Houseboat Design Characteristics

Discussion in 'Hydrodynamics and Aerodynamics' started by MrDillPickle, Mar 4, 2020.

  1. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member

    Hello everyone,
    Long time lurker first time poster here. I am in the process of designing a houseboat and I am struggling to answer some questions. The displacement hull will be 8' wide and 26' Long with a 7 foot front deck, 4 foot back deck with a 2 foot hull height, there will be a cabin on it and floatation pods/bulkheads in it. I have been able to calculate the LCG, TCG, VCG, CB,CF. The question I have is that right now my CG is in front of my CF by a couple feet. With that being said, will my boat be trimmed fore? In an ideal design, would you want the CG in a vertical line with the CF? Also, does anyone know how to calculate the force of wind to make a boat heel by "x°".
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    The vessel will be trimmed if the CoG and the center of buoyancy are not on the same vertical, regardless of the position of the CF.
    "In an ideal design, would you want the CG in a vertical line with the CF?" : no need.
    "Also, does anyone know how to calculate the force of wind to make a boat heel by "x °" ": Yes, but it is necessary to know the shapes of the ship, the surface exposed to the wind, the total weight of the ship, and something else .
     
  3. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member

    TANSL,
    Thanks for the reply. I was getting conflicting information from different sources. So in other words, I have a design draft and at that design draft the CoB is at the geometric center of the underwater portion of the hull and for the boat to have an even keel i need to ensure the CoG is above the CoB both longitudinally and Traverse. The CoF would then however be the "pivot point" for when altering trim. Is that in essence what you are saying? As far as the wind force, I wonder if it as simple as the force of the wind over the area perpendicular to the flow? And that force is like adding a weight the opposite side downwards? Im trying to also use this to figure out what size motor to use, I know the wind always messed with other houseboats i was on and sometimes couldn't control it with 30mph winds. The boat will be used in central Missouri lakes so huge waves are not a problem but 3 foot waves can happen in bad storms. And I know I could just build it and move everything inside around til it worked but having a methodical approach and knowing the abilities of the boat is much nicer to me. Plus I'm a math nerd...
     
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    The heel produced by the wind depends on the area exposed to the wind and also on the position of the barycenter of that surface. It is not, therefore, equivalent, although similar, to the heel produced when transferring a weight. Once that is known, we have to draw the curve of how the heeling arm varies as the boat's heel changes. That curve will cut to the curve of the righting arm (that depends on hull shapes, the boat weight and its CoG) in a point that represents the equilibrium point.
     

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  5. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member

    Awesome, time to crunch some numbers!
    Thank you!
     
  6. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    seite.png
    If you like look at this:
    Berechnung der Schwimmlage von Booten http://www.bootsphysik.de/index.php
    Click button top right "English"
    This calculation sheet shows the behaviour of an example hull if you shift masses (weight) or load or unload masses. It also calculates the GZ curve and so on. Use buttons marked with "i" for information.

    Regarding "math nerd": If you send me a data table "***.csv", which is describing the shape of your hull (I'll tell about data format) I will upload it and you can play with your own boat.
     
    Last edited: Mar 4, 2020
  7. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    In practical terms, the sort of wind strength that is going to have your houseboat heeling noticeably, are the conditions you either should not have ventured out in, or if caught out in them, then you abandon the heading that is putting you into that situation. You are worrying your head about things that are not that pertinent.
     
    bajansailor likes this.
  8. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member



    Heimfried,

    I will create that now! No particular format, as long as you can understand the dimensions?

    Best Regards,
    Pickle
     
  9. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    To take into account that the calculation of the heel due to the wind is not governed by the same formulas as the transfer or loading/unloading of weights.
     
  10. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member


    TANSL,
    I understand that now, however the unloading and loading formulas are very helpful! Thanks!

    Pickle
     
  11. MrDillPickle
    Joined: Mar 2020
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    Location: Central Missouri

    MrDillPickle Junior Member

    I created an Excel file for calculating the LCG, VCG, & TCG so that I can play with placement of equipment and the heavier objects. I'm using a type autoCad to find the CoB( mostly the center of the side of the hull as the boat mirrors across the keel) and moving the objects around until my LCG is at the same longitudinal distance from the stern as my COB and centered on the keel.
     
  12. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    Hi,

    no, no. It has to be a certain format. I didn't explain it then, because I didn't know, if you would be interested.

    I will do it now.
     
    Last edited: Mar 8, 2020
  13. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    The data table needed is a kind of offset table used in traditional boat building, just more formalised and of much more density.

    Basis is a right angular cartesian system of coordinates, right handed. Base plane is z = 0, z counts positive upwards. The base plane is parallel to the design waterline plane, The deepest point of the hull may touch the plane, but no point of hull is allowed to be under the plane z = 0.
    Plane x = 0 is placed behind the sternmost point of the hull, x counts positive forwards. The y = 0 plane splits the boat along keel line in 2 halfs. Because of the hull symmetry there is only half of the hull noted (port side), y positive. (The other half is mirrored.)
    The csv-table used contains in it first row 126 evenly spaced numbers starting in B1 with 0, ending in DW1 with the largest half breadth of the hull.
    The first column contains 376 evenly spaced numbers starting in A2 with 0 and ending in A377 with the x measure of the foremost point of hull.
    So there is a grid of 126 times 376 cells each is to be contain the z value (height) of the boat hull (outer skin) and the point described by the corresponding x and y values in row 1 and column 1.
    Cells with no hull point are left empty, so if you are looking at the table zooming out, there will be a distorted hull shape visible (pic below). Note: in the tables below the comma is used as decimal sign in most of europe, but a decimal point is no problem.
    All length measures in millimeters (mm).

    That is the most of it.

    Tabelle_csv_hull.jpg

    CSV_Umriss.png
     
    Last edited: Mar 8, 2020
  14. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    MrDillPickle
    Are you discouraged by the huge amount of necessary numbers? It looks very labour consuming, but it depends on the nature of data you already have. Most of the data I calculated automatically by linear interpolation of the frames outline and so on.
     
    Last edited: Mar 22, 2020

  15. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I encourage the OP to publish the hull lines so that experts here can identify any issues. Plus we love looking at hull lines!
     
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