Lately it seems every time people talk about GPS or Radar speeds, someone comes in and tells them that those readings are useless and that only Lap Times matter. To me this is like when I first started in this hobby and every time a guy like me (sport boater at the time) would make a comment I would be shot down by the 'do you race?' comment. That really got to me, and I am starting to find the 'Lap times' thingy annoying at times too! No offense to anyone.

Here is my take on this.

Lap Times: good to note and document improvements in DRIVER SKILLS. The shortest times obviously mean you are getting around said course faster. This can be either because of a faster boat OR driving a shorter course (closer on the buoys) OR a combination of both. This all changes when you are in the water with other obstacles such as other boats racing!

GPS - Radar: good to note and document improvements in BOAT SPEEDS. You should do several backing runs to confirm readings accuracy and rule out erroneous readings. In my opinion this is the only way for the common boater to register true speed of the boat short of running through a speed trap.


To sum it up, I think it is not only valid to use a GPS and/or radar gun to validate boat speed, it is the only effective AND accessible method for most boaters to do so. You can take lap times all day long if you want, but that will not necessarily tell you the boat is faster or slower, it will just tell you that the boat is getting around the course slower or faster. Could be that you are just not driving it in the same lanes all the time. Unless you are a robot and have perfect conditions and repeatability, you can BET you are not running the same laps all the time! Want to know your boat's speed?...put the GPS in!

I'm done... comments welcome!

marc i believe in every thing you hsve said,lap time is what you are doing that day on that track and how well you drive and will always be different another day.Gps is good for base lineing you and your equipment. calm water a good barometer and bouys you can base line and then you will know how well you are doing race day.If you race if you dont race trying to run your fastest lap with bouys is always fun.

We've been using GPS speeds for a long time. In tests of our SAW boats, the GPS always read a few mph less than the radar gun. I believe that this was due to the GPS reading lagging the speed as the boat accelerated very quickly. Recently we recorded speeds with three different GPS units in a full size boat. We used two Eagle Tree new fast update GPS units and a professional GPS speed indicator. All read the same maximum speed within less than 1 mph in the 90 to 100 mph area. I also have a graph of GPS speed through the traps at Legg Lake. The peak GPS speed was higher than the speed measured by the timer since it represents an average speed in the traps. The boat was still accelerating.

Lohring Miller

Thanks Lohring. Your test results are more proof that the GPS units are more than accurate enough for us to get speed readings from our boats. True sometimes you can get bogus readings, but filter those out and you have a pretty accurate tool with the GPS.

Right on Marc. I agree and being a sport boater it sometimes feels that if you do not race then you do not count. So again I agree and use both the tach and GPS to find out my speed. Lap times are important but as you say, you do not drive the same line every time. If you have MPH and the RPM then you know what is going on with your boat.

Regards
Tar

most boaters don't even take rpm into account.they just want to know how fast their boat is going right now! the higher the better which although not completely accurate is how they will beat their boating buds.

If you use an Eagle Tree data logger with their fast update GPS and an rpm sensor, you can get tons of information on how a boat behaves around a course. You can even embarrass yourself by plotting your course. It takes lots of patience and experience with the system. Most of my data comes from straight line testing, but I ran a data logger for one P Mono heat at the Electric Nationals this year. It was interesting.

Lohring Miller