Calculate Fish Lure Depth Behind Moving Boat

  • Thread starter LTLhawk
  • Start date
In summary, the depth of a fishing lure behind a boat traveling at a constant velocity can be calculated by measuring the angle of the line going down into the water and using the weight and drag of the line.
  • #1
LTLhawk
2
0
Can anyone help me with a formula to calculate the depth of a fishing lure behind a boat traveling at a constant velocity. Known: boat velocity, lure weight, distance behind the boat. Assumption: fishing rod tip is at water level.

Obviously I want to know how far down my lure is. Thanks for the help
 
Physics news on Phys.org
  • #2
Since the lure travels behind the boat at constant velocity, the forces acting on it must cancel in each direction. This gives the angle of the line. Using this and the total length of the line gives the depth of the lure.
[tex] depth = L \times \frac{weight \ difference}{tension} [/tex]
Where L is the total length of the line, tension is the tension in the line, and weight difference is the weight of the lure minus the weight of an amount water that has the same volume as the lure.

But I think an easier way would be to measure the angle of the line going down into the water.
When the angle is defined such that it is zero when it lies on the water surface, then:
[tex] L\sin(\theta) = depth \ of \ lure [/tex]
 
  • #3
BruceW said:
Since the lure travels behind the boat at constant velocity, the forces acting on it must cancel in each direction. This gives the angle of the line. Using this and the total length of the line gives the depth of the lure.
[tex] depth = L \times \frac{weight \ difference}{tension} [/tex]
Where L is the total length of the line, tension is the tension in the line, and weight difference is the weight of the lure minus the weight of an amount water that has the same volume as the lure.

But I think an easier way would be to measure the angle of the line going down into the water.
When the angle is defined such that it is zero when it lies on the water surface, then:
[tex] L\sin(\theta) = depth \ of \ lure [/tex]


No .. I don't think that is correct. The buoyant force can probably be neglected in this example ... the upward force on the lure comes from the component of the line tension normal to the water surface. That must balance the gravitational forces, while the parallel component of the tension would balance the viscous drag (friction) force on the lure. So, it seems like there must be some additional information about the shape of the lure and it's cross-sectional area, or some other way of calculating the friction forces on the lure.

Anyway, the depth of the lure will be given by the distance behind the boat time the tangent of the angle between the line and the water's surface. That tangent will be equal to the ratio of the gravitational force to the drag force.
 
  • #4
My equation is correct, I have accounted for the component of line tension normal to the water surface in the correct way.
Whether the buoyant force can be neglected or not depends on the density of the lure. If its density is much greater than the density of water, then the buoyant force can be neglected.

The weight and drag of the line also contribute to this problem, although I haven't accounted for them in my equation.
 
  • #5
This is good stuff... thanks guys.
 

1. How do you calculate the depth of a fish lure behind a moving boat?

The depth of a fish lure behind a moving boat can be calculated by using the following formula: Depth (in feet) = Speed of Boat (in MPH) x Time (in seconds) x 1.5. This formula assumes a standard trolling speed of 1.5 MPH and can be adjusted accordingly for different boat speeds.

2. What factors affect the depth of a fish lure behind a moving boat?

The depth of a fish lure behind a moving boat is affected by several factors including the speed of the boat, the type and weight of the lure, and the type of line being used. Other factors such as water depth and temperature can also impact the depth of the lure.

3. Can the depth of a fish lure behind a moving boat be calculated accurately?

While the formula mentioned above provides a general estimate, the exact depth of a fish lure behind a moving boat can be difficult to calculate accurately. Variables such as water currents and wind can also affect the depth of the lure, making it challenging to determine an exact depth.

4. How can you adjust the depth of a fish lure behind a moving boat?

The depth of a fish lure behind a moving boat can be adjusted by changing the speed of the boat, using different types of lures or lines, and adjusting the length of line between the lure and the boat. Experimenting with different combinations can help to find the desired depth for different fishing conditions.

5. Are there any tools or technologies that can help to calculate fish lure depth behind a moving boat?

Yes, there are several tools and technologies that can assist in calculating the depth of a fish lure behind a moving boat. These include fish finders, depth sounders, and trolling apps that use GPS and other data to track the depth of the lure. However, these tools should be used in conjunction with the formula and other factors mentioned above for the most accurate results.

Similar threads

Replies
17
Views
1K
  • Other Physics Topics
Replies
2
Views
3K
  • Introductory Physics Homework Help
Replies
2
Views
910
  • Introductory Physics Homework Help
Replies
2
Views
785
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Introductory Physics Homework Help
Replies
16
Views
2K
  • Introductory Physics Homework Help
Replies
17
Views
6K
  • Classical Physics
Replies
7
Views
743
Replies
6
Views
8K
Replies
13
Views
663
Back
Top