ply on frame

Discussion in 'Wooden Boat Building and Restoration' started by stubbymon, Oct 4, 2016.

  1. stubbymon
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    stubbymon Junior Member

    I am beginning research on a sailboat I would like to design snd build; 40 foot by 8 foot. I see frame designs with stringers and gussets. Sometimes the stringers are let into the frames flush and the frames flush with the ply. Other times they are fastened proud to the frames and the ply is hence attached only to the longitudinals. Is there some sort of flex in the second method that is superior? Should the stringers be bolted to the frames and not glued or screwed in . Also, why do gussets always have to be ply or metal? Wouldn't a piece of plank with the grain running along the diagonal , screwed and glued in, be stronger? I am not finding any answers in any of the usual texts, Glen-L is closest but the boats are too small. Has anyone written anything about modern day ply/frame/stringer construction. Seems everyone is wild about cold molding, but my design is best suited to ply panel and frame.Any thoughts?Thanks
     
  2. gonzo
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    gonzo Senior Member

    There are many methods that will provide equivalent results. The advantages of one over the other are not generic, but particular to a design and building technique. I think that you are overly general in your questions. Something you will hear a lot in the forum, is that a drawing is not a design. Try Gerr's book, it has a recipe type of approach that will save you a lot of calculations and engineering. The approach is conservative and not ultra-light, but generates good structural designs.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Designing a 40' yacht isn't an easy thing, even with Geer's book. Glen-L has some things to offer, such as the 36 series, which is a molded plywood design, as are the Yankee Star and StarPath. You can also find stock designs in this size, though hard chine, single skin plywood will be rare, simply because you need a fairly thick sheet to get sufficient hull strength, so multiple layers is a logical approuch. Given this, these layers are made much stronger/stiffer if bent over a round bilge hull form.

    Judging by your previous questions and your current post, I don't think you have the ability to "design" a 40' yacht. The next obvious question is "how many boats have you previously built?". The odds of completing a project of this scale, as one of your first attempts is shall we say, very, very low.

    To qualify my assumptions, if you have a reasonable grasp on basic engineering principles, you'd understand why some building types might "let" longitudinals into frames and why others might not. Moreover, you'd also have a grasp on the physical attributes of plywood (as a gusset for example) over solid wood. I'm not trying to be coy with you, just point out what seems pretty obvious to me. Can you learn the engineering and hydrodynamic fundamentals? Yeah, you sure can, but a 40' yacht right out of the gate - really? Maybe you should focus your initial effort, on the dinghy for the mother ship. You can employ the same building method and get a feel for how it works.
     
  4. stubbymon
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    stubbymon Junior Member

    I expected this sort of reply. " If you aren't a NA you can't design a boat". The fact is, I don't have to design a boat, only reduce the size of a boat already existing, which people have been doing for centuries. I am just looking for some input on construction details. I have been building successful boats for 40 years in the smaller sizes and working professionally building yachts up to 88 feet, both composite and wood. I had hoped I could get a simple answer to a simple question without going into a full biography of myself. Unfortunately I think too many people are discouraged by comments from experts that are not encouraging at all. In todays computer world, all questions can be answered satisfactorily, you just have to ask in the right place. I'll keep looking.
     
  5. PAR
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    PAR Yacht Designer/Builder

    No one said you have to be an NA, but you do have to have a reasonable grasp of the principles and concepts, plus the engineering background to pen up a safe/solid structure.

    Since you have some experence, you know what kind of project this is and possibly some of the issues it'll entail. You never mentioned downsizing an existing design, which is a different animal (you said you wanted to design and build, which is a big difference). 10% - 15% reductions are usually possible with yachts of this general size, but don't look for more than this or physics will come to play havoc with your reduction.

    Hey, I want to design and build a jet like a Cessna Citation CJ4, what do you think? Now, how would you answer this, if someone, without any background asked you? Both a 40' yacht and a CJ4 place humans, in what we engineers call and unnatural environment. If you fall from 35,000 feet or capsize and sink 50 miles off the coast, the outcome will be the same, hence the trepidation with folks wanting self designing these types of structures. I mean how hard could it be, right?
     
  6. Petros
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    Petros Senior Member


    That is a rather large project, doing both the design and the build will add a lot of time until you get it on the water. It might actually be faster, and save possible costly mistakes (so saving you lots of money) to have a design professional develop your ideas of what you want in to a quality boat. It will also add value to for resale to have a designer with a good reputation actually develop the plans for you. Or just stick with stock plans of popular designs, altering non-critical inteiror features to suite your needs.


    Each method has advantages, both can be made just as strong and light. Inlet stringers are a lot more work, with a lot of extra effort in the fitting of stringer to frame, but also can be used as water tight bulkheads. Depends on what your design objectives are. sometimes both methods are used on the same hull in different locations. This is where an experience designer can guild your choice.


    either method has been used, it depends on your design objectives. I have actually built small skin on frame kayaks and dingys that lash the stringers to the frames as well. It is light and actually stronger than fasteners, and will not corrode away. bolts are stronger but tend to concentrate the load transfer through fewer fasteners, with screwed joints you tend to use more screws, so it spreads the load over a larger area, screws are used where you might have more light frames, rather than a few heavy ones where you might use bolts, for example.

    fasteners that close to the end grain of sawn lumber tend to blow out, gussets also tend to distribute loads from different directions, so he plywood is stronger in that kind of application. If all the loads were in only one axis on a brace or gusset, than solid sawn lumber would be better, if you develop a good way to fasten the ends so you can transfer the loads and do not fail the end grain. A good wood design text book would teach you this kind of information, or if you allow a designer to work up all the many details (on a 40 ft wood boat!) than you do not have to worry about getting it all correct.

    you will need a whole library of costly technical books to know how to develop all of your details, and answer such specific questions. unless you just use an existing design about the size you want, and alter it to suite your needs.

    .
    You asked for our thoughts, so please do not be grumpy about what I am about to say. I am a licensed professional engineer that has worked in several industries (aerospace, automotive, etc), with 35+ years professional experiance, and have had my own engineering consulting firm for 25 years, an engineering degree from a big university, and have been licensed in two states. I have also designed and built perhaps 30 small boats (kayaks, dingys, canoes, sailboats) since I was 11 years old (and been around boats even longer), and have a whole library of marine engineering and Navel Architecture technical books, and I do not think I would want to design my own boat. Either I would find something that was professionally designed that is close, and alter it to suite my needs, or take my ideas to a design professional, and than only do the portions of the design that I know how to do. Otherwise the task is very large with lots of different design decisions to research and execute. That will take too long, not really save any money, and puts a lot of burden no me, and I already know most of the technical requirements for all the systems on a large sailboat. The time and investment, cost and frustration of building a boat that big means, at some point, I may want to sell it when I am done with it. Not likely I would get very much for it unless I have a well known and respected name as the NA or designer on it. In fact the value would be far more than what I would save in fees, let alone the savings in mistakes, wasted effort, and time.

    What I am saying is, I would not do it even though I have over 30 years small boat design and professional engineering experiance.

    Yes, you can design a boat, it is a lot of work to design a good boat, even if you have the knowledge and design experience. You sound like you have lots of excellent building experiance, so I suggest you do what you do best, make your design decisions and either find professional plans for something similar and incorporate your desires into it, or just bite the bullet and take your ideas and requirements to a reputable designer. It will save you money in the long run, and get you on the water faster, and safer than trying to do it all yourself.

    good luck.
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    Reducing the size of a boat is even more complicated than designing one, and it's not the best approach to get a good boat. None computer will design a boat, it's just a tool, like a saw or a planer, and you need the knowledge to use it efficiently.
    For designing a boat you need a certain amount of knowledge in different fields plus experience. And experience is acquired by training, so generally it's better to start with a small project.
    Last but not the least, designing yourself, while not being qualified, it's a big waste of precious time with big risk of failure on a very expensive in terms of money and time project.
    Any reasonable person weighting the pros and cons will arrive to the conclusion that it's not worth to be an amateur naval architect from scratch.
    Stock good plans are very cheap compared to the total price of a 40 feet boat. The best ones are precise, have all the details, and have a list of materials. That's worth hundreds of hours of work.
    Even customized plans are a small percentage of the total cost of a boat. If you find them expensive it's you have not idea of the final true cost.
    And most important you benefit of the experience and savoir-faire (the know how) of the naval architect.

    To answer to your first post, you have two ways to design a hull; longitudinal structure, or transversal structure.
    To oversimplify lets say that longitudinal structures as stringers are used with thin skins. So the bulkheads and ribs won't touch the skin which is too thin to withstand the local stresses induced by them.
    It's directly derived from the aviation techniques created during the 1930. You have also different schools of high ratio or low ratio stringers.
    The transversal structure will use thick skins supported by a few bulkheads.
    There are plenty of factors to take account, as habitability, insulation, humidity and finally weight and strength, general and local.
    That signifies that many structural calculations are needed, and various technical solutions will be considered depending of the materials you can obtain, their price and not the least the capacity and experience of the boatyard.
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    Petros, I do totally agree. I'm a retired naval engineer with experience with warships, fast patrol boats, fishing boats and racing multihulls.
    And if I want to build a "normal" boat I will call a NA for plans, as I know how many hours of work that represents, and I do not want to painfully do that has been already done by someone more qualified than me in his field. And I want to benefit from his experience.
     
  9. stubbymon
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    stubbymon Junior Member

    Thanks Ilan voyager and Petros. I have a lot more working for me than I have described. I just hate to impose on friends until I have checked other venues for info. I knew that what started out as a simple construction question would ultimately get NA's involved. People have been building boats without engineers for a long time. Often a new idea just has to walk out on a limb and do it. As far as being grumpy, well I have been doing things that people said I can't for a long time and I am still around. Also, I am the only one to benefit or suffer so I am not going to endanger anyone. Yes I do have lot of answers and confirmation is nice to hear once in a while, however rarely it happens. Sometimes the best way to get answers is to ruffle some feathers. Thanks for all your input.
     
  10. Ilan Voyager
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    Ilan Voyager Senior Member


    You're welcome. Now you know and your decision will be yours.
    A detail. Yes, lots of boats have been built without engineers by the method of trial and mistakes.
    When some fishermen or sailors were drowned because of some mistake, it was bad luck. Like the Vasa in Sweden. Note also that the naval carpenters who built the Vasa were mostly Dutch and expensively hired for the job as they had the formation and the experience.The King had not experience and listened to nobody, even his master carpenter and designer...
    I begun to learn naval carpentry end of the sixties in a traditional fishing boat shipyard at Camaret Britanny (after I switched to a very advanced shipyard in Sweden). No engineer. No NA. A master carpenter, a reputed one who built until 120 feet long fishing ships in classic wood.
    Simply my master carpenter have been building his fishing boats since 30 years, after learning during 5 years from a master carpenter who worked 20 years in the same kind of boats, and who himself learned carpentry after 5 years of apprenticeship with a master who has been making the same boats for 20 years.
    The three generations were "Compagnons du Devoir and Liberté", and that means they were educated, learned some basic maths, a lot of descriptive geometry and lofting, and had very solid notions of resistance of the materials they used, plus hundreds of technical tricks. A big data of empiricism.
    They passed the exams to be worker carpenter after the 5 years apprenticeship, and after 5 to 10 years of gaining experience in different yards they prepared their "chef d'oeuvre" - master opera- to be accepted as master carpenter in front of a jury of masters. After succeeding, the candidate was called master, had the right to wear the gold earring on the left ear, and only his very close friends, his mum and his wife would call him by his Christian name. For the others he was Master X.
    When you have such knowledge and experience you do not need a NE or NA to design and build a displacement wooden fishing boat for the Mer d'Iroise. All three had shipyards which made also beautiful classic wood sailboats on Naval Architects plans. As said once my master; for a fishing boat in the style of Camaret I need nobody but a yacht it's not the same thing.
     
  11. gonzo
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    gonzo Senior Member

    Boats built by shipwrights are usually of a type they are familiar with. Small changes are introduced through time as conditions or customers change. However, they don't stray too far from familiar techniques and shapes. Otherwise, they build to plans by a NA or engineer.
     

  12. Ilan Voyager
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    Ilan Voyager Senior Member

    Exactly. And they know the limits of their knowledge, so they do not adventure in terra incognita without a solid set of plans in hands.
    Mr Eugène Cornu, NA of very beautiful classic yachts in the forties and fifties used many times such boatyards but he designed the yachts to be built in the techniques that the carpenters knew already, or could learn easily always using the tooling they had already like the double planking.
    The keels were made traditionally with elm which could be found in very long pieces without defects. When the elm disappeared in Western Europe because of the dutch disease, all the yards in Brittany were in trouble at the beginning of the seventies. The master carpenters began to consult naval engineers and foreign carpenters to find replacement solutions.
    My old master called me. I designed and calculated a laminated keel and we worked on a a screwed and nailed lamination of iroko with a sealing of bisulfite rubber which could me made in a non heated shipyard with the existing tooling. Thirty five years later I must thank again the USDA which gave to me precious data and invaluable documentation.
    iroko wood was at this time rather common and dirt cheap but only found in ten feet planks. Now iroko is a luxury wood...
    The screwed nailed laminated keel in iroko was pretty successful, the longest one the shipyard made was 39 meters (128 feet) long for a "Mauritanian style" lobster fishing ship.
     
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