Testing the Capacity of a One Sheet Boat

Discussion in 'Boat Design' started by flo-mo, Aug 19, 2021.

  1. flo-mo
    Joined: Jul 2010
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    Location: Vienna, Austria

    flo-mo Junior Member

    Before I show the test results, I would like to briefly introduce the design.

    Photo journal of the build (including cutting pattern for the plywood): https://photos.app.goo.gl/GcoY7GfWbsE...
    WoodenBoat Forum thread: http://forum.woodenboat.com/showthrea...
    My website: http://flo-mo.weebly.com/


    The basic idea for this design is to create a boat hull with the highest possible load-bearing capacity from a single sheet of plywood. In this case, the 4 mm Sapele plywood sheet I used for this purpose is slightly larger than the most common format (250 x 125 cm instead of the usual 244 x 122 cm). According to my hydrostatic calculations, even with the 2.4% smaller version at a total displacement of 200 kg (two people 90 kg each + 16 kg boat weight + 4 kg for the oars), the freeboard is still 17.8 cm (7 inches).
    Disclaimer: This boat design is only to be understood as a water toy and its usability is accordingly limited.

    Last edited: Aug 19, 2021
  2. flo-mo
    Joined: Jul 2010
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    Location: Vienna, Austria

    flo-mo Junior Member

    This mini-video series is intended to show how the boat behaves under different loads under ideal conditions.
    Let's start with a person (85 kg), which together with the weight of the boat (16 kg) and the oars (4 kg) gives a displacement of 105 kg (fresh water).

    As I explained in the description of Part 1 of this series, the plywood sheet I used to build this One Sheet Boat is a little larger than the usual size (250 x 125 cm instead of the usual 244 x 122 cm). This means that if I used the more common format, the boat would be 2.4% smaller. I did hydrostatic calculations to determine the freeboard for both sizes of this design at the same displacement, so you can imagine how the smaller version would perform.

    Displacement 105 kg:
    Freeboard of the boat I built: 26.8 cm
    Freeboard using a 244 x122cm sheet: 25.5 cm

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  3. flo-mo
    Joined: Jul 2010
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    Location: Vienna, Austria

    flo-mo Junior Member

    This is pretty rough unedited footage, but still shows very well what I wanted to demonstrate.

    The shots of boarding the boat from the dock look like something out of a slapstick movie, but we managed to get seated without any major problems. Surprisingly, the seating arrangement also worked well for two adults without the need to remove the middle seat. To place the feet comfortably takes some arrangement, but is quite doable.

    The second half of the shots with swapped positions clearly show who is the better rower. My friend Markus (who I would like to thank again for inviting me to this charming place to make this footage -- also shout-out to his son an daughter for the camera work) has always enjoyed rowing and was surprised how quickly we progressed even with two people on board. He rowed two-thirds of the length of this small lake briskly back and forth (about 800 m) without making much effort.

    As a conclusion, I can say that the boat with two people on board on a beautiful summer day like this one on this small lake proved itself quite well under these particular circumstances. Still, it should be remembered that this is more of a water toy and therefore the range of use is very limited.

    Now for the bare facts: Displacement is 170 kg (crew 85 + 65 kg, boat weight 16 kg + 4 kg oars) with 21.7 cm freeboard, which would result in 20.2 cm freeboard for the 244 x122 cm sheet variant.

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  4. flo-mo
    Joined: Jul 2010
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    Location: Vienna, Austria

    flo-mo Junior Member

    Finally, we tried to test the limits of the load-bearing capacity by putting a third person on board.

    Now it becomes uncomfortable both in terms of space and stability and especially getting in and out of the boat turns into a real challenge. It is possible to row a short distance with three people on board, but for safety reasons I would definitely advise against it.
    It was fun to try it out, but only on the condition that everyone who participated was willing to take the risk of possibly ending up in the water. If that had happened, on a beautiful and warm summer day like this, we would have just laughed it off and considered the incident a welcome refreshment. Fortunately, everything went well and we were able to successfully complete the test series.

    Here are the final data about it:
    Displacement 215 kg (with the young woman): Freeboard of the boat I built: 18.4 cm Freeboard using a 244 x122cm sheet: 16.9 cm
    Displacement 240 kg (with the young man): Freeboard of the boat I built: 16.7 cm Freeboard using a 244 x122cm sheet: 15.1 cm

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  5. Skyak
    Joined: Jul 2012
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    Skyak Senior Member

    Good to see you here on BD forums. I am a fan of your work. This is a fine design demonstration of how optimizations find their limits in constraints. Within a 1 sheet size (surface area) limit, capacity increases as the form gets closer to the spherical limit, but in human capacity, ergonomics limited capacity long before. Three humans are a very poor fit despite having plenty of displacement capacity -your longer design would be a better, faster boat for 2. This design still might be better if two crew are not going far and often transport stowable weight -a tender. The oars are an awkward choice. They offer power this hull can't use and require space it doesn't have in operation and storage. I would favor a sculling oar and skeg.

    When people ask for max capacity tender I am always happy to point this design out. Thanks!
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  6. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    Awesome. I love everything about this concept. I have a Marine 19, which I dream of setting up for long distance coastal cruising and have been thinking about an appropriate scaled tender for her. One that can carry two people. This little boat looks like a great place to start.
  7. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    This is an extremely clever design. And well executed.

    Did you design this wit pencil and paper? If no, what software did you use?
  8. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

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  9. cracked_ribs
    Joined: Nov 2018
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    Location: Republic of Vancouver Island

    cracked_ribs Senior Member

    I have little to add but I am also a Flo-Mo fan - I spent a long time looking at his work before starting my current build. It's not closely related to any particular design, but I thought for a very long time about his take on the Fleet and why it is so appealing.

    It's all inspiring stuff to behold. I love looking at the designs on the Flo-Mo.weebly site; I've spent hours there.
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  10. Andrew Kirk
    Joined: Jul 2021
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    Location: Chorley UK

    Andrew Kirk Pedal boater.

    Fabulous work. I wish I had as much patience.

  11. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Here’s my version of “three men in a tub”
    This is an El Toro, it was VERY tender loaded like this.
    I really enjoyed this thread, thanks Flo Mo!
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