My Design - Trifoglio 25' - Suggestions & Opinions

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

  1. ExileMoon
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    ExileMoon Junior Member

    Perhaps you can consider a three-plate construction. The bottom of the boat uses one flat plate instead of a shallow V bottom where two plates are welded.
    36-donna-construction-01-large.jpg 36-donna-construction-02-large.jpg

    You can cut off the tip and tail of this boat to make it flat. This way the length can be shorter without losing hydraulic performance.
     
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  2. ExileMoon
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    ExileMoon Junior Member

    three-plate 10m sailboat.png

    I tried to draw a quick sketch, its structure is very simple.
     
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  3. DVV
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    DVV Junior Member

    I like it.
    I actually have a flat bottom version on the design. The reason for which I preferred a V bottom is due to the supposed pounding of scow bows in a chop.

    I could try a flat bottom aft, and some v at bow level.

    Anyway, I love the design you proposed. Did you build it yourself? Is the keel made of lead? How dod you realize it?
     
  4. ExileMoon
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    ExileMoon Junior Member

    I just drew a rough sketch. There are still many steps to take to turn it into a practical drawing.

    As an example:
    If you plan to use plywood to build this boat, then you have to consider that the general size of plywood is 2440x1220mm, so if we plan to use the width of a board to form the boat's side, obviously, the width of the side board shown in the current drawings has exceeded this the scale is up. Then we need to adjust the plan so that the board width meets the specifications of the plywood.

    Give another example:
    The boat uses three plates to form the main part of the hull. If it is made of plywood, because the thickness of the board is very large, so that the ship board has enough thickness, then the rigidity can be satisfied. But if you try to use steel plates, because the thickness of the material is too thin, a large area of the flat plate will cause the plane stiffness to be too weak, which is obviously not a good choice. The aluminum plate is somewhere in between.

    Regarding the question of the keel, this one I painted is just a very ordinary choice. However, if it is a three-board boat, my preferred choice is to use a retractable center plate instead of a fixed fin keel. Because the three-board boat is a flat-bottomed boat, it has the ability to navigate in shallow waters and sit on the beach.
     
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  5. DVV
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    DVV Junior Member

    The plan is to build the boat in plywood and epoxy (stitch & glue).
    Unfortunately the dimension you are referring is standard in US, but where I live - Italy - there are also different formats. No one of them is large enough for a one sheet bottom, though, so the advantage of a flat bottom is less.

    I dont like centerboards, I very much prefer leeboards: easier to build and less obtruding in the cabin (and I love the idea that they can be shaped as asymmetrical foils).
    But, where I came from, and where I sail, the problem of shallow draft is non existing, so the reason behind internal ballast is mainly that is easier to build.

    DV
     
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  6. ExileMoon
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    ExileMoon Junior Member

    you are right. This specification of 2440x1220mm is an imperial specification, in fact it is 8X4 feet. There are also 9500x1420mm specifications in China. Unfortunately, this specification is difficult to buy and there is no marine grade.

    In small boats of no more than 8m, the width of each board can be controlled below 1.2m with the three-board hull, provided that the width of the hull is not too wide, such as 2.2m (this width allows you to put the boat into In the container). Even 2.88m is fine, but it takes 5 boards.
    2800-2200.png

    The biggest problem with the lift-type centerboard is that it takes up valuable cabin space, especially on small boats. The fixed fin keel I drew is a method that American yachts are used to. This method can get a lot of cabin space, but it also leads to a deep draft.

    But if some kind of fin board is not used at all, the crosswind sailing performance of the boat will be limited.

    I feel great about your idea of using Leeboard. Leeboard combines the dual advantages of large-capacity cabin space and shallow draft. And there is no need to punch holes in the bottom of the ship, so the structure is simpler and more reliable.
     
    Last edited: May 24, 2021
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  7. ExileMoon
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    ExileMoon Junior Member

    IMG_1216.JPG
    American style leeboard. This is a 20-foot flat bottom sailboat used in the inner waters, side wall is upright and the draft is very shallow.

    50023951_2222331414701899_3707927498080649216_o.jpg
    A simple open boat equipped with Junk rig.


    The sidewalls of flat-bottomed sailboats used in the ocean usually have a large camber,The draft of the hull is relatively large. Although it has a flat bottom, it exhibits performance similar to that of a deep V hull.
     
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  8. DVV
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    DVV Junior Member

    The first sharpie looks like a Jim Michalik AF series.
    The second boat - which I like a lot - is simple and nice, and I like the rig setting.

    I love very very much Chinese Junks. I collected all the info that I could and some great books on them, thanks to the Junk Rig Association, but technical info and plans of old junks are still unknown to the west, due to the lack of source. I see you are in Shangai, is it possible, from where you are to access to more complete info about those magnificent vessels?
     
  9. ExileMoon
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    ExileMoon Junior Member

    It is a pity that although China still estimated that there were at least 20,000 JUNKs at sea in the 1960s, they were gradually replaced by motor boats in the 1970s and 1980s. Today, there are no pure JUNKs in China's waters. Yes, there are no traditional sailing boats, and even sails are rarely seen on the sea. China has now become a desert of sailing.

    Although some people have tried to restore the past, this effort still has little effect.
     
  10. ExileMoon
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    ExileMoon Junior Member

    I read your previous post and it feels like you want a flat-headed Chinese hull. For example, like this:
    太湖五桅帆船.jpg

    江苏沿海五桅沙船模型.jpg
    Traditional Chinese sailboats can be roughly divided into two types. One type is flat-headed and flat-bottomed. This type of ship mainly sails in internal waters and shallow sea. There is another type with sharp bottoms, but their bows are usually cut into flat heads. This type of ship basically appears in coastal areas.

    Of course this is not absolute. When the flat-bottomed boats are large enough (that is, when the draft is deep enough), their performance at sea is no different from that of sharp-bottomed boats. The largest Chinese sailboat (about 60m long) recorded in the photo is also flat-bottomed. You can also know from reality that all modern ships over 1,000 tons are flat-bottomed ships, and there is no problem that sharp-bottomed ships are more suitable for sea navigation than flat-bottomed ships (actually, the seaworthiness is determined by the depth of the draft).

    Another problem is that I saw that the flat-top boat you painted earlier is somewhat different from the real Chinese small flat-top flat-bottom boat. These boats actually have a very large forward inclination angle(>45) where they meet the surface of the water.
    平头船船艏.png
    Some boats may be more upright, but these boats are usually slow, or their flat head is relatively narrow (actually sharper) , or although it looks wide on the deck, but it is narrow at the waterline.

    太湖帆船.jpg
    This photo is of Lake Taihu sailing boats. These boats have low freeboards and shallow drafts, making them unsuitable for going to sea. Pay attention to the motor boat at the forefront. The hulls of these sailing boats are the same as this motor boat.
     
    Last edited: May 26, 2021
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  11. DVV
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    DVV Junior Member

    Thank you for the info, this helps me to clarify some things.

    The truth is that my main objective was to design a boat to build for me: I wanted it to be:
    - scow bowed, as I think this shape has more pro than cons;
    - very easy and cheap to build, as I want to be able to build it for real;

    I tried to push the design a bit towards the Junk/Sampan shape, but that was too difficult for my skills (this is my first design). It is difficult to design something so different from what you've always seen and sailed, so I ended up with a more ore less traditional 'western' hull with a scow bow.

    But, as you suggest, I am really interested in flat bottomed - flat headed junk boats (but also to other type of junks). You know, the structure of these vessels is totally different from what can be found in wester hulls: for example the strength is given by the heavy sides, and not by a strong keel as in western boat. They appear to be unballasted, so I guess all the righting moment, even when knocked down, comes from the high stern and bow.

    The low freeboard square headed internal water boat in the picture is exactly what I would like to try as my next design. A small boat to use in inland waters, I will use it as a benchmark.

    You appear to have quite a good knowledge about junks, could you suggest me something to read to help me improve my skill?

    DV
     
  12. ExileMoon
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    ExileMoon Junior Member

    Flat-head flat-bottomed internal water sailboats do not require ballast. The sides are usually straight and the hull appears relatively flat. This causes their roll righting torque to be similar to that of a catamaran: a small inclination angle can provide a large initial angle. Stabilize the torque. In this case, even if ballast is installed on the bottom of the bilge, it is of little use. Another reason is that the wind in the internal water is relatively small, so there is no need to worry about the ship being blown over.

    If you intend to use this type of ship at sea, you should deepen the hull draft and increase the freeboard height, and increase the ballast. Traditionally, ballast is usually rocks on the bottom of the ship (fixed with some cement-like glue). Chinese sailing boats do not place ballast outside the hull (such as fin keel), but there are temporary ballasts to deal with storms: some cages filled with rocks are lowered from the side with ropes, which can increase the resistance to storms. ability. We must realize that this is just a way to deal with storms, not as a structure of a boat.
    Cargo ships usually fix heavy cargo in the silo to achieve ballast without reducing the cargo load.

    Some wooden fishing boats in modern China still use the ancient ballast method, but the improvement is to pour concrete into the bottom of the boat. A large number of steel fishing boats do the same. This ballast method is very cheap, only a few tenths of the price of lead ballast, and does not require heating. In addition, the strength of the bottom of the ship is greatly enhanced by pouring concrete. The cost is only a few centimeters higher than the lead and the cabin height will be lowered by a few centimeters. These are completely acceptable.
    Because of the flat and wide bottom of these boats, only a thin ballast thickness is required to obtain a sufficiently large ballast weight.

    In terms of books, I don't have anything to recommend. There are very few books in this area. Many foreign books are about sail rig, but very little about hulls. They collected a lot of information about the shape of the JUNK, but it didn't help us much. I think the real objects and drawings can provide more help.
    src=http___img6.baixing.net_5708bb1e1af14cd5c81a71a32436b25f.jpg_xl&refer=http___img6.baixing.jpg
    A traditional flat-head flat-bottomed inner water hull is like this. This ship is about 5 meters long, you can zoom in and out proportionally. The boat is made of galvanized steel, but the line type is the same as the traditional wooden boat.

    It may be a little bit difficult to make this shape with plywood. Because plywood is more difficult to make bow and stern bottom bends, unless you use very thin plywood to finish it in multiple layers.

    There is a sealed cabin at the bow and stern, which can ensure that the boat will not sink even if it capsizes. Traditional wooden boats also look like they are on the outside, but they are not hermetically sealed. This change may be made in the 1970s when a large number of ferro-cement boats appeared in China. In order to ensure safety, sealed cabins were made. Then this design was continued.

    1368409008_707289368.jpg
    The way they are floating on the water. You can notice that this is a boat with outboard engines. Oh, there are almost no sailboats in China now.
    20210526230421.png
    This boat is actually very close in shape, that is, the place where the bow and the bottom of the boat meet need to be rounded.

    Chinese style narrow boat.png
    A few years ago, I designed a narrow boat with a Chinese hull that could be used to navigate the narrow British canals. This is just a sketch, but it is a more accurate representation of the shape of the hull, with only a slight change: the bow is more upright on the waterline, which is a change to shorten the length of the hull.
    I put this drawing here and you can use it. I don't know what version of the software you are using, so I exported it to the earlier Rhino 4.0. hope it is of help to you.
     

    Attached Files:

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  13. DVV
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    DVV Junior Member

    Thank you so much!!!
    As you said, there are just few books on the subject, and most of them are focused on the junk rig - which is also very interesting.
    But now I want to understand better the hull shape of old Junks, and you gave me more info in two posts than all the book I read in years.
    I'm playing with the Rino model, I'm afraid I'll ask you some more questions.

    Thank you again!

    PS are there still some junks to see in the shangai area?
     
  14. ExileMoon
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    ExileMoon Junior Member

    I have never seen any Junk in Shanghai. Only a few models can be seen in the museum.
    上海历史博物馆新馆.jpg


    I know that in another ancient city with a long history of navigation near Ningbo, there are about 4 Junks. But even these 4 junks are all modern-built antique motor sailing ships. They rarely use sails to sail, and perhaps they have never sailed in their careers. I only know that one of them, named "Green Eyebrow", had sailed during the sea trial. But now the "Green Eyebrow" have been removed mast and become a barge.
    Green Eyebrow.jpg


    In Taihu Lake, a large lake west of Shanghai, dozens of inland water fishing junks survived. They are mainly old ships built in the 1980s, and many of them are cement ships. Among them are 2 very old wooden junks. They survived because they existed as sightseeing tours.

    Some sailing boats can often be seen on this lake, but all of them are sailing boats for modern sports competitions. No one plays junk, because there is no junk international game.
    taihu sailboats.jpg
     

  15. DVV
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    DVV Junior Member

    This week end I played with Freeship and Rhino, I wanted to try a smaller boat flat-headed and flat-bottomed.
    By observing the pictures you suggested me, and the books that I have, I decided to have a bow which is gradually increasing its rake, with la large radius curve.
    The stern, on the contrary, is higher more straight, and the radius of the hull curve much smaller.

    May I ask you your opinion? What do you think? Schermata 2021-05-31 alle 09.46.21.png
     
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