human powered boat stability ideas

Discussion in 'Boat Design' started by gregk, Oct 10, 2007.

  1. gregk
    Joined: Aug 2006
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10

    gregk GregK

  2. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,742
    Likes: 125, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    Here is a 'recreational', sleek, recumbent ped-yak

    I like the 'dagger board/drive-train' idea. Looks like you feather the prop and can pull it all the way out.

    Maybe the prop could be handily detached and the board re-inserted in combination with a sail rig (she already has a rudder).

    Perhaps the existing dagger board trunk's sturdiness could be leveraged as structure for the mast.

    Looks as though the seating is rather high, might just be for comfort. I don't see why it couldn't drop 12".
  3. messabout
    Joined: Jan 2006
    Posts: 3,113
    Likes: 279, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    The bulb and fin idea for stability is very sound on paper. However, in practice there are some very real risks. You are designing a fairly lightweight boat. When you hang a blob of lead on a pendulum you are asking for problems that are mainly structural. Not a big problem for a big boat, but serious for a pedal boat. Less serious, but worthy of attention, is that the pendulum will act as its' name implies and induce pitching. Not a problem while playing around some sunny afternoon. For a long voyage ,it will be debilitating. Also make the pedaler work harder. There is the problem with fouling too. You get into a bunch of sea grass and you wont like the underwater appendage for long. On the plus side the ballasted boat will be potentially self righting. A non ballasted boat can also be self righting if it is dynamicly unstable in the inverted position. The pix in your blog look like you are already aware of the necessary design features for self righting.

    I vote for the deployable outrigger idea. They can be both extended and retracted with simple blocks and lines. The retractor lines could also be arranged so that they can be operated from the deck as well as the interior. Real adventurous project you have going. I wish you all the best.
    1 person likes this.
  4. gregk
    Joined: Aug 2006
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10

    gregk GregK

    disadvantages to a keel

    Messabout said:

    I TOTALLY agree. This issue has been bothering me all day. I finished a drawing of the keel this morning and at the gym later on, I picked up a 100 lb dumb bell and it scared the crap out of me! I can't imagine that thing hanging 3.5 feet below my thin kayak hull!!!

    The other issue is that during my test with 50 pounds of ballast on a temporary keel (see the video: ), I still couldn't really get out of the boat and sit on the top deck - it was touch and go. On the ocean, I would be risking tipping over and falling off for sure. A keel with ballast doesn't really start to offset a weight until the moment arm is nearly horizontal - you know?

    The use of some temporary outriggers has always appealed to me because it offers me very solid temporary stability when NOT underway, and won't 'drag' me down when underway. If I can be satisfied that a design for outriggers can be EASILY retracted upon a capsize, AND that they can be made robust enough to withstand some serious ocean pounding, then I feel like I might like to pursue that option rather than a keel.
  5. Guest625101138

    Guest625101138 Previous Member

    The keel has to be carefully designed. The stress at the hull mounting is high simply because you are aiming for low drag but the moment at the connection is still high.

    For the current boat the combination of internal ballast for operating stability and deployable outriggers in the sliding tube for the temporary stability, required for entering and exiting, may be the best compromise.

    Rick W.
  6. Chris Ostlind

    Chris Ostlind Previous Member


    For a ballast solution you could also do something like this form. The U-shape foil can be fabricated to provide a minimal amount of lift for the speeds you will be seeing. The structure necessary for the daggerboard slots will be at the far outside of the hull shell, therefore, not interfering with interior space. The U-bulb can be deployed whenever you need it and retracted to a formed indentation in the hull when pulled up, leaving only half the bulb below the hull surface and always providing an element of stability enhancement even when raised and passive.

    You eliminate the floats, the armature for the floats and their potential for being broken, You have a very strong self-righting aspect to the craft and generally simplify the whole process for rough weather stability.

    This is just at the conceptual stage, I have not done any numbers to see how big or how deep it would need to go, but it does answer many of the issues associated with the other possible solutions.

    Kick it around and feel free to go with it if it looks like it will work for you.

    Tom Speer, on this list, is a really bright guy with foil applications and could probably whip-up the needed foil sections and any transitional sections that would do you right in this application.

    I should probably say that something very much like this was done by Jon Howes and James Macnaghten with their "Loop Keel" concept. howes

    There are some differences in that Howes/Macnaghten are aiming their device at monohull sailing vessels and the keel is meant to rotate around the longitudinal axis of the yacht, providing a canting keel style, righting moment effect against the heeling moments.

    This suggestion on my part is an entirely less complex device with only up and down motion associated. It has no other purpose than to provide enhanced stability and save interior space. I suspect that there will be little, to no, value as a foiled lifting device due to added drag and the relative low speeds of the vessel. If the lift can partially cancel-out some of the drag, then it is a very positive conclusion.

    Good luck,

    Chris Ostlind

    Attached Files:

  7. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Sorry, I'm unable to view your website on this (work) PC, so this may already be covered, but have you considered a forward hung rudder? There is a paper on this in the latest Small Craft Transactions published by RINA. Basically the forward mounted rudder acts like the front wheel on a bike and provides dynamic stability (same as when cycling slowly the front wheel is turned a lot to keep you steady - if it was the back wheel that that steered bikes would be much harder to control). You still need outriggers for when the boat is at rest, but the advantage is that you can use a much thinner main hull with less resistance. I wasn't 100% convinced by the idea, but it might be worth considering.
  8. gregk
    Joined: Aug 2006
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10

    gregk GregK

    to keel or not to keel

    Thanks for your input!! After careful consideration, I think I am going to go with a retractable outrigger for this prototype. For the final ocean boat, it would be possible to build small recesses into the sides of WiTHiN to hold smooth, rounded floats. And as per Richard R's ideas, these outriggers could be activated by a parallelogram frame.

    For now, these are not intended to be used while underway, so the odd shape on the floats shouldn't matter as long as I have enough flotation to stand up and climb out on deck, etc.

    Upon a capsize with the floats extended, I should be able to easily retract them in from inside the cockpit to allow her to roll upright. WiTHiN is currently very unstable upside down and I don't think the addition of these side 'wings' (outriggers in the retracted position) will affect that.

    A consideration is that they will be adding some weight to a point above the roll center, so that will need to be offset with more ballast on the floor.







  9. rob denney
    Joined: Feb 2005
    Posts: 763
    Likes: 122, Points: 43, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member


    Maybe use one outrigger, less than 50% filled with water. This will be a little larger but almost 50% lighter when not in use, less drag and simpler. If the water is in the bottom half of the outrigger hull, with drain holes just above the upright waterline, it will empty when inverted, making recovery easy, maybe automatic.

    Or one outrigger, but set up so that the boat is angled towards it when it is deployed. This will move your weight towards the outrigger when you are on the deck or moving about.

    I would use inflatable bags instead of solid outriggers. Hollow beam with the bags sealed to the ends. Pump them up (high volume, low pressure pump, maybe lung power), they deploy. Deflate them, and suck or pull them into the end of the tube.


  10. blared
    Joined: Aug 2005
    Posts: 2,655
    Likes: 4, Points: 48, Legacy Rep: 14
    Location: Orlando

    blared ALFA

    Well i had an idea too.. does'nt look clean as yours but here it is....;)

  11. gregk
    Joined: Aug 2006
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10

    gregk GregK

    Floats test

    Thanks for all of your comments and suggestions regarding the stability issue with my human powered ocean boat.

    I ended up building some retractable outriggers. Here is the YouTube vid of the lake test:

    They work well for stability on calm water or temporary stability in rougher conditions. They work for testing purposes on this prototype boat, but I still do not think they are a solution for the actual ocean boat. I think a keel is the way to go.

    Greg K
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.