8x9" coil vs 3x18" coverage

[jabbo]

With the 18" coil being 2 times the length of the 8x9 it seems like we are getting 2 times the coverage. A little calculation shows not 2 times more, but only 1.5 times. Considering both coils are held 1.25" above the ground when sweeping. If both coils penetrated the soil to the same depth then the 3x18 would cover 2 times the area of the 8x9, but the 8x9 goes deeper.

 

[slingshot]

Are you sure? Can you send me one for a couple of months for testing?:clsoedeyes:

 

[tvr]

If I make some assumptions on simple shapes of coverage in the ground and then base the depth on some air tests and assuming mild ground then approximations of swept ground volume are ...

A cone shape for the 9 x8: a 9 inch long coil going 12 inches deep gives a cross sectional area of 1/2 of 9 x 12 = 54 square inches.

A rectangular shape for the cleansweep:18 inches long going 8 inches deep it gives a cross sectional area of 18 X 8 = 144 square inches.

So if the sweep is four feet long the 9x8 sweeps about 48 X 54 = 2592 cubic inches and the clean sweep 48 X 144 = 6912 cubic inches.

Now the kicker, to get the cone shape coverage to 8 inches deep on the 9x8 coil, you need to overlap the sweep by 2/3 (can only move the coil forward 3 inches since the cone is only 3 inches wide at 8 inches deep). The clean sweep does not need the overlap.

If you assume the cone shape is more elliptical, then it isn't quite as much of a difference as this simplified example, but it is still pretty significant.
Cheers,
tvr

 

[jabbo]

TVR, thanks for the input.

 

[tvr]

Jabbo,
As you know, bad ground and trash masking is going to affect the usefulness of the bigger coil more. I love the cleansweep for playgrounds and sports fields ... except the couple of fields I hunt that are VERY trashy. On those I move all the way down to the 5.75 inch concentric.
tvr

 

[jabbo]

TVR, the 3x18 on my Golden is really great in tot lot wood chips. Most tot lots are hit regularly so I search only the shallow stuff, the 3x18 gets me in and out fast. It doesn't go deep enough in the grass, thats when I use the 8x9. In the woods and for deep old coins I use the ID Edge. Jabbo