GPS speedo - SOG or SOW

[dabear]

When using a GPS speedometer what speed reading would be more accurate speed over ground or speed over water ? 

What system is used by law enforcement to determine speed on the water ?  Which system updates faster I notice over a second lag time with speed over ground ?    Joe R

[HewesYourDaddy]

If I'm not mistaken, they should be exactly the same unless one is giving a readout in knots. 

[hurricane]

SOG, I would assume to be what the PD uses. They are both accurate just different measures

SOW takes into account the current. To calculate SOW I would think you would need a paddle wheel type speedometer, along with SOG. 

[dabear]

I have placed both my Speed Over Ground and speed over water on the same screen on my HD2 this way I can monitor them side by side and see what they read. I was told the HD2 has a setting to adjust how often it will up date on the speed over water set up.  Told it was 1 to 5 seconds . Hope I can adj to the 1. second update . Also was told that a lot of fisherman use the sow when trolling because a lure that needs to move a exact speed.   Hope next time out that I will be able to tell if they read the same or not.   Joe R

[hurricane]

Yep SOW is a nice feature when trolling, but you have to know the speed of the water current to get SOW. Without knowing how fast the water itself is moving, you can't calculate it. 

[polliwog]

I look at my SOG on the GPS and the Speed shown on the engine speedo gauge to show the effect of the current.  It works pretty well.  I go up a big river with good current flow on the out going tide and it can be a 2 mph difference. 

[Nag Juice]

SOG is the only thing that matters to me. SOW is handy when you're doing some precision Mode III Navigation, but not on a flats boat.

[dabear]

1 hour ago, Nag Juice said:

SOG is the only thing that matters to me. SOW is handy when you're doing some precision Mode III Navigation, but not on a flats boat.

I am not into any fancy navigation ,  90% of my fish trips we just want to stay in the water and off the oyster bars.Kind of like the Alan Jackson song 5 o'clock somewhere . Only use nav when we are out of town.  I use the GPS when I am fine tuning a prop and wanted to use the fastest update and most accurate speed.  When we are someplace I have not been in a while we use binoculars our compass and a map. Between that and the Lawrence we have managed to find our way back to the ramp .  Don't want to name the boat the SS Minnow. Don't get me wrong I would have no problem being  on a Island with Mary Ann and Ginger . 

[mulligan]

I have no clue as to which has the fastest update.  I know I use SOG which does have some lag for the display but does record the max speed even though it might not display it while running.  Example, I may only see a max speed of 45 while running but when I go look at the max speed in the trip log it may show a max of 47.

[Nag Juice]

On 8/18/2017 at 10:41 AM, dabear said:

I am not into any fancy navigation ,  90% of my fish trips we just want to stay in the water and off the oyster bars.Kind of like the Alan Jackson song 5 o'clock somewhere . Only use nav when we are out of town.  I use the GPS when I am fine tuning a prop and wanted to use the fastest update and most accurate speed.  When we are someplace I have not been in a while we use binoculars our compass and a map. Between that and the Lawrence we have managed to find our way back to the ramp .  Don't want to name the boat the SS Minnow. Don't get me wrong I would have no problem being  on a Island with Mary Ann and Ginger . 

Use SOG and make sure your chart card is updated. Electronic navigation is primarily used on most ships now. Drop a few waypoints if you're in new territory and connect the dots on the way back. Paper charts need to be corrected too. USCG issues monthly NTMs and LNTMs for corrections. It's much easier to do it electronically.