My Design - Trifoglio 25' - Suggestions & Opinions

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

  1. DVV
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    DVV Junior Member

    Thank you for the reply.
    There are two main reasons. First (and probably most important) I found it difficult to design a single chine hull. Single chine hulls are unseen in areas I go for sailing. Never saw one for real. Also multichine are extremely rare. I just could not design a single chine hull that looked like something seaworthy. Its difficult - at least for me - to design just using calculations, I need to be driven by some sense of proportions.
    The second reason is that I started the design bearing in mind Mikhalik Piccup Pram (you can see it clearly in the bow). He designed also Piccup Squared, which is the same boat with a single chine. On his website I found a comparison he made between the two, and his conclusions where there is not much difference at all. The mutichine one is said to be slightly better in rough conditions, and this was enough for me to adopt it.
    Moreover, it is a multichine, but the panels between sides and bottom (don know how to call them in Eng) are quite small in relation to the other two. Mikhalik illustrates them like if you cut off just the 'shoulders' of the hull, to give rough seas less surface to grip on. I thought that with these proportions the effect you refer to - presenting a flat surface to the waves when heeled upwind - should be non that strong.
    Do you think this is a wrong assumption?

    Thank you again

    DVV
     
  2. gonzo
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    gonzo Senior Member

    I think it is a wrong assumption. Sailing sharpies, which have a flat bottom, pound much less when they are heeled over. On the multichine, there is a flat panel hitting the waves instead of a vee (formed by the bottom and side).
     
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  3. DVV
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    DVV Junior Member

    Dear Gonzo,
    I've read many posts of yours in this forum, and it looks like your knowledge on boat is much bigger than mine. I wish I could use it asking a few questions to help me to proceed.

    I love sharpies - even if I saw them just studying The Sharpie Book -, I know they are known to behave remarkably well, especially upwind and in rough weather. In general I love box boats, and I agree that the chine between bottom and side is perfect to cut the water when the boat is heeled. But, they usually do not have an external ballast, and you have to be careful about over pressing them by not reducing the sail area properly.
    The idea I started with was a flat bottomed scow with internal ballast and leeboards. But I was not able to get the Angle of Vanishing Stability that I wanted (and that I'm used to), without using shapes that did not seem right for to the eyes. Moreover, the theory of sharpies says to keep the side height low and the length beam ration from 4 up, and I did not want to go in that direction.
    All these pints pushed me to step back a bit, and I added a more traditional - if I can say this.. - deep keel with external ballast. This allows me to have a higher side, and a more reassuring AVG. As you say, being a flat bottomed vessel, by doing this I loose the sharp corner, so well suited to cut the water (and the design becomes less exotic, from where I came from).
    I will go back to the design, to try some adjustment. But I first want to ask you again: dont you think that such a small surface - the middle panel would be roughly 150 to 200mm - should not give sensible pounding when heeled? Even if, for sure, it would be flat to the eater surface when upwind. I know I will loose something, without the corners, I am willing to accept this, in order to have a deeper hull wo increasing displacement too much, but I do not want to build an extreme pounding vessel, so I would be grateful if you could share with me - again - your opinion of the things I wrote.

    Thank you for your observation. It is quite exiting just to be here ad receive comments on a design I made!

    DVV
     
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  4. gonzo
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    gonzo Senior Member

    I think that the width of the panel is quite small and probably won't affect it so much. You will loose some stability compared to a single chine, but since you are using external ballast it can be compensated for. It will be a small advantage on light winds. The construction will require a bit more labor. However, aesthetics are a major consideration. Nobody wants an ugly boat and your design looks very nice.
     
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  5. DVV
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    DVV Junior Member

    Thank you very much for sharing with me your considerations. Sorry if I reply just now, but yesterday all my attention was toward Le Cam and Ecoffier :)
     
  6. DVV
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    DVV Junior Member

    Update: few changes to obtain proper displacement after the correct dimensions and weight for ply panels has been set (I was a bit on the light side).
    Deck was cut open and interiors details slightly modified.
    New keel designed (little bigger). Now using offsets to define details of bulkhead dimensions.
    Wish I could start building a balsa model soon...

    DVV Schermata 2020-12-05 alle 22.46.02.png
     
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  7. fallguy
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    fallguy Senior Member

    I don't profess to be an expert, but not sure I understand the reasons for the scow.
     
  8. bajansailor
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    bajansailor Marine Surveyor

    DVV, what modelling / CAD program are you using for the above illustrations?

    Just a thought, re going to windward it might be useful to have the flat bow transom a bit higher out of the water (rather than what is shown in a side profile drawing on the previous page of this thread) - this might help the boat to ride over the waves rather than having to punch into them?
     
  9. DVV
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    DVV Junior Member

    I am using freeship!+ and Rhino for Mac for the last illustration posted, but mainly the first.
    About the bow, the modification you suggest may be interesting, at the beginning it was higher, but than I had to make it a little lower for the displacement.
    I hope the inclination of the bow will make punding less extreme, when heeled. But I'm not sure about that..
     
  10. fallguy
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    fallguy Senior Member

    It isn't pounding that worried me, but braking.

    To add, if you come up against a big wave or heavy chop or boat wake; the scow will probably slow the boat when so low to water.

    The only benefit I see to the scow is cheaper to slip the boat. And I believe the tradeoff not worthy or you'd see the scow in many sailboats.

    But I also think you ought to pay attention to Gonzo. His critique is an interesting one.
     
    Last edited: Dec 7, 2020
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  11. DVV
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    DVV Junior Member

    Sorry I did not see you post before!

    You know, scows are a wide debated topic. I am a lover of scows, so I guess my replies may be considered biased.
    Once a read an interview of Bob Perry, in which he said that once he saw the first scow bowed mini (the Magnum) thought 'Let's hope it wont be fast!', but I knew it would have been, because from the design point of view, scows work.
    The main advantage is that waterlines are less curved in respect of a traditional design. A little bit like a catamaran, just with the space between hulls closed. This gives more balanced lines, especially true for todays planning hulls that have a large transom. Triangular shaped of modern hulls, when heeled, lay on their leeward side, and the windward side 'points down'. The boat does not proceed on the direction of the longitudinal axe. In this aspect a scow hull is more balanced.
    Anything comes at a price, and scows are said to be pounding on upcoming waves. But if we compare a triangular hull with a scow, we could say that when a triangular hull face a wave - given its position explained above - it submerges the windward side, which pushes the bow down. On a scow, the buoyancy of the bow is larger, and this help it to be submerged less frequently, and, given a bow not flat but with an angle as the one in the design, even if submerged, does not present a flat surface to the water. It presents a side that should be inclined in a way to push the bow out of the water.

    Chinese junks had generally a flat large bow, and they kept on using them for something like 3000 years. Once I read that archeologists think that when first vessels were built, 'our' first hulls were dogout canoes, using large threes, and the 'pointed' shape evolved from that input. In Easter regions they did not have large trees but bamboo, so they started with rafts. Large bows evolved from that. I found it an interesting explanation for the point shaped bows we are more used to.

    May be I'm just fascinated by the new shape, but I believe it has more pro than cons (there are always cons). Scow bows are a thing in racing. In Mini there are a lot of scows. IMOCA banned it for now, but last generation hulls found a way to move anyway in that direction (L'Occitance en provence the most advanced example).

    As I told gonzo, I started with the idea of a box shape, but I was not able to design a proper hull, with the AVS and the displacement the worked for me.

    I hope I replied you question.
    Thank you

    DVV

    Edit: this was an answer to the following post, sorry
     
    Last edited: Dec 7, 2020
  12. fallguy
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    fallguy Senior Member

    I am building a scow tender. I just think it looks like a brake here. Perhaps moving the front lower chine up can reduce braking effects in heavier waves.
     
  13. DVV
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    DVV Junior Member

    About breaking. I agree, the bow can brake. Given its shape it is more subject to be punished.
    I designed three (or four?) longitudinal stiffeners that divides the part of the hull in front of the first bulkhead into small watertight compartments. Hope this makes ot strong enough. I was also thinking to make them self flooding, though a small hole on the bottom of each one, as I read old junks had. This should add weight in form of water just when needed, in the bow area.
    I intend to build her wo any hole, and then if its the case try this solution.

    DVV
     
  14. DVV
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    DVV Junior Member

    You are the second person that give me this suggestion. I'm afraid I should try something in that direction..
    May I ask which design are you building? There are many scow dingy that I like.
    If I increase the height of the bow, I will loose some displacement there. I guess I could move the keel a bit back to compensate, to keep the trim at zero moving the Center of Gravity.
    I remember a Bolger famous design of a pram with an extremely high bow, that was expected to be very good when facing waves.
    I think I'll give it a try, lets see what I came out with..

    Thank you!

    DVV
     

  15. fallguy
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    fallguy Senior Member

    How do you lose displacement? Gonna have to explain that one to me.

    where is the waterline on the scow?

    I am building an ultralight rowing dinghy. Not in the same class as your work. It is also a private design, not yet released to the public and not my design.
     
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