iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
A red flag with a white diagonal stripe is a diver-down warning: it signals that divers may be in the water nearby. Keep clear and slow down as local rules require. It is not a distress flag, and it is not interchangeable with the blue-and-white Code Flag Alpha.
What the red-and-white flag means
The red-and-white diver-down flag marks an area where a diver may be underwater. It is a warning to nearby boaters, not a signal that the boat itself is in distress or unable to maneuver. In the United States, it is a familiar signal in recreational diving; rules and conventions can differ elsewhere.
The U.S. Coast Guard distinguishes this traditional warning from Code Flag Alpha. In its Local Notice to Mariners dated April 13, 2025, the Coast Guard says the belief that Alpha replaced the traditional diver flag is incorrect: “The ‘A’ flag signal is a navigation signal for a vessel, just like a ball or a diamond, while the red-and-white flag is a traditional sign that a diving operation is taking place.”
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →How the diver-down flag differs from Code Flag Alpha
| Signal | Appearance | Meaning | What a boater should do |
|---|---|---|---|
| Diver-down flag | Red square or rectangle with a white diagonal stripe | Divers may be in the water nearby | Keep clear and follow the local distance and speed rules. |
| Code Flag Alpha | Blue and white, in the international code-flag form | A vessel is restricted in its ability to maneuver during applicable diving operations | Recognize it as a vessel navigation signal; do not treat it as a substitute for the red-and-white diver-down warning. |
Under Rule 27(e) of the U.S. Coast Guard’s amalgamated Navigation Rules, a vessel engaged in diving operations that cannot practically show the signals specified elsewhere in Rule 27 must display three all-round lights in a vertical line—red, white, red—and a rigid International Code Flag A at least one meter high and visible all around. That rule concerns signals for a vessel in a particular operating condition; it does not make Alpha and the diver-down flag interchangeable.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
What to do when you see a diver-down flag
- Keep well clear of the flagged area and remain alert for divers who may be below the surface.
- Reduce speed as required by the rules for that waterway.
- Do not pass between the flag and the likely dive area if doing so could put divers at risk.
- Check the local boating rules for the required separation and speed. There is no single distance in the cited U.S. state examples that applies everywhere.
For example, Florida’s divers-down warning-device rules require boaters to make reasonable efforts to stay at least 300 feet away in open water and 100 feet away in rivers, inlets, or navigation channels. Within those distances, boaters must slow to idle speed. Pennsylvania’s Aids to Navigation guidance gives a different state example: stay at least 100 feet from areas marked by either diving sign. These figures are state-specific, not universal standards.
Florida display rules—and why local checks matter
Florida’s requirements illustrate how display rules can vary by jurisdiction. The Florida Fish and Wildlife Conservation Commission says its diver-down rules apply when a person is wholly or partly submerged while using a face mask and snorkel or underwater breathing apparatus. The warning device must show a red rectangle or square with a white diagonal stripe.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
- A symbol displayed on the water must be at least 12 by 12 inches; one displayed on a vessel must be at least 20 by 24 inches.
- On a vessel, the symbol must be placed at the highest point where it is unobstructed in every direction.
- A flag must show the symbol on both faces and be stiffened or constructed to remain extended in little or no wind.
- The device may not be displayed when divers are out of the water.
Divers Alert Network’s safe-boating guidance recommends matching minimum display sizes of 20 by 24 inches from a vessel and 12 by 12 inches from a buoy, and advises keeping flags stiff, unfurled, and recognizable. That is safety guidance; Florida law governs in Florida, and boaters elsewhere should check their own local requirements.
Recommended Free Tools
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.
