• Maneuvering a Single Engine Boat Part 1 - The Basics

    Many new boat owners consider driving a boat to be similar to driving a car. However there are many differences between the two.

    Drive is a term usually associated with a land based vehicle, and loosely means to direct the motion and course of that vehicle, while operate and maneuver mean to direct or control with purpose and precision. Pay attention to that second definition, it implies that the operator should possess a certain level of knowledge and skill. Armed with a little knowledge and dedicated practice you will quickly learn to maneuver a boat instead of drive a boat. Now lets move on to some of the basic concepts to get you on your way.

    Turning
    When you turn a car, you are steering from the front by changing the direction of the tires. The friction of the front tires with the road surface cause the front of the car to turn while the rear tires pivot to follow the new path. On the other hand when you maneuver a boat you are steering from the stern either using a rudder, an outboard motor or stern drive. The boat turns due to thrust being directed laterally left or right forcing the stern to move sideways. Since water provides less friction than pavement, when the stern moves one way the bow of the boat moves in the opposite direction.

    What causes this behavior?

    Pivot Point
    Since a boat operates on the water where friction is less than pavement, the boat will pivot or rotate around a point somewhere along its centerline. This point is the center of rotation and is referred to as the pivot point.

    The pivot point's exact location will differ for each boat and will also shift depending on whether the boat is moving fore or aft. On most single engine boats the pivot point is located approximately 1/4 to 1/3 of the boats length from the bow while the boat moves forward and approximately 1/4 to 1/3 of the boats length from the stern while maneuvering in reverse.


    Attachment 1019


    The video below demonstrates the principle of pivot points.









    Without skillful maneuvering, a single engine boat cannot spin in place like a twin engine boat but instead follows a small arc while it turns. This may prompt you to ask, why is the pivot point important? There are several reasons which will be discussed in later articles on maneuvering but for now lets look at one example.

    In the video below the boat will be turning to starboard. Using the vertical red line as a reference, watch the behavior of the bow versus the stern. You will notice the bow begins to move to starboard which is logical for the direction of turn. However the stern of the boat will move to port as the boat begins to pivot. Not only does the stern move to port but it will move further and at a faster rate to port than the bow moves to starboard.









    Spend some time around your local dock and you will see this behavior demonstrated on a frequent basis. Boaters that are unaware of this basic principle will bounce along the dock with a look of indignation on their faces as they try to get underway.

    Important Concept 1
    If you begin a turn while maneuvering forward, the stern of the boat will move in the direction opposite the turn. It will swing faster and along a wider arc than the bow. If maneuvering in reverse the opposite is true.



    Skidding
    As long as the car's tires maintain the proper friction when you make a turn, the car will follow the desired path. However, when a boat negotiates a turn it will skid to the outside since water provides less friction. The boat's speed and hull design will determine how much a boat skids during turns.

    Attachment 1020
    Important Concept 2

    Due to less friction a boat will skid to the outside of turns causing the turn radius to be larger than envisioned, plan accordingly.


    Prop Walk
    When the propeller on your boat rotates it is producing thrust, either in the forward or reverse direction. As the propeller rotates it also produces a small amount of lateral thrust that will tend to push the boat's stern sideways.

    When viewed from the rear a right handed propeller rotates clockwise on an engine producing forward thrust. At the same time it also produces lateral thrust that pushes the boat's stern to starboard. If the engine is producing reverse thrust the opposite is true and the lateral thrust pushes the stern to port. If you are dealing with a left hand propeller the behavior is reversed.

    Prop walk is more prevalent during slow speeds and can make close quarters maneuvering more challenging. Each boat has its own unique behavior and some boats experience the effects of prop walk more in reverse than in forward. You will need to experiment to determine how prop walk affects your boat.

    A detailed discussion of the forces involved that cause prop walk would take several pages to explain in detail. Since there are many excellent sources available on the internet we will forgo a detailed explanation here.

    In the video below you will notice when the boat is placed in forward with idle thrust the boat begins moving forward and the stern begins to drift to starboard.








    Prop Walk is not limited to slow speed maneuvering but is also present while maneuvering at cruising speeds. Manufacturers use a variety of method to counter these effects at high speed. Some of the most common methods are offsetting the propeller shaft from the centerline of the boat or by installing a trim tab on the sterndrive. Boats with two props that rotate in opposite directions do not experience prop walk since the forces on the propellers cancel each other out.




    Stay tuned for more maneuvering articles!



    thanks to Cap'n Ray and Lotus for contributing to this article!
    elementis, Torch, Ana and 1 others like this.

     

    Comments 11 Comments
    1. 25thmustang's Avatar
      25thmustang -
      That was a great read! Can't view the videos on my phone but I will be sure to watch them on the computer.
    1. TimG's Avatar
      TimG -
      Thank you! I spent about a week looking into html 5 compatible ways to show the animations but all of the products available have so many bugs you cannot use them. Hopefully something good will come along soon.
    1. Cap'n Ray's Avatar
      Cap'n Ray -
      It's is just that type of 'small issue' that I think about when I consider all you do to keep the forum running... You are tireless and amazingly motivated Tim! I'll keep my eyes peeled for a product that will help with the video, I have some contacts in the a/v world that may be able to offer suggestions. Keep up the great work, this forum has a great admin!
    1. TimG's Avatar
      TimG -
      I appreciate the kind words, I have been learning and working with Adobe Edge and Wallaby and neither will do what I need at this point. It is surprising that the developers are so slow to produce a product similar to flash that will work.
    1. Cap'n Ray's Avatar
      Cap'n Ray -
      I suppose when something like flash is SO popular, there's not much call for something 'like' it. But that's just a hunch. There's gotta be something that will do what's needed. I've noticed a lot of external linking to YouTube on other forums- maybe that's the "for now" solution?
    1. lotus's Avatar
      lotus -
      An excellent article that should be read by all. One practical fundamental that hasn't been mentioned is that, when doing precise manouvering, you should always put the drive in neutral before turning the wheel to avoid having conflicting thrust that will affect the manouver you are trying.

      For example, if you are approaching the dock with the intention of docking on the starboard side you will come in at about a 35 degree angle and, about 10 - 15 feet out will turn hard to port. The idea being to let the boat drift slowly up to the dock and then a bit of reverse thrust with the wheel hard starboard will stop the boat and pull the aft end toward the dock so that you are parallel with the dock. If you leave thrust on (either forward or reverse) while turning the wheel the result will be to stop the arcing forward motion. Reverse thrust then may get you sort of near the dock but you will be well behind the point you wanted to be at.
    1. TimG's Avatar
      TimG -
      Lotus that is an excellent point, i added a statement at the bottom of the article. Thank you!
    1. mijenjo's Avatar
      mijenjo -
      When will you have part two?
    1. TimG's Avatar
      TimG -
      mijenjo I am not sure but it is on the list. I have been so busy lately the list is getting longer and longer.
    1. DixieBoys's Avatar
      DixieBoys -
      I have a single LH inboard. I seems it does not matter what speed I am doing in reverse. The stern stills kick to starboard. I just plan to approach the dock on the port side. Launching from the trailer I have learned to walk the boat with reverse and a little forward motion to keep the boat on a straight line back and pray that anyone around me knows to keep their distance until I make the hard port turn in forward. I have thought about trim tab trolling motors or bow thruster but the cost keeps me walking the dog.
    1. TimG's Avatar
      TimG -
      DixieBoys I have had others that have made similar statements about their particular boats and the only thing we could figure was the hull design. You have the added disadvantage of having no directional control unless you are moving water across your rudder. I wouldn't worry too much about trying to counter it with a thruster etc. It sounds like you are already ahead of the game by using it to your advantage and counteracting it. This will make you a much more skilled captain for sure. The problem with most boaters is they don't realize it is going on, so they fight and fight not really know what they are fighting.
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