Reducing detector drag in water (hydrodynamic drag)

[Kennert-333]

Many of the stock VLF coils are not designed to flow through the water with little resistance, and the same goes for many of the shafts.

Has anyone been experimenting with ways to reduce the drag when swinging a detector in the water, or even underwater? If so, what were your results?

Some thoughts (questions) about this topic....
1. Assuming you are in waist deep water, how much of the drag is from the coil, and how much is from the shaft?
2. Has anyone created coil covers designed specifically to reduce the drag? How well did it work?
3. Is anyone replacing shafts to reduce the drag? I saw one person that had replaced the stock shaft with a golf club shaft to reduce drag but I am not sure how well it really worked.

There seem to be only a few comments here and there in the forum on this topic, but I am wondering if anyone has more they could share about it.

[Carl-NC]

This issue is almost universally ignored by manufacturers. For many years I've argued that a good coil for water is simply a skinny donut with a center pivot, similar to the old Garrett BFO coils. You want to minimize flat areas (such as with a Tesoro concentric) because wave action will cause the coil to flop.

I suspect with most detectors the coil itself is the dominant problem, maybe 70%. The shaft drag is maximum at the coil where you have full motion, and almost zero at the arm rest where there is little swing motion. A circular tube is pretty good and only a flattened oval might be better, or a smaller round tube. A big clevis or big rod clamps might cause more drag than the rod itself. I'd try swinging the detector in water without the coil attached to see how it compares.

First Texas accidentally designed a really good coil for water:

I say accidentally because the design was chosen mostly for looks, but I took it in the water and it was quite easy to swing and didn't flop. As far as I can remember, it's the easiest coil I've even pushed through water.