Layout Off a Set of Lines - L. Francis Herreshoff

Discussion in 'Boat Design' started by DCockey, Sep 12, 2013.

  1. DCockey
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    DCockey Senior Member

    L. Francis Herreshoff (LFH) described his method of developing the lines of a hull, which he called "Laying Off a Set of Lines", in The Common Sense of Yacht Design (1946, The Rudder Publishing Company). While LFH was drawing the lines on paper for a sailing yacht, his methodology is applicable for developing a set of lines on a computer with suitable CAD software. Here is a summary of the method:

    1. Select the location of the load waterline (LWL).

    2. Select the location of the centerline [actually centerplane]. [In CAD this usually passes through the coordinate origin.]

    3. Select the spacing of the cross sections.

    4. Sheer and profile in sideview. Generally LFH drew the sail plan before the lines so the sheer line and profile in sideview had already been drawn and were transferred to the line drawing.

    5. Deck line as seen from above.

    6. LWL as seen from above.

    7. Halfbreadth of the face line or profile and keel bottom.

    8. Top of the lead ballast.

    9. Midship section at largest part of the vessel; section about halfway from the midships section to the bow; section about halfway to the stern.

    10. Location of the first diagonal on the body plane or sections. Usual for this to be at an angle of 45 degrees radiating from the LWL.

    11. Create the first diagonal passing through the sections drawn in the previous step and halfbreadth of the face line or profile. Alter the sections as needed for the diagonal to be fair.

    12. First buttock line passing though the halfbreadth, sections and diagonal (seven points in total).

    13,14. Two waterlines, one above and one below the LWL.

    15, 16, 17, 18. Four more sections, each halfway between previously drawn sections.

    19. Another diagonal, also at 45 degrees, below the first diagonal.

    20, 21. Two additional waterlines, one above and one below the LWL.

    22, 23. Two additional buttock lines.

    24. Upper diagonal.

    Remainder of sections.

    Remainder of waterlines, buttocks and diagonals.
     
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  2. DCockey
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    DCockey Senior Member

    At the conclusion of the chapter on "Laying Off a Set of Lines", L. Francis Herreshoff said:
    Before closing this chapter I would like to say that I consider a model the best way of all to develop the shape of a vessel, particularly those new and different shapes, and will mention that my father, N. G. Herreshoff, never used lines but always a model for developing his shapes.
     
  3. DCockey
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    DCockey Senior Member

    L. Francis Herreshoff on drawing orientation:
    It is customary to draw the bow facing the right hand, or east side, of the drawing, and this custom came from making a model first with the stations laid off on its centerline reading from left to right, but when the model was turned over and laid on the drawing (to draw the pencil around to get the sheer and profile) then the station numbers read from right to left. Some designers have the yacht facing either way; my father did about as many one way as the other.
     
  4. DCockey
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    DCockey Senior Member

    L. Francis Herreshoff made an interesting comment on station spacing.
    The spacing of the cross sections on the longitudinal views should be given some thought, for if an even spacing in feet can be adopted it is a help in laying down the lines full size. While it is true that some designers still use an outmoded method of calculating displacement that necessitates the waterline length to be divided in ten parts, still this is unfair to the mold loftsman, and besides generallay ten divisions are not enough to give the true shape of the yacht.​
    Keep in mind that this comment was published in 1946 before digital computers were used in yacht design. In another chapter of The Common Sense of Yacht Design L. Francis Herreshoff described his philosophy on calculating displacement. He used a planimeter to measure the area of each cross section, and then multiplied the sum of the cross sectional areas by the waterline spacing between cross sections. Herreshoff argued that since the longitudinal curve of displacement is convex in the middle and hollow at the ends the errors of over-estimating the displacement at the ends and under-estimating the displacement in the middle effectively cancel.
     
  5. FAST FRED
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    FAST FRED Senior Member

    Keep in mind that this comment was published in 1946 before digital computers were used in yacht design.

    Back when boats were fine looking !
     
  6. DCockey
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    DCockey Senior Member

    L. Francis Herreshoff on mid-section area:
    Many designers have to measure the area of the midship section to make it correspond to some predetermined midship section coefficient, but if you really have a clear picture in your mind of the shape you want and a sense of proportion there is no need of this, particularly in boats of less than fifty feet waterline, or unless you are to make a radical departure from the usual model.​
    L. Francis Herreshoff's approach to boat design was more empirical than mathematical, and he tended towards the "if it looks right it probably is right" school of design.
     
  7. Tad
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    Tad Boat Designer

    In the first post #9 needs to include the transom. The lines terminate at the stem and transom, therefore you need to fair to those points.
     
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  8. DCockey
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    DCockey Senior Member

    I agree. Herreshoff didn't mention the transom, and the example he showed was the Marco Polo which is a double-ender. I intended to add a comment about the transom but forgot to so thanks for catching it.
     
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