too much weight for my solar powered pontoon styled boat

Discussion in 'Stability' started by Captain Sunset, Mar 5, 2019.

  1. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    If it's something of common sense I'm sure that you, alone, can find the answer.
    What does "less roll" mean? Less roll angle (under what circumstances?) or shorter rolling period or what else?
     
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  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The bigger pontoon will decrease stability more than the smaller one. How much is something that can be calculated or measured. Measuring is easier and you can download the instructions to comply with CE standards.
     
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  3. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member

    thanks Gonzo, intuitively, i also think a bigger pontoon will decrease stability (i noticed some high speed tritoons use that propriety of a bigger middle pontoon to make a better carving boat)
    I will do bath tub tests tomorrow. it is almost midnight here.
    I will probably go with the same sized middle pontoon if the tests confirm my intuition.
    The CE regulations are ok. I have already passed them and they allow quite drastic changes as they categorize my vessel as prototype (experimental)
    Government officials came by and love the project and also give me advice, for which i am very grateful.

    I am not sure the same applies to me, as my boat will never glide across the surface but will always remains a true displacement vessel. which is why i will test...
     
  4. messabout
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    messabout Senior Member

    Captain, the numbers are an essential bit of information if your question is to be answered reliably.

    Generally speaking the addition of a center hull will cause the roll tendency to increase if the center hull is allowed to displace some water. If it does not displace water then there will be no additional flotation. You want additional flotation so, Yes, the roll tendency will increase...............Think of it as if the center hull is a pivot point.....like a play ground See-Saw.

    How much the tendency to roll or list will become, is a function of the displacement of the center hull. Consider that a smaller center hull will imply that the outer hulls will be more deeply immersed before the center hull has any influence on the total flotation....or more properly the sum of the displacements. Here is where the deal gets a little bit sticky. If your hulls are round then in the case where the sinkage is more than half the diameter of the pontoons, then the pontoons become less and less effective in terms of weight support..................bottom line is that a smaller diameter center pontoon may get you in trouble. A pontoon of equal diameter to the outer ones appears to be the more advisable option
     
  5. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member

    thanks for explaining further...

    total weight will be about 7110 kg
    beam is 4 m exactly from center of starboard hull to center of port hull.
    the hulls are 12meters long. they consist each of 8 middle sections and two nose sections of the following type:
    Dimensional Drawings https://www.swiss-boats.com/schwimmk%C3%B6rper-pontons-1/dimensional-drawings/
    this page has dimensional drawings as well as exact depth of the hull under various loads.

    I am considering going with the same hull for a center hull, another option would be:
    Schwimmsteg Ponton Hausboot mit Kunststoff Schwimmkörper https://shop.technus.de/schwimmkoerper/speedy/index.php (scroll to the bottom for an overview of the model range, i am thinking of adding the regular Speedy line models https://shop.technus.de/downloads/typ01speedymitte1.pdf

    the weight is balanced out between the hulls (and no weight is directly above an outer hull, the hulls are further out from the cabin walls)

    the boat is solar powered, so speed is not the aim, but keeping resistance as low as possible to get around with as little energy as possible is.
    This is a link to my vessel as it was. It loads quite slowly, it is a 3 minute clip made by a tv station for a human interest program.
    Captain Sunset https://www.een.be/video/iedereen-beroemd/captain-sunset (the video player will appear under the header after loading the page)

    this is a clip from last sunday when the roof went on top:

    can you load a sketchup file? if you can i can also try to add a sketchup file
     
  6. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member

    twothird perspective two hulls.jpg frontal two hulls.jpg
    it took me a while to find the buttons to publish these sketches....
    but the third pontoon in the middle is my worry at the moment...
    haha .... the invisible one! should it be bigger? or the same size? smaller definitely not as i need the extra flotation capacity!
     
  7. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    Hi Captain Sunset,

    to estimate the differences in heeling behaviour (roll) between different types of a additional pontoon in the center, it should be calculated. A few years ago I did a website, which does such kind of calculations and also displays the results graphically. There is a "2D-Boots-Rechner" which provides the calculation of GZ curves (heeling arm versus heeling angle).

    If you are interested try "www.bootsphysik.de". Button top right "English", then click link "2D-Boots-Rechner" in the top line; then button "choose/alter frames". There are two Kats, but no Tri.
    If you click the Kat it is loaded and appears at the calculation sheet. Click "righting lever curve", wait until response and click it again and so on, may be 4 or 5 times. You can load and unload masses which means to change displacement. Use buttons " i " for information.

    Ask questions, if you like. If you find the calculations useful I would "create" a trimaran (or 2 or 3 of the for comparison) if I find time for it.
     
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  8. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    "the most important for me is to not decrease the stability The boat should remain as level as possible at all times since she is used for living on.

    Speed is not my aim, but having very little power since i only use solar, i am still concerned with hydrodynamics."

    Okay.
    Quoted above are highlights from your original post.
    Based on this, and your willingness to expand,
    I would recommend you create larger pontoons to replace what you have now.
    Sell the current pontoons.
    I believe this would best suit your needs and your future as a live-a-board.
     
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  9. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Depending on the constrains, it may be cheaper to add length to the existing pontoons. It would also make the hulls more efficient at the shown displacement speeds.
     
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  10. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member

    thank you Heimfried, I will use the calculator later today or tomorrow! I look forward to playing around with it!
     
  11. Captain Sunset
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    Captain Sunset Junior Member

    gonzo, i agree with your assessment, however, it is not very easy to make them longer and still rigid enough, because it are all seperate modules, i am definitely still thinking along that path!
     
    Last edited: Mar 9, 2019
  12. Captain Sunset
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    Captain Sunset Junior Member

    Hallo Heimfried, can i alter the length and beam values for example? (nice calculator by the way!)
     
  13. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    No, sorry. The 2D calculator has only an implicit length to accelerate the calculations, no trim at all (is fixed to zero). There are heel calculations possible only. If you change to the "3D-Boots-Rechner" there is trim also. But there is only one given monohull to play with.

    Regarding changes in the 2D version it is only possible to stretch or reduce the height of the chosen frame (via "choose/alter frames", buttons "Height * Factor" and other).

    If you are fit with Excel speadsheets (or similar software) you could "create" your boat/hull yourselve in an ".csv" file which I would upload. Then you can play with it online.
    Necessary is an array of numbers which represents the shape of the surface of the hull (one hull = half of the boat). It looks (2D) like the attached pics. This are simply the cartesian co-ordinates of hull surface points (all given in mm): row 1 contains the breadth (y value), column A the lenght (x value). The cell "F4", value 0,10..., means the point situated y = 32 mm from center plane and x = 4000 mm from stern has a height if 0.10 mm above the base plane. More details if you are willing to engage with the csv sheets.
     
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  14. Heimfried
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    Heimfried Senior Member

    Forgot to add the pics.

    (Remark: the numbers shown are values belonging to another hull - not the Kat shown.)
     

    Attached Files:

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  15. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member

    sorry, i forgot how to use excel, it is too long ago. If i had the time, i would come to learn it from you in a crash course :)
    thank you anyhow for your effort. I am still looking at making the hulls longer with two center pieces each... it would make the hulls be about 60 cm deep in the water.... Prop diameter is 30 cm, so it would be possible to fit the props behind the hulls and not have them be deeper than the hull, which is a good thing to avoid damage to the props...
    I am still figuring out how i would pull it off to get the hull from the boat without the boat being damaged, take the end piece of and insert the two new middle pieces, reinforce everything without adding too much additional hight (i try to keep a bridge clearance of 3,45m so France stays an option to travel).... it is a puzzle. but simply adding two hull pieces to each side would probably be the cheapest and perhaps best. It will be a tight fit with the weight but tight is good...
    If I would add three hull sections to each side, the boat would become over 15m length, which would cause difficulties later on if i want to travel in Germany.
    I am just thinking out loud here. I hope that is ok.

    a sketch with two hulls added... and some possible future fantasy additions like vertical wind generators or something equally cool to test. (example in this link: Vertical axis wind turbines : pics https://www.reddit.com/r/pics/comments/258a76/vertical_axis_wind_turbines/ there are other shapes of course, but judging by the thread there, they may be worth exploring for me in the future?)
     

    Attached Files:

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