Inexpensive, DIY auto-bailer solutions for small sailing dinghies

Discussion in 'Boat Design' started by laukejas, Aug 9, 2019.

  1. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Hi,

    A few days ago I was discussing with a good sailor friend of mine, about the possible solutions for constructing an auto-bailer for small home-made dinghies with traditional cockpits (no sandwitch floor or open transom). As we see it, there are two ways of getting that water out (be it from spray, capsize, rain, etc.)

    1. Floor-mounted auto-bailer;
    2. Flaps in the transom.

    Now, for the first option, there are commercially available auto-bailers that utilize the negative pressure under the hull when the boat is underway, like Elvstrom:

    [​IMG]

    ... which are ridiculously expensive. And then there are small bailers like the one used in Laser class:

    [​IMG]

    ...which have a small opening and are only suitable for very small cockpit volumes.

    So, me and my friend are considering, is it at all possible to make an effective, watertight, and sturdy enough bailer like the Elvstrom, in typical garage workshop conditions? Could such a thing be made without specialized sheet bending machinery? Or could it be made from some other materials instead, maybe even 3D-printed? Have any of you ever built such a thing?

    The second option, flaps on the transom, would be much easier to build, as it is a simple door that can be kept shut with a piece of string or some simple lock, opening only one way. Just a piece of plywood on hinges and some rubber to make it watertight. Problem is, since a typical sailing dinghy has considerable rocker, the transom flaps would stop being effective at some point, because the water would accumulate at the lowest point in the hull (midships), rather than reaching the transom.

    My friend argues that the remainder of the water in the cockpit could be get rid off by trimming the boat (shifting crew weight aft), so that the hull bottom would be tilted downwards towards the transom, and the water would flow there and reach the flaps. That sounds reasonable to me, with one caveat. When the boat is underway, especially at higher speeds, waterflow separates from the transom (semi-planning), and as such, the suction cannot occur. The water would have to slowly flow out on it's own, with the boat being at a very awkward trim angle. Not good during racing. Also, the hull, especially the rocker curve, must be designed in a way that would make it possible to get the water all the way to the transom flaps by trimming it the boat, which might be a limiting factor in the over design.

    These are the two options we have discussed. Do you know of any other auto-bailer solutions? Or have you ever seen or built a DIY version of an Elvstrom bailer?
     
  2. jehardiman
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    jehardiman Senior Member

    Any class rules or hull projection restrictions? Yes, there are simple fixed educator designs, but most require a bung. BTW, Elvstrom bailers are dangerous, and I've got the scars to prove it!
     
  3. laukejas
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    laukejas Senior Member

    No restrictions. The bottom would most likely be made from 6mm plywood or 8mm cedar. The important part is that the bailer must not cause any additional drag when closed, and it must not leak when closed. I heard horrors about Elvstrom bailers, how they go about removing some toes, or even cut feet in half... So I certainly hope there is a safer way as well.
     
  4. Blueknarr
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    Blueknarr Senior Member

    A drink I had awhile back had home made bailers. It was a small diameter tube bent to be parallel to hull. A simple cork was stuffed into it to prevent refilling.

    Mostly worked well. Sometimes the cork was accidentally dislodged.
     
  5. laukejas
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    laukejas Senior Member

    Interesting. If I understand this right, the tube is bent parallel to the hull, on the inside of the hull? And then it terminates flush with the outside of the hull? Doesn't this tube hole cause turbulence, since the cork doesn't reach all the way through the tube?
     
  6. Blueknarr
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    Blueknarr Senior Member

    No. It was flush on the inside. Bent to point aft on the exterior. Probably created turbulence.
     
  7. laukejas
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    laukejas Senior Member

    Okay, I see. Thank you!

    Keep these ideas coming, guys :)
     
  8. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'd like something cheap, lightweight and simple that doesn't require or involve any new holes in the hull, mostly to suck water out of the seat of my SOT kayak. I'm imagining some sort of flexible pump that works either by stomping (rocking) with foot or even with buttocks (when seated in kayak). Pumping action would send water over the side by means of flexible tube.

    Ideally, it might have TWO pickup tubes that would work if EITHER one was in water, the 'dry' one not hurting the pumping too much, so once "rigged" could be counted on to suck the last little bits of water regardless of which tack you were on, or if water was collecting in more than one spot. It would be about like a Whoopie-Cushion. https://www.amazon.com/2CHILL-Whoop...56&hvtargid=aud-801381245258:pla-798330328255 Foot operation might be improved by sandwiching the thing between the floor and a small flat object. Whoopie says "self inflating". Beef up that feature and it would automatically suck and fill with water, then you apply force and pressure to pump, repeat.

    The most important feature would be that it wouldn't be a "feature" of the boat, just another thingy you could use on any boat.

    Of course, that wouldn't be a true SELF baler, but I wouldn't mind exploring the "over the gunnel tube" concept as a true self baler that used sucking generated by a trailed tube with suction-maximizing terminus. I figure most of the need for baler would also be when the boat is moving fairly fast.

    Not sure how all this would function but it does remind me of another question: The guy that invented the Bag-Pipes...what was he REALLY trying to make???
     
  9. messabout
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    messabout Senior Member

    The Sunfish bailer is dead simple and it works well enough. It consists of a small clam shell like protrusion with the open part aimed aft. A plug in the inside of the boat seals it when not in use. Sure it makes some turbulence but I suspect that it does not create a measurable amount of drag. By the time the fluid flow gets to the point of extraction the flow is already turbulent except at very slow boat speed.

    My preference is transom flaps. I never had any trouble with them on my Windmill, Thistle, and several odd ball sail boats. I used plexi glass or similar transparent flaps. I could easily see what was happening at the transom which might be useful for fore/aft trim adjustments.
     
  10. jehardiman
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    jehardiman Senior Member

    Eductors work by creating a local low pressure, so generally a fixed educator would always be in the flow. The other thing is the area, to drain faster you need more inlet and outlet area; of course the inlet area need to be sealed once the cockpit is dry and for slow speeds. I have designed and implemented several eductors, but never a fixed seal for one. The easiest would be a 1" hole drilled through the hull. On the outside would be a hollow wedge 1 1/2" inches along flow, 2" across flow and 1/2" high. The thin part of the wedge starts at the leading edge of the hole and the trailing edge of the wedge is 1/2" aft of the hole. You could use a bung or either a inside or outside flap seal. Let me think about it for a few days and I could probably come up with a 3D printable unit through bolted with the outside wedge and some workable inside seal.

    Edit to add; Oh yeah, needs to be step and butt proof also.
     
  11. laukejas
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    laukejas Senior Member

    I had that kind of idea. I had an air pump that looks very much like the one in your link. Unfortunately, when I tried it on water, it just didn't work. Well, it kind of did - but it would fill extremely slowly, because the water is much more viscous. I suppose a water pump of this kind would have to be designed somewhat differently, but I've never been able to source one.

    Yes, such bailer would be fairly simple to construct. But as you said, it protrudes through the hull... Which causes some drag (maybe not much, as you suggested), but it seems like a fragile thing to have protruding out like this. Beaching, launching, grounding.... I can think of dozens of scenarios that could rip this bailer off. Sure, you can be extra careful... But things happen.

    About transom flaps - in these boats you mentioned, was it possible to get ALL of the water out through the transom flaps?

    If you could make that 3D model, it would be great! But would this design protrude permanently, or would it be retractable? I didn't quite get that part. I should have mentioned in my first post that retractability is kind of a requirement, due to the afore-mentioned drag... And the hazard of damaging the device during accidental groundings or out-of-the-water handling.
     
  12. portacruise
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    portacruise Senior Member

    Battery powered pump with a water pressure sensing switch and the intake at the lowest shaped spot, where the water will accumulate.
     
  13. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    I agree with Porta, a small bilge pump, a small lithium battery.
    Solar or not. Just take it home and charge it.
    Perhaps less drag in the long run...
     
  14. laukejas
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    laukejas Senior Member

    Electric solutions are surely possible, but I wanted to investigate the mechanical ones more in this thread :) Something like Elvstrom, only homemade, would be ideal, if it's possible to build without leaking and without any permanently protruding parts on the outside of the hull.
     

  15. Squidly-Diddly
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    Squidly-Diddly Senior Member

    take two sheets of semi-stiff flexible plastic and glue to either side of bag and connect the sheets with a sprung "C" joint/hinge of some sort to increase self-filling force.
    These say "extra thick" but I think you'd want about 2-3X as stiff. https://www.amazon.com/NIROLLE-Flex...cutting board&qid=1565461893&s=gateway&sr=8-9

    As for the "C", I guess you could go with either smaller version of these and use the handle end instead of jaws. https://www.amazon.com/dp/B07FPTTMKT/ref=twister_B07GZXHB2X?_encoding=UTF8&psc=1 You could use cutting board itself as spring and just fold it over the bag, but I don't think cutting board plastic is very springy. Probably not very good for gluing either.
     
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