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Help finding the equation to multiple graphs

I hope that I am posting this to the most appropriate place. I have tried to get help to this problem in a Physics forum but I think that they are making the problem more complex than it is. So any help from you Math people would be appreciated.

Here is my original post:

I need some help finding the equation to a graph. The graph data is pictured below.

The graph is for a piece of fishing equipment that is used to get your fishing line out and away from your boat and down to your desired depth.

Here is the data that we have using actual tests. It's not exact which I why I want to find an equation for this;

http://www.slidediver.com/img/dptchart1.jpg

http://www.slidediver.com/img/dptchart2.jpg

Here is an explanation of the data:

The depth (in green) is the target depth that we wish to achieve.

Ring: Each data set was done with a ring attached that increases the surface area of the diver. There are two sizes that we call #2 and #3

Speed: This is how fast the boat is moving. We did sample data for 2.8 MPH and 2.3 MPH. I am hoping that we can compute data for speeds down to 1 MPH.

12" lead is a constant so ignore that.

Angle Settings (blue): This is a dial that sets the angle of the dive. This can be set from 0-6 in increments of 1/2. It makes the diver move away from the boat.

Length (red): This is how much line needs to be sent out to achieve the desired depth.

In actual use here is how it should work:

I am trolling at 2.3 MPH, I have a #2 ring on my diver and I'm setting my angle at 3. I see fish on my graph at 25 feet down. How much line do I need to send out to get down to 25 feet? (In this case it would be 92ft)

Here is a picture of the diver:

http://www.coldwatertackle.com/image...structions.jpg

Some of the original data from field testing is attached.