Joining Plywood

Discussion in 'Boat Design' started by cangrejero, Jan 10, 2016.

  1. cangrejero
    Joined: Jan 2016
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    Location: Puerto Rico

    cangrejero New Member

    Before someone kills me, please understand that I have never built a boat. The closest I've been to building one was riding the boat. I'm 66 years old and I'm going to build a boat. Don't care if it floats or not.

    The boat I will build will follow the plans found here. I know a little about working with wood and am able to understand how to cut the plywood, etc. I have two concerns, though. First, I don't know if it's a good idea to build a boat with 1/4in plywood. Second, since I'll have to join the bottom and sides with a batten, etc, I'd like to know how thick the plywood can be for me to be able to bend it and still meet my goal. I would like to use something thicker than 1/4in plywood.

    Apologize if I'm in the wrong forum and will appreciate any help. Thanks!

    PS: Boat will be used in lakes and calm waters only; no open or rough seas.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You should follow the instructions in the plans. If you don't trust the plans, find some you do. Why do you want to use thicker plywood? 1/4" is usually adequate for a 12' boat.
     
  3. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    SimplePlywoodBoat

    My first attempt at a small boat in 1/4 inch plywood, with fiberglass/epoxy covering the exterior of the hull. This simple boat is 10 ft - 8 inches long, and the 1/4 inch plywood is OK, I would not recommend anything heavier.

    I was however concerned about stepping inside the hull, or droping something heavy on the bottom of the boat, so I made a floor assembly of ordinary wood lath that fits inside the hull.

    A simple and rewarding project for an amature builder in wood. Not to difficult, and very similar to what you are planning.
     

    Attached Files:

  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    You've never built a boat, but are second guessing the plans already? I'm not particularly fond of the plans you intend to build from, but they're within norms, for a boat of this size and configuration. The Hannu plans clearly state he's not responsible for the end result. In other words, if you build to these plans, he's not suggesting it'll be very good or even float right side up. Judging by it's scantling and general shape, I'll bet it'll float right side up, though I don't think much more of a designer that can't stand behind his work.

    You might want to set your goals a bit higher than this and lastly, be careful what you wish for . . .
     
  5. WhiteDwarf
    Joined: Jun 2011
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    Location: Sydney

    WhiteDwarf White Dwarf

    The OP doesn't give much detail of the prospective boat or its use. It would be best to ascertain more details, propulsion, location of use etc, before drilling to far into the question.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You clicked on the "here" in the OP ?
     
  7. WhiteDwarf
    Joined: Jun 2011
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    Location: Sydney

    WhiteDwarf White Dwarf

    Embarrassed

    Thanks Mr. Efficiency
     
  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I missed it the first time too. :D It is not the most attractive looking little boat either !
     
  9. cangrejero
    Joined: Jan 2016
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    Location: Puerto Rico

    cangrejero New Member

    Joinning Plywood

    Thanks to all of you who responded.:p
     
  10. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    We still did not tell you about the usual methods for joining plywood butts.

    The more elegant method is called scarphing, or scarpfing if you prefer that spelling. The ends of the ply where the joint is to be made is tapered for a distance of about eight to ten times the thickness, from full thickness down to a feather edge. Do this on both the pieces to be joined and match the tapers, glue the mated parts together. Caution! This is a tedious job that demands precision and great care in the matching and gluing process. I do not recommend that method for beginners. Explore the internet and you can find detailed instructions for doing it this way.

    The other method, which is more practical, especially for an inexperienced builder, is the simple butt block method. Butt the ends together and glue a narrow strip of ply over the butt joints. About a four inch wide butt block will be OK for a boat of this kind. You can probably find details of this method if you explore the internet. This is the easy way to do it and it is a reliable method if you do it with some care. Stagger the butt joints so that the bottom butt will be at the opposite end of the boat from the butt joints that make the sides.

    About the boat itself.........I join the other assessments that this is not a great design. It will, however, serve the purpose and should give you satisfactory service. The boat is a displacement type which means that it will not plane and so it will be slow. It will row well enough unless you intend to go long distances. If you put a motor on it, two horsepower is enough. You might also use an electric trolling motor with good result.

    Do not be misled by assuming that a computer drawn and detailed boat is somehow the best. Computers do what the operator tells it to do and no more. The old adage still applies.......GIGO

    Welcome to the forum. We will do our best to help if help is needed. Meanwhile do not be insulted if we nit pick your selection of boat plans.

    Here's wishing you the best of luck with your build. Go make some sawdust.
     
  11. cangrejero
    Joined: Jan 2016
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    cangrejero New Member

    Appreciate your concern about the "nit picking". The best lessons I've had where those that ended with a kick in the but. The best to you and the others that cared to answer and, if the boat sinks, I'll post a picture. Thanks a buch!
     
  12. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    If you build the proposed design (I'm with PAR, it's not all that great) 6mm ply is plenty strong enough. However the floor needs 4 or 5 long battens around 16-20mm thick and approx 40-50m wide so that it supports your weight (feet) properly. This will make it pretty durable and is well worth the extra trouble.
     
  13. cangrejero
    Joined: Jan 2016
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    Location: Puerto Rico

    cangrejero New Member

    I'm with PAR, too. So far, you guys are giving me what I wished for. Take care!
     
  14. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    Butt Joints

    The simple butt block method recommended by messabout is fine for your build, and plenty strong enough. The bottom should have its butt joint forward, and the sides should have their butt joints aft, located where curvature is minimized.

    One potential issue with the butt block vs. the scarfed joint is where the block has to be cut down where it crosses a chine or sheer longitudinal wood members. In this case just use a router to cut away the butt block where it would interfere with the longitudinal wood members.

    For this type of construction I have added a layer of fiberglass cloth to the assembly, as shown in the attached picture, which also shows the butt block cut away where the chine piece will be located.
     

    Attached Files:


  15. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Welcome Cangrejero.

    The appeal of Hannu’s Boatyard for me is the simplicity of the boats and the clarity of the building instructions. It is helpful to read about the other designs on his website (the smaller Portugese dinghy for example) which will fill out more detail on building methods and thinking.

    The simpler boats seem to be very quick to build, and easily achievable for beginners like myself, with very limited time available. The setting out patterns for cutting the parts from a minimum number of sheets of ply are also very helpful.

    For me, starting with a build that I am confident I can complete without running out of time/energy/motivation is high on the list of priorities, and most of Hannus designs offer that.

    However, I would be building mostly for the satisfaction of building a boat that I can enjoy pottering about in safe and sheltered conditions, as you mention. If I were looking for something more seaworthy, high performance, or higher standard of finish, I would be looking at more sophisticated plans, by other designers as already mentioned several times.

    For me the downside here is that I do not have the time available to be confident of completing a very complex design or highly skilled build before running out of energy/motivation, and so I would need to look to a professional build, if I could afford it.

    I would add to the comments on the ply thickness, and your first post that my instinct when making stuff always tends to be to overstructure, but when using a small boat, I want it to be lighter:

    My first boat a 16ft, 650kg (ballasted) trailer sailer, I am selling.

    My second boat, a cobbled together 18ft pedal catamaran is a great, but at some 140kg, is too heavy for two people to easily manoeuvre on the beach without a trolley.

    My third boat, a 16ft sailing trimaran, is the boat I use most, and at 100kg rigged, empty can be carried by two people.

    My fourth boat is likely to be a rebuild of my pedal catamaran, and I will be disappointed if I cannot reduce the previous weight by at least half.

    I’m learning to beware of too much weight and would echo the advice to follow the designers plans!

    I have used the butt joint with a lapping piece as described by others several times in quick, simple (rough and ready!) boat builds. It is very easy, and perfectly strong enough for the job (preferably not in a sharply curved area) though not the most elegant of joints.

    Just my tuppenth worth.
     
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