dumping bilge through oar power

Discussion in 'Hydrodynamics and Aerodynamics' started by dcnblues, Jun 5, 2011.

  1. gonzo
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    gonzo Senior Member

    That is a standard bailer system, which he doesn't like.
     
  2. whitepointer23

    whitepointer23 Previous Member

    sorry gonzo, i thought you mean't a dinghy bailer that goes in the bottom.
     
  3. dcnblues
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    dcnblues Senior Member

    White, I did indeed. And I remain unimpressed with them. If you have good speed (like a sailing dinghy or to a lesser extent a sculling shell) they will indeed drain water, slowly, and at the expense of significant drag. They then need to be locked shut, and you need a bulletproof installation not to get water into your hull structure. For slow speed like an ocean rower, particularly one that's getting swamped, they'd be worse than useless.

    For ocean rowing, the stability gains in keeping mass as low as possible preclude having your floor above the water line. You'd loose more than 'a bit' of stability while doing so. This is all right (and cool) in a wide boat built for surf (I'd love to try one in surf even if I've never seen one built for solo rowing), but for a narrower, faster boat, not an option.
     
  4. gonzo
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    gonzo Senior Member

    Have you ever used a bailer? They don't swamp your boat or create a lot of drag. When the speed decreases, the flap keeps water from coming in.
     
  5. dcnblues
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    dcnblues Senior Member

    Yes, I have used them, as I said, on rowing shells and sailboats. Just ask laser racers how much they've always liked theirs. I've never seen one whose flap reliably 'keeps water from coming in,' especially in a boat that isn't moving.
     
  6. rwatson
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    rwatson Senior Member

    Its true you dont need the angst of foot or bum fiddling when you are trying to get some rowing done.

    If you are putting a rowing seat in, (on rollers, to move fore and aft), that would be an ideal canditate to attach a line to, that operated some kind of pump.
     
  7. viking north
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    viking north VINLAND

    Dcnblues As an experienced open ocean rower I can attest it is almost impossible to maintain a constant speed in the sea state you are describing where the boat is taking on water. It's a situation where one is struggling to get up the face of a wave one minute and fighting to control the surfing speed down the back in the next. This also occurs but to a lesser level when attacking or running diagionally in non breaking seas, which by the way is the most efficient expeniture of energy when seas are present. Whether creating suction or inertia to move water you need good forward motion(speed cycles) to move the water back and out. This is going to be very difficult to achieve while the boat is in the correct trim to do so,due to the short time duration. During the surfing part of the cycle you have the speed with very little spent energy but the boat trim is wrong to expell water. While in the trough and at the beginning of the wave face cycle there is a possibility to create some positive bailing conditions but the timing is short especially if the crests are close causing a drop in forward momentum, which of course is counterproductive. I think your idea could work but with very limited success being too subject to co-operating sea conditions which as you know is not always the case. However it is an interesting concept and it is always refreshing to see independent thought and an inventive mind at work in this conformist world we live in today. My advise experiment you've nothing to lose but do it close to shore :)

    A yacht is not defined by the vessel but by the care and love of her owner--
     
  8. dcnblues
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    dcnblues Senior Member

    Thanks Viking. I'm largely in agreement with you about how difficult it would be to get this functional.

    I'm thinking about a boat with enough reserve buoyancy that you could still sit in it even when swamped. And rowing it conditions mild enough to only ship mild, non-performance affecting amounts of water. Heavier conditions I just wouldn't go out, or get home quickly.

    However, in case of something unusual, say a heavy freighter wake you happen to not see that dumps in a wave's worth, I'd love having a system that could use your existing acceleration to clean out the boat. I still think it's doable, but it would depend on so many variables that it'll be hard to design right the first time.

    The biggest problem is keeping a scupper gate above the water line from shipping water from a following wave. One would think there'd be a good design for that by now, but I haven't seen one. (Ball valves? Please. More complaints on internet than compliments).

    Possibly (though I shudder a bit at this) something powered, electric, driven by a smart small programmed chip. I want to start playing with Arduino anyway. My project's not looking good at the moment anyway, but I do thank you for seeming to get my question. Very grateful for your wise comment.
     
  9. thedutchtouch
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    thedutchtouch Junior Member

    sliding seat or fixed? if sliding it seems that you could mount some sort of piston to the seat and have one end fixed in the boat, a bit of hose and some one way valves and you're in buisiness
     
  10. dcnblues
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    dcnblues Senior Member

    I'm sorry my original post didn't make clear: A sliding seat.

    And that would be a different solution, and one that would require additional energy. I'm looking for a solution elegant enough to use the energy already being put into pulling the oars.

    (However, to do it your way, it makes more sense to me to have a rotating turbine pump with a ripcord that you could hook and unhook to the seat).
     
  11. dcnblues
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    dcnblues Senior Member

    My concept is inertia only, and with practice, the timing could be achieved. One quibble with your comments: the 'drop in forward momentum' would actually not be counterproductive. Imagine the boat stopped, so the water in bilge has zero inertia. The wave face hits, tilts the boat stern down. The oars grab, and take a strong bite, accelerating the boat up to somewhere around 3-5 knots. The boat is sliding away from the bilge water, forward and up. The stern of the bilge will slam into that slack water with kinetic energy, enough to lift some of it above the water line. Designing a scupper to let it out is the trick. Also the shape of the bilge. And to keep that scupper from shipping water (the tricky part).

    Speed is also something I've considered. Consider a through-hull with a rigid cable (in the stern). The cable is attached to a propeller. The pilot releases the cable and slides the prop out into the water stream. The flow turns the prop. The prop turns the cable. The cable turns as it goes through the hull (on sealed bearings) and drives some kind of pump. When retracted, the prop is flush against the hull in it's own recession.

    Problem there is of course drag, adding to expended energy.
     
  12. dcnblues
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    dcnblues Senior Member

    A powered scupper gate might be another solution. Strong enough to prevent water from entering when following waves put it under water, fast enough to open and close only when the water needs to get out. Perhaps with a thumb switch wired to the oar grip. Calibrating a sensor and programming a chip to get this timing right would be a ton of work. Of course, that's adding a battery, motor, and wiring to the weight of the boat, and rigging it to be waterproof and reliable.

    Still, a battery and wiring would allow for a lighting system which would allow rowing after dark, which has a certain appeal. Hmmmm.
     
  13. dcnblues
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    dcnblues Senior Member

    I was also hoping to get a real pro's comments as my grasp on hydraulics / hydrodynamics is at a layman's level.

    Suppose you design a bilge that is cylindrical. At 1/4 of the boats length from the stern, it starts narrowing in diameter. It exits just above the water line at the tail of the boat, and it's diameter is significantly smaller (1/4 the size before it started to narrow? More? I don't know).

    Now, put an upward gooseneck in the bilge/tube, one that gets it well above waterline. Assuming enough water to fill this bilge tube, as it accelerates (relatively) aft, the diameter constriction will increase its pressure and velocity (right?) Enough to get it over the upward bend (yes, in theory, but how much)?

    It seems doable, but I've never seen or heard of something like this. If it's not practical, there has to be good science as to why. But with a narrow enough bilge, I can easily see this working, even if for only small amounts of water with each stroke.
     
  14. Tim B
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    Tim B Senior Member

    A battery and submersible in-line pump work wonders. I use the system on a dinghy, and when you're single-handing (two-man boat) it really makes life easier. Fit the pump as low as possible (ideally below the water-tight floor, then fit a skin-fitting through the floor at the lowest point. As long as the pump is at the lowest point, then it will "self-prime" (read fill up with water) itself. Run the exit tube up the keel and add a gooseneck if you don't like non-return valves (I find the small ones clog a lot).

    Switches etc. are best in a sealed panel within easy reach (at least as a backup/override). Any articulated electrical equipment (ie. switch on wire) is prone to failure. You may consider a solar panel to top-up the battery, if you are rowing for any considerable period. A water-level switch is also worthwile. This can be as simple as a float and magnet in a tube.

    Keep it simple and maintainable. Good luck,

    Tim B.
     

  15. science abuse
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    science abuse Junior Member

    For what its worth, I've been putting extensive thought into this problem for a couple of years. My work is centered specifically around rough condintions, rowing through the break, and shedding lots of water.
    Though I've come up with a few pumping solutions that can work off either oar or electic/solar power, the only solution that makes any sense is to have a tightly sealed, self bailing hull. I've been out in rough conditions and have ben swamped by single waves. It makes my 16ft skiff impossible to control, way too much weight. You need to loose it fast. What I settled on as best solution is a hull design resembling the Hunter dailsailer line, with the stern almost entirely open:
    http://www.sailboatlistings.com/sailimg/m/9070/main.jpg
    Water comes in and goes out, quickly.

    For pumping, I picked up and cylindrical "fluid transfer pump", which can be connected to the oar and the hull. With a bit of math, you figure out your stroke curve, and therefore how long your connecting shaft needs to be to give you a full pump of water per every stroke. You could set them up to pump off your sliding seat. Mount one to both sides for balance, and prepare for a bit of extra drag. I cannot speak to its reliability, as I've only used it for a few pumps so far. it may wear quickly, especially with salt water. Keep that in mind when selecting a pump.
     
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