SibLim update

<< First  < Prev   1   2   3   4   5   ...   Next >  Last >> 
  • 19 Nov 2021 21:01
    Reply # 12138010 on 4315719
    Anonymous member (Administrator)

    Er...

    now I took the liberty and made a try (2-3 actually). The idea was to start with the Ingeborg sail, but somehow end up with a flat (..3° is flat...) boom.
    In my first round, I simply modified the bottom panel until the (shortened) boom had a rise of 3°. This may possibly work, but since it looked odd even to my tolerant eyes, I decided to spare you.


    On the shown version (“Sail 1.7”) I only kept the 3-panel top section from Ingeborg’s sail. This has proven to perform very well, and it appeared to be a good fit on FanShi ’ s mast. The lower four panels were then fanned very gently, 1.5° pr. batten, down to the 3° boom.
    With the shown yard, there is room for shifting the sail both forward or aft to find the best steering balance. In the shown position, the CE of sail 1.7 sits about 32cm aft of that of the original sail.

    Obviously, the space for the sheets will be short, but so it will be with any solution with a low-angle boom. I would consider having running topping lifts.

    Worth considering?

    Arne

     

  • 19 Nov 2021 14:00
    Reply # 12137294 on 4315719

    Arne wrote:

    Annie wrote:
    ... However, sooner or later I think I will need to change to a sail with a much more horizontal boom and a yard that can hang naturally.  In the meantime, I feel much happier with how the boat is sailing and the relatively small amount of camber built into the sail seems sufficent to get her to windward.

    Annie,
    Maybe you could persuade David to draw you a Fantail-style sail? This would be easy to set further aft, and the boom is nearly horizontal.
    Good luck!

    Arne

    PS: Should this discussion about FanShi be given its own topic?

    Arne,

    Yes, I've moved it out of the SibLim 10m topic, where it wasn't relevant.

    And no, I don't think it would be a good idea to go back exactly to the Fantail planform. That was just too extreme. But maybe something that heads gently in that general direction?

    What Fanshi seems to need, as Annie is saying, is a yard at a steeper angle, to reduce the amount of area forward of the mast - I agree. And a lower clew would make life easier, certainly. 

    H'mm...

    I wonder whether it would be enough to remake just the top panel? I find that by simply rotating the existing yard by 15˚ and making the luff of the top panel 200mm and the leech 2150mm, I can bring the whole sail aft by 300mm. 

    1 file
  • 10 Mar 2021 18:16
    Reply # 10182919 on 10065452
    Arne wrote:

    Thanks, David for the numbers, most interesting.
    I notice that she shares some main dimensions with the Alo 28, Johanna. She have about the same length and beam in the waterline, and almost the same displacement.
    The difference is that Johanna has 1400kg finkeel and the SibLim design has about 40cm wider beam over all than the Alo.

    From the numbers it appears that the outside keel is 791kg and then there is 400kg inside ballast. Was FanShi actually built this way?

    Another thing; the vertical CB of the whole underwater body is given as 0.41m.
    Then the vertical (z plane?) COG of the whole boat is 0.761m, or well above the waterline. Does that mean that she is unstable within the first couple of degrees heel? Practical sailing has already shown that this is not a problem. I am just curious if the description ‘corky’ could have something to do with this.

    Arne


    Now I'm back into Freeship, and I can update these numbers.

    The draught of Fanshi is 71cm and the all-external ballast is 1218kg. The vertical CG is given as 58.7cm, but this is measured from the baseline which I've set at the lowest point of the hull, so that actually, it's around 20cm below the DWL. 

    And another point: this calculation was without the mast, sail, battens, parts of the fitout, equipment, personal items and stores, etc, which will have raised it to be at or just above the DWL, as is normal for sailing vessels. A motor vessel with no rig and no need for stiffness under sail will have its CG designed to be much closer to the metacentric height, so as to slow down the roll and make the motion more comfortable and less 'corky'. 

    1 file
  • 13 Feb 2021 16:06
    Reply # 10092357 on 4315719
    Annie, FanShi is a beautiful boat and you can be more than proud about what you have accomplished. Really inspirational. A big thank you to both of you for documenting the entire process so detailed and making SibLim open source!
  • 07 Feb 2021 14:33
    Reply # 10067306 on 4315719

    Annie, I only just caught up with the launching blog entry - congratulations on a fabulous project.

    We (Louise and I) can also add our weight to the fact that Arne's sail making instructions are perfect, and make the process clear, even to people like us who have never owned a yacht or made a sail - he deserves a medal!

    We (Lou) also did all the sewing on the boat (sails, covers, cushions etc) with a 30-year old domestic Brother machine, and as you discovered, it really made a great job of it.

    We just need to get out of lock-down now, and we can get someone with a bit of experience on-board to help us understand how to better sail her, and evaluate what we made...

    Either way, well done! and thanks for all the blogging.

    :-) 

    Last modified: 22 Feb 2021 11:54 | Anonymous member
  • 06 Feb 2021 16:15
    Reply # 10065822 on 4315719
    Anonymous member (Administrator)

    Thanks, David,
    and thanks to Ueli as well. The metacentric height is a bit in the fog to me, but I will read myself up on it. There is so much to learn...

    Arne

  • 06 Feb 2021 15:15
    Reply # 10065678 on 4315719

    hi arne

    Arne Kverneland wrote:

    …the vertical CB of the whole underwater body is given as 0.41m.

    Then the vertical (z plane?) COG of the whole boat is 0.761m, or well above the waterline. Does that mean that she is unstable within the first couple of degrees heel?

    the center of gravity doesn't need to be below the waterline to keep the boat stable. it needs to be below the metacentric height (initial mc of siblim is 1.791 m).

    ueli

  • 06 Feb 2021 14:08
    Reply # 10065596 on 4315719

    Ah, no, this can't be the latest version, but I'm unable to go back into the Freeship model and check it at the moment. One thing that I'm sure of is that Annie let me add 50mm more draught,  3 layers of steel plate instead of 2, so the ballast is all external, a bit lower, and its weight is 1200kg.

  • 06 Feb 2021 12:45
    Reply # 10065452 on 4315719
    Anonymous member (Administrator)

    Thanks, David for the numbers, most interesting.
    I notice that she shares some main dimensions with the Alo 28, Johanna. She have about the same length and beam in the waterline, and almost the same displacement.
    The difference is that Johanna has 1400kg finkeel and the SibLim design has about 40cm wider beam over all than the Alo.

    From the numbers it appears that the outside keel is 791kg and then there is 400kg inside ballast. Was FanShi actually built this way?

    Another thing; the vertical CB of the whole underwater body is given as 0.41m.
    Then the vertical (z plane?) COG of the whole boat is 0.761m, or well above the waterline. Does that mean that she is unstable within the first couple of degrees heel? Practical sailing has already shown that this is not a problem. I am just curious if the description ‘corky’ could have something to do with this.

    Arne


  • 06 Feb 2021 08:16
    Reply # 10065218 on 10063585
    Arne wrote:

    ‘Corky movement’
    I think that is a result of the detail I like most on FanShi. It is my view that David has chosen just about the best mid-section you can have on a shallow-draught boat. It ensures a narrow boat in the waterline (dimensions, please) for good light-wind performance, and then, as the boat heels, the wide ‘cheek’ ducks under and the centre of buoyancy literally jumps sideways and stretches the righting arm. Excellent! In addition, this section helps to lower the cabin sole for better headroom. The slightly ‘corky’ movement is a little price to pay to get a seaworthy boat with shallow draught.

    Congratulations, both to the Builder and the Designer!

    Arne

    Hydrostatics results are attached, for all the dimensions and ratios.
    1 file
<< First  < Prev   1   2   3   4   5   ...   Next >  Last >> 
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software