want to build small sailing tri. need help please

Discussion in 'Multihulls' started by tour, Feb 24, 2013.

  1. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

  2. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member


    I see the scarab as a different boat for different intents. I don't want or need a cabin, and don't mind wet and wild since the boat would only be used for daysailing near shore. Think beach cat not weekender.
  3. oldsailor7
    Joined: May 2008
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    Location: Sydney Australia

    oldsailor7 Senior Member

    Why try and re-invent the wheel.
    There are plenty of good and available plans of Tris which meet your requirements and only involve simple carpentry.
    Buy the plans . Buy the wood and epoxy and get cracking.
    Stick to the design,and don't think you know better than the designer and start making changes. You will be surprised how well it will turn out. :D
    1 person likes this.
  4. 2far2drive
    Joined: Nov 2011
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    Location: Houston, TX

    2far2drive Senior Member

    I dont support this argument. Sure, the Scarab may look a little more "production" and less boxy (I personally think the strike looks awesome), but here are some basic numbers I run on everything these days. I wrote my own Texel Ratings/Bruce Number calculator in Python. While these numbers do not indicate everything, they give me a base idea of the performance aspects of each design. Here are the outputs as follows.

    Scarab 18:
    weight = 345kg
    length = 5.51m
    sail area (main + jib) = 22.8m2
    Texel Rating = 147.3668970370803
    Bruce Number = 1.7162610380799437
    sail area (main + spin) = 31.5m2
    Texel Rating = 129.49400303545696
    Bruce Number = 2.017303289951323

    Strike 18:
    weight = 250kg
    length = 5.5m
    sail area (main + jib) = 19.1m2
    Texel Rating = 142.49331726935216
    Bruce Number = 1.7488757895374496
    Sail area (main + spin) = 28.5m2
    Texel Rating = 121.41431666467759
    Bruce Number = 2.1363121576380975

    The numbers for the Strike 18 indicate it using the Quatro16 rig. These numbers were based off of the study plan numbers and the screecher Richard uses on his own boat. Richard used a cut down Tornado mast with a totaly height of either 25.5 or 26ft IIRC. I bought a nacra 5.2 (with a smaller mast) for my boat and my mast height is 28.1ft (hobie 18?) so with the Strike, you can increase your SA a little but you may be reefing sooner than other boats.

    I like Team Scarab's boats a lot. But their numbers just dont show what I like to see, especially for all the effort of foam sandwich with moulded grp akas.
  5. tour
    Joined: Feb 2013
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    Location: rsa

    tour Junior Member

    hei guys.
    thanks for all of the positive info so far. it has been a rattle of the head or a shake up of what i want...
    flying the vaka had never been my intention but a fast comfortable and easy seaworthy small tri had been. frank smoot's way of building, e.g building and shaping hull and then strengthening with bulkheads after had seemed like the most basic and easy way of doing things. i had sailed a dhow in mozambique before and that is basicly an old dead hollowed out tree with a bedsheet for sails.so anything can sail. how well is a different story...

    therefore this thread was started to get a rough idea on shape and form for speed and practicality. obviously if i decide to build without a well known plan i would like to get it as good as possible.

    with all of the info given i have started re thinking my original plan and what i want to do with this tri. as there are many photos of homemade tris built from old beachcats and keelboats with amas and even pvc piping. they all seem to sail but maybe not the fastest or most prettyist either but the owners are getting loads of fun out of them.

    so now i am torn between getting a plan or frankensteining a cool homemade tri. the latter option still tickles my fancy alot. so say i decide to follow this route how do i shape my vaka and amas to not screw it up completely???

    at this moment i am thinking of frank's method of building, he has a good practical idea for someone like me.
    1 so from a sideview of the hull, i gather, it will require a pretty curved bottom? (looking at most of the plans out there) will the curve sit in the middle? or more forward (1st quarter or only the first 1/3) and taper up to the stern???
    2 flat bottomed is the easiest but for slightly rougher waters bays or coves and not open ocean would a chined small tapered V be important?

    i can understand that designing a tri is not as simple as a few pointers. but if all info gathered here can produce a good idea i might give it a shot. if not then it'll have to be a detailed plan from one of the designers.so lets just see what pointers can be shared here for a +- 5 meter fairly thin vaka with a cross 18 or strike 16 seating arrangement
    for a fastish tri.

    all replies welcome as i am sure there might be more people out there with similar dreams.
  6. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

    Dont !
    Plans are cheap as. Maybe after building a boat or two try your own, but first up ?
    I wouldn't.
  7. CutOnce

    CutOnce Previous Member

    Red's right. I learned more about keeping things light and avoiding overbuilding by working as a helper to a professional than I ever would have trying on my own. The whole point of boat building is getting the strongest possible boat at the lightest weight. Building heavy can actually make things weaker, because more structure is needed to support more weight.

    There are lessons taught by pros that will make the difference between success and failure in your build. Resin mixing, measuring and accuracy was one lesson I have learned from watching a pro. It does make a serious difference if you forget or add that last pump of hardener. It does matter if your mixing container is contaminated.

    Good plans from a designer who writes for first time builders will realistically make the difference between a failure and a success. Frank Smoot's "simple" foam forming exercise and glassing was done after he had built several boats. He had hundreds of hours accumulated experience glassing, fairing and sanding before he produced his great looking 24'er.

    Fairing and sanding alone is the single longest stage of the build. There is real technique in applying fairing compound. It can't be learned on the go without help or reference material and instruction.

    You may have a local community college that offers a "build a canoe" class. If so, take it. Buy Canoecraft (the book). Buy the Gougeon Brother's book. Do the homework necessary to give you the ability to succeed.

    Build a Puddle Duck Racer. Really, build one and I'm certain the net time to build your tri will be lower than just starting to build your tri on the same date. You can give the PDR away to a kid, relative or local Scout troop. Given the technique you will learn and the efficiencies you gain by the experience your tri build will be net cheaper than if you don't build a PDR.

    If you are like most of us, you will ignore all this advice and do things your way. And then you get to write this post yourself in four years time. The circle of life. Sigh.

  8. Jetboy
    Joined: Feb 2012
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    Location: USA

    Jetboy Senior Member

    I can surely agree with CutOnce.

    I have plans and building my first boat has been a LOT more difficult than I had envisioned. The $150 for plans was well worth it.
  9. AnthonyW
    Joined: Oct 2012
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    Location: Cape Town, South Africa

    AnthonyW Senior Member

    I am busy building a home made tri down in South Africa. Using the 18ft Windrush from Selway Fisher (modified - pics of it on their site) as a main hull, and outriggers from a local 13.5ft cat called a Nomad. The build has been remarkably easy, and looking at Frank's tri and the Osprey from Solway-Dory, the cross beams should be easy to assemble from aluminium masts or marine grade aluminium piping. I spent a lot of time looking at plans for existing trimarans, including the Cross 18, the W17, Strike etc, but I really wanted a cat ketch rig and something simple, and looking at the Osprey from Solway Dory (not Selway Fisher) and its simplicity, I thought I would give it (a homemade tri, not the Osprey - too expensive to import to SA) a crack. Turns out that with a table saw and expoxy and cable ties it is pretty simple to build a hull, even for someone who is by profession a lawyer and who had never done woodwork before. Sure it might not work with the catamaran outriggers that well, but with a couple of hours on Hulls you can design your own, and I am doing just that to build once the borrowed outriggers have been tested. So I wouldn't be too shy of giving something new a go if you have the attitude of it being a learning experience. I have managed to put the hull together, fillet and glass with relatively little time and effort, and am already planning a bigger hull - something close to the Waterman canoe, stretched, with raised sides. Quite a few Selway Fisher canoes have been made into tris, and with decent bouyancy in place and a partly covered deck I am sure they would cope well in a bit of chop. Paul Fisher does modifications to his plans - maybe drop him an email. He can take a day or two to respond, but if you are serious he will do modifications to an existing boat for a very reasonable fee, and he gives good advice if you are suggesting something that is unlikely to work.

    What I can say is that I wouldn't mess with an existing design without chatting to the designer. Either go exotic and DIY as I have and have fun, or go with something that has already been designed. In the latter case the design probably accommodates things you haven't thought of, and probably doesn't need 'fixing'.

    I also bought the small trimaran book from the Small Trimaran's website. Some very interesting homemade tri's on that site, well worth looking at, all kinds of things there from mono's converted to trimarans, to very small tri's. The book covers interviews with a number of small trimaran manufacturers/designers, and is very interesting reading. Its USD 11 for an electronic version. Worth a read.
    Last edited: Feb 27, 2013
  10. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    buy a kit for a stitch-and-glue or a strip built kayak (plans are included). It will give you good building experince, the boat is small enough and the kit cheap enough that it will likely get finished fairly quickly and you will have something to get you out on the water.

    Once you built it and have some fun in it, than buy an old hobie 14 and use the amas and the sail to turn the sea kayak into a small tri. Best study some plans on other small tries to see how they attach the beams to the center hull.

    And while you are building your kayak hull from a kit, keep your eyes open for a used small tri. likely before you are done you can find a nice fixer tri for cheap. The kayak kit just gave you something to keep you out of trouble while waiting for a good deal on a small tri to come along.

    Things always change as you go along, just get started on something and see where it leads you. That has been my experience. Better to get started on something than to spend months, or even years, thinking about it.

  11. 2far2drive
    Joined: Nov 2011
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    Location: Houston, TX

    2far2drive Senior Member

    I cannot agree more with the above mentioned advice to buy plans. Even if you succeed, and you might, it will be a long hard road with many failures and setbacks. Sometimes those things motivate people, to me I want to build a nice looking boat that sails well. Can I design a boat thats sails fast and decent? i think so. will it look good? hell no.

    If you build a contraption that sails decent but looks terrible, I guess as long as you are happy then what does it matter. I like to have some pride in the things I build and I know for a fact that I wouldnt want to be sailing something made out of pvc pipe and tubes and what have you. Your mileage may vary.

    I had zero boat building experience and my buddy graciously brought me under his wing to rebuild his Crowther Buccaneer 28 trimaran I convinced him to buy. He has spent several weeks in Maine in boat building school so he has a strong methodology and understands the work.

    The next thing I know, Im interpretting plans, drawn 35 years ago by a designer who passed away many years ago as well, meaning NO SUPPORT. We reverse engineered what we didnt understand and went for it. Check the Buccaneer 28 thread on here, thats my handy work once my buddy trained me and turned me loose. I built that ama almost single-handed, and I had never even touched a japanese pull saw prior to this experience. The best thing was, I built a great bit by hand with block planes and smoothing planes and the pull saw. One of the greatest things I learned was to organize my workspace and build a plan of how to work for the day. Plans taught me that. If you start on your own thing, you will waste sooooo much time doing the things out of order just because your mind is wrapped around a design you have, with zero prior building experience and you will be waiting for epoxy to cure, parts to arrive and what have you.

    Seriously, build a PDR. It will set you back $300 and teach you what you need to know.

    The Gougeon book is now free to download from their site, its literally the bible on this stuff. There are a few others but read as much as you can and I cannot stress enough, build something with plans first.
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