Small Boats built by cold molding

Discussion in 'Wooden Boat Building and Restoration' started by Fernao, Mar 19, 2013.

  1. Fernao
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    Fernao Junior Member

    Dear Forum:

    I want to eventually build my "retirement home with junk sails". However, I need to learn to build via cold molding.

    Does anyone know of anywhere where I can find plans of small boats. 3-5 meters (10-15 ft. +-)?
    I was thinking that I can build a small boat first by cold molding and then apply those skills to my "retirement home" of 12.5 meters.

    Please let me know.

    Many thanks!!!

    Fernao
     
  2. micah719
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    micah719 Plotting Dreamer

    Try googling "John Welsford", he has some lovely and well-proven boats; and unlike the equally legendary Ian Oughtred, he does not have a visceral aversion to the Junk rig. Welsford's boats seem to be designed more with lapstrake ply in mind, and Mr Oughtred literally wrote the book on the method.

    I was surprised to read the other day that the Spruce Goose, Howard Hughe's giant seaplane, was cold molded. The process I think was called Duramold or something similar, and was 80% stronger than aluminium. Nice choice of material, and rig...all the best and keep us posted!
     
  3. upchurchmr
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    upchurchmr Senior Member

    Talk to Corley about his 25' cold molded Trimaran from Crowther.
    That would give you 2 smaller hulls to practice on then the bigger center hull.
    And it would be fun to sail. No Junk rig though.

    Micah,

    Don't believe everything you read about cold molded wood being 80% stronger than aluminum. It is literally impossible, depending upon what kind of physical property you are talking about.

    If you are talking about buckling at very thin aluminum gages it might be possible. But you really need to be talking about strength/ weight to make an accurate comparison.

    There is a reason why the Spruce Goose never flew out of ground effect.
     
  4. gonzo
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    gonzo Senior Member

  5. PAR
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    PAR Yacht Designer/Builder

    Is there a reason you want to build using cold molded techniques? I ask because it's not one of the easiest methods and can be time consuming as well.

    As far as novice built cold molded designs, the pickings are slim, again because the method requires some pretty good fitting skills and an extensive jig, which many methods don't need. This said, most round bilge designs can be converted to molded construction pretty easily, so if you find a lapstrake (for example) you like, it could be converted to molded.
     
  6. messabout
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    messabout Senior Member

    Geougeon Brothers On Boat Construction; is a book that is a useful addition to any boat builders library. The book has a section that deals with cold molding at some length. ISBN 0-87812-166-8

    Cold molded boats can be beautiful structures inside and out. But the method is labor intensive and demands a degree of skill that not everyone has. Light and strong and clean; yes, easy; no. Also, it is not a cheap way to go. The veneers and adhesives you will use cost a plenty if you are to get high quality.
     
  7. DCockey
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    DCockey Senior Member

  8. micah719
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    micah719 Plotting Dreamer

    upchurchmr

    Yes, you're right in pointing that out....what I should have said was strength-to-weight.
     
  9. ancient kayaker
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    ancient kayaker aka Terry Haines

    Strength-to-weight of Alum Alloy (6061) is approx 5x that of wood, taking the average of cross-grain and with-grain strengths for the later.
     
  10. upchurchmr
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    upchurchmr Senior Member

    Strength is often not the critical property.
    Stiffness, section modulus (related to buckling), and bonding strength is often the critical feature.
    Minimum gage is also important. Why don't we see aluminum kayaks? Because reducing the thickness of the skin by 5x would result in .050 skins (compared to 1/4" wood - I'm assuming you are using cedar) which would dent when you set it down.
     
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    I'm imagining my 15 lb canoe built steel to the same weight, about 0.01!!! To flimsy to even carry, and don't sneeze whatever you do. That wouldn't stand the impact of a large fish (they seem rather clumsy around here, my kayak has been thumped several times) let alone a rock.

    Yes I use cedar, okoume ply, some oak and all the usual suspects - except glass. Ally is handy for making up odd bits, easier to get than SS, the rudder of one of my kayaks has Aluminum brackets to replace the ones that were missing on delivery: it was paddling time and I couldn't wait for replacements . . .
     

  12. Petros
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    Petros Senior Member

    You can not really compare the properties of the materials directly, but as an optimized structural design for each of the materials in the application. I once did an engineering comparison of various construction materials for a light homebuilt aircraft wing structure made from wood, aluminum, steel tube frame and fiberglass. Each one assumes that the design is optimized for the properties of each material (i.e an all wood wing structure would look very different than an aluminum alloy one and a fiberglass one). All were to the same load conditions, and external shape.

    when optimized the strength to weigh ratio was similar for aluminum and steel tube, wood with fabric had the lightest weight per square foot of wing area (to the same strength standard as the others). Wood has twice the stiffness per pound as fiberglass. That means to get a wing with the same stiffness, the all fiberglass one would weigh twice as much as the all wood one. So if stiffness is an important consideration wood was better.

    All of the materials had various advantages and disadvantages where there was no clear "winner", both boats and light aircraft have been built with all of these materials.

    Wood had by far the cost advantage, its strength per cost ratio was the best. Wood is usually more labor intensive, so overall cost was about the same as the others if you are paying for labor, but with a home built that is only a secondary consideration.

    It comes down to secondary considerations; your skills and personal preference (I do not care to work with fiberglass for example, and my welding skills are not very good either). I like working with wood so that was the only rationalization I needed. Wood will also have higher maintenance costs, which on a large boat is not an insignificant consideration.

    I have seen similar comparisons for a 40 ft yacht hull in wood, fiberglass and I think aluminum, all were very similar in finshed cost and weight, in this comparison wood was a cheaper to build by about 12 percent. All other properties were all pretty close together. I can not remember where I read it, so please do not ask me to site the source.

    The only time you will get much better strength to weight ratios is to go to more costly and exotic materials and much more costly construction methods.

    So wood is still a very viable construction method, particularly for the home builder. With some care in the detailing and finishing, and storage, the maintenance issue can also be minimized.
     
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