Non-foiling trimarans under 20'

Discussion in 'Multihulls' started by Tom Makes Things, Sep 25, 2019.

  1. upchurchmr
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    upchurchmr Senior Member

    Kleppar,

    I admit to being of a "highly critical nature", all my former co-workers knew that and realized they had to have their story straight when we needed to discuss a topic.
    I'm no longer sure that is "good" or "bad" anymore.
    But.

    I fundamentally want a day sailing trimaran version of a Tornado Catamaran.
    Meaning very light, high powered (the sailor taking care of safety by their actions), and reasonable cost (that's a debatable description, even in my mind).

    My bias for the performance means no plywood chines (the smoothly curved Tornado is an example), sufficiently sized centerboard or daggerboard, tall rig, and enough ama volume to keep the hull on top of the water (including the bow).
    I also don't want aka to ama connections to slam into "normal" waves slowing down the boat. Folding is desired (although this goes directly against minimum weight).

    Most offered boats do not have enough sail area/ tall enough rig.

    Strike 15 - a pretty good boat, aesthetically I wouldn't have a flat bowed multihull for any reason, but this could be fixed. Don't want a plywood main hull. The enclosed cockpit looks like a sandbox - not a fan. The larger ama's might work but I don't know what a "soft chine" means. The aka's would dig into waves when pressed hard.

    Kanka 14 - too small, all I've seen is an illustration. Too many of those end up being very far from the finished boat. I'm not a fan of "stealth" shaping when it doesn't mean anything. Have any been launched? The web site was last updated in 2018.

    Astus - You couldn't find one of those for sale for at least a 1000 miles from north texas, and the only report by a buyer was truely horrifying for the money that was paid - too many problems that the owner had to invent a way to fix.

    W17 - Someone here said it was a "cruiser". That was a pretty good summary to me. It may be a very good boat for many.

    One boat I probably would like is the Discovery 21. Except for the antiquated folding method (too much weight too high when on the trailer), and the cost (ridiculous). It also was not the subject of this thread at 21 feet.

    I have always looked for a self build boat. Since I am too nit picking for my own good, that is becoming less important.

    I'm going to stop commenting, probably I'm just disrupting the wa of this thread, and not helping the OP in any way.
     
  2. kleppar
    Joined: Jan 2016
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    kleppar Junior Member

    Thanks for comprehensive answer, but with your experience - why not design a boat yourself?
    I agree that Discovery 21 is a nice boat; however the folding system seems a bit scary. Also 21 ft. would be too long for my purpose (and outside the scope of this thread).
     
  3. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Kleppar,

    Thanks for the boost to my ego, but reading responses by some here who are actually experts gives me an understanding of what I don't know.
    My understanding of the history and developments in aero structures might allow me to make some useful suggestions for military aircraft (fighters actually, not cargo aircraft and certainly not commercial aircraft)
    To some extent in aero, I know what I don't know, but in boats I would be just guessing.
    My comments here mostly comes from basic engineering knowledge - of some use, but sadly lacking for good design.
    I have had the conceit that I could do it, but like most things, it would require several redesign/rebuild steps.

    I understand about the under 20 limit, my build limit would be 18' without renting a barn.
    The Discovery 21 folding does seem like you would be under a guillotine during the folding, doesn't it.
    I use to trailer a 10' wide Tornado, hiked up at 45 degrees to meet trailering laws here. One time a storm blew in while I was taking it home on the freeway - 70mph.
    The gust pushed on the tramp, pushed the trailer sideways until it was about 45 degrees to the car - coming up on a bridge abuttment.
    luckily the gust passed, the trailer straightened out, and I got to keep the boat.
    I don't want anything that high up in the air again.

    To be honest, not finding what I imagine I want, causes me to look at the W17 again and again. Even to the extent of redesigning some things out of the boat
    But I could probably do that with the old Cross 18 plans I have.
     
  4. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Multihull Structure Thoughts page 85 has more details but could be the base of a good tri. “Mosquito” is a 22 x 16 foot overall tri that was built in 7 months. The tri weighs 350 lbs without crew or stores. The 35 foot rotating carbon fibre mast (30 lbs comes off a Bimare Javelin 2 HT 18 foot cat) that carries a 215 square foot mainsail, 100 square foot foretriangle and a 215 square foot screacher. Main hull 22 foot long and 2 foot wide with rudder on main hull only. Daggerboards in the floats. Warning some of the numbers are approximate.
    Main hull is a partially tortured 3 panels of 4 mm ply with 11 x 25 mm wrc stringers, 2 stringers per hull side plus a keel batten. The 3 panels of 4 mm ply are shaped and angled at about 70 degrees bogged and glass taped before lightly torturing the side and centre bottom into shape. There are temporary 25 x 50 eternal gunnels strips to help form the shape of the main hull. The bulkheads are put in, bogged and glassed into position. The main hull has 25 x 25 mm gunnels. There are 4 mm ply crossarm bulkheads and half bulkheads for the bunk floor. The stringers are then slide in from aft into the length of the hull into slots precut into the bulkheads. Bows have a 10 degree half angle. Decks are 12 mm durakore (1.5 mm wrc skins on 9 mm end grain balsa) that is slightly curved over 4 mm ply deck beams around openings. Floats 4 mm tortured ply with 4 mm ply bulkheads. Ply panels wired together with sheets held at 20 degrees (angled apart at 140 degrees) and a 90 mm radius epoxy bog keel placed in before folding. The ply panels are folded to the gunnel line and bulkheads are epoxy bogged in. During the process hot wet towels were placed against the plywood to try and reduce the stress build up in the plywood.
     

    Attached Files:

  5. kleppar
    Joined: Jan 2016
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    kleppar Junior Member

    The designer informs me that W17 can and has been built of composite panels to save weight........If the will and financial capacity is available, a W17C can also be built using 6mm Corecell with carbon fiber skins, giving a much more interesting savings in weight."
     
  6. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Attached Files:

    Last edited: Sep 4, 2020
  7. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

    I like the sophisticated videos of TomKirkman1 with the Astus 16,5 because he put the cameras in order to show how work the hulls and the tri as a whole, instructive for such small trimarans, on flat water though. The smaller the tri, the most important the payload influence, the same tri could be "racing " with one adult and "recreational" with 2 adults or a family payload, the ama could > 100 % Displacement for the first case and < 100% for the second one.
     
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  8. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    I was in France last year and dropped by Astus and spoke with Jean-Hubert - lovely guy.

    We took the Astus 16.5 out for a sail in light winds and it was a real slug. The sliding mechanism was absolutely rock solid but the fittings on the boat seemed somehow a bit cheap.

    It was only the basic recreational version as well - it felt like it really needed the Sport model larger sail area.

    Tom knows his stuff and thrashes it and his report is very off putting - I'm also not convinced about the beams sitting on the top of the floats - we get a lot of heavy chop here in the Solent in the UK and they look like they will slow the boat significantly.

    Size wise this would be ideal for me but doesn't feel right to spend circa £25k.

    I like the added dihedral on the beams of the Weta with the vertical beams connecting the floats to the main beams - seems the Astus would also benefit from this as an idea.

    I've just made a new larger float for my isofrankenmaran test bed - it is approx 460 litres and weighs 24kg compared to the previous 250 litres which weighs 21kg.

    I just need to lash up a trampoline (I'm using the tramp frames from my kayakmaran on the other side) so I can just plop it in the water.

    Overall, I'm really conflicted about how to progress at the moment. I'm clearing out a load of my work shortly so I will actually have to to build and sail - not had time for either really for the last few years - just some occasional trips out on on my F16 with my wife - great fun but I'm struggling to trapeze now due to years of damage.

    I've got Sting 600 #2 plans and think that really could be a winner and I'm also speaking to Len about possibly buying Sting #1 to save me some time in the build - I can then update it with several things to make it how I want it over time but get out sailing which is most important.

    It is pretty weighty - if I build I will certainly lighten it up.

    However, my alternative is to see how this new float performs then get on with replacing the ISO hull, making the beams but use my F16 mast and rig on the machine which should really shift - loads of power and will come in well under 200kg. That combined with significantly more power from the F16 rig would certainly make for an Astus 16.5 beater for a fraction of the cost.

    Only problem there is that I am interested in the idea of having both a non-foiling and a foiling option as per Sting....

    Anyway, here is an image of the isofrankenmaran with the old black float and the new float just lashed on:

    [​IMG]

    A total bodge but simply using it to get a feel of the volumes and shapes.

    When were test sailing it a couple of years ago as a proa with only the one black float, this thing just flew along.

    The Weta like vertical beam helped keep the beams above the water - they were in fact a bit too tall and kept the mast almost vertical so it remained totally powered up.

    We broke the beams in half landing after taking over a wave in some heavy winds. However, it proved the concept but I've simply not had time to revisit until the last couple of weekends. It was never meant to be sailed hard - just for testing close in but it had lasted well and I decided to thrash and got caught in a bad squall.

    I've made stronger beams now - same 70mm x 2mm but with 5mm flat bar riveted along the bottom. Will last for some more testing anyway.

    Making the main hull narrower than this ISO hull and then doing the same folding approach as the Sting seems like a good way to go for me.

    The vertical beam on the right is I think a bit too long and will probably need reducing but we'll once I've sorted the additional angled support bars from the front beams out the inner edge of the floats. I couldn't get the front beams any further forward due the internal metal mast support frame in the ISO so the front is a bit sloppy without some small support bars.

    Sorry for the ramble - rather conflicted as I said, but looking to finally having time to progress whatever I decide to finally do!
     
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  9. Cholsson
    Joined: Aug 2015
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    Cholsson Junior Member

    About Weta and Astus performance, Tom is really pushing his Astus, and I would love to compare the performance against that on.
    We have some Wetas and Hobies in my local water, but they never dare to show up at our Club races! It would be very intresting for me, to see if they where slower or faster in different wind directions and wind speeds.
    Heres from my sailing last week, before the start of the race. After the start, the wind died ,and nothing fun to show. I came among the last boats (keelboats) in handicap...
    BUT I tried to push it a bit anyway
     
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  10. kleppar
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    kleppar Junior Member

    I have looked at Sting 600 - too heavy, too big, and probably too high tech for my purpose. From what I have read so far I have narrowed down my candidates to the production Astus 16.5 (I can buy a slightly used sport version for USD 18500) and W17. Both these boats can carry several passengers, are reasonably fast and are quite comfortable. W17 with its flat bottom is probably better for beach launching and retrieving.
     
  11. Doug Halsey
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    Doug Halsey Senior Member

    The OP hasn't visited this site since last October, so I wouldn't be concerned about their requirements. Let's hear more about yours.
     
  12. kleppar
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    Location: Stavanger, Norway

    kleppar Junior Member

  13. Zilver
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    Zilver Junior Member

  14. Doug Halsey
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    Doug Halsey Senior Member


  15. kleppar
    Joined: Jan 2016
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    kleppar Junior Member

    Russel, I have been in contact with the builder, and it is also possible to make a longer version.
     
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