Small trimarans under 20'

Discussion in 'Multihulls' started by Doug Lord, Jun 24, 2012.

  1. tour
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    tour Junior Member

    As you all can see she needs a more wave pearsing vaka bow and also a little deflector. The next hull will be higher/taller maybe 300mm
     
  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Looks like virtually a production boat. Very well done.
    What would you do about the wet boat issue. That seems to be the nature of the boat, same as a Hobie 18.

    Sorry, I just saw your last post.

    Marc
     
  3. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    20' tri

    ======================
    Would you build tooling for the ama in addition to the main hull? Do you think you would use carbon cross arms and mast?
    Good luck!
     
  4. rcnesneg
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    rcnesneg Senior Member

    Very well done! If it weren't for the Hobie mainsail I would say it's some obscure trimaran nobody has heard of that they didn't make very many of! Do you have any video footage? How does she do in rougher conditions?
     
  5. tour
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    tour Junior Member

    Thank you for the positive remarks.
    Doug with "tooling" i assume you mean. Are we going to mould out our own ama hulls? And the answer is yes.
    This had been our first prototype and the results had been great. The plan is not for a racer but rather a fast, stable, fun and safe daysailor and camping style weekender. At the moment we are using Hobie 18 parts to keep the costs down.
    This one had been built for my personal use but after testing and using her this last month we thought that it might actually be worth a shot building a few therefore my questions regarding international conditions and needs.

    Carbonfibre? Maybe but not necessarily.We loaded her with 400 kgs of weight and she was still very fast. So using carbon would make her very expensive to build with not enough return, maybe a glass and carbon mix?

    Rougher conditions? The area where we use her gets very windy. Regularly up to 35 knots in summer. In 15 - 20 knots you can still use full main and jib. after that full the jib or reef the main, we have 2 reefing points in the main. Beating into chop she is very wet. The next one will be dryer and should weight in at 350 to 370 kgs all in.
    We do get serious tidal and wind generated lagoon chop +- 1 meter high with short intervals. She punches through very well but wet....
    I had sailed her in a downwind run with 2 x reefs and noo jib in 45 knots of wind and she felt very stable and safe. bad judgement call on my behalf but it gave me great confidence in this vessel. i would not want to beat into those conditions though...
    Crossbeams? We will probably be making them out of glass/carbon mix and make her trailerable. Have a friend at North Sails that will come for a sail soon to give input and mast and sail options soon....
    No videos thus far as its been testing only.
    regards Rudi
     
  6. rcnesneg
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    rcnesneg Senior Member

    You should do some video footage! I can't wait to see. Sounds like a tough seaworthy boat!
     
  7. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Thanks for the response, Rudi-best of luck!
     
  8. 3 in One
    Joined: Jan 2016
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    Location: Cape Town South Africa

    3 in One Junior Member

    After I saw all the excitement about the new Astus 16.5 and thought I should share a few images of our little project.
    It is a prototype 4,6m family oriented Trimaran that was designed and constructed by a friend that is yacht builder in Cape Town South Africa.
    We have been sailing it for a year and have made small detail adjustments to the design. During the last winter we decided to experiment with longer ama's as a result the existing ones (we have a spare set of the original design) were cut in two and 900mm was added to the length of the ama's at the deepest part of the pontoons.
    We sailed it in strong and light wind and it is brilliant, after a few more tests we will tweak the design and make them in Carbon to get back to the original design weight.
    The hull is a vacuum bagged honeycomb glass fibre construction.
    The main hull, beams and ama's weighed in at 138kg before we decided to lengthen the ama's, added here and there etc. we have not bothered to re-weigh it but it is obviously heavier.
    The mast is a rotating carbon section (designed for this boat) with rope rigging. We recently added a system to adjust the shrouds primarily to control the fore-stay tension. A by product of this exercise was that we can now also adjust the angle of the mast sideways for sailing upwind if we feel the need.
    The beams are carbon with very thin GRP fairings on the front, to reduce wind and water drag.
    The jib, fully battened main and asymmetrical spinnaker were made by North sails for this boat, the jib and spinnaker are on roller reefers. We don't have a boom.
    Because the wind conditions where we sail is extremely variable and mostly very strong in the summer months and gale-force in the winter. We opted for a safe sail plan (excluding the spinnaker it is a little less than a Hobie 14) until we have sorted out the hulls detail design.
    We often sailed it at 14 Knots with two people on it with the shorter Ama's but found that the lee pontoon would become submerged in big gusts, It can now do the same speed with the longer ama's without submerging the lee ama, the longer ama's radically improved the boats longitudinal motion through chop, strong wind, on a beat, it now slices through it.
    It is by far the easiest boat that I have ever sailed in any conditions, compared to the 505's I raced in my younger days this boat is an absolute pleasure.
    You can sail it with novices take a cool box for a picnic or go wild in wind when everybody is heading for the shore.
    I often sail it single handed, because it is a small boat it responds very to having less weight on it- I have sail it with the asymmetrical in the same wind conditions we would sail two up and it is stable, fast and fun.
     

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  9. Doug Lord
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    Doug Lord Flight Ready

    Outstanding! Can you post some more pictures? With the longer ama will she fly the main hull? Have you considered foil assist?
    What is the overall beam? Have you got a name for the boat?
     
  10. Gary Baigent
    Joined: Jul 2005
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    Gary Baigent Senior Member

    FF's sake Doug, why do you always bleat on about flying main hull and then the inevitable foil assist BS. You can see this is a small and basic trimaran with carefully thought out and practical small boat solutions.
    KISS, remember that clever man's quote?
     
  11. 3 in One
    Joined: Jan 2016
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    Location: Cape Town South Africa

    3 in One Junior Member

    The beam is 3.8m
    It is a small "family" boat with a built in righting moment. It is Not a racer.
    The substantial righting moment immediately comes into play the minute it starts to lean over, the crew does not have to jump around to avoid a capsize, as a result it is a very stable platform that does not heel over much and as a result is much faster, definitely dryer up to the point (where all small boats will be wet) and it is easier to sail than a similar size family type monohull dinghy.
    Small boats must deal with the same sea state that big boats must deal with when the wind increases, with the disadvantage that they don't have the hull length to span the waves.
    The result is that a boat of this length unfortunately pitch a lot to get over or through short waves when they get to deck height, with smart helming you can pick a path through some of it but eventually it will get out of phase and there is no other option but to slam into the waves, loose speed and fall over due to the increase in lateral forces when the momentum is lost.
    If you want to fly the main hull the ama must not only provide the righting moment it must also "float" the entire weight of the boat. To do that it must have a lot more buoyancy in the pontoons than a cat of the same size.
    More buoyancy leads to more drag, more weight but the sum will still not work because in chop you want less of all of that Because it is still a short boat.
    The buoyancy in the bow section of the main hull was calculated to resist any tendency to nose dive on a reach with the bag, it's never been submerged, the bow's bottom entry point is generally just above the water. It is a reverse bow.
    That combined with the additional buoyancy of the lee ama (that is on a separate path to the main hull through the waves) there is a significant damping effect in the pitch moment because in choppy water the ama will rarely encounter the same wave on exactly the same line or wave angle as the main hull.
    If you remove the main hull because it is flying all the pitch forces will have to be dealt with by the ama.
    We chose to share the loads with the main hull carrying most of it as a result the boat beats very well into the wind with a "nice" motion for a short boat, because it is not loosing all its momentum because of violent pitching the sails does not stall and it drives the boat through the waves when it cannot go over it. As expected if you slam into a wave some of it will spray over the boat, if you don't like that don't go sailing.
    We have considered adding foils to the spare set of ama's if the longer ama's did not work as expected and try it just for fun but realize that it will introduce a whole lot of other challenges that we don't think will benefit a family boat.
    At the moment we are very happy with the result of the longer ama's because it is adding buoyancy over the full spectrum of conditions not just in ideal wind and wave conditions.
    I have come to the conclusion that a family boat of this size is the most fun for everyone in wind of about 6-10 knots of wind in flat water, before the waves pick up, we have recorded very similar speeds to what we did in much stronger wind. In stronger wind it looses momentum through the waves and it is much wetter.
    In any event most families head for the shore and shelter if the wind picks up a lot.
    No we don't have a name for the boat.
     
  12. 3 in One
    Joined: Jan 2016
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    3 in One Junior Member

    Herewith a few photos of the boat with the smaller ama's than what we are currently using.
     

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  13. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Thanks. You have a very good looking boat. Foils aren't about just speed-they can help a boat handle rough water better. And from a marketing perspective could help sell a boat these days. But whether the added cost is worth it in your target market is a real question.
    I'm wondering what you think the advantages of your boat are over something like the Astus 16? You've obviously spent a lot of time developing the boat.
    I wish you good luck!
     
  14. Cholsson
    Joined: Aug 2015
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    Cholsson Junior Member

    Your 3 in One boat looks sooo cool. Please shoot some movie when you sail! It looks faster and more slim than the Weta 14.4. Like the revers bow. Want! :)

    br
    Chris
    www.chryz10.com
     

  15. BrianPearson
    Joined: Dec 2010
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    Location: GB

    BrianPearson Junior Member

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