Using a GPS to set a course

[Mrs blueskyracer]

Ok, guys and gals.....

Is there anyone out there who has set a turn in a race course using their handheld GPS to get the arc of the turn to match on each side of the apex buoy, and have the same size turn at each end of the course?

Knowing that all GPS units are different in the functions that they allow, does it matter which model (features) you have?

What is the procedure that you have used to setting the turn?

[Graham 18ce]

Well, not something that i have tried, the thought had crossed my mind before using Google maps to get an view of the water and place the bouys based on best possible arce and water usage.
However, I i have done geocaching before. The error built into the units (Around +- 20 feet) does make it a little tougher then you would think.
Most handheld units that allow mapping would be capable. You could use the topo map on the computer to view the water you are racing on and place the pins are way points on the course. Then go to the site and use the hand held unit to guid you to the point.

Built in error and bouy drift from slack line and actually getting the ancher to hit the right spot. You get a course relentively close to what you wanted, a great starting point i would imagine.

Be interesting to hear the results of someone who has actually tried it rather than just thought about it.

[sam]

If my calculations are right, possible 20 ft error would make it about 2% maximum error on a one mile course (because the turns would be approximately 1/2 mile apart)

[Brian10s]

Been thinking that we may have a record I mile course at the June 2010 Stock/Mod Western Divisonals at Oroville. use a GPS to get a fix on the buoys after Russ Dodge sets up the course. Then for the Nationals in August use the GPS readings for buoy placement. Russ says it would be close. I am not saying we will have a record 1 mile approved for records course at the Nationals. Just as close as possible to 1 mile course.

I did this before (not on a surveyed course though) at Franklin, PA for the Mod Nationals. We put in a course for our Spring race that was really good and then logged it into a gps using way points. Went back later in the year and tried to duplicate the course. It worked well up to a point. Each time you turn on your GPS you have a level of accuracy - and depending on the time of year (tree coverage) or the time of day (sat coverage) you get a different level of accuracy. The 2nd attempt was close to the original but not exact - we had to smooth out the turns and such. It was ok to try but took a ton of time (telling the boat driver 10ft this way, 5 ft that way, etc) and the results were not quite "perfect".

[Mrs blueskyracer]

Brian,
(Please remember that I am a blonde) I know how to mark way points on my GPS, so I can mark the first point, drive say 700 feet and mark a second point, how do you determine where the apex of the turn would be. Somehow I feel like the solution to this is so easy I am missing it. How do you determine if you want to drive 300, 400 or 700 feet from point 1 to point 2? I just know I am overthinking this how mess. I am not concerned about the site being exactly the same everytime, I am just trying to determine how to get turns to match at each end.

[jpro60]

I set up the course at Eatonville this year using a handheld GPS (garmin e-trex), I'll try to break it into the steps I used, and give an example. 1) First I drove the patrol boat down the front straight (estimating where the front straight should be) with the unit telling me my heading. 2) Then I set up waypoints for the middle of my turns, 1 for each turn distance between the two dictated by lake size/ estimate based on desired course size. 3) Then I layed in the buoys using bearing mode and distance from the waypoint.

So, for an example;
1) lets say my heading down the front straight was 290
2) then I layed in my turn middle of turn markers/ gps waypoints
3) then lay in the buoys. For example since my heading down the straight was 290 I'm going to put in the first entrance pin 90 degrees off of that. So, 290+90=380-360=20 So I'd put in that first turn entrance pin at a bearing of 020 degrees from my central waypoint, at the desired distance, at Eatonville it was 500 feet i believe.
To finish the expample, say I wanted a 5 pin corner. I'd lay in the entrance at 020 bearing, 2nd pin at 335 bearing, apex at 290 bearing, 4th pin at 245 bearing, and exit at 200 bearing. Repeat in turn 2.
Hope that helps,
Mike

[Bill Huson]

Ugh . . .

I have one GPS - a rather pricey Furano unit on my 23' Parker. Big screen - good for old feeble eyes. I use it for point-and-shoot boat driving. From my rough guess by noting the boat position on the screen and then looking at the actual nav marks on the water, 20' accuracy is extremely optimistic. +/- 200' maybe. I kid thee not.

[A/B Speedliner]

Course layout

I was not going to open my mouth but I am from the northeast and it hard for me not to offer my comments.
A few facts, I am a licensed Land Surveyor and also a Professional Engineer, actually retired. I have experience in laying out race courses from laying out the President Cup race in Washington to laying out courses for our local club. I also owned a company that sold high end GPS equipment and ran a school in operating the equipment.
We originally laid out a course from a measured base line on shore that was either measured with electronic measuring devices or using a calibrated invar steel tape. We then using pre computed coordinates for the various bouys, turning, start/finish and saftey, turned computed angles simultaneously from each end of the baseline. Where they intersected was where the bouy was placed.
This evolved into turning one angle and using a reflector board mounted on the stern of the boat setting an electronic measured distance along the line to the corrindnates of the bouy. I have never used GPS to layout a course but I do not see why it could not be done. The equipment is available to locate points to less then a centimeter using satelites and a land based transmitting station. The only problem is the cost of the equipment, I would try to find a local surveyor that would be willing to work for what ever advertising you can offer.

The use of handheld GPS receivers is problematic in as stated in previous posts the accuracy of hand helds with base station corrections could range for 20 feet to hundreds of feet depending number of satelites available, arrangements of the satelites, weather conditions, condition of the batteries, operator error etc. On the good side if only 20 feet was the error but it was in opposite dirrections at each end of the course the length of the course would be out about 126 feet, on a one mile couse 2.4%. I think if the error was at the other extreme the persons laying out the course would see the 200 foot error so lets say there was a 75 ft error on each end of the course in setting the entrance and exit bouys so the radius was 75 feet greater or less then calculated the course would be 471 feet longer or shorter than expected that is nearly 10% difference.

Well that is my thoughts on the process and I still think you should try to find a surveyor will to work with your club,

David Van Weele

[Mrs blueskyracer]

A/B Speedliner - I certainly agree that is the most accurate way to layout a course. For smaller clubs however that might be cost prohibitive. But I like your idea to do it in trade for some advertising. And.... your comments are welcome, thank your for speaking up.

[A/B Speedliner]

Course layout

This is a link to an article on layout of the course for the Gold Cup in Detroit. It appeared in this months POB (Point of Begining) magazine, a publication for surveyors. http://www.pobonline.com/Articles/Co...00000000671907

It appears the surveyors in Michigan volunteer for this.

[blueskyracer]

Nice article. Sounds like a pain.