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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    Captain Sunset Junior Member

    sorry, center to center is 370 cm
    total width is 442 cm
    i measured from the outside of the leg to the outside of the leg on which the chassis is resting instead of center to center.
    i will try to add a sketch with measurements from the sketch that are accurate
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    That seems pretty dangerous to me. It's not "common sense".
     
  3. Captain Sunset
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    Captain Sunset Junior Member

  4. Captain Sunset
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    Captain Sunset Junior Member

    thank you, i will take it in consideration
     
  5. Heimfried
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    Heimfried Senior Member

    Attached a simplified simulation of your boat without the elongation you think at. The cross section of the hulls are simple boxes with same area as yout hulls - this should be good enough to estimate the hydrostatic behaviour.
    The lenght is 11,00 m, the beam 4,75 m, displacement 7110 kg, in the middle the deck is raised to 50 cm above top of pontoons.
    It is a quick and dirty thing and possibly contains errors.
    Kat-BE.jpg
     
    Last edited: Mar 11, 2019
  6. Heimfried
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    Heimfried Senior Member

    New pic, beam corrected to 4450 mm.
    If you want to play with it: www.bootsphysik.de/bootxpBE.php
    Choose the square prism top left. (the link will only be working temporarily).

    Kat-BE2.jpg
     
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  7. Captain Sunset
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    Captain Sunset Junior Member

    thank you, i will look into it tomorrow!
     
  8. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    What percentage of the total gross weight of the boat will each pontoon support before submerging?

    It is not at all easy to explain.
    Compare the reserve buoyancy of any other type of boat in your length: monohull, catamaran, trimaran to a pontoon boat.
    Your pontoons are all you have for buoyancy
    Pontoon boats roll over. Why? Because they have inadequate buoyancy in their pontoons.
    You may be okay for weeks, months, even years maybe, until the right combination of factors come together and you're easy over.
    Hire a local professional. Any engineer could help you.
    No offence, but it's pretty basic applied trigonometry.
     
  9. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Nice project Captain Sunset! I love it!

    It appears from the drawings you linked that the pontoons are only 3m in diameter so they don't have too much buoyancy. Not sure how they can be submerged 55cm? Did you link the wrong ones?? Maybe I'm missing something?

    Anyways 15cm remaining with 60cm submerged would not work. I'm a total beginner though. But imagine any kind of strong wind could easily tip your boat over, it seems top heavy. Where is your center of gravity? You have a pretty big sail there. Or one or two of the compartments could get a leak or a hole. You would want more than enough buoyancy.

    370cm beam with 180cm center of gravity would seem to be very easy to roll over from wind alone. Murphy's law, if a combination of circumstances can lead to a catastrophic failure, given enough time it will inevitably fail. A large wake, wind, some guests running to one side of the boat, a leak.

    Maybe build (much) bigger pontoons out of plywood + epoxy + fiberglass and space them a bit further apart. Needs to be engineered to take the loads but materials aren't that expensive and it would be easy to build.

    If those are aluminium trusses or hulls you should also look into galvanic corrosion. As far as I understand it (and I'm a newbie) almost any metal that can rust and is in electrical contact with your aluminium, will not rust. Instead the attached aluminium will rust because it acts as an sacrificial anode. It's not that critical without saltwater but still might be a huge problem. So you need to get familiar with that, use stainless hardware and fasteners and/or electrically insulate the aluminium and avoid things getting wet or standing water. AND add an sacrificial anode for the aluminium itself. Can all be solved but you need to understand it and might have to go over every aspect of your boat. Again, this is just "as far as I know".

    Btw I think you also need the rhine-patent if you have more than 3.68 KW engine. For other rivers in Germany you need another thing if your motor is above 11kW. Doesn't cost too much though, it it might be good to know these things haha. I'd be curious how the regulations are in other European countries and if the german SBS(?) buys you anything there.

    Oh awesome! I'm also dreaming of building a solar catamaran. Do you have a build thread?
     
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  10. Heimfried
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    Heimfried Senior Member

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  11. gonzo
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    gonzo Senior Member

    The reserve buoyancy of a round pontoon decreases rapidly once it is submerged past half depth. If you only have about 1/5 of the diameter above water, that will give the vessel minimal reserve buoyancy and affect the ultimately stability.
     
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  12. TANSL
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    TANSL Senior Member

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

    thanks for helping me figuring out this puzzle... the pontoons i am using are U shaped. ( Schwimmkörpereigenschaften https://www.swiss-boats.com/schwimmk%C3%B6rper-pontons-1/ )
    At the moment i am considering elongating my existing pontoons (each one consists of 8 middle sections and two end sections) by another 5 sections each. I would remain under 20 meters, which is necessary if i don 't want to go through a whole new set of legal prerequisites. Regretfully I will be over 15 meters meaning I will probably never cruise on the Rhine as they ask a difficult and expensive to obtain paper for boats bigger than 15 meters.
     
  14. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    I'd take a breath, spend a week in the library and read a few more books so you better understand the stability calculations. I don't think you've solved the puzzle yet. Don't be hasty. You want to sleep soundly on your boat.

    You could also share a better or clearer drawing. Length, width, distances, weights. You might get more help that way.

    Longer pontoons won't fix the stability issue over about 20¬į heel. You essentially have a large sail and the high center of gravity you'll just roll over and sink with even just a modest storm, gust of wind or large wake or another boat pushing against you accidentally. I think the suggestions so far were:
    • Lower your center of gravity and/or
    • Space your pontoons wider apart
    • Add "sister" pontoons to the outside
    • Build or buy bigger pontoons
    • Reduce weight (on top)
    I haven't found any real simple pontoon plans but I'm sure they are out there. Imagine just buying a bunch of 2.5cm thick outdoor plywood sheets, screwing them together and then painting them inside and out a few times with epoxy and "wallpapering" them with fiberglass cloth. There is a lot to learn about this too but it's not hard. Wood sealed with epoxy lasts a long long time. This would not cost you much. And thicker pontoons that aren't immersed as much or are even slightly longer (even just from 14 to 15m) can make your boat faster and use less energy. Your pontoons might sell for more than DIY ones AND you could get improved range / speed for your houseboat.
     
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  15. Heimfried
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    Heimfried Senior Member

    The large area solar equipment brings a lot of weight with it you connot escape. Therefore is choosing PE pontoons not a good choice, they are heavy too (and pricey). This choice is not unavoidable contrary to the solar panels. Your pontoon hull weighs 30 kg per Meter, my plywood hull is 85 kg and 6,35 m, so 13,4 kg/m (hulls are already epoxied and glassed) Comparing the same lenght they would have lesser drag, more buoyancy and offer the possibility to store gear, what means to lower the CoG.

    Before you order 10 more pontoon elements, think again. You will not only add buoyancy but a lot of weight also.
     
    Last edited: Mar 14, 2019
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