I was just wondering should I get the 8 inch or the 10 inch coil. Will be using this mostly for east coast beach and surf. Please any advice will be greatly appreciated. Thanks
Nutsdad:
It is easiest to see the difference that the size of a coil makes by determining the surface area of the ground that will be under the coil with the formula: ( Pie times the actual diameter of search coil squared divided by 4).
Coils of 8" diameter and less are considered small field coils. As the stock 8” search coil is actually 7.25” there is 41.36 square inches of ground under that coil.
Coils of 10" diameter or more are considered large field coils. There is 78.675 square inches of soil under that search coil.
By comparing the surface area under each coil it is easy to see that the surface area under an 8" coil is only 1/2 that of a 10" coil. Or looking at it the other way a 10" search coil sees twice the surface as an 8" coil sees.
I use a rough rule to thumb to determine the maximum depth that I can detect a quarter size clad or silver coin under ideal conditions by adding two inches for spill over to the actual diameter of the search coil. Under ideal conditions, I should be able to detect a quarter size copper clad or hopefully silver coin at 9.25" with an 8" search coil, and at 12" with a 10" search coil.
If you multiply the maximum depth under Ideal conditions by the actual width of the search coil you can visualize the volume of sand that you may have to dig for a target under the search coil: 382.52 cu in for the 8" coil and 944.1 cu in for the 10” coil for the 10" coil. The point I am trying to make is that the 8" DD stock coil is much more precise and easier to pin point with.
Each coil has its advantages and disadvantages. What is best for you will depend upon: your metal detecting skills, where you treasure hunt and your treasure hunting style.
If you usually treasure hunt between closely spaced in rocks, trashy areas, or in the trough a small field coil (8” diameter or smaller is best)”.
- It is more sensitive to smaller items such as gold chains – which are very difficult to detect unless bunched, like in a ball, or there is a large clasp or an item item hanging on the chain as the detector only sees one link at a time.
` A small field coil is easier to handle in strong currents and waves, as there is less drag in the water.
- As the search coil is smaller, you can use of a smaller stand up water scoop or increase your ability to retrieve the target with a larger stand up water scoop on the first try which is important when hunting in waves /soft wet sand before it is washed away (light objects) or sucked under too deep to retrieve.
Small field coils work well in trashy areas /numerous close targets as the metal detector has less surface area under it to process: {complex ground matrix, hot rocks, trash, target(s). I look at the ground matrix (ferrous particles, mineralization, etc) as a wild card as it depends on the geographic location and it can change rapidly.
As I mostly treasure hunt on small and narrow beaches where there are strong waves, and currents, I prefer small field coils Since there is less surface area under a small field coil to process, you can sweep the coil faster before it nulls.
Most detectorists start out with or use the 10” large field search coil as their go to beach detector as it allows them to cover more search area and detect deeper than a small field coil. As it is more difficult to pin point with you will most likely see the treasure hunter using a larger stand up water scoop with a 9 ½ to 7 inch wide basket.
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