The best measurement is who crosses the finish line first. Most of the time it's the only boat running and he was not the fastest.
David
True...but I am 2 hours away from any clubs that race RC boats. I do drive the trip to OK city at least half a dozen times a year just to run up there with them...but no one up there even owns a radar gun that I know of.
Anyhow, my point...if I run alone, it is easier to test with the GPS...or for that matter, even if I am not running alone. Take an engine that does NOT have a third channel radio connected to it. Put a GPS in the boat, run two laps, then bring it in. Now lean, or richen it an eighth turn and do it again. Did it speed up or slow down?? Adjust accordingly... GPS has been a very useful tool for this.
Another example...if I have three props that all are the same. I can GPS all three props, and find that one is actually 2 MPH faster than the other two. Nothing I know anything about...I sharpened and balanced them all myself...used the same method on all of them, yet one is noticable faster than the other. I found this with a GPS.
Hardware...ever wonder how much speed you will gain by making certain changes to the hardware on the boat?? GPS will tell you. I did a lot of testing to design a rudder blade for an RTR boat. When I was done I wound up with a rudder that has a visable increase in speed, and did not hurt handling at all.
Pipes...run the boat two laps, pull your pipe out (or push it in) an quarter inch, then run two more laps. Was it faster or slower?? Can you see a 1 or 2 MPH difference in speed at 55 MPH?? I can't... The GPS can!!!
OK...now try running your boat, and holding a radar gun at the same time...
Biggest problem I have with the GPS, is keeping them in the boat, and keeping them dry. One of my GPS units is at the bottom of the pond in Carrolton TX (learned a lesson from that). Another one has cracks in the case, and if it gets submerged, the screen with fade out (dry it out and it will work again another day). Third one still works fine...
Sean