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Author Topic: Cold underwater detecting question.  (Read 445 times)

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Offline Davidloc

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Cold underwater detecting question.
« on: February 27, 2019, 06:22:42 PM »
I will be detecting underwater using a pair of Grey Ghost Amphibian head phones and would like to know if they are loud enough to go through a 5mm diving hood. The water will be too cold to dive without a hood for the first week or so (between -1 and -4 C)  but is doable with a full cold suit.  Does anyone have experience with cold water and under water detecting ?

Offline JOE S (INDY)

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Re: Cold underwater detecting question.
« Reply #1 on: February 27, 2019, 09:13:19 PM »
Yes David, I happen to know about cold water - I mine in Alaska.  For years I used melt water 20 minutes downstream from a glacier for all my mining activity.  Because of that, the stream temperature, at it's warmest, was just a few degrees above 0 deg C.  Those very few who dredged underwater were firmly dedicated to heated water being pumped inside their wetsuits although later drysuits made some appearances.  No one ever detected underwater at those temperatures.  Underwater detecting (you, not just the waterproof head of the detector) at the temperatures you mentioned will last (or should last) about 30 seconds, max.  Just not practical in the slightest.   

If you are wisely not planning on total immersion then do not wear a hood under the earphones - but rather just a warm knit ski cap or two over your head and the headset.  I have found that audible nuances from the detector are ever so much more important than personal style and total visual presentation - don't you agree?   <-party->

The hood is singularly designed, and specifically used, for thermal (and so it turns out auditory) insulation from outside things - "things" meaning very cold water temperatures.  ANY insulation, of ANY type, impedes sound transmission - and that impediment is directly related to the insulation's thermal efficiency.   7 mm is the optimum and usual cold water thickness for dredgers while 5 mm is marginal.

So, I suggest that you detect the stream bed outside the water and only occasionally get the detector's head wet (if it is actually waterproof). 

BTW, daytime -1 to -4 deg C. is still below freezing - and at those temperatures the ground is usually frozen solid - meaning you should defer any and all streamside detecting activity until well past the spring's thaw (we call it "Break-Up" up North, and possibly you do as well?).
Wiser Mining Through Endless Personal Mistakes

Offline Davidloc

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Re: Cold underwater detecting question.
« Reply #2 on: February 28, 2019, 07:28:49 AM »
Thank you so much for a very complete answer. I will be using a Garrett ATX with the Grey Ghost Amphibians and after carefully lubing the seals on the controller head , I tested the whole unit in the deep end of a local indoor pool (no scuba gear though) and everything was fine where I kept the head at above 9 feet with the coil extending down to about 14 ft. I tested the 8" mono and 12 " DD for 15 minutes per coil. I have two other coils (20" and 13" mono) but these would be awkward in the water and will only be used on the shore line so were not tested in the pool.   

I will not be going in the water until the daytime temperature holds at above 5C. I was referring to the expected temperature range of the water not the air temp.  I picked up an Aqualung 5mm hood and gloves because the 7mm gear was too bulky to manipulate the detector and a hand dredge. The 7mm hood passed vitually nothing even at full volume and the 5 mm passed enough that I was hoping the water in between the hood and the headphones would project the sound more clearly using the neoprene as a diaphragm to get it to the eardrum. You clearly answered this and I have already tried the stupid mistake  of making a hole over each ear in cold water a few years back and never again. The vertigo made it almost an emergency even at 6C water temp.

Offline sunshine

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Re: Cold underwater detecting question.
« Reply #3 on: March 04, 2019, 11:48:05 AM »
I had two immediate thoughts and one was already answered.  ;-)

It will all depend on what you want your detector to detect.  Sometimes, all you need to find are heavies, even if they are just nails and other iron.  That gives a loud bang on a detector.  If you want to be able to hear the whispers of small gold while underwater in moving water, good luck with that, especially wearing neoprene over your ears.  Instead, I would suggest an underwater vibrating pinpointer and forget the detector until things warm up. 

My second thought was cutting out 1 or both ear holes.  I have not tried this, but thought it would work OK.  My earphones have a plug in each earphone that is removed to allow water in, so you don't have pressure issues and hurt your eardrum.  However, you said exposing the ears in the hood gave you vertigo.   I am not sure how that happened.  It is called inner-ear barotrauma and usually caused by tight fitting hoods over the ears, so the opposite of what should have happened.   I think maybe it was your headphones and not the open ears in the hood. 
See my YouTube channel for fun amateur video:
https://www.youtube.com/channel/UCnz8kX6AZOeZbRt0F9XqVJA

Offline Lanny

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Re: Cold underwater detecting question.
« Reply #4 on: March 12, 2019, 11:52:55 PM »
I will be detecting underwater using a pair of Grey Ghost Amphibian head phones and would like to know if they are loud enough to go through a 5mm diving hood. The water will be too cold to dive without a hood for the first week or so (between -1 and -4 C)  but is doable with a full cold suit.  Does anyone have experience with cold water and under water detecting ?

I've dredged in cold water, and done underwater detecting, yes. Used to check the bedrock after dredging with a fully waterproof pulse detector with accompanying headphones, and where I dredged, the water always gave me "brain-freeze" unless I wore a 7mm hood  while I was dredging.

However, I'm with Sunshine about how the 7mm neoprene cuts out the subtle sounds which are important for hearing signals trapped down in the bedrock, unless you get a signal from  a  meaty "ripper" that really screams. Now, a fellow dredging buddy of mine used to wear a welder's cap (lighter, cotton material) that would keep him just warm enough to not get total brain freeze, but only for short stints. But, I do like the idea of ear-holes cut out of a 7mm hood, and I wish I'd have tried that as hopefully the seal of the headphones would stop the ears from numbing up. (-1 to -4 is stinkin' cold though . . .)

All the best,

Lanny

Offline Davidloc

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Re: Cold underwater detecting question.
« Reply #5 on: April 21, 2019, 06:56:32 PM »
In very cold water DO NOT cut ear holes out. I did this in James Bay about 25 years ago and had to be pulled out by my safety. The vertigo will cripple most when the water is really cold within a minute or two.