Rock, Not Roll

Thank you to everyone who has joined the blog recently. Many of you have made comments about your concern for the ballast and the horizontal stability of the tsunamiball. Here is what I am looking at:

The round shape of the tsunamiball makes for a very strong hull shape, but a lousy shape for horizontal stability. I knew this was an issue very early on. In fact, this issue is why the boat is called the tsunamiball, but the shape is decidedly not a ball. I sacrificed the strength of the sphere to buy more fore-aft stability and put more oxygen in the boat, which I plan on being airtight.

So now… horizontal stability.

After all of the plywood layers are added I’ll weigh what I have and start the math to get the weight ratio above and below the waterline right. I expect what I will need is a good sized steel keel, which will get bolted through the outer hull and into the frame of the boat. The idea is to put as much of the ballast requirement into the keel, as far below the waterline as I can.

I’m thinking the keel could be similar  to a  folkboat, which is a traditional wooden sailing boat that has a very heavy steel keel (1ton+)) to keep her upright in rough conditions and full sail.

Another option would be to try a less traditional approach and do a double keel, which would have the added benefit of keeping the boat upright and stable for the majority of its time on land? The thickness and height of the keel will depend on the weight for ballast that I need to get the right waterline.

Initial sketch for a double-keel made of steel

Initial sketch for a double-keel made of steel

I was also wondering if there was a benefit to closing off the double keel, so it was more of a box? Would this give me a lot more stability as the water trapped in the box would be like an anchor, keeping the boat from much horizontal movement at all? If you know the answer, let me know. :)

I expect the single keel is simpler to maintain, better for the centerline architecture of the vessel, and makes navigation a lot more responsive and predictable.

I would love comments.

 

9 responses to “Rock, Not Roll

  1. I have a feeling a single keel would be more stable than a double. I think one attachment point would make it easier to keep the boat upright. It might be a good idea to attach some type of pontoons as a secondary stabilizer system. The only concern with that would be objects hitting the pontoons. Also once the water settles the boat would not be upright on the land in case it was needed as a shelter. This might be something to think about since there most likely would not be any place to live once the water settled. Just a thought….if you had pontoons designed for after the big wave, they could be dropped in after. These could have solar panels and propeller system. This could be a back up or secondary movement device and the solar could double for power for your living needs and essential power. Just a thought. I love that you are doing this. Great project, I’m sure it will lead to many wonderful things later…even if there is no flood!
    Cheers,
    Charles in Dubai

  2. A couple of observations – if there is no planned propulsion unit is the addition of a prow redundant? I suspect the ‘double keel’ concept has a lot of merit over the single keel. A gel cell battery bank to power lighting, GPS and emergency beacon would make a handy contribution to the ballast.

    Time for some model making and bath tub testin perhaps.

    • Mick,

      Thanks for the comment. I think the model making is a very good idea.

      I am also planning on adding a motor, but to be honest my first priority was to make a rock solid capsule first. Now that I have made progress on that front I am turning to the next 3 challenges:
      1. Stabilize the boat horizontally in the water without further compromising the integrity of the hull from lateral impact.
      2. Restraint and impact systems inside the boat for riders
      3. Durable propulsion and power system that can operate without eating up oxygen and can continue to function after impact.

      Looks like #1 and #3 should be designed hand-in-hand, so look for those sketches soon.

      Thanks again Mick. Keep the comments coming.

      -Chris

  3. Chris – this is completely inspiring and engaging to me as a fellow builder. If not for my day job, i’d volunteer to help you out! I’m wondering – will you be at the Maker Faire in May in some capacity? If so, i’ll come by and say hi.

    • Mark,

      Thanks for the compliment and the terrific offer. There is always room for another pair of hands on the boat. :)

      I would have loved to make it to Maker Faire (it is one of my favorite events of the year), but I’m not quite ready to move the tsunamiball quite yet. Maybe next year.

      Respectfully,
      Chris Robinson

  4. Chris,
    I’d think enclosing the keel could have an additional purpose, if you added a simple submersible pump and some way to remotely control a valve. After placing it in the water you could add or subtract weight by allowing it to fill operating the valve and you could pump it back out through a check valve. Also, the rear of enclosed double keep may provide the best location for battery storage and a protected electric drive or propulsion system.

    You might think about some mechanism for installing a protected solar plate to recharge the batteries, in case there’s a prolonged stay required.

    I’m looking forward to hearing more.

    I appreciate this project for its challenge and intent.
    Ed Leonard

    • Ed,

      Thanks for the thoughtful comment. Yes, please stay tuned as I step through the keel. I like the idea of putting more weight under the boat than in the bottom of the existing capsule. What do you think about an open Metal frame, similar to the double keel sketch, but with a crossing member at the bottom of the keel and another directly under the capsule? I was wondering if this was a good or a bad idea. Perhaps it is good, because when it is submerged, then the rectangle could act as an anchoring agent, preventing horizontal movement. If it is open front and back, then water could easily pass through it, fore to aft, so it would not inhibit propulsion.

      In addition, because there is a big welded box, the shape would be pretty strong against impact and could protect the propulsion system from impact as well.

      Hmmm?

      Thanks again. :D
      -Chris

  5. I’d be hesitant about the double enclosed keel. A keel essentially reduces the side to side role of the craft. Surface area is not the only factor in determining the keel’s effectiveness. A long keel can almost be thought of as a lever, using the mechanical advantage of its length to keep the craft upright.

    -Evan

    Disclaimer: I am a sixteen year old tinkerer, the above comment is based on intuition and a day spent sailing a sunfish sans centerboard.

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