Hybrid 6.3 metre cruising trimaran

Discussion in 'Multihulls' started by aussiebushman, May 16, 2010.

  1. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    The start of this discussion was "Fixed or rotating mast' but the focus has changed onto the hull shapes so it seems best to start a new thread. I'd also like to thank those long-suffering members who have contributed so far to the debate and hope I have learned something from their input.

    The main argument stated by various members was the lack of flare on the Trinardo hull Kjell designed it for closed Swedish waters and a wave height of around 300 mm. Here is Eastern Australia, anything up to 3 meters might be considered normal. The boat will be for cruising only and do not care about the top speed - comfort and safety and much more important. The payload with 2 persons and cruising gear should be around 500 Kg

    Here is the status so far:

    • An A Class cat has been acquired and the beams cut in half
    • The trailer and supporting points for the amas will continue to determine the overall trailable width of 2.5 metres
    • The cat hulls have been repaired and glassed to add strength and rigidity
    • New beams have been constructed with the original beams now being telescopic lower sections and new upper beams have been made from 100 X 50 alloy box section. The latter are demountable at the outer ends and fold up for transport. When extended the total beam becomed 4.6 metres.
    • Building frames for the Trinardo centre hull have been made and mounted onto the trailer. However, these will now be removed and replaced with new frames for a different Vaka giving more lift and flare.
    The left hand picture shows the original Trinardo hull shape at the mid section overlayed with the Scarab 24 shape in red. This version loses a lot of internal boat space. The other illustration is the Trinardo shape in grey, overlaid with the Catri 24 shape in red. This is by far my preference because as I see it, the Catri version provides what seems to be the better results, namely:
    • Greater flare than the Trinardo
    • It still fits comfortably between the ama-supporting points on the trailer
    • More usable usable space and headroom
    • Would still work with my modified beam structure with only minor changes


      • Coimments on suitability of the Catri Vaka would be very welcome. Another question is - are the A Class Amas too small to work with this Vaka?

        Thanks and regards

        Alan
     

    Attached Files:

  2. jamez
    Joined: Feb 2007
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    Location: Auckland, New Zealand

    jamez Senior Member



    • In a word, yes. Heres a question. What is the total immersed displacement of an A class hull? Now compare that with the displacemnt at DWL of the main hull you're intending to use. If the floats don't have enough buoyancy it will be like sailing a mono without any ballast. 100% like a Bucc 24 works ok although some newer designs are in the vicinity of 120 - 150% or more.

      I dicked around with this donor tri idea for years after being offered a cheap Tornado. It is tempting to try and save money this way. But what you could end up with is something (a submersible float tri) whose time has long gone. That said the Kelsell Typhoon was successful but had a far more minimalist main hull than the one under consideration here.

      http://monstersailing.blogspot.com/

      check http://www.boatdesign.net/forums/boat-design/nacra-5-8-based-trimaran-10076.html
     
  3. Richard Woods
    Joined: Jun 2006
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    An A class has an effective length of say 5m, hull width 200mm, depth 300mm

    So total disp is 5 x .3 x .2 max = .3T That doesn't sound a lot does it?? A 6.3m trimaran will probably weigh 400kgs min plus crew and gear say 200kgs min. So I think you'd need to look for at least 6ookgs disp on your outrigger.

    For a 6.3m mainhull I'd be very tempted by the Hobie 18

    On my Strike 18 trimaran I used 18sqm hulls but I cut them down to 4.8m (16ft) by cutting just in front of the mast beam. A lot of work even though they were solid glass hulls which are much easier to join than foam hulls.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    Thanks Richard

    This is exactly the specific detail I need to work out what to do. There may be a couple of different ways to fix this and your comments would be invaluable. The options seem to be as follows:

    • Throw away the A Class and find a Hobie 18 - not quite as simple as it sounds for all sorts of reasons
    • Fatten up the A Class hulls considerably with foam and glass over the lot - this sounds like a lot of work, but it is within my skills and budget and would have the merit of making them stronger, as well as giving as much extra displacement as needed
    • Glass the hulls and build new slots into them for hydrofoil blades - just like the Catri. Maybe I'm just silly, but I'd like your opinion whether this might be the best option of the lot.

    As mentioned earlier, I'm semi retired and time/labour is no problem - money is.

    Regards

    Alan
     
  5. aussiebushman
    Joined: Oct 2009
    Posts: 270
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    Location: Taralga NSW

    aussiebushman Innovator

    Forgot to mention that the existing A Class hulls are actually thin ply with a few internal timber stringers and some foam stiffeners. It looks as though the gelcoat was applied straight over the ply so there is virtually no strength in them. This the other reason why a glass/epoxy outer skin will be applied, so bulking up the shape with foam at the same time is no big deal

    Alan
     

  6. Richard Woods
    Joined: Jun 2006
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    Sorry I haven't read all the previous thread, but I have now. As you said starting a new one makes sense.

    Its getting boring, but again I agree with Catsketcher, get a Hobie 18. The A class hull (and rig to be honest) is probably the worst one to use. Imagine coming off a wave at speed, close to pitchpoling. There is a lot of load out there on your outrigger bows! You don't want to do a Team Phillips

    I think you'll find it quicker to start a new outrigger from scratch rather than try to add foam and glass, always a complicated thing - how do you then attach the beams (make new bhds, keep the same mountings on a wider heavier hull?) and how do you fair it into the bow? Never mind the hours fairing the glass overlaps you'll have.

    Sorry to be negative, especially after you've made a start.


    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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