21' proa design New Zealand

Discussion in 'Boat Design' started by DanielConti, May 2, 2015.

  1. DanielConti
    Joined: Apr 2015
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    DanielConti Junior Member

    In September I am going to New Zealand on a two year working holiday visa. My dream is to sail my own boat to Milford Sound. I want a proa because they are fast and look excellent and have plenty of deck space for cruising in the sun.

    This is my design.

    The vitalstastics

    Lee hull (with the mast)
    Waterline: 21′
    Beam at waterline: 1′
    Displacement: 68kg

    Windward hull (accomodation)
    Waterline: 21′
    Beam at waterline: 2′
    Displacement: 136kg

    Centre to centre beam: 10′

    Hull displacement: approx 204kg
    Draft: 2″

    Rig: Single junk rig. 120 sq ft approx

    This design borrows from both 'Ping Pong' and 'Sidecar' and joins them in a way that I understan, to make a fast but cheap and easy to make boat. I am giving myself a GBP3000 budget.

    image.jpg

    This is a ‘weight to windward’ design of pacific proa, giving greater stability than a more conventional ‘flying’ design.

    I have four crossbeams instead of the more conventional two, generally something more often seen on catamaran. This may be a case of structural overbuilding but I want to feel safe in this thing. I feel that with a hull made of 4mm marine ply I could use a little extra support for the extremeties of the boat wich would otherwise stick 7′ free from any lateral support. The four beams will have strong internal support built into the bulkhead below as well as longitudinal support from one crossbeam to another. There are other advantages too. I am now able to build the rudders closer to the end of the hull, increasing their leverage. I will also be able to string trampoline mesh between the outer and inner crossbeams, doubling the available deck area.

    I have increased the length of the hulls from previous designs, as well as making the ama and vaka the same length. This was after I saw a similar design called ‘Ping Pong’ by Terho Halme. It has equal length hulls and sails just fine. It solves several problems for me. The problem I was having with the ‘weight to windward’ design was not having enough space or displacement in the windward accomodation hull. Having a 21′ windward hull solves it nicely. By sacrificing a bit of inside space the hull can be made to be 2′ high with an additional 1′ cabin top. This still leaves space for two to sleep, head to head instead of next to each other. The space will allow two to sit and face each other with space to cook or play chess inbetween when they are not sleeping. However generally, while sailing, two crew members would not be taking sleeping shifts at the same time. If moored or at anchor there is space on the 49 sq ft deck to pitch a tent.

    I have chosen to step the mast to the crossbeams rather than into a hull. I want a mostly freestanding mast for ease of manufacture. Stepping the mast inside the hull raises problems that I can just avoid. Furthermore, having the mast on the crossbeams allows me to move it, repair it and generally be able to access any part of it without having to mess with an integral part of the boats structure.

    The unloaded displacement is 204kg for 2″ draft. Day tripping with three or four people would be around the maximum displacement of 520kg which would give a draft of about 6″. Adequate for smooth seas.

    The only real complexities are the angled, three chine hulls. I feel they are quite necessary to avoid slamming into waves at high speeds, so they stay. Because the boat has no rocker so it is a manageable level of complexity.

    Can I just say a quick thank you to the people who shot down my previous ideas :) I really appreciate that I did not have to learn from my mistakes the hard way. I think this one is a goer though.
     
  2. messabout
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    messabout Senior Member

    Three chine hulls can do just fine with some rocker. Using some rocker will cause a the panels to be somewhat edge curved and thus use a bit more material.

    A 21 foot waterline boat is going to be a bear to turn or tack unless you do raise the ends some. A boat that is fast and is cranky about turning can get you into deep trouble.
     
  3. Rastapop
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    Rastapop Naval Architect

    Have you checked the weight distribution to see whether the "deck" will actually sit horizontally like that?

    I count a single chine, not three? (Two if you include the cabin extension)

    The flattish bottom that your chine gives will encourage slamming, not reduce it. Although the ends are very fine, so perhaps it won't be an issue.
     
  4. DanielConti
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    DanielConti Junior Member

    @messabout: I wrote no rocker, but now I think about it the depth of the middle of the boat will be 3" deeper than either prow. Would this be enough? I was thinking that large rudders very near the end would allow me to turn.

    @rastapop: I may be using the wrong terminology. I was counting each 'corner' of the underside of the hull as a chine. With regards to slamming, surely having the hull angled as it is on the plan would be better than a flat bottom?
    How would I calculate weight distribution? The ama has a third of the displacement and the vaka has two thirds.
     
  5. peterAustralia
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    peterAustralia Senior Member

    Hi Daniel

    Its your business what you choose to do. Russ Brown who designed and built Jzerro, Kauri and Cimba proas wrote that shunting proas work well on larger boats however he did not recommend shunting for smaller boats. For smaller boats the tacking system seems to work better, mainly because it is simpler. On a large boat, you can save a lot of weight using the proa configuration. My 2 cents worth is look at a tacking craft, rigs are simpler, rudder is simpler. Just my opinion thats all

    http://www.salmoboats.com/salmo_24_canoe_outrigger.html
    http://www.tacking-outrigger.com/robert_gillet.html
    http://www.creartisto.com/sansboussole/bateau.html#Hautdepage
    http://www.flaquita.net/
    http://www.tacking-outrigger.com/TO18b.html
     
  6. DanielConti
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    DanielConti Junior Member

    @peterAustralia: Thanks for the post. I will have a think about a tacking boat and add a drawing if one occurs.
    My main counterpoint to the simplicity arguement is that all that will be saved is an extra rudder and a few more ropes for the rig (since I am using a junk rig). I would probably need to build a centerboard or dagger board anyway so the simplicity saving is, to my mind, quite minor.
    Besides, because the boat is light and well reinforced I will be able to tack should I need to.
     
  7. Rastapop
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    Rastapop Naval Architect

    Yes, what you have is better than a flat bottom.


    In a nutshell, if the arma is 1/3 the mass, it must displace 1/3 of all displaced water.
     
  8. tom kane
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    tom kane Senior Member

    You should do a lot of research about seas and weather in that area of New Zealand you want to visit before you consider any type of boat.
     
  9. peterAustralia
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    peterAustralia Senior Member

    hi daniel

    Junk rig sound fine, low cost, simple, easy to reef.

    Your design is OK, not awful,, but so so. I think your ends are a bit fine, could definitely be improved by having fuller ends. The other suggestion is the deadrise angle for your hull bottom, it looks very shallow, maybe 10 degrees. My guess is something like 30 degrees would give less pounding and take more of the lateral resistance away from the board. If you have a flattish bottom, your going to have to rely on the board a lot, again just a suggestion, which you are free to completely ignore
     
  10. peterAustralia
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    peterAustralia Senior Member

    Looking at Tehro Halme's Ping Pong proa, his next boat was the EQL-7 proa (7 meters = 22ft or so), you notice that on his second boat he has gone from a flat bottom to a vee shaped bottom, deadrise angle 45 degrees at a guess. Maybe email Tehro and ask him why he went from a flat bottom in this first boat to a vee bottom in his second boat.

    http://wikiproa.pbworks.com/w/page/14592535/Terho Halme's "Ping-Pong"

    Note his ama is a single chine design, deadrise maybe 65 degrees, and then almost vertical above the chine, very much like a traditional trimaran ama
     
  11. lucdekeyser
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    lucdekeyser Senior Member

    free radical

    free radical is a shunting proa from NZ designer doing well in NZ waters. To maximize time sailing in these two years, I would buy his plans, quickly build it close to his residence and start sailing. Or, even better, buy the boat from him and be off.
     
  12. DanielConti
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    DanielConti Junior Member

    @lucdekeyser: I have seen his boat and considered it, however it has such a small maximum carrying capacity (150kg) that only one person could go camping/sailing in it. I have also emailed him about getting some plans, no reply so far...
     
  13. motorbike
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    motorbike Senior Member

    Building a proa, nice. Cruising it to Milford sound, dumb idea.

    For the budget I imagine you have and a 21ft proa? I would not venture further south than the Hauraki Gulf, and that in autumn at the latest.

    The next shot in this series shows the waterfalls being blown to spray before they hit the sea. Don't be fooled by the tourist postcards; to approach this remote, rugged and dangerous area by sea in anything other that a well found vessel is foolhardy.

    [​IMG]
     
  14. WindRaf
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    WindRaf Senior Member

    According to me you can get a boat easier to build and better in performance with only sections trapezoidal, widening slightly the hull at the top and slightly increasing the draft.
    Two edges in less and better penetration.
    And you thought at the traditional proa, with the amas downwind asymmetric,
    without dagger board?
     

  15. DanielConti
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    DanielConti Junior Member

    @motorbike: Ha! Holy cow...I had thought it was a bit beyond my reach actually but that picture confirms it. I'm still going to build something, but perhaps I will limit myself to North Island...Thank you.

    @Windraf: I have nothing against the shorter style of ama. My only issue is that on a weight to windward it would not have enough displacement to deal with the weight and pressure from the sail.
     
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