Half Time Question - Pivot Points

[kaydano]

A boat has two pivot points, one near the front of the boat when going forward, one near the back when going in reverse. The pivot point is the point at which the boat pivots in a turn. When going forward, and turning to port, the stern kicks out to starboard more than the bow turns to port. Since the outboard causes the stern to swing out more than the bow turns in, the pivot point of the boat is near the front of the boat (for example, the pivot point might be 1/3rd the distance from the front of the boat to the back). Likewise, in a reverse turn, the bow swings out more than stern, so the pivot point of the boat moves toward the stern end of the boat (lets say 1/3rd the distance from the stern).

Let's say you are at a dead stop, no wind, no current. You turn hard to port (turn the wheel as far as it goes), and you instantly accelerate to 2000 rpm. The boat travels in an arc to port. Let's say you stop exactly when the boat is facing 180 degrees from the direction you started. Now, you put it in reverse, instantly go to 2000 rpm, travel in a reverse arc until you are back to your original bearing (you're back at the zero degrees starting point).

Two questions:

1) At the end of the above maneuver, are you in the EXACT same spot as when you started?

2) If yes, does the boat travel the exact same arc in each direction (is the forward arc identical to the reverse arc)? Or are they two different arcs, but each starts/stops at the same point?

Keep in mind the pivot points...

This is not a trick question. I don't know the answer.

 

[liljake83]

my head just exploded after reading this too much thinking involved

 

[Big E]

No.

The turning radius is different because the motor input has more influence in reverse at slow speeds. Think of your motor as your hand and the boat as a piece of rope. Try pushing the rope compared to pulling it and see which has more control. Obviously the boat will handle better in forward when underway. Low speed manuevering will also be affected by the direction of rotation of the prop. You will find that at slow speed it will turn better in one direction than in the other-whether forward or reverse.

Knowing the difference in how your boat handles at slow speed is important. Imagine getting into a tight harbor on a windy day, you just left the gas dock and need to spin around to leave.

You will have a tough time spinning around in the wind using the forward gear, especially if you are getting blown toward a dock full of expensive boats with their owners/witnesses present.

Just back out far enough to get yourself some room to turn around, cause where you point the motor in reverse the boat will follow.