My Design - Trifoglio 25' - Suggestions & Opinions

Discussion in 'Sailboats' started by DVV, Nov 20, 2020.

  1. ExileMoon
    Joined: Oct 2009
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    Location: Shanghai

    ExileMoon Junior Member

    Very good, especially the line shape of the ship's side in the side view, you are correct, usually the stern is higher than the bow. In addition, the bow is usually narrower than the stern.
    For internal water ships, the width of the bow is relatively large, and for ocean ships, the width of the bow is relatively small, especially near the waterline, which is basically close to a sharp corner.

    As you can see from the elevation view, your siding is close to a perfectly straight line. This is the norm in modern shipbuilding, because it is easier to manufacture and the cross-sections are the same.
    But if it is bent a little, the strength can be greatly improved (actually, the rigidity is increased, and then the strength of the thin plate is not easily collapsed under pressure).

    The widest part of the hull is about 2/5~1/3 near the stern.

    chinese hull.png

    RHINO has a curvature check tool, you can use it to check the curvature of a curve or surface. An ideal shell plate bending can be considered as follows:
    It maintains a stable curvature in the middle (like a circular arc, the curvature does not change), while the curvature at both ends gradually decreases and transitions to a straight line. This is because the end of the plate cannot produce curvature during manufacturing.
     
    Last edited: May 31, 2021
  2. DVV
    Joined: Nov 2020
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    Location: Italy

    DVV Junior Member

    This helps me a lot in understanding junk design.
    It seems to me that if you want a deeper hull you just decrease the dimension of the flat area on the bottom of the hull, as I've seen in the Amoy Fisher/Trader.
    Junks decks are very high at stern and bow. This seem to me a way to increase the distance between the heavy bottom of the vessel, and the buoyant part (bow and stern). So, in case the boat gets knocked flat, it should have enough leverage to go back to the right position. The fact that the stern may be hollowed out seems to confirm this view.
    Is this interpretation correct in your opinion?

    DVV
     
  3. ExileMoon
    Joined: Oct 2009
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    ExileMoon Junior Member

    In ancient ships, the bow and stern were generally taller, and it was not unique with Chinese junk. The main reason is probably to improve seaworthiness and avoid splashing waves on the deck.
    泉州深沪杨良盾先生所作泉州湾后诸宋船结构展示模型.jpg
    An ancient ocean-going JUNK model, 1200 AD, recovered from archaeological excavations. Please note that its sails are made of bamboo mats, not cloth.

    Some boats, as you said, are built with towering bows and sterns in order to make the boats resistant to overturning. However, the prerequisite for this design is that these parts must be completely sealed.
    IMG_8531-Marc-Dupavillon1-e1416837324987.jpg

    But the traditional JUNK does not have this kind of sealing.
    If it is a flat inner water boat, this slight height is not enough to reverse the flip. On a sea-going vessel with a larger aspect ratio (and also a larger size), there is usually no large roll. I don’t think the ancients would have this kind of consciousness: a ship can return to right after it rolls over 90 degrees, although it is possible to achieve this effect.
    744e48d8a63b4d4091ae3b097606097b_th.jpg
    This is the simulation version of the previous 1200AD model. The sail does not respect history.

    After entering modern times, the characteristics of these ancient ships with high bow and stern gradually weakened, and the hull gradually became flat. It is more obvious on large ships.

    Ning Po Museum.jpg
    This large junk named NingPo (1753~1930) hull is similar to an enlarged version of “green eyebrows”.
     
    Last edited: Jun 2, 2021
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  4. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Does that model of the ancient junk sport Lazy Jacks? Very cool.

    -Will
     
  5. DVV
    Joined: Nov 2020
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    Location: Italy

    DVV Junior Member

    I modified my design to meet your suggestions.
    I dont want to make it too difficult to build.
    Sides are now shaped. The widest point 2/5 to stern (I guess).
    To make it easier to build in plywood, I was thinking about making bow and stern less rounded: increase the heigh of the bottom slowly, and then make a sharp corner to a flat surface. This way I wont need to use many layers of thin ply to make the corner. I think I've seen something like that on Junks and Sampans of the Jung Tze.
    Do you think it could work?

    Schermata 2021-06-06 alle 22.12.08.png
     
  6. ExileMoon
    Joined: Oct 2009
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    ExileMoon Junior Member

    I noticed that your boat is 25 feet, so according to your current design, its bottom width will be close to 2m, which seems to have some disadvantages for the size of the plywood. Maybe you should tilt the side to make the bottom plate narrower to fit the width of the plywood.

    Of course, you can also consider installing the plywood horizontally, and use its length to build the width of the bottom plate.
     

  7. DVV
    Joined: Nov 2020
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    Location: Italy

    DVV Junior Member

    Not this design.
    The 'big' one is too expensive to build for me right now. So I switched to a smaller boat, to use in lakes.
    I did buy the construction plan for Jim Mickalik Piccup Pram, but I would prefer to build something designed by me, and this seems to me a good occasion to experiment with a full flat bottom. This design is 3.8 meters long and 1 meter wide.
     
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