Finally remembered an example... A canoe of all things.

Discussion in 'Boat Design' started by Schoonner, Dec 21, 2011.

  1. Schoonner
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    Schoonner Senior Member

    I remembered a way to make a vessel float even if the hull has filled with water. The aluminum canoes that were at summer camp so many years ago reminded me.

    We had to learn to row a canoe that has capsized back to the shore. We had to go something like 300 yards with two people paddling a canoe that was completely submerged under the water and trying to roll upwards out from underneath you. (The sailboat keel would stop that nonsense.)

    Could a safety device use the insides of the mast like a snorkel and inflate something like car tire inner tubes around the stem and stern of a vessel to make it float even if it were hit amidships by a rogue wave and the hatches were open?

    The rubber might be made like a childs balloon or something so that if It hit the bottom or another boat it would deform instead of deflate and also be somewhat self repairing to a point? (You can stick a lubricated knitting needle straight through a balloon and pull it back out without it deflating... well, you can once anyways.)

    I've seen sunken fishing boats recovered with car tire inner tubes before and you can actually lift a LOT with only a pair inflated tubes.

    Maybe even have a snorkel for the engine so that it can be started and under water and you aren't stuck without power.

    Something like this:
    [​IMG]

    The device could probably even be switched on using a float and lever like the thing that shuts off the water in the toilet of most homes to keep the tank from overflowing.
     
  2. Dirteater
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    Dirteater Senior Member

    I've believe a pool-noodle holds up around 110 lbs.
    I'm trying to remember the name of the old painted tan/fake wood-grain aluminum canoes, I seem to remember an Indian Chief was painted on the bow.
    the also had a kind of 1/2 pool-noodle down each side of the canoe. It was a mass production boat I think, Sold by Sears or something like that.

    someone here might remember,
    its probably a classic now.

    your question reminded me of that canoe.
    ( I should try to find the picture )
     
  3. Schoonner
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    Schoonner Senior Member

    Just to brag a little, I used to be the only one who could take all the wake that the counselor who was head of the boat stuff could muster with a 15ft boat they used for water skiing and still stay upright. He got a little angry and started running the power boat in figure eights pretty close to me trying to get me to capsize and I kept having to swing the bow around this way and that to keep from getting swamped.

    It stopped being a game after a while though and I had to go to shore cause he was getting mad. Kinda scared me really and I almost tipped her over just so he would stop, but I'm stubborn like that. LOL!
     
  4. WestVanHan
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    WestVanHan Not a Senior Member

    IIRC one cubic foot of air will lift 64 pounds in salt,and 62 pounds in fresh.
     
  5. Schoonner
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    Schoonner Senior Member

    In that case, it will take 46.875 cubic feet of balloons to keep a Neptune 24 just beneath the waves. That means that I would need a snorkel some 8 ft higher than the lowest floating level to keep the engine running in 6ft waves. More than that if some of the balloons broke. Especially if it unbalanced the load and tilted the boat sideways. I think it would be better to have some reserve balloons which means that I'd need more than 150 square foot of material to make the balloons.

    I will have to look at a mechanical method of inflation, such as when the switch is flipped, the balloons will have springs that will push the insides of the balloons apart and inflate with the negative pressure that is created.

    Or, I could compress the air into a container like a scuba tank or two, and when the switch is flipped it releases the compressed air.

    Maybe something like Helium would take less volume than air because it is lighter than air?
     
  6. messabout
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    messabout Senior Member

    Dirteater; Beware! A pool noodle will hold up only about eleven pounds. That statement is based on a noodle with a diameter of 3 inches and a length of 48 inches. A hundred ten pound displacement noodle would need a little more than 3000 cubic inches of volume. Such a noodle could be.....say 60 inches long and 8 inches in diameter. or some combination of dimensions that would yield the necessary 3000+ cubic inches.
     
  7. Submarine Tom

    Submarine Tom Previous Member

    What is being overlooked here is density. I am 200 pounds but float with my lungs full of air. I sink if I exhale though.

    An outboard engine weighing 100 pounds on land only weighs about 70 pounds when submerged.

    How much does your Neptune 24 weigh submerged? You'll need more than that to keep it afloat.

    Compressed CO2 (carbon dioxide) in cylinders is an excellent gas to inflate floatation devices.

    -Tom
     
  8. Schoonner
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    Schoonner Senior Member

    WOW! How does one measure the weight of something that is submerged? Will I have to account for the water inside the hull and lift some of it too?
     
  9. messabout
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    messabout Senior Member

    Schooner; To answer your questions....First one first. Imagine that you have a sealed box that measures exactly 12 inches by 12 inches by 12 inches. Let the box contain something heavy like concrete or whatever. Weigh the box and its contents before it is tossed in the water. Suppose that it weighed 100 pounds. Now tie a line to the box and throw it over the side. Measure the weight while submerged with a fishermans scale.

    The box displaces one cubic foot of water (12 x 12 x12 = 1728 cubic inches which is exactly one cubic foot) The weight of the displaced water is 62.4 pounds per foot cubed, if fresh water, and 64 pounds per cubic foot for salt water. Actually those figures can vary slightly with temperature and contamination but they are close enough for practical purposes. Lets use salt water for this arithmetic. the box weighed 100 pounds and it displaces 64 pounds of salt water. Your scale for the immersed box will read 100 -64 =36 pounds. That's the general idea. Of course it will be difficult but not impossible to pre-determine the displacement of your outboard motor.

    About the canoe....If the canoe was half full you'd have to support the weight of the boat as well as all the water in it. If the canoe was awash...well that is a whole different deal because there would be no boundry between the water inside and the water outside. In either case it would be a chore to lift the boat out of the water.

    An aluminum canoe would sink unless it had some sort of flotation a fiberglass one would probably go down too. A wooden canoe would probably not sink because wood is lighter than water.

    We dumped the canoe because we had enjoyed too much of our beer and we were a little tipsy. The few cans that we had left would probably not sink in salt water but they probably would in fresh water because the cans weigh about two ounces and the beer has approximately the same specific gravity as fresh water. An old greek guy named Archimedes figured all this out a long time ago. (the ancient greeks did indeed have beer) If you want to get better details about the subject, just dial up Archimedes principle on Wikipedia.

    I await speculation by others about whether the beer would sink. If in bottles it surely would sink........I think.
     
  10. Schoonner
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    Schoonner Senior Member

    Ahh, so by displacing water with air, a balloon floats because the air is lighter than water. So, it is all about how much water is displaced by something lighter than the water. A boat however can be heavier than water, but sit on top of it because it displaces more weight in water than it weighs? Cool!

    So, it's a simple math problem then. I have to find out the volume of the Neptune24's structure vs it's weight and subtract the weight of the same amount of volume of water, then I will know how much it volume of water I will have to displace to keep it floating. I have a feeling it will be a lot less than I originally planned.

    I found out that the canoes have the front and rear pointy ends sealed off from the inside and the compartments trap air which gives them the reserve buoyancy.
     
  11. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I proposed adding Helicopter style emergency inflatable floats on keelboats

    so they would go straight down and stay there if swamped or holed.

    I've heard of liferafts stored inside under deck with big "DO NOT INFLATE INSIDE" directions, but I'm thinking "maybe that is exactly what I'd want to do" if the inflatable was designed to do that.

    I think I'd like a swamped boat, rather than a little raft and boat that sank in a mile of water.

    I'd think a swamped keel boat with a bunch of inflatables in the cabins would ride out a storm pretty well.
     
  12. Schoonner
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    Schoonner Senior Member

    Yeah! Just make sure nobody is inside the cabin when the thing inflates. That might be a problem..

    Maybe a bunch of smaller ones that could move out of the way if you wanted them to. I mean you wouldn't have to fill the entire cabins right? Just maybe the vee berth and the space beneath the cockpit. I mean how many cubic ft is a normal vee berth?

    I have seen a video of a concrete sailboat that the transom stuck out of the water and the bow was on the bottom 10 ft down, but it rolled and bobbed up and down in the waves because the rear berths were water tight. If the Vee berth were water tight, it might have still been floating. Especially if it were sealed with an innertube like structure.

    now that I watch the video again, http://www.youtube.com/watch?v=2dlCyH4g6yo , I think maybe it is actually the vee berth that is trying to float.
     
  13. Schoonner
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    Schoonner Senior Member

    I think maybe a catamaran would be easiest to do this with, just make a pair of inflatables between the hulls...
     
  14. Schoonner
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    Schoonner Senior Member

    I think maybe a catamaran would be easiest to do this with, just make a pair of inflatables between the hulls...

    Either that, or something like this, http://www.skirayachtdesign.com/elgeeclass.html
    [​IMG]

    I think it would be best to make an inflatable on something like that which would be housed above the waterline outside the hull folded accordian style along the rubbing strake, or whatever it is called along the edge where the deck and hull meet and down the sides of the hull so that it makes a small rubber water tight package and when it inflates it lines the hull and just makes like a high, thick chunk of rubber which would gradually flare out the upper part of the hull all the way around. Then when folded it, it makes a small package which would be good for a slightly flared hull shape. I will probably have to draw a section of it for you huh...

    It would inflate and only add a little thickness to the hull.

    There could also be inflatables which would inflate along the insides of the cabin roof to have the most usable area, while allowing for the most head room, It could even whistle as it takes up head room and fill slowly enough that it shouldn't knock someone down while only having to take a few inches of head room to accomplish it's goal of extra emergency reserve buoyancy. Or make it manually operated, since other inflatables could be inflated in the bilge automatically, and along the transom and vee berth where it is too thin to really do anything else with.

    EDIT, I think I would only need 2 cu ft along the length of the hull to displace enough to account for the weight of the hull and the engine, but I have no idea if I'm doing the math right.

    EDIT2:: I think the problem with using a float to inflate the devices is that if it capsized it would also trigger inflation, and it might be impossible to put her back upright without letting the air out. Humm.... Maybe that's a good thing cause if you can get the hatch open you could swim inside it and it might trap air... for a little while.... idk, I will have to think a lot and do some theory testing.
     

  15. rwatson
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    rwatson Senior Member

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