SLSC Race Analytics

Document Revision: v1.22 | Last Updated: July 23, 2026

The Overview

Hey everyone — I've been building a race analysis tool for the club. Here's what it is, how you can participate, and what you'll get out of it.

What Is It?

A web-based system that records your race and replays it on a satellite map of Saratoga Lake. You can scrub through the timeline, watch your boat move around the course, and see your speed at every moment of the race.

The system lives on Cloudflare and runs in any browser — phone, tablet, or laptop. The bigger, the better.

The Big Choice: Two Ways to Record

To participate, you need to record your GPS track while you sail. You have two options, and each comes with a major trade-off. Please read carefully.

Option 1: The Web App (The Easiest Way)

You simply click a link on your phone, enter your boat name, and press "START LOGGING". At the end of the race, you must first press "STOP LOGGING", and then press "UPLOAD". There are no App Store downloads required and no files to manually share.

THE CATCH: You must keep your phone screen turned ON and the browser open the entire race. If you press the physical power button to lock your phone, or if you switch apps, Apple and Google will immediately kill the GPS connection. Your recording will stop and you will be left with large gaps in your track. (The app attempts to save any data recorded before the lock to your phone's local storage, but a complete track requires the screen to stay on.)

Option 2: Third-Party App Store Apps (The Bulletproof Way)

You download a completely separate third-party GPS app from the Apple App Store or Google Play Store. Because it is built specifically for your phone's OS, it has special permissions to run perfectly in the background.

THE BENEFIT: You can lock your phone screen, throw it in a dry bag, and it will record flawlessly. (Just make sure the bag is kept near the surface or deck line — do not bury it deep inside a fiberglass bilge or enclosed cabin where satellite GPS signals cannot be received.)
THE CATCH: It requires more work. You must install the app, and after racing, you must manually find the file, tap "Share", and upload it to the club website yourself.

The Three Web Apps: Install to Home Screen

CLARIFICATION: The "Three Web Apps" below are the custom tools built for the club. They are entirely separate from the Third-Party App Store Apps mentioned in Option 2!

To make accessing our club tools a 1-tap process in the future, the system is split into three separate web apps. You can install any or all of them directly to your phone's home screen, depending on which logging option you choose to use — you don't need all 3! They will behave exactly like native app icons.

App Name	Direct Web Address & Purpose
Logger - SLSC Fleet	https://slsc-fleet-logger.pages.dev Opens straight to the GPS recording screen. FOR OPTION 1 ONLY Use this ON THE WATER if you are recording your race using Option 1. (Warning: screen must stay on, phone cannot be locked. If you cannot guarantee the screen will stay unlocked, use Option 2, understanding there will be more user involvement on the back side to achieve reliability.)
Uploader - SLSC Fleet	https://slsc-fleet-logger.pages.dev/upload.html Opens straight to the file upload screen. FOR OPTION 2 ONLY Use this ON SHORE after the race if you recorded using Option 2 (Open GPX Tracker or GPSLogger).
Viewer - SLSC Fleet	https://slsc-fleet-logger.pages.dev/viewer.html Opens straight to the interactive map and race playback viewer. USED BY EVERYONE Use this ON SHORE (or at the bar) to watch the fleet's tracks after everyone has uploaded.

How to Install the Apps:

iPhone & iPad: Open any of the links above in Safari, tap the Share button (square with arrow) at the bottom (or top on iPad), and select "Add to Home Screen". It will download the bright yellow SLSC boat icon.
Android (Phone/Tablet): Open any of the links above in Chrome. Chrome may automatically prompt you to install. If it doesn't, tap the three-dot menu at the top right, and select "Install app" (or "Add to Home screen"). Note: The app will be placed in your App Drawer by default.
Laptops & PCs (Windows & Mac): Open the link and press Ctrl + D (or Cmd + D on Mac) to bookmark the page for easy access.

Detailed Setup Instructions by Phone Type

📱 iPhone (iOS)

If using Option 1 (The Web App):

BROWSER REQUIRED: Use Safari only. Do NOT use DuckDuckGo, Brave, Chrome, Firefox, or any other browser on iPhone. Apple restricts GPS access to Safari for web apps. Any other browser will either block GPS entirely or behave unpredictably.

Go to Settings → Display & Brightness → Auto-Lock and set it to NEVER. This is the single most important step — if you skip it, your phone will lock itself and kill the GPS.
Go to Settings → Privacy & Security → Location Services. Make sure it is ON.
Scroll down to Safari Websites → set to "While Using the App" and turn Precise Location ON.
Open the Web App link in Safari, press START, and leave the screen on during the race.

If using Option 2 (Native App):

Download Open GPX Tracker from the App Store (Free).
Start a track before your race. You can safely lock your phone screen.
After the race, stop the track, tap the Share icon, and select "Save to Files" to save the .gpx file to your phone.
Open Safari, go to the club's upload page, and tap "Choose File" to select and upload the file you just saved.

iPhone Note: iPhone apps only record position, not hardware speed. The viewer will calculate your speed afterward. The track will look identical, but the speed chart may be slightly jittery at very low speeds.

🤖 Android

If using Option 1 (The Web App):

BROWSER REQUIRED: Use Google Chrome only. Do NOT use DuckDuckGo, Brave, Firefox, or any other browser. Privacy-focused browsers deliberately block the GPS and screen-awake features this app depends on. The app will fail silently or give inaccurate data if opened in the wrong browser.

Go to Settings → Display → Screen timeout and set it to the maximum your phone allows. Most Android phones top out at 30 minutes — that is fine. The web app's built-in screen-awake code will attempt to hold the screen on past that limit, but it is not guaranteed on every phone model.
Open the Web App link in Chrome. When Chrome asks for location, tap Allow (choose Precise if asked).
Press START. The web app will attempt to automatically hold your screen awake, but you must not press the power button to lock the phone.

If using Option 2 (Native App):

Download GPSLogger (by Mendhak) from F-Droid (Free).
Start logging. You can safely lock your phone screen.
After the race, stop logging. Open Chrome, go to the club's upload page, tap "Choose File", and select the newest .csv file from your Recent files list.

Summary Comparison

Feature	Option 1: Web App (Link)	Option 2: Native App (Install)
Ease of Use	✅ 1-Click Simple	⚠️ Multi-step export required
Records with screen locked?	❌ No. (GPS will be lost)	✅ Yes. (Flawless background logging)
Install Required?	✅ No (Just click the link)	❌ Yes (App Store/Play Store)
Browser requirement	❌ Strict. iPhone: Safari only. Android: Chrome only. Other browsers will break GPS.	✅ None. No browser involved.

What Will I See in the Viewer?

Your track on a satellite map with a playback timeline, a speed-over-time chart, and a data dashboard showing your Speed Over Ground (SOG) and Course Over Ground (COG) at every moment. For the Flying Scot fleet, additional performance data (Target Speed, VMG, and Delta) is available. Important: To receive this advanced performance data, your boat name MUST include "FS" (FS #### Name). If your boat name does not contain "FS", the viewer will safely assume you are sailing a different class (like a Thistle or Ensign) and will only show standard data.

Note: This tool is still actively being developed. Don't expect full functionality immediately. Feature updates will roll out continuously and will not be announced individually; however, they will be live every time you reopen the link.

The Deeper Dive

The Website — How It Works, Pros, and Cons

The viewer is a static website hosted on Cloudflare Pages. "Static" means there is no heavy server running behind it — the website files (HTML, JavaScript, map tiles) are served directly to your browser, and all the heavy data processing happens locally on your device.

Trimming Your Data (Start / End Time)

Your GPS logger records from the moment you start it — which might be at the dock, while motoring out, or even on the drive to the lake. The viewer features quick-preset buttons (e.g., Sunday 13:30–17:30 or Wednesday 17:30–20:00) as well as manual Start Time and End Time fields where you can enter any custom race window. Only the data within that window will be displayed on the map and used for speed & distance calculations, keeping the view focused strictly on the racing rather than the commute.

Why the Speed Difference Between Android and iPhone?

A phone's GPS chip internally calculates speed using Doppler shift — the same physics that makes an ambulance siren change pitch. This hardware-derived speed is very accurate, even at low boat speeds.

On Android, apps like GPSLogger can access this hardware speed directly and write it into the file.

On iPhone, apps like Open GPX Tracker only record latitude, longitude, and time. Speed must be calculated afterward by measuring how far you moved between two consecutive 1-second GPS fixes. At normal sailing speeds (3+ knots), this works well. At very low speeds (during a tack or sitting head-to-wind), the position change between fixes is so small that GPS error becomes a factor, making the derived speed jittery.

Practical impact: Your track on the map looks identical on both platforms. The speed chart from an iPhone will have slightly more "noise" in it, but the overall trends (fast sections, slow sections) will be clearly visible and useful.

Recording Settings — Important

For the GPS data to be useful for race analysis, the app must record a position every 1 second (called "1Hz" logging). Both recommended apps do this by default.

Do not use apps like Strava or Garmin Connect for recording. These apps compress GPS data to save battery, sometimes recording a point only every 5-10 seconds. A tack takes about 5 seconds — if the app skips recording during that window, your track will show a straight line through the water instead of the actual maneuver.

Privacy & Data Storage (Important)

Day-by-Day Storage: The Web App stores your GPS data on a day-by-day basis inside your browser. If you start it at home to test it, stop it, and then start it again at the club for the race, both tracks will be in the file and uploaded together. If you do not want your home location shown, you MUST press the "CLEAR TODAY'S DATA" button before starting your actual race log at the club.
Your GPS track is only uploaded to the club's Cloudflare bucket if you explicitly press the "Upload" button.
You can use the website entirely offline or locally without uploading anything.
Self-Service Deletion: You have full control over your uploaded tracks. When you upload a track (through the Uploader app), you'll see a 6-digit delete code on screen right after it finishes. 📸 Take a screenshot of that screen — that code is what lets you delete your own track later, from any device. The code is also automatically remembered on the phone/browser you uploaded from, so deleting from that same device needs no code at all — just press the 🗑️ icon next to your boat in the Viewer.
Cross-Device Deletion & Browser Clearing: If you clear your browser's history/cookies/cache, or want to delete from a different phone/computer than the one you uploaded from, the Viewer will ask for your 6-digit delete code — enter the one from your screenshot. If you didn't save it, or you uploaded a legacy track before this feature was built, you will need to contact Bernie by text at (518) 982-9927. His Master Admin Code overrides the system and can delete any file.

Note: I do not have an Apple/iOS phone, so I have no idea what problems will be with that system. Please contact me with any issues you find.

Questions? Reach out to Bernie by text at (518) 982-9927.