Hobie/J24 Trimaran Conversion

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

  1. Delane
    Joined: Apr 2005
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    Delane Senior Member

    I've just bought a j24 and have a Hobie 20. I'm thinking about converting the J into a Tri. The thought is to use the rear traveler as an area to tie in a spar and go under the hull on the front end jsut behind the mast. I think this would be a very fast stable boat. I love speed with a little comfort. Any thoughts out there?
     
  2. DaveB
    Joined: Dec 2003
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    DaveB Senior Member

    Great to think about ideas like that, but it might be more involved than you realize... Might wind up costing you more than it would to go out n' buy a tri... after trading in what you've got n' buying used of course... I think that tri hulls are designed knowing that they will have the outer hulls for stability... A J24 isn't... it's pretty beamy in comparison so it has form stability... it also has a whopping big keel! To take advantage of the hulls you'd want to increase the size of your rig which isn't trivial... new sails, new mast, new standing rigging, possibly re-inforcing required... The keel'd have to go too... I guess it just seems like a lot of work for a non-ideal solution... A purpose built tri like a dragonfly'd perform much better... Also, your boats are popular classes and by modifying them as required you'd destroy the resale value... If I were you I'd think about selling them and buying a used tri... dragonfly, farrier or something like that...

    Just my two cents...

    Dave
     
  3. Doug Lord

    Doug Lord Guest

    j24 tri

    I think Dave is 100% right. In addition, the beam to length ratio of the j24 hull will not be very good compared to a boat designed to be a tri keeping speeds pretty slow.
     
  4. yokebutt
    Joined: Aug 2004
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    yokebutt Boatbuilder

    Somebody did mate a wabbit with a hobie 16 a few years ago, don't know how the offspring turned out though.

    Yokebutt.
     
  5. mackid068
    Joined: Feb 2005
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    mackid068 Semi-Newbie Posts Often

    Not worth it. 2 boats are certainly better than one.
     
  6. Delane
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    Delane Senior Member

    Thanks guys for your imput. I know the ration isn't close to ideal, and planned to remove 90% of the keel and add a foam and fiber stub of maybe 2 feet and use daggers on the Hobie hull for pointing. Without changing the mast and reducing the weight of the keel (900), figure I could at least reach speeds of around 10 knots up and 18 down. The center hull minus the keel should plane at around 12.
     
  7. CT 249
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    CT 249 Senior Member

    Reducing the wieight of the J keel by 90% saves....what about 800 lb?

    Adding the weight of the Hobie 20 and crossbeams of sufficient strength adds what, 350 lb and a lot of wetted surface area? So you've taken 550lb out of the boat, BUT added foils that will be very highly loaded (only the lee one will be in the water and it was designed for much less sideforce at higher speeds) and windage and wsa, and you expect to increase speed? Umm, sorry, I've seen a couple of attempts at this and they are utter failures.

    Re speeds; a Farrier F720 trimaran is about the same pace as a J/24 all round the track and it has a much slimmer main hull and bigger, better outer hulls, plus a better rig IIRC. The J/24 rig is not much chop when it comes to low drag sailing which a tri needs. The J/24 hull is a fat little thing, it's nothing like a real tri hull.
     
  8. mackid068
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    mackid068 Semi-Newbie Posts Often

    do what you like, but post pics...PLEASE!!
     
  9. Chris Ostlind

    Chris Ostlind Previous Member

    Hobie Tri

    There's a guy near Perth, named Barry Sanders, who was building a wild thing tri from a sharpie skiff, I believe, and a Hobie 18. This boat has yards of aluminum structural rigging and is set to run with a dual H18 rig set as a schooner setup. I haven't seen or heard from him in a year or more, but I would hazard a guess that his stuff can be found with a Google of some sort.

    If that doesn't work you can post a query with the Multihull Boatbuilders site on Yahoo. Someone there will know how to find him.

    Chris
     
  10. Delane
    Joined: Apr 2005
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    Delane Senior Member

    CT 249, thank you for the imput. I disagree about a F720 pacing around at the same speeds as a J24, and I'm pretty sure the H20 hulls can take side loads at any speed. I've had two on the wire a me at the hot seat, flying a hull in heavy seas to windward and just pounding the waves at 24 knots. I'm certain the H20 will take the loading of the J rig, especially when reducing the load with bodies on the windward side. I'm in the process now of determining the best location to bolt in the main cross members to the J hull. I plan to have the J hull projected out in front of the H hull to allow more initial loading (learned this from another site) and allow easier tacks. Also thinking a full batten main will help performance. Cris, thanks for the info. I'll try to find that guy, and let you know. Later

    Delane
     
  11. lanekthomas

    lanekthomas Guest

    I have effected a similar conversion of a 16 ft Lone Star mono and Hobie 16s. Speed is less than the Hobie 16, but greater than the Lone Star. Very pleased with the performance, just more weather helm than I care for.
     
  12. CT 249
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    CT 249 Senior Member

    Re "CT 249, thank you for the imput. I disagree about a F720 pacing around at the same speeds as a J24"

    You may well be right, but US Portsmouth yardsticks put the TT 720 at 79.X, and the J/24 at 80.X. So Portsmouth thinks they are the same speed. Most Australian races give the TT720 a rating in that sort of speed and when I sailed the agent's TT720 we were about that pace and the Trailertri agent reckoned that was the normal speed. Ditto when I raced against TT680s and TT720s, mainly on a 26' Mull. I see that Mull is still rated faster than Farrier 25s in the biggest Australian race. Then again, a lightweight and modified TT720 rates very quickly. The TTs are wonderful, wonderful boat (I want one, I have advised friends to get one, I really enjoy sailing them) they are just an older cruiser/racer and that is reflected in their performance.

    They are also pushing the limits in terms of having an unusually beamy main hull, but it's still much, much narrower than a J's hull. Considering how much importance multi designers like Nigel Irens, Peteghem/Proviot and Dick Newick place on having a narrow beam/length ratio, it would seem highly unusual that a much beamier boat would go all that well.

    "I'm pretty sure the H20 hulls can take side loads at any speed."

    Sure, I was just wondering about the sideloads of the rig; not structurally, but in terms of overloading the optimum lift/drag ratio for the Hobie centreboards which are smaller than the sort of board you'd put on a boat with the J style of rig.
     
  13. Delane
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    Delane Senior Member

    The start of the J conversion is near with most of the other items finished. I've completely refurbished nearly everything on the boat to include electrical, wood, tabernacle deck step, spreader thru bar mod, paint, etc. I've cut the cross bars to 18ft each. Next is fabricating a jig to accurately mark the locations for cutting the holes for the cross bars. Have a plan and drawings of how to support the cross bars through the hulls. No less than bullet proof will work since I ocean sail to local islands in varing conditions. The aluminum pipes are 5.5 inches accross and 3/8 thick, each weighing about 90lbs. Considering drilling litening holes to reduce weight by 25% and yet maintain at least 80% strengh. Rear cross bar just under the companion way and the other just in front of the compression post. Next remove the keel and seal up the keel stud holes, and launch with the approximate weight of items not on board to measure the new waterline. This will determine exact hole locations for the bars and mounting distance to hulls. My guess is it will float about an inch higher than before with a reduction of about 650lbs. Then fabricate a foam and fiberglass foil that will help with leeway and in addition dagger boards for the outer hulls. I welcome any helpful suggestions.
     
  14. tspeer
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    tspeer Senior Member

    Put the saw down and step away from the boat. Keep your hands in the air, and nobody gets hurt.

    You're missing the whole point of a trimaran - how to have a narrow hull without the excess weight of a heavy keel to keep it upright. Converting a J24 to a trimaran is preserving the worst features of both types. You have the high wetted surface of the floats and the beam of the monohull.

    You've refurbished the J24 - you now have a nice monohull. If you want a trimaran, sell the J and get a trimaran. Despite the common cliche, a trimaran is not really "a monohull with training wheels." These mono-to-tri conversions inevitably end up as dogs. And they ruin a perfectly good monohull.
     

  15. frosh
    Joined: Jan 2005
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    frosh Senior Member

    Trimaran conversion

    Hi Delane, excellent advice from Tspeer; take it before it is too late. When you find out after spending your hard earned money and countless hours of work, that the new boat doesnt really work you wont be able to give it away. It is inevitable that such boat wont come remotely close in performance to any Farrier Tri. Either get one of those, or build one if you want a construction project, or stay with a J24.
     
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