversion throws a bit of water around above 12 knots, becoming a fire-hose at 15 knots. Great fun though. It's a bit more of a "mongrel" now, as I broke the mast a while ago, caught in a 40 knot blow. The soling sails had no reefing and dropping sail would have been dangerous, so nature dropped the rig. The cheapest replacement was an old dragon rig so I now have 20% more sail. That's what you do when the rig breaks. I also have a big reef.
    I love my boat. It's cost me half the price of a ply trailer tri, even with the broken rig and I've had a lot of fun building and sailing her. Highest speed recorded on the GPS is 24 knots on the day the rig went, when I suspect there was very little of the soling in the water. I'll try to get an action shot to post, she looks the part when the spray is flying.

    Take care
    Harry
     
  4. upchurchmr
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    upchurchmr Senior Member

    I hope you draw this up before you start making things.

    If you put an ama under the Vaka you are going to float this very high. There is no purpose in doing this. If you are going to build another ama anyway, just make a whole new Vaka.

    I suggest you just use the J-24 hull without adding the hull changes. It has worked for one guy. Be happy with that.

    If you put a bottom hump on the J-24 how are you going to attach the aka's? Sloping down to the amas?

    Bad.

    Marc
     
  5. Delane
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    Delane Senior Member

    Hello Harry,

    Sounds like you're having a blast with your creation! Would love to see some action video some day. Thanks for your suggestions and yes I thought about different methods of building. I'll post some visual aids of my building plan when finalized. Simple, strong and effective is the goal.


    Marc,

    Thought about drawings and I'm not adding a huge hump so large that it's going to float me up over more than a foot. When I build the form I can roughly calculate the volume and this have an idea how much rise to expect. The goal is to minimize the drag effect of the (mono hull) and cause the hull to perform more like a purpose built Tri with a similar shape. Will also drop down the Ama's to compensate for the rise. Think when i post some drawing this will become clearer. The boat will reach her full potential, I won't be happy with anything less.

    Happy New Years Everyone!
     
  6. Delane
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    Delane Senior Member

    Commitment Phase (Building the Hardback)

    And with that said, the trailer/boat is leveled and hardback is constructed for lack of better words and soon will finalize the fabrication of my station jig pattern thingamajiger that will slide down the hardback to each frame location. I'm looking at two options for the stern most frame. 1. Start out fat and plumb with the stern (U shaped measuring 22D X 20W) and continue forward until terminating in a sharp wave cutting nose that will extend past the original waterline by nearly 16 inches. Or option 2. Start with a tapered stern frame ( 10D X 10W) to reduce the affect on rudder control and to control excess volume in the stern. On the web I encounter two schools of thought on stern profile and the answers vary based on the boat era, type of Tri and the Author. I've decided to use 10mm ply for the frames and sheeting prior to layup but may consider other options. And because many will ask, the hardback is only there for determining the shape and exact location of the frames. Afterwards I'll set up the hardback next to the boat, narrow the top pipes and slide the frames (each having two each alignment holes same as the pipe) into position upside down, add stringers/sheeting and begin to glass. When completed I'll cut the slot for the dagger board, lift the boat up and slide the completed hull assemble up to the original hull and tab it into the hull and glass around the dagger board slot opening. I welcome and suggestions that may help achieve the desired goal. I've never built a hull like this and only going with what I know and have studied on the web/forums.
     
  7. Delane
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    Delane Senior Member

  8. Zeeerga
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    Zeeerga New Member

    A mono hull thinking about tri

    I have a 16 footer fiberglass monohull, and the image of 2 outriggers attached to the sides passed by my dreams many times... The topic with its 9 pages with all this development, almost brought tears to my eyes,

    I have a friend that have an old 14 foot HC forggoten in his backyard, and those ideas came back again to my mind.

    I´m not thinking in convert my monohull in a tri, but to make a central hull for the 2 floaters. (maybe convert ,maybe not...)

    Cause of my line of work (Laser cut and robotic welding supervisor) I can use laser cut almost free, and I was thinking about using some of the F concepts, (foldable) in a pair of struturaded (like a airplane wing) aluminium arcs made of a hollow irregular boxes linking one ama to each other, and in the middle, attaching to the central hull, without making considerable holes, almost like a ring around the hull in the 2 conecting areas.

    What proportion should I use, by your experience, for the HC 14 floaters, would be the size of the central hull? use the 24 to 20 like yours? Or would be in my case 16 to 14, more or less?

    And if try to make a new central hull, should have a narrow plannig form?

    Sorry for my mistakes, cause english is not my first language

    thanks,

    Serguei - Brazil
     
  9. Delane
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    Delane Senior Member

    Serguei,

    Well you have lots of options.

    1. You could use the 16 Mono with the 14 hulls and have a fun little boat with great performance. Fixed beams would be the easiest but you could build them to slide/fold to make trailer-able.
    2. You could build a Vaca (Center Hull) maybe around 20 feet long U shaped measuring around 2 feet across and maybe 3 feet deep with about a 14 to 16 foot beam. Some have built similar boats and they really zip along quite well if you don't mine getting a little wet.

    Search a little on the forum, you might find others that have done similar projects and may inspire some great ideas.
     
  10. Zeeerga
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    Zeeerga New Member

    A mono hull thinking about tri

    Thanks for the repply, I´ll grow this idea of a tri, remembering these 2 amas in my friend´s backyard,.

    Im reading all that I can in the forum, and the slide concept now works better for me, I´ll read, read and read before deciding the way to go.

    In your videos, your J24/HC20 seems to sail very nice. Congrats for her

    Serguei
     
  11. Delane
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    Delane Senior Member

    The Need For Speed! Progress of Phase 2

    Note sure if you can really call her a J anymore but here's some of the progress this far. Current plan is to float after Gelcoating to establish new waterline and then drop the Ama's and Motor mount. Decided to offset the rudder to the Starboard side of the new appendage. Yes the tiller will still be in the center though.
     

    Attached Files:

  12. Delane
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    Delane Senior Member

    More Photo's

    Rudder location. Not mounted, just taking a look. Thinking about mounting swim ladder in the middle.
     

    Attached Files:

  13. oldsailor7
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    oldsailor7 Senior Member

    Words fail me. :rolleyes:
     
  14. oldsailor7
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    oldsailor7 Senior Member

    I'm sorry Delaine, I am not trying to be Snide. But I really don't know where to start in commenting on the evolution of your Tri.

    I have never liked the J24.
    I always considered it as a fat little Mono with a heavy keel. It's performance was nothing to write home about ---but it was a successful class racer.
    As a pocket cruiser it was unpleasant. It rolled horribly, it had convex decks, it had low "safety" rails which were so low they were more likely to trip you overboard rather than save you.
    A couple of years ago I was offered one for free because the owner couldn't sell it.
    I turned it down. :rolleyes:

    Although the hull has a typical mono low B/L ratio, stripped of it's dead weight keel it has the opportunity to plane, given enough sail power. As a Tri you had the opportunity to add a great deal more sail power.
    Your conversion was sufficient to give you a pleasant sailing boat, although I worried about the holes you drilled in the cross arms and the lack of water stays.
    Water stays protect the crossarms from bending stress and convert it into compressive stress which the tubular arms can handle very well.

    However I can't understand why you wanted to add the add the underbody to the hull except for its ability for reduce leeway. It is a good semicircular section for low friction drag, but the straight keel line
    is going to slow down your ability to turn quickly and the flat back end is going to produce a lot of vortex drag and turbulence which will affect the operation of the rudder, particularly when turning to Port.
    Just my 2C worth.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    ==================
    For some reason I can't open those files-any chance of a jpeg?
     
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