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Thread: Getting on step - going with or against the current

  1. #1
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    Default Getting on step - going with or against the current

    A friend asked me this question at a poker game recently and to be honest I never gave it any thought until he asked:

    If you are running to moose camp carrying a ton (at least!) of gas and gear in a river boat is it easier to get on step running with the current or against it?

    My gut tells me it would easier to get on step going with the current because it would be easier to pick up speed.

    Thoughts?
    Tennessee

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    Moderator stid2677's Avatar
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    It has been my experience that a boat is just like an airplane, take off into the wind, not with a tail wind. Much easier getting on step into the current, also getting as shallow as you can makes a HUGE difference, in shallow water you get "ground effect" that pushes back up against the boat and helps get it on step.

    An airplane or helicopter will take off and fly close to the ground heavy and slow and will try to stall if you pull up and away from the ground before you have enough airspeed.

    JMHO

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  3. #3
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    Does this really require thought?
    Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence. Albert Einstein

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    Moderator LuJon's Avatar
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    I find the same as stid. The current is free speed when getting on step and shallower is better.... Well to a point! I can also run up river on step much slower than down stream.

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    Member Dirtofak's Avatar
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    I have tried a few different things. Each has their own time. I have had great success floating with the current until I hit a deeper hole then nailing it. I have used a hard right or left turn to raise the jet up a bit. It works when light or over some weedbeds. An S turn can buy some speed when there is only a short hole to launch out of.

    When I am loaded up to near max (as no one ever overloads a boat in AK) I try to get to my magic 12 MPH then hit it. It seems like 12 MPH is where I can lift off with the least chance of rocks or weeds blocking the impeller.
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    Member f0zzy2's Avatar
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    It's easiest to get on step going upstream. It can make a big difference if your stuck going down stream and can't get back on step. Turn around get it up turn back down down stream and pick a new line.

  7. #7

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    So does the same thought process occur if your in the middle of the inlet and the tide is running hard. Can you get on step faster going with the tide or against the tide? Honestly it makes absolutley no difference unless you consider the additional speed and associated drag from the increased speed through the air. So without question you will get on step faster going up stream only because of the decreased speed through the air which equates to less drag unless the wind is blowing down stream faster than the current is running.

    There that's my 2 cents.

  8. #8
    Member Rock_skipper's Avatar
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    It really depends on the motor you are running, been traveling rivers for more than 40 years here in the interior.

    I have been in 24' boats with a 25hp 2000lb loaded, and you will have to get out and pull it upstream/ get out and let it down stream, been in boats that were powered by 100hp+ and it really dos'nt make much of a differance as long as you know where to go, ( the key word is KNOW, lol )

    You will tell the differance anytime you go from deep water to shallow regardless if you are going up or down, but the trick is to know what is down river instead of up, because you only have one shot at a downriver bonzi, lol

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    Exactly like a airplane, compare speed through the air and speed over the ground.........
    Same, same if perfect calm, say take off speed is 35 MPH, with a 10 MPH head wind your ground speed is 25 on lift off, but speed at the pitot tube (Air speed) is 35.

    So relate that to water and the speed you need to get on step, you will need to reach the same speed on top (or through) the water no matter going up or down, (Like a wing that creates lift, water flow lifts the boat) but will need to travel farther to reach the same speed going downriver, and actually will have more wind resistance going down stream because your over the ground speed is faster and the air resistance doubles as your speed increases.............. or some such math that escapes me at the moment.

    Quote Originally Posted by stid2677 View Post
    It has been my experience that a boat is just like an airplane, take off into the wind, not with a tail wind. Much easier getting on step into the current, also getting as shallow as you can makes a HUGE difference, in shallow water you get "ground effect" that pushes back up against the boat and helps get it on step.

    An airplane or helicopter will take off and fly close to the ground heavy and slow and will try to stall if you pull up and away from the ground before you have enough airspeed.

    JMHO

    Steve
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  10. #10

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    Snowwolfe,


    whatablast and AKgramps are on the right track. At a given weight, a planing boat hull will lift up out of its resting depth to be on step at a particular water speed.


    Let’s say the depth of your boat’s keel is 10 inches when the boat is at rest. Now, increase the water speed to let’s say 12 mph and it will lift up substantially so that maybe now your keel is only 6 inches deep. Accelerate to a water speed of 20 mph, and your keel may be only 4 inches deep. Finally, at 35 mph of water speed, you may be displacing only 3 inches of water. (Cross a shallow gravel bar, and you might feel your hull rise up another half inch or more from ground effect.)


    The accelerating boat will lift up at its greatest rate early in the run, but the rate of lifting tapers off rapidly. That water speed at which you consider yourself “on step” or “planing” is on a continuum. It’s subjective, because it depends on your assumptions of what constitutes planing. In the example above, the keel depth varies from 10 inches to 3 inches. This is a 7 inch range. The 6 inch keel depth assumed at 12 mph means the boat has lifted 4 inches out of a maximum possible lift of 7 inches. This is 57 % of the maximum possible lift. If you assume lifting a boat half of its maximum lift is “on step”, then you’re already there. If you assume a boat must lift at least 60% to be “on step”, then you’re still ploughing.


    Water speed governs how much the hull will lift. Ground speed is irrelevant. Take an example of a river with a 6 mph current. If you consider yourself “on step” at a water speed of 12 mph, then you will be “on step” when your ground speed is 6 mph going upstream, and when your ground speed is 18 mph going downstream.


    In calm air, your airspeed would match your groundspeed. The greater airspeed in the downstream case would cause more parasitic drag which would hinder the boat from reaching it’s planing water speed as quickly. But, if there is no wind to amplify or attenuate the air speed, the practical effect of airspeed may not be very significant in determining how long it takes to reach planing water speed.


    Parasitic drag from air (or water) resistance varies in accordance with the inverse square law. That is, doubling airspeed will increase drag by a factor of 4, tripling airspeed will increase drag by a factor of 9, quadrupling airspeed will increase the parasitic drag by a factor of 16, and so forth. This means that drag is negligible at slow speeds, but builds very rapidly as speed increases steadily.


    I do see a practical problem in trying to get on step while going upstream. The jet intake will be stationary over the bottom at first, and then will pass over the bottom more slowly while accelerating upstream. If the water is shallow, this gives gravel more time to be sucked off the bottom and be pulled into the impeller.

  11. #11
    Member Jimw's Avatar
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    Up stream seems best for my application. If i am loaded heavy 2000+ lbs ease on the throttle and work the wheel side to side as more throttle is applied slowly. I will "feel" the boat begain to climb out of the whole and over the bow wave. The key is slowly, remebering that when throttle is applied it will create a "whole" under the boat. If the boat doesnt have forward movement the whole will not fill in as quickly as the pump takes it out causing a cavitation issue. I have no expirence with outboard or sport jet applications. My heavy boat with a 350 at the stearn and loaded heavy makes big whole in the water. I can put out a 3-4' wake starting out heavy.
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  12. #12

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    It is like a plane. A boat will get on step at a given weight at the same water speed going either against or with the current, the only difference is the actual distance covered getting to that speed. Obviously it covers more ground with a 10kt current at your back and less with you facing it.

  13. #13
    Member Yukoner's Avatar
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    Our moose camp is up a very shallow river, and with any sort of load, I can't get on step fast enough to avoid the shallows just downstream. However, there is a very convenient large creek coming in river right just downstream, and it works out that if I give her full throttle and aim for where the creek dumps in, the turbulence there always gets me on step quick. Its kind of an act of faith, and the passengers always seem agitated as I head towards the shore full throttle, but it always works. Just like a float plane taking off with zero wind, and getting a gust of headwind at the right moment, free speed.
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  14. #14

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    Quote Originally Posted by Yukoner View Post
    Its kind of an act of faith,
    Especially the first time you ever tried it I bet!

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