OK, update on the project and it looks like it works! But of course have to do an actual hunt to see if there are any issues I'm not seeing.
Here's a picture of the setup. What you see here is a 23" inch extension. I had to shorten it from 30" after a mock hunt in my yard. Read below to find out why. Also have a few tips I think are real important for the bag mounting and such with issues I noticed could be a problem, but were easily fixed with a little imagination. Nothing major, just a little precaution insurance on a few things, such as the pole maybe rubbing the bag/box, but I've got a simple fix for that.
Going to paint the extension black once I'm sure it works in the water fine at this length. Also, that blue thing you see below the box is the zip lock's zipper on the bag. The black thing just above that is the velcro loop I used to seal the bag around the coil cable. The zip lock zipper was zipped closed all the way to the corner of the bag right up against the coil cable, then I used the velcro loop to seal the bag around the cable.
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I picked up a box of 2.5 gallon 14 & 3/8 x 16" zip lock bags. This is more than big enough and probably too big to really need, but I just wanted to make sure I had a bag that was plenty big enough, as I ran out of the ones I stick the GT in when I chest mount it in the Minelab bag and couldn't remember what size they were. Main thing is you want the bag plenty long enough so that it can be sealed to the coil cable in two different spots with velcro loops or zip ties for double insurance against water getting in should you dunk the box by accident somehow.
Anyway, stuck the control box into the bag faceplate first, then pushed the control box to one side of the bag so I could zip the bag all the way closed to where it stops right at the corner of the zipper when it hits the coil cable. Now you only have to worry about sealing the bag around the coil cable right at that corner. For the picture I just used one velcro loop to seal it just to show for the photo. Worked like a charm.
Taped the control box onto the extension shaft for first try here to see how everything goes. I used Tyvek tape as it's very waterproof (won't come apart when wet) and also doesn't look quite as hillbilly-ish as duct tape.
Wanted to seal the bag first at the cable to there are no slack issues putting the control box back in/sealing for future hunts with the bag taped to the pole, as if you do it right you can just take the control box out of the bag and no need to use/tape a new bag to the pole each hunter when swapping between your land and water rigs.
After taping the bag/box to the shaft found an issue right off the bat. I didn't leave any slack at the bottom of the bag so the control knows where almost impossible to change. You've got to leave a half inch or so of slack at the bottom of the bag so you can turn knows/etc. No biggie, as I mainly wanted to see how the balance was. Here's what I found out...
With the 30" extension the balance wasn't too bad, but yea....The coil was trying to lift on me a bit when swinging around in my driveway on a mock hunt. While it wasn't a big issue, I can see how that might wear you out after a few hours. On the other hand, once water is around the shaft and coil perhaps it won't be trying to lift like that?
Anyway, I am right handed but I always hold my long handled scoop in my left hand and use it and my foot to scoop targets, so my right arm is always in the arm cup and holding the grip. Once I scoop up the target I always bring the scoop up by my right hand and then let go of the grip and pick the target out of the scoop right handed.
So if the shaft continues to try to lift a bit in the water even when you take your hand off the grip to pick the target out of the basket, I guess one easy fix is to just put your foot on top of the coil on the ground while doing that.
Really the coil doesn't lift much when I let go of the grip, just 4" or so, as even without my hand on the grip the stock Minelab arm cup (I use the stock shaft for water hunting and a homemade light shaft for land hunting) and it's heavy duty stock arm strap really hugs your arm, so even without your hand on the grip the shaft is very much in your control with the arm cup/strap securely around your arm. Just be darn sure that strap is secure and the shaft isn't going to break free of you if you let go of the grip.
But I decided that slight downward force I was having to give the coil to swing around the driveway might wear me out after a bit of time. I suspect in the water the shaft/coil might stop the "lift" pressure but who's to say without trying? So I decided to shorten the extension a bit, dropping the control box one full control box length. I cut the extension down to a length of 23". Re-taped the control box/bag onto the end of it, and gave it another shot in the driveway.
NOW We are talking! No coil lift at all that I can tell. I checked the balance point and it's halfway between the grip and the arm cup. Seems perfect to me.
Put the coil (10" Tornado) on the ground and let go of the grip like I was reaching into the scoop to pluck out the target. The coil didn't try to leave the ground. Now, I have a lighter 3 cell lipo in my alkaline holder, so if you still find the coil tries to lift a hair or something just stick the front of your foot on the coil while using your right hand to pluck the target out of the basket.
Conversely if you are using a heavier coil like a 15x12 or WOT I'm sure that would get rid of any slight coil lifting you might have with heavier 8AA batteries or the stock rechargeable pack. On the other hand, I guess if you do have a lifting issue you could also put a weight right below your grip like a led weight or a small ziplock bag filled with sand attached to the shaft, but I highly doubt you'll have an issue, and you can also just shorten your extension more to get it where you want things...Or don't even shorten it and of course just slide the box/bag down the shaft a bit until you figure out what the right balance/height is for you, and then cut off the excess extension length after that.
With my extension at 23" in length, in hunting position the control box is right at the height of my head. Maybe a little higher than that. I took some measurements in hunting position and I can safely wade to about (sorry, no other way to put it...) somewhere past niple
deep and the top of my shoulder!, so long as there aren't waves of course.
I'm VERY happy with what I'm seeing here, as my Excal friends almost never go any deeper than that as it gets to be hard to hunt when you are say neck deep, trying to scoop and keep your head above water. That's why many guys don't even use waterproof headphones on their water machines, because if your head is getting wet due to waves you probably are way too deep for that kind of waves on that day to even be able to hunting much at all anyway without getting knocked around badly.
A few more notes of concern...I'm thinking that rather than tape the bag somewhat loosely so that I can remove/replace the control box and re-use the same bag over and over, I might just go ahead and tape the bag/box tight. A quick cut with a razor blade down the pole and the bag rips apart and out comes your box. I don't think I want the box loose in there moving around a bit. On the other hand, you could put some kind of sponge padding on the top and bottom of the box before putting it in the bag. That way even taped tight you have enough cushion to squeeze the box in and out of the bag using the same bag over and over. I like that idea and think I'll try it.
Also, even if you don't care about re-using the bag and plan to tape it tightly to the box, I would still put some kind of foam padding OUTSIDE the bag between the bag and the pole. Why? Two things- so the pole isn't rubbing against the bag over time and working a hole into it, and also so that it's not rubbing on the top of your control box gumming it up. I fear that the pole over time might rub the GT's mounting bracket locations on the box and make it sloppy to replace back on the box clip on the land shaft.
I'm probably going to put flat foam/sponge material inside the bag top/bottom/and sides around the control box so I can squeeze the box in and out of the bag even with the bag/box tapes tightly to the pole. That way I can squeeze the control box in and out and the bag stays on the pole for re-use. I'm also going to put foam padding between the pole and the bag so no worries of the pole rubbing a hole in the bag too. Both those things I think are a good idea to do, both for bag re-use and also to protect the top of the bag and control box from being rubbed by the pole. Just remember to leave some slack at the back of the bag when you tape it up so that the controls can be adjusted. If the bag is pulled tight against the face plate it won't make it easy to change things, and it also might throw a switch or something without you knowing it.
So here's what I'd do if I were you. Start with a 30" extension. Mount everything and test it out. If the coil is trying to life too much on you and you think that might wear you out on a long hunt, then slide the bag/box down the shaft the length of your control box and re-test. Keep adjusting until you find where you don't really notice any coil lift that might where you out over the hours of a long hunt. For me that's a 23" shaft extension, and that puts the control box at least as high as my head in normal hunting position.
PS-
Important note here: If you use a snap pin and not a bolt and wing nut for taking off the extension during transport of in your car, two things- Don't wrap the coil cable so tight around the shaft that you can't lay the extension along side your shaft when broken down, and more importantly make sure you've got something with you to poke the snap pin heads one at a time into the shaft so you can pull it and the extension out. Probably one of your car or house keys will work. All you need to do is poke one of the snap pin heads in, then put slight sideways pressure on the extension so the head doesn't pop back out. Then flip over to the other side and push that head in and the extension should slide right out with the snap pin still in place. Was easy to do so I don't see any hassles here, so long as you got something to poke in the heads with. In a bind after a hunt you could probably find a small stick to do it if your keys are too blunt. Just would hate to see somebody after a hunt unable to take off the extension for transport.
Tomorrow morning I plan on the first try in the water. I will report back with how it panned out and how deep I was able to comfortably go without having to look back constantly to keep an eye on the box height. Even if the box gets dunked I doubt water will be able to get into the bag, but don't want to take that risk myself.