W17 Trimaran?

Discussion in 'Boat Design' started by upchurchmr, Jan 15, 2017.

  1. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    I am interested in building a small Trimaran.
    17' max length, because my garage is only 19 x 19.

    The W17 is one of the few home building tris I have seen that interests me.

    The SOR:
    17' max (+ a few inches)
    Day sailing - no cabin.
    1-2 persons
    Wide beam. Some foldup variation.
    Relatively large sail area. (I have a classic Tornado rig and a Hobie 16 rig)
    Greater than 100% ama volume - to fly the main hull.
    Most likely strip planked with glass. Possibly plywood, but I don't really like flat surfaces.
    No lifting foils - at least to start.

    The website: http://smalltridesign.com/W17/greybox/W17-Trimaran.html
    Obligatory picture:
    [​IMG]

    Is there another forum more likely to discuss this boat or other optional ones?
    Any building blogs? Besides on the W-17 website.


    FYI, others I have considered:
    Cross 18 (I have plans)
    Searunner 16, 18 (too heavy, I'd prefer not plywood, I don't like the folding mechanism)
    Smoot - various sizes. I'd prefer more sail carrying ability.
    Kurt Hughes - amazingly expensive plans
    Woods Strike 16 - I'd prefer not plywood, it has a smaller sail area IMHO.

    Now that I've shown you how picky I am, I'd appreciate any suggestions you have. :D
     
  2. Corley
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    Corley epoxy coated

    I think you have covered the bases pretty well, there are no other small trimarans I can think of that fit your stated brief better than the W17.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    W17

    It appears that from what the designers says that the boat is not designed to fly the main hull-unless I missed something.
    If you want to fly the main hull using ama buoyancy alone you probably want an ama with total buoyancy around 200% or more-otherwise the immersed shape of the ama may be real draggy. Also, it would be beneficial to know the angle of heel of the boat when the main hull is just clear-there is wide variation in trimarans from about 10 degrees to over 26 degrees. There is a thread in multihulls that looks at this for various trimarans.......*
    A warning: from 100% on up especially when flying the main hull, the chance of a capsize/pitchpole goes way up and the extra buoyancy guarantees the boat will invert.

    * http://www.boatdesign.net/forums/multihulls/trimarans-angle-heel-main-hull-takeoff-39553.html
     
  4. upchurchmr
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    upchurchmr Senior Member

    Not the suggestion I wanted.

    The W17 is essentially a modified Cross 18 with a more primitive Piver ama (triangle with the tip cut off. The main hull is also more primitive than a Cross18 being a simple rectangular section. The rocker is much less in a more modern style.
     
  5. upchurchmr
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    upchurchmr Senior Member

    Doug,

    That is why I specified ama greater than 100% buoyancy.
    The picture I showed is the boat at its practical limit. The designer stated that the rear ama was unfaired so that when it caught a lot of water you would know when to back off the power. As you can see the main hull is not out of the water.

    So what is the magic of 200% vs 150%?
     
  6. Corley
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    Corley epoxy coated

    Is the designer of the W17 willing to draw a larger float for you? He seems like a good sort so I'm sure he could help there. 200% gives more beam clearance when loaded. Kurt Hughes also has done some float designs for dragonfly trimarans like the 800 to get the volume up and give them better performance. I don't think Kurt's plans are that expensive for what you get have you considered his 16' model you could easily extend it a bit to meet your requirements and CM build method so not flat ply, $480 US doesn't seem too bad? He is happy to run some mods through on his stock plans to make them better fit your needs at a moderate cost as well.

    http://www.multihulldesigns.com/designs_stock/daysail/16_tri.htm

    Non foiling racing trimarans gradually evolved towards 300% floats but they are pretty bulky and you pay a weight penalty for that extra volume which means greater global loads and more sail area to keep things powered up. A friend of mine Andrew is having a 40' Shuttleworth trimaran built in the Phillipines with 300% floats and due to some clever design and chamfering by the design office they don't look too bad only betraying their bulk in the top view. Target weight in racing trim is 2.4 tonne with some cruising amenity and space onboard it seems positively palatial in there compared to an F40 trimaran.

    http://trimaranproject.blogspot.com.au/2016/08/new-shuttleworth-40-racercruiser.html
     
  7. upchurchmr
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    upchurchmr Senior Member

    I had an email conversation with the designer and he was not interested in alternatives.
    He was responsive to my questions which I appreciated.

    It would be easy enough to come up with an alternative ama for strip planking with a larger volume, I would just like both ama and main hull to be similar.

    Thanks for the info about your friends boat but 4.2 tonne is really out of range for me.

    Something more similar to your Kraken is what I need. But shorter.
     
  8. Vantage475T
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    Vantage475T Vantage475T

    Not really ny other oprions

    When I was looking around for something max 4.75m I didn't find any other options.
    I want something for 1-2 light bodies but storage is a real problem locally with few options.
    The Weta was too small and expensive for me
    The Richard Woods Zeta again a bit small but liked it
    The Strike 15 not so keen on the shape really
    The Strike 16 as for 15 - not so keen on the shape

    and couldn't really find anything else.

    I contacted Richard and I actually got the Zest and 15 plans and he was very helpful in some back and forth but I decided they were not really suitable.

    I am now using my ISO dinghy as a test bed for a skiff trimaran at 4.75m long and looking forward to moving that forward (thread elsehwere in mutlihulls).

    There really is very little in this arena - the W17 would have been my choice otherwise but I can't park it easily where I am with that little bit of extra length.

    What is the weight of the standard W17 - can't seem to find any info on that?
     
  9. Corley
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    Corley epoxy coated

    175kg according to the specs page:

    http://smalltridesign.com/W17/study-profile.html
     
  10. Vantage475T
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    Vantage475T Vantage475T

    Thanks I missed that but I've also found now it in my original notes as 185kg.

    I am a complete tool.

    Weight wise we thought that was looking like more than we could easily get in and out of the water.

    Although we are both strong we are both light and we've struggled moving other heavier boats around easily on the land. A factor that would def put my wife off and make it less likely to use it a lot.

    Currently the ISO is about 100kg hull - not sure of all up weight. Taking the 20kg float off makes it fine, with one float on as much we want to shift I think.

    I am just lashing up a prototype hub powered electric dolly contraption that we can use to drag the boat around hopefully.

    The plan is to be able to use it for the boat and also use it for wheelbarrows in the garden when my neck/backhands aren't working.

    May well be a pile of ***** but is worth a morning welding up some scrap steel tube.
     
  11. upchurchmr
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    upchurchmr Senior Member

    Bump, just hoping someone sees this and has a suggestion.
     
  12. Stumble
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    Stumble Senior Member

    If moving the weight around is an issue then don't hamper the design, just get better beach wheels. A four wheel set of CatTrax would make a 175kg boat trivial to move.
     
  13. upchurchmr
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    upchurchmr Senior Member

    No the issue is having a design to my SOR - primarily not using plywood instead of strip planked.
    Or at least having a design that has a nice smoothly curved shape.

    I fully expect to use a trailer to launch.
     
  14. W17 designer
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    W17 designer Senior Member

    Greetings to all small tri enthusiasts:
    Being just too busy with other projects and priorities, I sadly missed this posting back in January 2017.

    As the above is a good example of someone totally missing the mark on what the W17 is all about, it justifies clarification. For 70 years now, I have played around with hard chine designs and initially did what most other designers did … used them as a way to simplify construction, but basically attempting to simulate a round-bilge form. However, in my later years, I came to appreciate that a far more efficient use can be made of hard chines if we forget that approach and instead, use them in a manner that can actually improve efficiency, rather than compromise it. The W17 represents my latest thinking on this and the boat has been so successful in demonstrating the improvements, that following an independent and enthusiastic review of the boats performance in WoodenBoat Magazine (#254), Professional Boatbuilder encouraged me to write a Design Brief on the more technical reasons behind the simple hull shapes. This was recently published (Oct/Nov 2017) and as it’s not read by all readers, I can now see there is a need to make a copy available, something I will do via my website once the issue is archived (Dec).
    From this, the reader should be able to better appreciate the subtle differences with the now outdated designs of Piver and Cross that ‘upchurchmr’ refers to. Far from being ‘more primitive’, the new shapes offer significant advantages in many areas and the PBB article covers this. But meanwhile, let me say this.

    By copying round bilge design with multichines, one is adding complexity that is often not justified and the result will never be as good as the rounded original. Chines will also typically follow buttock lines and curve up at the ends. However, with the ‘back-to-basics’ approach that the PBB article describes, one can achieve both a lower wave-making resistance as well as significantly reduced leeway, with the latter generally being enough to offset the added frictional resistance (compared to rounded sections) when sailing to windward. Also, the deep, boxy shape of the main hull is an excellent way to carry displacement well down below the critical surface interface and I predict you’ll see more craft taking advantage of such improvements in the future. Far from being ‘primitive’, some are already even considering this a new break-through design. As always, time will tell.

    Also, while writing … I saw it mentioned elsewhere that I had been approached to consider increasing the ama volume in order to fly a hull. While it’s reported that I was not supportive of the idea for this boat, my reason was not given, so here it is. “Any increase in ama volume directly affects the required strength of the aka or cross beam and as this folding boat has a mid-beam hinge and latch, this would result in major re-design for that area, which is just not justified”. If built to minimum design weight, the boat can just about lift off the center hull when only one person is on the boat … but not with two. It was designed at this limit for safety reasons. best, mike.
     

  15. upchurchmr
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    upchurchmr Senior Member

    Thanks for your comment.

    But, its really interesting that "By copying round bilge design with multichines, one is adding complexity that is often not justified and the result will never be as good as the rounded original."

    So multichine is not as good as round. I had a conversation with you previously and stated the same thing. Interesting that you defended the square section chine hull, when your "proposed" bigger boat was round bilged.
    How then can single chine (square) be better than round bilge. Please note that I mean performance as related to "better". There are lots of other criteria that might be appropriate.
    How come the larger boat uses round bilge and is not the "improved shape" - the square section?

    There certainly are other boats using square section like Richard Woods small trimarans, and the small Seaclipper boats.

    Looking forward to your reasons why the square section is "better". I would have been interested in your discussion 3 years ago when I asked. I would remind you that I asked if you would revise the lines to a round hull for me.

    Come now - total redesign required for flying the main hull with 2? Like most things (improvements?) it is just an incremental increase in the loads.
    A Cross 18 has been reported to fly the main hull just fine, its a lot more simple than the W17 design. The limited beam means this might not really provide much performance improvement. What would the critical feature on the W17 be? The hinge bolts, or bearing of the bolts on the hinge plate, or hinge plate to wood ama, or the wood?

    I actually would not suggest the Cross 18 is better than the W17. Individual boats - especially homebuilt- vary so much in construction and equipment I don't really know how you could ever make a meaningful comparison on the water.
    Not to talk about the differences in how boats are sailed depending up on the owner. There is a recent youtube about a Cross 18 in the Texas 200, where the main is always reefed when clearly not overloaded by windspeed - everyone has their preferences.

    Looking forward to your article.
     
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