Purpose
This app sets a windward-leeward race course that's square to the wind at Clinton Marina, using a pre-calculated ring of 36 GPS "drop points" spaced 10° apart around a fixed course center. One boat sails a short 2-tack wind check to find the course number. That number gets radioed to any other boats helping set marks — each boat enters the same number and taps a button to be guided to its own mark, no wind check required on their end.
Key Terms
- Drop Point (DP) / Course Number: one of 36 fixed GPS positions, numbered 0–35, arranged in a circle around the course center. DP 0 is due north; numbers increase clockwise (DP 9 = east, DP 18 = south, DP 27 = west). "Course number" and "drop point" mean the same thing here.
- Wind Check: the 2-tack test — sail starboard, then port, holding each for 1:30 — used to work out true wind direction, tacking angle, and the course number. Only needs to be run once, by one boat.
- Windward Drop Point: the drop point matching the wind direction. This is where the windward mark gets dropped.
- Leeward Drop Point: the drop point directly opposite the windward one (course number + 18, wrapping past 35 back to 0). The center reference point for the starting line.
- Boat / Pin: the two actual ends of the starting line, offset on either side of the reciprocal drop point — Boat to starboard, Pin to port (facing the windward mark) — sized by how many boats are racing.
- Helper Boat: any vessel using this app to navigate to a mark. Only one helper boat needs to run the wind check; the others just enter the course number.
Course Geometry
Center40.152433, -88.831085
Radius≈ 326.4 m (1,071 ft)
Diameter (DP0–DP18)≈ 652.7 m (0.41 mi)
Spacing10° per drop point
Setup Procedure
Needs the app open over HTTPS with location & motion access allowed to get live GPS/compass data.
Step 1 — Wind Check (one boat, once)
- Tap Start Wind Check. On iPhone, tap "Enable compass & location" when prompted.
- Sail upwind on starboard tack. The first 10 seconds are just to get up to speed and aren't recorded; the app then records your heading for 1:30.
- When told, tack and hold port tack the same way — 10s to get up to speed, then 1:30 recorded.
- The app averages your heading on each tack to find the tacking angle and true wind direction, announces the course number out loud, and fills it into the Course # field in the Set Course card below. It does not start navigating automatically.
- Radio that course number to any other boats helping set marks.
Step 2 — Set Course (any helper boat)
In the Set Course card: dial in the Course # (auto-filled after a wind check, or entered manually from the radio call) and the number of boats racing, then tap one of:
- Set Windward Mark — navigates to the course drop point with a distance readout and spoken tack calls, whether or not this device ran the wind check itself. If it measured the wind directly, tack calls use that; otherwise they use an approximate wind direction backed out of the course number (since that's how the number was derived in the first place) with a typical assumed tacking angle. Announces "Drop the mark" within 60 feet. Afterward, tap "Mark dropped — sailing downwind" to continue to the reciprocal drop point, where it announces "Set Starting Line Here" within 60 feet — a plain center reference for the line.
- Set Boat / Set Pin — navigates straight to the actual starboard or port end of the starting line (offset from the reciprocal drop point by 1.5 × boats × 19 ft ÷ 2 on each side). Announces "Arrived, set the boat/pin here" within 10 feet.
Worked Example
Wind check finds the wind is from roughly 004° with an 86° tacking angle. The app sets Course # to 0, speaks "Wind is from 4 degrees, course number 0," and closes. The crew radios "course zero" to the pin boat. Either boat can now tap Set Windward Mark to sail to DP 0 with tack calls — the pin boat gets these too even though it never measured the wind itself, using the approximate 45°-per-side assumption off Course # 0. First boat there drops the windward mark at 60 ft. The pin boat, with 10 boats racing entered, taps Set Pin and is guided straight to a point roughly 71 ft west of DP 18, arriving within 10 ft. A third boat taps Set Boat and is guided to the matching point east of DP 18 for the RC boat.
Good to Know
- These points are on open water — normal mapping apps can't compute turn-by-turn "directions" across a lake, which is why the app guides you with live bearing/distance instead.
- Tack and jibe calls use a simplified model based on the tacking angle — either measured by this device's own wind check, or a typical 45°-per-side assumption when navigating off a radioed course number instead. Good for getting into the right zone, not a substitute for reading your own laylines. Boat/Pin navigation never gives tack calls, since positioning the line isn't an upwind leg.
- Every leg gets a spoken "[X] feet to go" update roughly every 30 seconds, so you don't need to watch the screen while under way — not just at tack changes and arrival.
- Audio uses your phone's built-in text-to-speech, so it works without an internet connection once the page is loaded.
Drop Point Map
Real-world location of the course on Clinton Marina.
Same diagram as in the GPS Assisted Course Setup document. Cardinal drop points (0/9/18/27) shown in red.
All Drop Point Coordinates
Decimal-degree GPS coordinates for all 36 drop points.
| DP | Latitude | Longitude |
|---|
| 0 | 40.155373 | -88.831085 |
| 1 | 40.155328 | -88.830420 |
| 2 | 40.155195 | -88.829775 |
| 3 | 40.154979 | -88.829169 |
| 4 | 40.154685 | -88.828623 |
| 5 | 40.154323 | -88.828150 |
| 6 | 40.153903 | -88.827767 |
| 7 | 40.153439 | -88.827485 |
| 8 | 40.152944 | -88.827313 |
| 9 | 40.152433 | -88.827254 |
| 10 | 40.151923 | -88.827313 |
| 11 | 40.151428 | -88.827485 |
| 12 | 40.150964 | -88.827768 |
| 13 | 40.150544 | -88.828151 |
| 14 | 40.150182 | -88.828623 |
| 15 | 40.149888 | -88.829170 |
| 16 | 40.149671 | -88.829775 |
| 17 | 40.149539 | -88.830420 |
| 18 | 40.149494 | -88.831085 |
| 19 | 40.149539 | -88.831750 |
| 20 | 40.149671 | -88.832395 |
| 21 | 40.149888 | -88.833000 |
| 22 | 40.150182 | -88.833547 |
| 23 | 40.150544 | -88.834019 |
| 24 | 40.150964 | -88.834402 |
| 25 | 40.151428 | -88.834684 |
| 26 | 40.151923 | -88.834857 |
| 27 | 40.152433 | -88.834915 |
| 28 | 40.152944 | -88.834857 |
| 29 | 40.153439 | -88.834684 |
| 30 | 40.153903 | -88.834402 |
| 31 | 40.154323 | -88.834019 |
| 32 | 40.154685 | -88.833547 |
| 33 | 40.154979 | -88.833000 |
| 34 | 40.155195 | -88.832395 |
| 35 | 40.155328 | -88.831750 |