Humminbird Side Imaging Forums
General => General Discussion => Topic started by: ITGEEK on May 14, 2012, 09:20:57 AM
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Folks,
I did a recording a few weeks ago, and I found a nice rock pile.
I created a Waypoint on my machine after viewing the recording using Humviewer.
I went out last weekend, excited to fish this rock pile.
I targeted the Waypoint and proceeded to try and get on top of it,
but I never could. I tried like hell, but I could not get on top of it.
It was a little windy, and there was some current, and I did get close a couple of times.
I even had some throwable buoys ready to visually mark the spot once I got on top of it.
But I never got close enough to throw a buoy.
I was extremely frustrated, to say the least.
Has anybody else here had the same problem?
Can anybody offer any tips?
Thanks in advance.
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I'm pretty new to the game, but I've found this particularly challenging also; especially so with a pontoon that needs about 30 yards to do a 180! LOL Not to mention that the slightest breeze makes the boat a wind sail. I did find that my tracks were worthwhile though yesterday. Snagged my first legal walleye of the year and was "almost" able to follow the exact same track again and sure enough, snagged another one not too far away from the first. I can't wait until I can completely fathom all of the features these units have to offer.... I hope some experts reply with some tips!
Mark
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IMO and IRT the two units I own...
Internal GPS 798 = good luck finding the same spot (GPS/mapping almost useless when accuracy really matters).
External GPS 898 = no issues finding the same spot.
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I often have the same problem. First off how far is your GPS puck in relation to your transducer? And check your GPS signal to see what kind of connection you have and number of feet of error it's showing. Both these factors can make getting on the exact spot hard. Hope this helps.
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I have no gps installation or accuracy issues at all.
I guess it's more of a navigating issue while trying to look at the map and
fight the wind and current.
Also, the boat doesn't stop on a dime, so it's easy to drift past a spot.
In theory, marking waypoints and returning to them is simple, but
I find in real life, it is extremely difficult.
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Not knowing which position format you are using I would suggest the decimal degrees. This is a five position placemark and the last digit in the decimal is only about a 3 foot/1meter of change. We use this for searches as it is very accurate..
Chuck
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ITGEEK, Chuck has a point in ref to SAR deg/min/sec v decimal degrees. It is simpler to request someone to go 300'/100m than than to say/plot/map/in field pin point deg.min.sec. some people just cant get there head around deg.min.sec. thing.
I just installed a Minn Kota 80# 60 inch with the I-Pilot last week on my Flats boat, The mark a spot and return button is the coolest thing. You mark the spot the later tell it to go to the way point along the last track logged.
So mark a WP on the trolling motor, mark a WP on the trolling motor GPS and let the trolling motor GPS system do the work!
Oh, $1600.00 motor, 300.00 batts, $175.00 batt box's, $125.00 plugs wire etc, $ 110.00 quick release plate.
I hope my wife does not see this!!!!!!!!!! Got to empty the trash NOW ! ):
Roddy
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I am using the most accurate GPS format for waypointing, ??.?????
Man Roddy, you are spending some big bucks.
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Could someone elaborate a little on the most accurate position format? Is it "dd.ddddd?" I'm assuming my 898 is still set to the default? It's at home and I'm at work so I can't check it now, but I would have had no idea one was more accurate than another, at least I don't recall the manual saying anything to that effect. ???
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I'm no GPS expert, but I was told (I think on this site), that the Decimal Format
was the most precise.
I borrowed the below from a web site (these are the different GPS formats out there).
Decimal Format:38.33915 -77.07127
GPS Format:DDD MM.MMM N 38° 20.349 W 077° 04.276 (I think this is the Humminbird default)
Degrees, Minutes Seconds Format:DDD MM SS.SSS N 38° 20' 20.9400" W 77° 4' 16.5612"
As you can see, with GPS Format and Degrees, Minutes, Seconds Format, you've only
got 3 decimals.
With any real number, the more decimals you have, the more precise, so Decimal Format
is the most precise.
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The positioning format can be stated in Degrees or Degrees and Minutes or Degrees, Minutes and Seconds.
These are relative to the equator and the prime meridian and expressed as North and West or South and East of the these two points.
For Example North 24 degrees and West 078 degrees. To get a closer placement you can state Degrees and minutes. Example North 24 degrees 13 minutes and West 078 degrees 22 minutes.
And so forth such as North 24 degrees 13 minutes 12 seconds and west 078 degrees 22 minutes 36 seconds.
Accuracy can be gotten closer by breaking the expressed value with a decimal place. Some of these can be 1 decimal and up to 8 decimal points. Only one decimal position allowed per value. So it would be North 24.12345 degrees and west 078.12345 degrees. OR North 24 degrees 13.12345 minutes and West 078 degrees 22.12345 minutes. the same holds for using the seconds.
However for the best accuracy and to give directions the Mercator meter system is the best.
Here the places are expressed in meters North (or South) of the equator and meters West (or East) of the prime meridian broken up into segments of 1000 meter increments.
so when you want to navigate to a place it is go north 125 meters and West 5 meters. A meter is a meter is a meter.
There is more to this but this should give some idea to GPS positioning.
Manufactures then design their units to work in a default positioning but sometimes give the user the ability to change the desired output. Some allow for 1 decimal place and others will go up to 8 places. So not all units are standard.
I wont even go into Datums right now..
If you use the GPS I would suggest exploring the technical piece of GPS. You cant get lost and you can always go to a specific place..
Chuck
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Thanks ITGEEK. I will check it when I get home. What I really need though is a pontoon that starts, stops and turns on a dime! hahaha I reeeaaaallly wish Roddy had not mentioned the Terrova with the i-Pilot...... My wish list gets longer and more expensive every day. LOL I'm using a 13 y/o Motor Guide w/a wireless foot pad that I control with my hand because it's such a pita to control with my foot. It was one of the early Motor Guide wireless models before Minn Kota sued them for patent infringement for copying the wireless technology. It was a pretty cool motor in it's day, much like my old HB LCR400ID was, but the technology has come so far in trolling motors too. hahaha I'm leaving it on the boat at the dock in the hopes that someone will be stupid enough to steal it so I can justify to the wife springing for a new one. ;D ;D ;D
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Adding to my previous post we find that it is much easier to navigate using the decimal degrees than any of the others..
However if you drop a waypoint you just drive your boat over the waypoint and check the gps reading..
Chuck
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Just to add to what has already been mentioned. Its important your gps antenna is on top/above the transducer for accuracy. If normal accuracy is 3 to 8 feet and your antenna is 5 to 8 feet from the transducer you have a accuracy of 8 to 16 feet. making it tougher to get on the spot. its not possable to have your unit on the console with internal gps to be on top of the transducer unless you use an external antenna. way point accuracy is important but it is lost if your not marking what you are seeing.
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Another important thing to remember is that the boat heading (and normally the transducer heading) is not necessarily the same as the "Course Made Good" (CMG) based on GPS positions.
If there are strong currents and wind and your targets are far away from the track, this error may be large. The image below illustrates this:
The boat (and the transducer) is pointing to starboard by 20 degrees relative to CMG.
The Brown image is calculated based on the assumption that the transducer is aligned with CMG.
The Blue images are based on a "pointing angle" of 20 degrees (i.e. you point the vessel 20 degrees into the wind/current in order to stay on track of the survey line)
In essence: When making a mark, also take note of the heading of the boat relative to CMG and remember that the position of your targets may need to be adjusted for this heading error. (It is therefore also important to make a mark at the track-line, since that is the "point of rotation" for this correction.)
If your boat is drifting while recording, the difference between CMG and the heading of the boat may be very large, and even completely flipped 180 degrees (...drifting backwards). In that case, if you mark targets at a certain range, the marks may even be interpreted as being on the WRONG side, since there is no available information about the actual heading of the transducer. (i.e. everything is based on the CMG from the GPS)
(A heading sensor would be a nice addition to the GPS-puck...)
Tore
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Great info and recommendation, Tore.
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Weekend Warrior, Its a saltwater ST with I-Pilot. Working on wiring to hook the I-Pilot to the 1198. Pre plan long track with fishing way points on the 1198 and have the trolling I-Pilot slave off the 1198 while I fish.
Roddy
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Tore
As Bob B said, great info. Thanks for posting it. Another condition I hadn't considered. Great explanation also.
Mike