i had asked humingbird about there 580 combo finder being that i have a yamaha motor the speedo tub is allways pluged  so i asked if this unit had a gps speed  feature  there answer was as followed  

gps speed is only available  on select views  you can get the paddle wheel for speed [ dont want a paddle  that is the idea for gps ]  and they also said the speed sensor is digital.  i know that ia'm not very smart but i do not understand  there answer  that gps speed is only avaible on select views. need some help  thank you ken

i guess there is not a topic for electronics  on site  

I assume they mean on select screens. I have a garmin and I can only get the gps speed "displayed" when I am in full screen map view(location only). If I have it set for split screen (depth and location), or full screen depth finder, the speed is not displayed.  I assume this is because the screen would be to cluttered.

On the 580 you get gps speed on the sonar and map screens.  It will not show up on the flasher screen.

If you want the straight scoop, go to the Humminbird website and download the manual for the 580. You will see that the user can select what and where on the screen a digital display can be placed. When the manual downloads, the picture of the unit on the first page shows a split screen with GPS mapping and sonar along with temp, depth, and speed.

thanks guys this is the first time it got explained to me that i can understand