Controls for balancing tanks

Discussion in 'Boat Design' started by Quietboats, Jul 13, 2011.

  1. Quietboats
    Joined: Feb 2004
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    Location: Marshallberg, North Carolina

    Quietboats Junior Member

    Hello, I am working on a 26.5' length x 6.5' beam double ended launch. It will have an enclosed aft cabin with open cockpit forward. I want to install a couple 8 cubic foot ballast tanks fore and aft for balancing out the load depending on where passengers are sitting. I am wondering if anyone knows of an inclinometer setup which would automatically transfer the water as needed to keep the boat level fore and aft. Ideally I would like to have a system where water could be pumped in and out as well to compensate for total load but that may be asking too much.

    Any help would be most appreciated. Thanks!
     

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  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    The drawing shows a sweet looking, vintage style, boat.

    Moving water ballast would seem to be a straightforward matter of using float switches from a water well system. Two pumps, two switches,some solenoid valves, and you should have a workable system. On the other hand, this seems like a lot of hassle just to affect trim. The passengers and certain items of gear, are much more easily moved than all that water. Additionally the water will add 500 pounds more or less to total displacement (assuming 4 cubic feet of water per tank). Extra displacement increases power absorption etc..
     
  3. Submarine Tom

    Submarine Tom Previous Member

    Seems like a great idea but probably not worth the hassle, weight penalty and time delay of pumping. Water storage tanks may be a good way to go. Levels and draw could be planned ahead according to anticipated load distribution that day.

    -Tom
     
  4. thudpucker
    Joined: Jul 2007
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    Location: Al.

    thudpucker Senior Member

    I saw an earlier SubMarine on Hist Channel that had a Sliding weight in the Keel area for just that. However they got the weight too far Fwd and couldnt retrieve it and took that final plunge out of control. All the way to the Scene of the Crash.

    Messabout's switches are a great approach for Auto. But you might make a set of switches for that use, controlled by the Brainiac at the helm.
     
  5. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Interesting problem. You want a very slow response that ignores pitching due to waves and draws very little power. I think I might use a closed system and pump air with a fish tank pump. Pump is on or off. A level sensor routes the air from bow to stern or vis versa. So there is a cross connection for air and another for water. It might be cheaper to use two pumps rather than electric valves. Level sensor turns pumps on alternately.
     
    Last edited: Jul 14, 2011
  6. srimes
    Joined: Sep 2008
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    Location: Oregon

    srimes Senior Member

    I wouldn't want it to be automatic, because it'll run all the time if there are any waves. You'd have to have an intellegent system that took the average over a longer time (say 1-5 minutes) before responding. If you want auto I'd have it manually activated. Just push the "level" button before setting off. But there isn't much point to that, so just have it all manually controlled.

    I wouldn't run a pipe between the tanks, too far. Just fill/empty each individually with manual control. That will allow you to adjust trim and total ballast at the same time.
     
  7. Poida
    Joined: Apr 2006
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    Location: Australia

    Poida Senior Member

    Nice looking boat.

    Marine safety here Western Australia, advises when under way that passengers should be seated to avoid losing balance and getting injured and advised to evenly distribute passengers for equalibrium. So I assume the system is not to be used when in open water.

    Also when travelling passengers moving side to side create more of a problem that fore and aft.

    The only time I can see this unit usefull is on calm waters while cruising during a drinks and nibbles tour.

    So, let's start by saying I know stuff all about anything, but here's my bit.

    Pumping water from one tank to the other seems too slow, and can't keep up with a person walking.

    Suggestion 1. Have a tank at the stern only making the stern lower and control the level with trim tabs. This will be more responsive and you may probably be able to get the tabs on either side work independantly to correct roll.

    Suggestion 2. Probably as dumb as suggestion 1. Have a pipe running from end to end half full of water. A pendalum switch will turn a screw, which in turn will tilt the pipe fore or aft allowing the water to compensate. Baffles should be in place to prevent a sudden rush of water. This will also be more responsive than pumping water.

    The boat is not big so I can envisage by the time the pump starts and pumps water, due to a person walking one way, another person would walk the other way and start the pump pumping backwards.
     
  8. Quietboats
    Joined: Feb 2004
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    Location: Marshallberg, North Carolina

    Quietboats Junior Member

    Thanks for all the input. I had assumed there were similar requirements on larger vesssels and hoped I could just use the electronic controls for this system. Yes, it would have to take a reading over a long period of time--say 3 or 4 wave periods so it is not constantly adjusting.

    My biggest concern is all the passengers will want to be in one area depending on weather conditons--I am planning on a capacity of 8 adults but 4-6 is will probably be more common. There will be two pilot stations on either side of the forward cabin wall so the driver will always be with the passengers. I'm afraid with everyone up front the prop will be out of the water somewhat--not good. Also, I don't think there is enough bouyancy aft to have the boat look even remotely respectable with everyone in the cabin.

    This is a slow speed electric boat with a 2' wide boxed keel below so there is more buoyancy under the cabin than might be assumed from the drawing. The batteries are located forward in the keel with the motor in the aft section. So at 6 knots, trim tabs are out of the question.

    I guess the simple solution, at least as far as I've come up with so far, is to have three tanks--one center under the cockpit sole as the main supply tank, and one both aft and fore. Then just simply pump water to whatever tank needs it by looking at a inclinometer gage. I was just hoping for something a little more automatic. Any further ideas will be most appreciated. Thanks again! Tom
     
  9. Submarine Tom

    Submarine Tom Previous Member

    You don't need a centre tank, just split the difference between the fore and aft tanks. But it's a huge waste of buoyancy (the enemy of speed).

    -Tom
     
  10. Quietboats
    Joined: Feb 2004
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    Location: Marshallberg, North Carolina

    Quietboats Junior Member

    After reading srimes post again--that makes a lot of sense to have only two tanks and just keep it manual by filling individually--still it is fun to think of ways to compexify everything.

    And Poida, yes the boat is mainly a "drinks and nibbles" operation. I do like your suggestion of the tilting pipe--quite a novel idea--I just don't know if I can fit one big enough for the job physically into the boat. And yeah, I do worry about the side to side load but think moving passengers will have to suffice for that problem.
     
  11. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    You don't need a smart controller if the pump is slow enough. Yes , it would run all the time- at about 10 watts. When trimmed, it would would spend equal time pumping each way. A simple bang-bang controller would do. Compare 10 watts to the drag penalty of an out of trim hull in Michlet.
     
  12. Quietboats
    Joined: Feb 2004
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    Location: Marshallberg, North Carolina

    Quietboats Junior Member

    Submarine Tom: You beat me to it--yes you are right the center tank can go. Also, this is a displacement hull so weight means something but not as much as trim. Thanks though.
     
  13. Submarine Tom

    Submarine Tom Previous Member

    Sounds like you've got it all figured out.

    Good luck.

    -Tom
     
  14. Poida
    Joined: Apr 2006
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    Location: Australia

    Poida Senior Member

    Now I'm thinking of another solution even dumber than the last two.

    It appears that the boat ballast tanks will be utilised for socialising. Best use for a boat.

    However, instead of controlling the ballast of the boat, control the movement of the passengers.

    I figured that, according the cramps law, that an there should be around 1 person per metre of boat. Around 3 feet, for countries that still use feet, toes or ankles for measuring, this means that the craft can comfortably carry 8 passengers.

    All the people can not stand in the same spot, unless they stand on each other's shoulders. The size of the tanks intended, in cubic toes, from my calculations would be around the weight of 3 medium sized people.

    This means you would expect everyone except one person the be at one end of the boat at one time. It seems a bit of an overkill.

    Anyway, I think it would be easier to control where the people are wqithout them even knowing that they are being controlled.

    1st. Have your drinks in 3 eskies. One at the front for spirits ( the correct term being the pointy end), one midships for cool drink and one at the rear (the blunt end) for beer. This will keep people counter balancing each other as they move around for drinks.

    2nd. Put captive nuts in the deck so you can screw some tables down, that can be easily removed for fishing etc. Because the tables are in the way people can't all congregate in one spot.

    3rd. Don't have areas where people can sit in one spot. Across the blunt end is where people like to sit. Place a railing across with just enough gap for one person.

    Having said all that I really think that putting ballast tanks in a boat with pumps etc. is simply installing another thing in a boat that can go wrong, and when it does it will be worse than not having it.
     

  15. Submarine Tom

    Submarine Tom Previous Member

    He wont find ballast tanks effective for his needs. I know this but Tom still needs to learn it the hard way as he refuses to give up on the idea.

    Live ballast (i.e. passengers) is definitely the way to trim the boat. But, again, Tom doesn't seem willing to make this allowance.

    -STom
     
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