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Re: [pop-pop-steamboats] Re: Pop Pop 16' canoe

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  • Donald Qualls
    ... There are two factors at work here (maybe three). First, fineness ratio; generally, for a given displacement, the finer hull (longer and narrower) will
    Message 1 of 15 , Aug 2, 2009
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      sydneygreenestreet wrote:
      > So a
      > longer boat of similar beam to a shorter boat will require less power
      > to get it to go faster that the shorter boat. ie a boat 12' by 4'
      > will need more power that a 20' x 4' boat to travel at the same speed
      > ergo a 16' x 3' canoe (you call them Indian canoes made famous by
      > Nelson Eddy and Jannete MacDonald to me they are classed as yes you
      > guessed it Empire Canoes)will need less power to travel at the same
      > speed as an 8' x 4'6" snub nosed dinghy....
      >

      There are two factors at work here (maybe three). First, fineness
      ratio; generally, for a given displacement, the "finer" hull (longer and
      narrower) will require less power at any speed than the less fine,
      though refinements in the shape beneath the waterline can reduce power
      requirement, up to a point, for any fineness.

      Second, hull speed; there's a speed, for any given waterline length of
      displacement hull (that is, a hull supported only by buoyancy, not by
      dynamic forces), above which the power requirement for greater speed
      increases very sharply, and that speed is the one at which the trough
      following the bow wave just reaches the stern (since the speed of common
      waves in water is fixed, this comes to a specific speed for any given
      hull length). Hull speed is why the aircraft carrier is typically the
      fastest ship in a fleet, even though destroyers have much higher power
      to weight ratio; a modern supercarrier will have a hull speed in excess
      of forty knots, while a destroyer is limited to not much over twenty,
      and a tender (basically a miniature tanker, not much bigger than an
      oceangoing tug) may have to plug along at twelve to fifteen. A transom
      stern can help here, because it provides an effective lengthening of the
      waterline at speed when the water takes time to fill in behind the boat.

      The potential third factor is the one mentioned relative to hull speed:
      if a hull planes, that is, is partly supported by dynamic forces, it can
      go faster than hull speed without the precipitous increase in required
      power. This is why a tug with five thousand horsepower on tap can still
      only churn away at ten or twelve knots, while a runabout with as little
      as fifty horsepower can manage thirty-five (and with a couple hundred
      can go sixty): the runabout is using hydrodynamic lift to climb over the
      bow wave instead of wasting horsepower just building it higher and higher.

      This is applicable to pop-pop boats because every one I've seen is a
      displacement hull; even if the hull is correctly shaped to plane,
      pop-pop motors don't have enough power to climb up onto the bow wave, so
      none of them will go faster than hull speed -- which is pretty slow for
      a boat with a waterline length of, at most, a couple feet.

      For the application of a people (and dog) carrying canoe, it's unlikely
      an reasonably sized power plant will push a canoe significantly faster
      than a couple strong paddlers. Beyond that, wind forces on the hull's
      freeboard can be high enough to upset a paddler (I recall it being quite
      difficult to paddle upwind with a single person in the stern, because
      the available steering force was barely able to overcome the weathervane
      effect) and are likely to swamp the thrust available from even a fairly
      large pop-pop. On the other hand, if you have a canoe to experiment on,
      and the tubing and burner to play with, the worst you'll likely do is
      set fire to the canoe, sink an open bottle of LPG (which will pop up
      again when it gets sufficiently empty), and have to swim for land with
      your water dog towing you...

      --
      If, through hard work and perseverance, you finally get what you want,
      it's probably a sign you weren't dreaming big enough.

      Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

      Opinions expressed are my own -- take them for what they're worth
      and don't expect them to be perfect.
    • Jean-Yves Renaud
      Additional comments to message #1632 and 1634 from Sydney and Donald. 1°) The speed of a boat is stable when the hydrodynamic resistance is equal to the
      Message 2 of 15 , Aug 2, 2009
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        Additional comments to message #1632 and 1634 from Sydney and Donald.
        1°) The speed of a boat is stable when the hydrodynamic resistance is equal to the propulsive thrust. The hydrodynamic resistance is the sum of frictional resistance, wave resistance, and air resistance.
        The frictional resistance and air resistance evolve with the square of the boat velocity.
        The wave resistance is something much more complicated. For light displacement boats, when planning conditions are met it can decrease (and then increase again with the boat velocity). Unlikely to decrease for a canoe due to the shape of the hull.
        Whatever, pop-pop propulsive power is so minute that there is no chance of planning of a canoe.

        2°) To get the same thrust, 2 (or more) small engines are preferable to a big one because multiple engines are lighter and smaller, and because they develop a higher jet speed, which means a possible higher boat speed.
        Go to www.eclecticspace.net (it is not a commercial site), click on "pop-pop", then on the English flag, then on "To know more…" and scroll down to open the 3rd document from the bottom of the list: It is entitled "Engine/hull adaptation". Look at the graph at the end of this document. It expresses clearly the limits of pop-pop propulsion.


        --- In pop-pop-steamboats@yahoogroups.com, Donald Qualls <silent1@...> wrote:
        >
        > sydneygreenestreet wrote:
        > > So a
        > > longer boat of similar beam to a shorter boat will require less power
        > > to get it to go faster that the shorter boat. ie a boat 12' by 4'
        > > will need more power that a 20' x 4' boat to travel at the same speed
        > > ergo a 16' x 3' canoe (you call them Indian canoes made famous by
        > > Nelson Eddy and Jannete MacDonald to me they are classed as yes you
        > > guessed it Empire Canoes)will need less power to travel at the same
        > > speed as an 8' x 4'6" snub nosed dinghy....
        > >
        >
        > There are two factors at work here (maybe three). First, fineness
        > ratio; generally, for a given displacement, the "finer" hull (longer and
        > narrower) will require less power at any speed than the less fine,
        > though refinements in the shape beneath the waterline can reduce power
        > requirement, up to a point, for any fineness.
        >
        > Second, hull speed; there's a speed, for any given waterline length of
        > displacement hull (that is, a hull supported only by buoyancy, not by
        > dynamic forces), above which the power requirement for greater speed
        > increases very sharply, and that speed is the one at which the trough
        > following the bow wave just reaches the stern (since the speed of common
        > waves in water is fixed, this comes to a specific speed for any given
        > hull length). Hull speed is why the aircraft carrier is typically the
        > fastest ship in a fleet, even though destroyers have much higher power
        > to weight ratio; a modern supercarrier will have a hull speed in excess
        > of forty knots, while a destroyer is limited to not much over twenty,
        > and a tender (basically a miniature tanker, not much bigger than an
        > oceangoing tug) may have to plug along at twelve to fifteen. A transom
        > stern can help here, because it provides an effective lengthening of the
        > waterline at speed when the water takes time to fill in behind the boat.
        >
        > The potential third factor is the one mentioned relative to hull speed:
        > if a hull planes, that is, is partly supported by dynamic forces, it can
        > go faster than hull speed without the precipitous increase in required
        > power. This is why a tug with five thousand horsepower on tap can still
        > only churn away at ten or twelve knots, while a runabout with as little
        > as fifty horsepower can manage thirty-five (and with a couple hundred
        > can go sixty): the runabout is using hydrodynamic lift to climb over the
        > bow wave instead of wasting horsepower just building it higher and higher.
        >
        > This is applicable to pop-pop boats because every one I've seen is a
        > displacement hull; even if the hull is correctly shaped to plane,
        > pop-pop motors don't have enough power to climb up onto the bow wave, so
        > none of them will go faster than hull speed -- which is pretty slow for
        > a boat with a waterline length of, at most, a couple feet.
        >
        > For the application of a people (and dog) carrying canoe, it's unlikely
        > an reasonably sized power plant will push a canoe significantly faster
        > than a couple strong paddlers. Beyond that, wind forces on the hull's
        > freeboard can be high enough to upset a paddler (I recall it being quite
        > difficult to paddle upwind with a single person in the stern, because
        > the available steering force was barely able to overcome the weathervane
        > effect) and are likely to swamp the thrust available from even a fairly
        > large pop-pop. On the other hand, if you have a canoe to experiment on,
        > and the tubing and burner to play with, the worst you'll likely do is
        > set fire to the canoe, sink an open bottle of LPG (which will pop up
        > again when it gets sufficiently empty), and have to swim for land with
        > your water dog towing you...
        >
        > --
        > If, through hard work and perseverance, you finally get what you want,
        > it's probably a sign you weren't dreaming big enough.
        >
        > Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
        >
        > Opinions expressed are my own -- take them for what they're worth
        > and don't expect them to be perfect.
        >
      • sydneygreenestreet
        No one has mentioned hull Squat the phenomenom that occurs when traveling at speed in shallow water.... Seriously I don t expect speed in excess of around 2
        Message 3 of 15 , Aug 4, 2009
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          No one has mentioned "hull Squat" the phenomenom that occurs when traveling at speed in shallow water....
          Seriously I don't expect speed in excess of around 2 - 3 knots, serious paddlers can get considerably faster than this....Canoes are about as fine as you can get and move efficiently with little effort, just as any Canadian....
        • David Halfpenny
          ... From: sydneygreenestreet ... I learned a lot about canoes one day on the Cam. I was coxing (steering) a racing eight
          Message 4 of 15 , Aug 4, 2009
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            --------------------------------------------------
            From: "sydneygreenestreet" <sydneygreenestreet@...>

            > No one has mentioned "hull Squat" the phenomenom that occurs when
            > traveling at speed in shallow water....
            > Seriously I don't expect speed in excess of around 2 - 3 knots, serious
            > paddlers can get considerably faster than this....Canoes are about as
            > fine as you can get and move efficiently with little effort, just as any
            > Canadian....
            >
            I learned a lot about canoes one day on the Cam.

            I was coxing (steering) a racing eight parked at the bank, and past came
            two big red-faced lads paddling furiously in a double canoe, throwing up a
            mighty wake. Behind them was a slight young schoolboy on a scull boat (two
            oars). He was waiting courteously behind them, just touching his blades
            lightly in the water a couple of times a minute to keep up with the canoe.

            OK, I can handle a kayak in choppy water, and if I were hunting beaver in
            the northern territories I'd take the canoe every time, but the contrast in
            mechanical efficiency was staggering! Rowing coaches use bicycles because
            they have to to keep in sight of the crew.

            David 1/2d
          • Donald Qualls
            ... Assuming the boats were similar in length, this is about what you d expect -- the finer scull requires a little less power at any speed below hull speed,
            Message 5 of 15 , Aug 4, 2009
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              David Halfpenny wrote:
              > I learned a lot about canoes one day on the Cam.
              >
              > I was coxing (steering) a racing eight parked at the bank, and past came
              > two big red-faced lads paddling furiously in a double canoe, throwing up a
              > mighty wake. Behind them was a slight young schoolboy on a scull boat (two
              > oars). He was waiting courteously behind them, just touching his blades
              > lightly in the water a couple of times a minute to keep up with the canoe.

              Assuming the boats were similar in length, this is about what you'd
              expect -- the finer scull requires a little less power at any speed
              below hull speed, but any attempt to exceed hull speed will soak up a
              tremendous amount of power. Compounding this is the fact that a common
              sliding seat single scull is several times more efficient in converting
              muscle power into forward motion than a canoe with conventional paddles
              (so is a kayak, come to that) -- that is, for a given amount of required
              power, less effort is demanded of the rower than of canoe paddlers.

              --
              If, through hard work and perseverance, you finally get what you want,
              it's probably a sign you weren't dreaming big enough.

              Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

              Opinions expressed are my own -- take them for what they're worth
              and don't expect them to be perfect.
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