ToadWhisperer
Member
How do you divers and snorkelers grid areas underwater? I have a hard enough time keeping track when wading, but once my head goes underwater I'm just clueless in low visibility lakes.
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Underwater Gridding?
- Thread starter ToadWhisperer
- Start date
OldBeechnut
Well-known member
Well, I will probable look like a fool on this one but I have a place where just started detecting this summer that has been out of use for many years, I hunt it waist to chest deep, using a GPS when I hunt. I take a old umbrella pole {1" Dia} which has the screw bottom for screwing into the sand with a 15 foot 1/4" rope firmly tied to the middle of the pole. I pick a hot spot, Screw the pole into the sand, walk out 15 feet, clip the rope to my pouch belt and spiral around the pole, SLOWLY winding the rope around the pole and Fully covering a 30 foot area. Using the GPS to mark the finds with Waypoints plus marking the area hunted by using the trail tracker. Used it two hunts now, Works Great, work underwater? Not sure, But it should..............................joe
go to http://www.ucidiver.com/jackstay.htm this should be a start,,,,there are many searches but the jackstay is one of the best,,,if your in a tight area make a rectangle out of 3/4 pvc maby 3 ft by 6 ft and just flip it end over end, this is good like if someone lost a ring off the side of a dock. on the jackstay dont forget to overlap your coil swings, slow and good luck,,,try www.ucidiver.com,,,,,,then tactics,,,,then search patterns,,,,then jack stay
ToadWhisperer
Member
normdiver said:
Very interesting site, Thanks!
ToadWhisperer
Member
I've been considering a way to use my GPS in a small drybag on my wrist. I wonder how well it would pickup satellite signals underwater?
OldBeechnut said:
OldBeechnut
Well-known member
I use the garmin etrex vista cx, water proof and hangs around my neck, tucked into my PFD vest pocket. I'm sure it will have no problems getting fixs on the sats underwater, but you can call garmin. I like it because i don't end up hunting the same area over, or if I have a spot I want to hit again, very easy to find that location. Comes with the software so you can map out where you've been on google maps, you just have to set markers and the software does the rest..............joe
ToadWhisperer
Member
I have a Etrex Vista HCx also. According to Garmin, it "can withstand accidental immersion in one meter of water for up to 30 minutes".
I was looking at this-> http://www.leisurepro.com/Prod/CategoryID_2021/Context_965/Sort_Stock/DescSort_0/APC210.html?Hit=1
Supposed to be good down to 5 meters (15 ft)
I was looking at this-> http://www.leisurepro.com/Prod/CategoryID_2021/Context_965/Sort_Stock/DescSort_0/APC210.html?Hit=1
Supposed to be good down to 5 meters (15 ft)
grumpyolman
New member
Hey folks! The GPS is NOT a good way to keep track of where you have searched. Unless your GPS is one of the new ones, like a year old, it is good for general navigation but to mark a spot hunt it and to come back tomorrow and not hunt the same spot again, just isn't going to happen. The GPSs all have DOP (dissolution of position) or EPE (estimated positional error) ratings. That will vary from place to place and from a particular time of day compared to a different time another day. The two factors that affect that are the number of satellites that happen to be near you when you take a reading and if you are in a place where you have clear access to the satellites compared to with whatever the situation is the next time you use the GPS.
Most of the GPSs will report the EPE or the DOP if you know where to look for it within the screens. It's usually measured in feet and a DOP of 17' means the GPS is only accurately measuring and reporting where you are with an accuracy of a 17' area. That's OK to find the Old Oak Tree again, but it's not good enough to use it as device to accurately grid a search area. Also, there is no standard reached by the industry about how to measure and calculate what the DOP or EPE is. Some GPS manufacturers will tell you how they determine that number and others will claim it's proprietary. They'll give you the number but there's no way to verify their numbers.
The GPS is not intended for mapping. That's what you are attempting to do if you want it to accurately establish a search grid. For that you need the equipment the map makers use and that's GIS. It's pricey, highly technical, and takes significant training to use it properly.
The most recent GPSs we got for our Search and Rescue unit, usually have an EPE of 7' or so. That's only that good when we are in an open area, out of the brush, and happen to have quite a few satellites overhead. At a night training, we had people place a golf tee in the grass and mark the position. They were to walk another 20 steps to some other random place and put a second golf tee in the ground. They'd then tell the GPS to GoTo the first tee and would follow the directions the GPS was indicating. A lot of the folks got directed right back to the first tee. However, if they came back the next day and asked the GPS to GoTo the first tee, it might lead them 20' away from where it indicated the previous night. That's for all the reasons I explained. In SAR if we can get within 100' of somebody in the brush whose lost, we can shout and walk to them using the sound of their response. So for most needs, an EPE of 20' is a non issue. I hope you can see it does not have the accuracy needed for gridding.
Watch the police when an accident reconstruction team is calcualting what happened. They don't use GPSs. They use laser transits. Me thinks a laser transit is far too complicated for metal detecting a paticular grid.
The circle search above is a good one. Also the jack stay described. If you are diving a white 50' rope anchored on each end with a weight is a good line to follow. Detect it going both directions then move it over 2-3' and do it again. That would probably even work wading if you had clear water. There a good section on this forum about using GPSs and reading maps. Good moderator who knows his stuff. Jump over there and ask him about using the GPS for establishing a grid. Just hate to see folks get all jazzed about discovering a technical way to grid search a hot area and knowing it will not give the accuracy needed for that. Don't mean to rain on your parade, but also hate to see you learn from trial and error and miss good targets and interfere with quality detecting time. jim
Most of the GPSs will report the EPE or the DOP if you know where to look for it within the screens. It's usually measured in feet and a DOP of 17' means the GPS is only accurately measuring and reporting where you are with an accuracy of a 17' area. That's OK to find the Old Oak Tree again, but it's not good enough to use it as device to accurately grid a search area. Also, there is no standard reached by the industry about how to measure and calculate what the DOP or EPE is. Some GPS manufacturers will tell you how they determine that number and others will claim it's proprietary. They'll give you the number but there's no way to verify their numbers.
The GPS is not intended for mapping. That's what you are attempting to do if you want it to accurately establish a search grid. For that you need the equipment the map makers use and that's GIS. It's pricey, highly technical, and takes significant training to use it properly.
The most recent GPSs we got for our Search and Rescue unit, usually have an EPE of 7' or so. That's only that good when we are in an open area, out of the brush, and happen to have quite a few satellites overhead. At a night training, we had people place a golf tee in the grass and mark the position. They were to walk another 20 steps to some other random place and put a second golf tee in the ground. They'd then tell the GPS to GoTo the first tee and would follow the directions the GPS was indicating. A lot of the folks got directed right back to the first tee. However, if they came back the next day and asked the GPS to GoTo the first tee, it might lead them 20' away from where it indicated the previous night. That's for all the reasons I explained. In SAR if we can get within 100' of somebody in the brush whose lost, we can shout and walk to them using the sound of their response. So for most needs, an EPE of 20' is a non issue. I hope you can see it does not have the accuracy needed for gridding.
Watch the police when an accident reconstruction team is calcualting what happened. They don't use GPSs. They use laser transits. Me thinks a laser transit is far too complicated for metal detecting a paticular grid.
The circle search above is a good one. Also the jack stay described. If you are diving a white 50' rope anchored on each end with a weight is a good line to follow. Detect it going both directions then move it over 2-3' and do it again. That would probably even work wading if you had clear water. There a good section on this forum about using GPSs and reading maps. Good moderator who knows his stuff. Jump over there and ask him about using the GPS for establishing a grid. Just hate to see folks get all jazzed about discovering a technical way to grid search a hot area and knowing it will not give the accuracy needed for that. Don't mean to rain on your parade, but also hate to see you learn from trial and error and miss good targets and interfere with quality detecting time. jim
OldBeechnut
Well-known member
Thanks GrumpOm, I knew about the DOP, read about it a few years back, good thing about this place the bottom changes very little during the weeks, so I can tell where I have been and not and it is a big place. One thing good is there are plenty of land markings to go by and with the GPs I do get a general Idea of, with the bottom not changing from the holes I have dug were I have been. Now to go back next year and hunt the place, that maybe a different story but I would have the map to the land marks still, they don't change. Like you said, the Old Oak trees. joe
ToadWhisperer
Member
Thanks Grunpy, better a little rain on my parade now than two or three days of it later.
JOHNMARKHAM
New member
this is very interesting info thanks guys
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john
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john