How to calculate midpoint draft depth of a keel/centerboard sailboat

Discussion in 'Sailboats' started by BGstar19, Aug 8, 2019.

  1. BGstar19
    Joined: Aug 2019
    Posts: 5
    Likes: 0, Points: 1
    Location: USA

    BGstar19 Junior Member

    I am looking for suggestions on how to calculate midpoint draft depth of a keel/centerboard sailboat.

    I am looking to use this to calculate theoretical PHRF base ratings using the Schell Regression Formula.

    My sailboat has a stub keel that extends an average of 12" below the hull having a length of about 10 feet. The centerboard extends about 4.3 feet with a 15" width along the center line of the sailboat when fully deployed.
     
  2. TANSL
    Joined: Sep 2011
    Posts: 5,583
    Likes: 161, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Could you make a schematic drawing of the point you want to calculate?
     
  3. BGstar19
    Joined: Aug 2019
    Posts: 5
    Likes: 0, Points: 1
    Location: USA

    BGstar19 Junior Member

    Stub keel centerboard sailboat schematic.jpg
     
  4. TANSL
    Joined: Sep 2011
    Posts: 5,583
    Likes: 161, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Well, that seems to be a very complicated "point," no wonder you have difficulties.
    I guess what you need to calculate is the position of the geometric center of the drift area. That is simpler but you will need to have a well-made drawing of that surface.
     
  5. BGstar19
    Joined: Aug 2019
    Posts: 5
    Likes: 0, Points: 1
    Location: USA

    BGstar19 Junior Member

    Here is a quick excel doc attached I used to attempt to calculate the approximate midpoint draft depth of a keel/centerboard sailboat

    What are your thoughts on this?
     

    Attached Files:

    Last edited: Aug 10, 2019
  6. TANSL
    Joined: Sep 2011
    Posts: 5,583
    Likes: 161, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I don't quite understand how it is intended to be done. It is trying (I think) to calculate the geometric center of the submerged area, projected on the longitudinal plane, but it seems to me that the procedure is very inaccurate. It is reducing everything to trapezes and that is only approximate.
    If you have any drawing software you can comfortably obtain much more correct results.
     
  7. BGstar19
    Joined: Aug 2019
    Posts: 5
    Likes: 0, Points: 1
    Location: USA

    BGstar19 Junior Member

    Tansl, as much as I appreciate your input I'm guessing you may be overthinking it.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 5,583
    Likes: 161, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    You may be right, although, if that is what I believe, the solution is very simple. But the truth, I have nothing clear what can be the "midpoint draft depth of a keel/centerboard". Nor does your drawing in post # 3 help me a lot to calculate anything. Perhaps, so that I don't have to think so much, you should clearly express what you need and use not-so-simple methods to calculate it. If what you need is to find the point where the ship's drift resistance is applied, the matter is very simple and I would not have to think almost anything.
     
  9. BGstar19
    Joined: Aug 2019
    Posts: 5
    Likes: 0, Points: 1
    Location: USA

    BGstar19 Junior Member

    Tansl,
    My hope was that there was some mathematical formula using easily defined sailboat measurements to make a determination as to the approximate average draft depth of the keel/centerboard sailboat. Apparently there is not.
    Thanks for your interest in my quest for an answer.
     

  10. TANSL
    Joined: Sep 2011
    Posts: 5,583
    Likes: 161, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Sorry for my insistence, please, this is the last time I intervened.
    There are formulas and procedures to calculate almost everything but my problem with you is that I don't know what "average draft depth of ...." means.
    Perhaps the fact that, for the moment, no one else has answered, in a forum as this one, with so many people willing to share their knowledge, it means something.
    Good luck.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.