Have a Garmin 182 chartplotter on the boat. I have been trying to put some numbers together to see how wel lthe prop is performing. After running the numbers I am coming up with some extremely low numbers on prop slip. I've checked the tach out with a digital tach and they match up for RPM. My question is can my GPS be optimistic on speed. Any ideas? Any help would be appreciated.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
GPS Question
- Thread starter 206LSdrvr
- Start date
I think the GPS can be a little off. Next time you are out, go to the GPS info page on the unit. See what the accuarcy is. This shows you the difference in feet or meters. It can be off by min of 3 feet using WAAS or off by up to 50 feet. So 50 feet per mile up to 50 MPH could make a difference of ??
THe 182 is WAAS capable. I have read somewhere, I think it might have been on OSO, something similar to what you mentioned. I am curious on how this would be determined and is there a formula to calculate for a correction. Right now when I used an online prop calculator I'm coming up with a prop slip of .05 or less. There are some race boats that would like to have those numbers. Garmin has some software upgrades for the 182, but I have got to order a cable so I can plug it into the computer.Castines said:I think the GPS can be a little off. Next time you are out, go to the GPS info page on the unit. See what the accuarcy is. This shows you the difference in feet or meters. It can be off by min of 3 feet using WAAS or off by up to 50 feet. So 50 feet per mile up to 50 MPH could make a difference of ??
The outdrive gear ratio affects things too. I have assumed that the gear ratio is 1.50. I went to Outdrive .Com to check for different drive gear ratios. They had a upper for an Alpha that had a 1.30 set of gears. In looking in my shop manual I found that Mercruiser did use 1.32 gears with a 454 C.I. engine. Think I may have to pull the boat out of the water and check the gears. This may solve the mystery.