too much weight for my solar powered pontoon styled boat

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

  1. Captain Sunset
    Joined: Jun 2012
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    Location: Belgium

    Captain Sunset Junior Member


    view from below: (top of the picture is the bow, bottom is stern )
     

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  2. Captain Sunset
    Joined: Jun 2012
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    Location: Belgium

    Captain Sunset Junior Member

    thank you all for your help in trying to think this through. I am going to go with extending the two existing hulls. The drawback that the boat will be somewhat low on the water does not weigh up for the improved hull speed, lesser cost, and unmatched stability when compared to a three hulled vessel. I could extend the boat even more to be less deep in the water, but I have set my boat length limit (for legal reasons) under 15 meter (LOA).
    This vessel's main goal is providing comfort for extended stays while still being able to move around using only solar energy. Stability and as small a fraction of the hullspeed necesseray have therefore been the deciding factors.
    The inland water system in Europe has almost zero current, and if you stay of the industrial routes and on the more scenic ones, chances of encountering waves are very small (due to speed limits as low as 4 km/h on the smaller scenic ones)
    the hulls will be submerged about 60 cm, meaning there is a 15 cm margin before sinking (lots of the inland shipping vessels use less than 15 cm for transporting their cargo! even on rougher patches like inland seas!). The deck and cabin on the deck are standing on legs on the hulls so the deck is an additional 55 cm above the hulls and the cabin itself is raised an additional 8 cm above the deck.
    She will look low on the water, but chances of having a rogue wave coming into the living quarters are extremely low i think.
    Again, thanks all for your insights!
    I am trying to order the additional hull elements today (it is an austrian firm and the language barrier always slows things down a bit)
     
  3. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    Hi, Captain Sunset,

    good luck with your build! I personally would prefer more reserve buoyancy. Your deckshouse will lead to an increase of heel caused by cross wind compared with the "open" Pontoon. If a sudden additional shift of weight (crew, "passengers", gear, load, ...) would submerge one of the hulls, there would be no more increase of the righting moment. So the additional 55 cm will mean nearly nothing.

    I'm just building a solar catamaran also, but only 6 m long. Perhaps we will meet someday on the water. Berlin has a lot of nice lakes and waterways.
     
    Last edited: Mar 11, 2019
  4. Captain Sunset
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    Captain Sunset Junior Member

    i know, but i think it is best for me to stay under 15 meters so i can still go anywhere without having to deal with the dreaded "rhine-patent".... if i add more extensions i will be longer than 15 meters, and one day i would like to cruise to Vienna and to the Black Sea ;-) i think it is not possible without crossing the sections where the rules for the Rhine patent apply.
    always welcome in belgium. I have a very nice spot to dock
     
  5. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    60cm draft versus 15cm freeboard is grossly inadequate, even with square-top pontoons.
    Each pontoon should have enough buoyancy to support the entire boat.
    10% reduction for sheltered waters depending on several other factors.
    For example, do you ever get snow?
    What do you estimate your food load to be as a live-a-board?
    Kayaks, SUP's, coolers guests may bring, dogs, dog food, etc, etc, etc.
    And, as mentioned, wind loads...
    And don't forget this can all happen at once...

    Captain Sunset, don't get me wrong, I love what you're doing here.
    I have a houseboat.
    I drive a pontoon boat for a living.
    I've designed and built winning race-boats.
    I have seen overloaded pontoon boats roll over at the dock due to snow loads.

    I suggest you do the math for the worst case scenario.
    Please don't rely on "feeling" that it is going to be okay.

    Best regards and good luck.
     
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  6. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Here's an idea:
    Could you "sister" pontoon a shallower float inboard of the existing floats?
    They wouldn't contact the water until ~15 degrees of list (roll).
    Added expense and weight I realize but rolling your house is not good.
     
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  7. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Here's another idea (I'm full of them aren't I? ... well, full of something anyway!)
    Remove the propulsion battery. Seriously.
    Doing so would make it a daylight only boat.
    Is this feasible?
    The weight reduction would be substantial.
    Crazy I know, but look at the title of your thread.
    I think that sums up your situation, no matter how unpalatable.
     
  8. Captain Sunset
    Joined: Jun 2012
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    Captain Sunset Junior Member


    it would be possible, but it would not make that much a significant weight gain, it would make me gain about a 100kg. (It is a 48V 160Ah LiFeYPO3 battery)
    and good ideas are great!
     
  9. Captain Sunset
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    Captain Sunset Junior Member

    I don 't see why one hull has to be able to keep the whole weight of the boat afloat.... The cabin is positioned between the hulls, so even when she is listing to one side because of wind, there will never be full weight on one pontoon....
     
  10. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    The additional 55 cm between the top of hulls and bridge deck seem to be nice to prevent wet feet. But this distance simultaneously pushes up the center of gravity (CoG). And the height of this CoG is critical regarding stability. Do you know, where your CoG is located? You should calculate it if not.
     
  11. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    Look at these graphs and numbers. It is a kat whith hulls in upright position immersed to about three quarter. And a vertical position of G (VCG = vertical CoG) which may be similar to yours in future. Heel is 20° she is nearly knocked down.

    A heel of 20° means normally nothing to a sailboat. But at a boat like yours (and mine) it means, everything in the cabin and on deck which is not well fixed, slides and/or falls to the "wrong" side, so shifting weight and making things worse.

    Kat_min_reserveauftrieb.jpg
     
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  12. Captain Sunset
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    Captain Sunset Junior Member

    Vertical Center of gravity would be situated about 180 cm above the pontoons.
     

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  13. Captain Sunset
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    Captain Sunset Junior Member

    if i would extend front and back of the pontoons (adding 5 center elements to each hull (4 extensions to the back, 1 to the front) each pontoon would be able to "lift" a little over 80% of the total boat weight.
    Also 12 persons (my legal limit) weighing 80 kg each, would submerge one pontoon by about 5 cm (= less than 1°) if they somehow manage to get all their weight on one pontoon (which is virtualy impossible to do from the deck)
     
  14. Captain Sunset
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    Captain Sunset Junior Member

    also, maybe i expressed myself wrong, freeboard would be 15 cm of the unsubmerged pontoon + 50 cm from where the deck starts. Beam is 442 cm. distance from the center of one hull to the center of the other hull is 400 cm
     

  15. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    The pontoons you linked to (#20, Swiss Boats AG) and which I understand are fitted to your boat, are 75 cm wide. Center to center = 400 cm + (left half) 75/2 cm + (right half) 75/2 cm = 475 cm.
    Did I miss something?
     
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