Book on designing and building a Catamaran

Discussion in 'Multihulls' started by DaveJ, Jun 16, 2009.

  1. DaveJ
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    DaveJ Senior Member

    With all the amateur boat building that is going on and with the increase in technology in materials and processes and their availability to the amateur builder and plus I love sailing, it has inspired me to build my own boat about the 40-50ft in size. Being a tinkerer type, I would like to dabble in designing it myself.

    So I’m asking if there is a good book I can read that will tell/teach me the concepts of designing a Cat. At the moment I own a Hobie 18 and understand the tuning of the rig but unsure if this methodology is transferable over to a bigger Cat. The book I’m looking for would have all the relevant information on rig type and placement, hull shapes, bridge height and anything else I can’t think off or don’t know to ask about. It would also need to talk about building methods.

    I know there are plenty of boat building books around, but all the one’s I’ve seen are aim at monohulls and only talk a little about multies, but I’m looking for one that is totally directed at mulihulls, you know what they say, once you go multi, you never go back :) .

  2. Ad Hoc
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    Ad Hoc Naval Architect

    Well, it also depends what you mean by "design".

    Since you need to draw a general arrangement of 'basically' what you would like. Lay outs size outfit etc etc.

    Then you need to work out the weight via a weight estimate. Once you ahve all this very basic info, you then have to work out what the main structural loads will be based upon your very quick/rough sketch.

    Then you design the structure to withstand the loads calculated, based upon the layout.

    After you have done this and designed the structure to take the loads, is the weight of this structure greater than you estimated?

    Is the speed then what you expect, from the above (because the weight has now gone up), if not how can you change it to get the speed you want. It then becomes a spiral of ever decreasing circles, the design spiral. Viz:
    1) compromise
    2) Another iteration of the design spiral.

    However, if you want to just draw up a boat, all you need is a computer and/or paper....some people call that "design", when it is just draughting.

    There is a lot in between the two also...

    As for Books....see above, it depends upon your view of "design"...books on how to draw 3D lines, or books on structural design or books on hydrodynamics really depends how much you want to do and into how much detail.

    The final solution, is YOUR solution, books and gudiance help, but youmust make the decsions
  3. DaveJ
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    DaveJ Senior Member

    Thanks for the reply Ad Hoc, you are on the right lines about the infomation i need. Weight, size, shape, layout, fitout, etc . . . is what i'm looking to find. I have the software to draw up the design of the boat, so no problem there.

    I guess at the end of the day i don't want to design a boat, spend hundreds of thousands of dollars on materials building it to find out that it sails faster in reverse than it does forward. There are alot of great plans out there that i could go and buy, knowing that i'm going to end with a good product. But there are inovations i would like to pickout from some of these plans and put it into the boat i want.

    Does that help you more into the book or books i'm looking for. When its comes to electronics, i have no problem (I'm an Avionics Tech) but the actual design of a saling vechile is still a black art to me, some questions are should i run a fraction rig or go full rig, the placement of the mast in relation to the center boards which is based on the type sails and sail area which is also based on the hull shape, as you can see i have no idea and looking to find the answers to these questions out.

  4. Ad Hoc
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    Ad Hoc Naval Architect


    Well, this is where it becomes a bit of risk mitigation then.

    Since what you're after is a kind of "sailing design for dummies". The problem with these approach is actually no different to a full on "Hydrodynamics of Sailing" by Marchaj. Once you ahve crunched the numbers, what "experience" of the calculations do you have to tell you what you have calculated is:
    1) correct
    2) it will work

    You will ostensibly be no different than a 1st year student.

    So, if you feel that if the design, as done by you, fails somewhat, would it matter financially or emotionally?

    That's the risk I'm referring to.

    Since there are plenty of armchair designers out there with their fancy colour plots all ready to give advice etc, but have never actually designed a real boat before, especially for someone else and their money!

    So, if you feel confident that once you start and you ahve access to correct professional guidance, when/where you need it as well as once completed the design, getting and independent review, just in case, then it is worth going for. BUT, if you need it to work and first time and to a tight budget, best get a professional naval architect to design the basics for you, and leave the detailing to you. That way you can ask why, from the data given and learn that way, and supplement this by reviewing it against the theory/books at your own leisure. As well as say "oh this great innovation I found" lets use it...and the reply will be "yes ok" or "hmmm...wont work in this application" etc.

    There are so many pitfalls out there, if you can afford to throw away money if the project fails, then that's fine, otherwise, i would seriously think about the approach needed.

    Since a 40~50ft catamaran, in reality wont be cheap, which everway you look at it...unless you have money to burn!
  5. nero
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    nero Senior Member

    There is not one book for designing multi-hull boats ... that I have found.

    It can be inexpensive in money ... but costly in time. I am at 24,000 USD for materials, and travel, and 5 building seasons in costs at present. It will go up more but not over 30,000 USD. Then of course there is the motors, props, sails etc.

    The hardest part today is the engineering of the main cross beam structure. There are very little examples on the web. If you do not have a compound curve in the beam and are PC based you will find capable software. I can not find a Mac OSX software that will do it. May have to break down and pay someone for this. TouchCad (new marine design training movie) has been an excellent 3D modeler. It figures the weights and surface area at the same time. Scaling the shapes without loosing fairness is easy also.

    One of the advantages of sailing faster backwards is that you can quickly back up and get out of trouble. (humor)

    Last edited: Jun 17, 2009
  6. AndrewK
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    AndrewK Senior Member

    Dave, I don't think there is such a book, but a book by Chris White Cruising Multihulls I think is the title is a good starting point. Also check for books by Derek Harvey once again not sure of the title, could be Multihull Sailing. I found these at the Hervey Bay library.
    Have a look at John Schuttleworth's website as well as the local designers.

    Fortunately I only wanted to build my own boat and not design one. I drew what I wanted and had an idea of the boats parameters which I took to a local designer and he did the rest. Now that I am building I have been doing some reading and trying to understand composite structures and the more I learn the more I realize how complex it is, at least for me it is.

    I live on the North side of Brisbane, send me a PM with your contact details, you are welcome to come and have a look at what I am doing and discuss further.

  7. grob
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    I would second "Chris White Cruising Multihulls" and would add "International Sailor's Multihull Guide: To the Best Cruising Catamarans & Trimarans by Kevin Jeffrey and Jeffrey Nan" Loads of boats and layout diagrams.

    Also "Principles of Yacht Design by Lars Larsson and Rolf E. Eliasson" this is a monohull book but many of the prinicples are still applicable.

    I think a good start would be to trawl through the boats in the these books then do layout drawings of what you want.

    There is no shame in subcontracting out and getting the structural work done professionally even the best designers do this.

    Good Luck

  8. Tad
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    Tad Boat Designer

    While there are no books published on designing your own catamaran, there is a very good chapter on the subject in Sailing Yacht Design, Practice, edited by Claughton, Wellicome, and Shenoi. The piece is "Case Study for a Modern Charter Catamaran" by Alexander Simonis and concerns the design of the Moorings 4500. Mr. Simonis provides some solid data on compatible boats, hullform, weights, structure, appendages, layups, etc. It provides at least a starting point in the procedure of designing a 40'-50' cat.

    This article and Principals of Yacht Design will be a start. Just realize that due to the completely different loading and stability characteristics of multihulls, many assumptions in Principals will be incorrect.
  9. DaveJ
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    DaveJ Senior Member

    Thanks everyone, you have given me a good starting point. I'm like a kid in a candy store. I was always going to read Chris's book, as i've heard from many different sources that its a must read. So since there is no book on designing and building a multihull, there would be a niche out there. Well i'm gunna run off and read these books.

  10. Richard Woods
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    Richard Woods Woods Designs

    I know you're going to say "well he would say that" but please think very seriously before designing and building your own 50ft catamaran. I had been sailing for 20 years, spent 3 years at college studying yacht design, made two Atlantic crossings and worked for both Derek Kelsall and James Wharram before I felt confident to design and build my first catamaran.

    I assume you have designed and built other things. Like the house you live in. That is a pretty trivial design exercise really. After all it is only a rectangular box that doesn't move. It doesn't even have to float. And clearly it is really easy to build, especially in wood.

    A car is also easy, even the big car makers buy in engines, wheels etc. Maybe you've designed and built your own airplane. Again relatively easy for you have to have some one inspect your work before you can fly.

    With a boat you're on your own.

    Ever wondered why so few yacht designers actually sail their own boats?? Nigel Irens once told me he doesn't like to sail his own designs any more - they are too frightening. And I know what he means. People always doubt their own work don't they? Beating to windward in a rising gale with your family on board is not the time to have doubts about your design/building ability.

    If I was to design a 50ft cat I'd be looking at about 2000 hours to produce a full set of plans. You would take longer. Remember that a computer and CAD software is only a glorified pencil. There is no button on my keyboard that says "50ft cat press here"

    Then it would take say 20,000 hours to build. And about AUD200,000 in materials

    That is a lot of money and probably 10% of your life gone to waste if it doesn't work out.

    You say you own a Hobie 18. So here's an idea. Why not make a central hull and convert the Hobie into a 20ft trimaran?? You could do it in a winter for the cost of say 12 sheets of plywood. Then if it works out (and you liked designing and building it) try a bigger boat.

    But to answer your original question. You will find a lot on hull shapes, daggerboards, rigs etc on my website (on the Articles pages and also in the FAQ's). There aren't very many multihull design books around, and most of those are dated. The best general book on yacht design is indeed Rolf Eliasson's. He is a very successful yacht designer and the book is up to date.

    Have you considered enrolling in the Westlawn Yacht Design course??

    Sorry to be so negative, but it is for your own (and also for your family) good!

    Richard Woods of Woods Designs
  11. DaveJ
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    DaveJ Senior Member

    Don't worry Richard, i'm not delusional in any sence to not understand the mamoth task it is to design and build a world crusier. I'm not going to knock up a 40ft boat jump aboard and expect to sail the world in it without doing some research. Have you heard of the 6 P's Prior Preperation Prevents Piss Poor Performance, i'm in the prior stage.

    Reading these books will give me an idea on what is required in a Cat, and know what to look for when buying a plan, just because the designer says its good, doesn't mean it is. Not putting anyone down, but i have learnt not to believe things just on face value.

    I like your idea for my hobie, but i have other plans for it.

    I guess my ultimate goal is to build a 40ft cat from a set of plans, learn heaps from this experiance and with this experiance build the the 50-60ft world crusier i really want.
  12. yipster
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    yipster designer

  13. Autodafe
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    Autodafe Senior Member

    Hi Dave,

    I'm in a similar position, looking to design and build an ocean cruising cat without a a lot of boat design experience.

    I've been researching for a couple of years and the short answer to your question is there is no such book. If you're designing multihulls you're on your own.
    While Chris Whites book isn't specifically a design book, but I'll add my voice to all the others recommending it.

    Classification rules (eg Lloyds Special Service Craft, DNV, ABS, etc) usually have some guidelines for multihulls, and typically say that multihulls "hulls" should be designed to monohull scantlings for local loadings (hull plating thickness, chainplate loads etc. - I'd recommend Larsson&Eliasson "Principles of Yacht Design" for this, but lots of books cover this in similar style) but have little guidance for global strength and stiffness, which often need to be calculated from first principles.
    Scantling rules tend to be on the conservative side for multihulls, but the only alternative for the amateur designing is to get aboard designs similar to what you want, that have been built and proved with measuring tape and calipers, and then base your design on this.

    This leaves the challenge of deciding realistic global load cases for the cross deck structure. A. Edmunds "Designing Power and Sail" has a very brief coverage of this, which says in essence that the cross deck bending strength should be designed to the maximum lateral righting moment of the vessel. It does not discuss torsional stiffness (Richard Woods has something on this on his website I think), a very conservative approach is to design for a torque equal to 0.5 x maximum displacement x LWL, that is taking the case where the vessel is supported only by diagonally opposite corners, as might happen in quartering seas.

    Designing your own is a big job, but at the end of it you're going to have a much better understanding of boats and sailing in general, and your vessel in particular than the average sailor.
  14. Ad Hoc
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    Ad Hoc Naval Architect

    I design commercial vessels rather than luxury/sailing cars. But as a rough and ready quick first stab to establish global scantlings, the pitch connecting moment (torsion) is roughly 3 times the transverse bending moment.

  15. Spiv
    Joined: Jun 2007
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    Spiv Ancient Mariner

    I am 56, built my first sailing boat 40y ago.
    Owned and raced 5 beach cats, owned and worked with a 40' mono, 18' home built cat, 18' shark cat, 30' Mantacat, 40' power aly cat, 42' composite sailing charter cat. The last 2 I actually built (in boatyards and with paid help).

    I worked as a commercial diver for more than 25y. I spent most of my life working on water.

    I am also a land and quantity surveyor and can draw and design, did 2y of the Westlawns school before having to stop to raise a family.

    I read most of those books mentioned above and another dozen, searched all cat web sites and designs.

    I love cats and I understand more about them than most people and now I want to retire on a sailing cat and cruise for the next .....years.
    However, there is no way I would design the hull and try to engineer my next boat/ home. My savings and my life ultimately depend on it's seaworthiness.

    Take the advice of the experts above and at least get the hull designed by a professional, then you can design the accommodation yourself if you want.
    You will still have to consider distribution of weight etc, but you can get advice on that.

    I contracted Richard Woods to design my hull and I am totally satisfied with the result.

    One last thing, if you really want to build it yourself, you probably can, but before you do that go and work in a boatyard. Books are great, but experience is invaluable.

    Good luck, I know EXACTLY how you feel!
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