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The Down Pedal

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  1. RiverDave
    If you are a modern day I/O boater you might not even know what a down pedal is in a boat. In V-Drives there is typically two pedals. A down pedal (or a switch on the dash or gunnel) and a gas pedal. V-Drives don't have "trim" like an I/O boat, so they have what is called "Cavitation Plates" on the back of them. They bend those plates up, neutral, down, or infinitely in between to adjust trim of the boat. By bending the plates they are actually bending the running surface on the back of the boat adding Hook (down) or Rocker (up) to the boat. They are basically an extremely efficient trim tab, that has the ability to add positive trim as well when they are in the up position. Picture a trim tab as dragging a plate in the water to create lift, where as a cavitation plate you can move it very little and create a ton of lift, via bending the running surface, instead of dragging something behind the boat.

    (Cav Plates on Phil's 21 Rush)
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    Some V-drives will actually have three pedals in the boat, The gas pedal, a down pedal (lower the plates), and an up pedal (pull the plates up). So lets talk about drag racing for a second as an example where an up pedal is commonly used.

    (3 pedal setup with a lock out handle on a Runner Bottom Flat called "Strange Behavior.")
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    Imagine leaving the start area and the first thing you are going to do is roll the boat on plane, your left foot is going to be leaning on the down pedal. As the boat accelerates you are creating transom lift to help roll the boat over (or in larger Horsepower applications keep the boat from just jumping straight up out of the water). In the mid range while the boat is accelerating hard you will still be using the down pedal while making adjustments to "set" the attitude of the boat as it goes down the track. The down pedal (bending the cav plates down) is leveraging against the constant acceleration, and thrust from the angle of the prop shaft, that is trying to lift the nose beyond where you are regulating it with the down pedal (and in big HP cases the throttle as well).

    (Single lock out handle with no left Pedal in this beautifully restored wood deck Schiada)
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    As the boat starts coming up on speed the acceleration will lessen and so does the bow lift, and at some point you would want to release the down pedal entirely, and you would be crossing over into an area where you want to pull the plates up, helping to carry the nose of the boat. This is where the up pedal would come into play. You could now push the up pedal and start to carry the nose to get even a little more out of it on the big end.

    The whole reason for the up pedal stems from water adhesion. If you set the plates all the way up, and you were running a fast boat, the water would actually run across the bottom of the boat and suck the plates down to just above neutral. How far above neutral would depend upon how much return spring pressure you had on the down pedal, and how fast you were going. So somebody put a pedal on the other side and now you could adjust it with your foot if you needed up trim.

    (Single down pedal in a Kurtis runner bottom)
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    In the evolution of thought (and horsepower) came the idea that instead of the up pedal, they could just set the plates up position, and make the return spring pressure so great that the water couldn't suck the plates down. The singular left pedal is now set so that "at rest" the plates are all the way up. Adding some pedal rotation would be neutral, and then as the pedal rotates further it would be continuing down.

    For marathon racing v-drives though, (keep in mind the linkage is all mechanical) the drivers have to overcome all of that extra spring pressure (on top of the force it takes to bend the plates, and the water pressure against them) for the duration of what could end up being a very long time. Back when men were men, they iron manned it and toughed it out. Their calf muscles on there left leg were as disproportionate as a teenagers arms just after they discovered their first skin rag.

    In the article of Phil's boat (The last Rush) you will see one solution to this problem where they Grier came up with a pretty clever way of solving that problem and still maintaining an entirely mechanical (meaning non assisted) linkage.

    (Phil's unique down Pedal on his 21 Rush)
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    Instead of a short throw, and short leverage rotating assembly that relies solely on the calf muscle, they made a long throw (more leverage = easier to move, but you have to move it farther) pedal that you actually push on with the larger muscles in your leg so a marathon driver doesn't get worn out. (Imagine the clutch pedal in a car)

    (Side shot of Phil's down pedal)
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    Circle racing isn't near as popular as it was back in the day, and the guys that built the boats for marathon racing are getting more and more scarce. This is why the setup in Phil's boat is incredibly rare, in fact I believe there's only two or three setups like this out there right now.

    In most other high horsepower cruiser applications they have things like lockout handles (the lever in between their legs, which allows you to set the plates to some attitude with a peddle override if you needed more) and you just deal with the spring pressure, or they flipped completely to electric actuators where you set the "trim" or the bend of the plates by hitting the switch up or down.

    (Single Down Pedal with a lock out handle on Joe Mitchell's 21 Hallett Vector "Coin Toss")
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    The pro's of a foot pedal over an electric actuator is the response on the boat is almost instant. If you come across rough water you can set the boat in a big hurry with your foot, where it might take a few seconds with an actuator.

    Which brings us to the most modern of times and technology. The die hards and racers don't want to deal with huge spring pressures, but they still like the instant response of a foot pedal. There has been two systems developed that solve the spring issue, but are still pedal actuated, and both are "assist" style systems. With these systems you can eliminate the "up" pedal, which inherently makes the boat easier to drive, but also adds a measure of safety. In the event of a mishap there is some opportunity for a drivers foot to possibly get caught between the up and the down pedal which could lead to a serious injury.

    (Cav Plates on a Runner Bottom Flat "Strange Behavior")
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    According to Clyde Church that exact scenario played out in Colorado when Dave Bryant was driving the SS-91 boat. He had gone into the first turn and hit some rough water. Dave's foot slipped off the down pedal and got wedged between the two pedals as he was coming out of the boat. It was at that point that Clyde and Phil Bergeron decided they needed to change something. Working together Clyde, Phil, and Dave developed the air assist system. (Patented on 9-14-2006)

    http://www.google.com/patents/US7380515

    US07380515-20080603-D00000.jpg

    The air assist system that has an extremely high pressure air bottle and integrates a piston inline with the mechanical linkage. As you press on the down pedal it releases air into that piston, and helps to overcome the spring pressure via air pressure, but still keeps everything mechanically in tact for response and "feel."

    (Air assist system installed inline without the springs, Photo courtesy of Dave Sammons)
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    The other basically works off a power steering pump that basically makes the pedal hydraulic and removes the spring problem from the equation entirely. I personally haven't driven either, so I can't speak to the pro's and cons of either with any experience.

    There's plenty of guys out there running up pedals, and single pedals with big springs. Clyde has been remarkably successful with his air assist system (built and sold by Phil Bergeron in AZ) having now sold over 100 kits on the open market to circle boat racers, drag racers, and river warriors alike. You will find a lot of cruisers with lock out handles and down pedals, and more mild mannered cruisers with just a lock out handle by itself. You will also find electric cav plates on everything from slow cruisers, to 1400 HP + Schiada's.

    (Single Down pedal and lock out on the infamous "Bodacious")
    IMG_3234.jpg

    In the case of Phil Axtel's Rush though, it's something uniquely special. Not because there's only a couple of them out there, but because it solves all the problems, by allowing the driver to use the larger muscles in his leg while lowering the resistance, versus some additional method of assistance. No matter how you look at it, that's just good old school engineering.

    written by RiverDave

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