you might want to keep some TUMS handy :Rofl
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GPS Way Points are not dead nuts no matter what, they put you in the general area. Once in the general area turn on 2D to find the exact spot. I use a internal GPS Helix 12 SI Gen 1 on my dash and find it is not a big deal finding my spots just takes a few minutes, I will then throw a marker once found.
I like to confirm my x marks the spot while traveling in two different directions at 90 degrees to each other. In other words, make a pass north to south, then make a pass east to west. I prefer to use my side imaging during these passes. I don't like driving over the spot and having prop wash disrupt the scene of the crime before it happens. Drop a marker buoy 10-15' away from the scene of the crime. Then position the boat to let the slaying begin...
:fish
Why 2d ? I mark stuff motoring with my Humminbird 1199 on console set on side imaging and linked up with Helix . I have my Helix 10 transducer mounted on trolling motor . Set on side imaging set at about 40' and small part split with map . Zoom in as you get closer till down to 10' scale , you will see what was marked on down or left or right as you pass over mark . Hard to miss once you learn to use your electronics . All way points marked will show up on both if linked while both units on . No problem with accuracy . (1199 and rear transducer about 6' apart) (Helix and transducer on trolling motor about 2' apart )
While the error distance introduced by the distance between transducer and head unit is minimal. The greatest error is broadcast via the GPS system. It can vary by up to +/- 3 meters in any direction. Your mark could be off by 10' in any direction even if everything in your boat was perfect and had zero error. The waypoint is a general location. To find the spot you need to scan or use a triangulation method. While DI or 2D are great tools, they also have limitations. They will only see at best the diameter equal to the distance to bottom. If your in 10' of water, your only going to see 10' (5' either side of the transducer) at a time. If your in 30' of water you will see 30' of water. You literally have to pass over the waypoint to see it and greatly increase the odds of spooking the fish. Not too mention your sonar will have trouble seeing though the prop wash you just created.
For me, the best option is to set my Side Imaging to read either the left or right side and pass the mark about 50' off to the side, make a 3/4 loop and pass the mark again at 90 degrees from the first pass. This gives me two points of reference and I can move in closer to drop a marker buoy. To elaborate- Cruise past about 50' to the right side of the waypoint with my SI set to read on the left side of the boat. Once I go passed my target turn to the right (away from my target) and make a loop so I can cross my wake and see the waypoint at a 90 degree angle from the first pass. Kind of like the old Clover-Leaf interstate on-off ramps. The benefits are you don't create prop wash in your fishing hole and don't spook the fish. Plus you can make a box around your target, not a circle, to find the exact spot.
I also like to start out fishing away from the spot to pick up any fish hanging around the outside edges, then work my way in slowely to the target. This is my method for open water submerged targets.
Don't forget to look up once in a while and actually fish. With a new toy you can forget why you are actually on the water.