We get this question a lot. Unfortunately, it is not a simple question to answer.
One answer that definitely has some truth to it is that the best GPS units are usually the most expensive ones you are willing to pay for. These devices, like many products, often get better with price.
One problem with this question is that frequently customers are looking for the best inexpensive GPS units. Though there are plenty of these units out there in many different styles, and many of them just meet the user’s needs, they still end up being far from ‘the best’ in terms of quality.
Here is some background on what makes a particular GPS design good at doing its job and the operating conditions that allow any GPS to work at its best.
All GPS receivers work best when certain conditions are present, only one of which is under your control: where the GPS antenna is placed.
GPS units work best when there are no obstructions between the GPS antenna and the sky. The more of the sky that is directly visible from the perspective of the antenna, the more satellites it will be able to acquire which, in turn, gives a stronger and more stable fix. This results in more accurate GPS sensor data being sent to the devices that use it.
If a GPS antenna is positioned inside a pilot-house or bridge, there is now a barrier between it and the sky. If said barrier happens to be made of metal, steel being the worst, the chances of acquiring satellite signals can be drastically reduced. Boaters will often put their portable GPS antenna near a window to partly overcome this problem, but it’s still only getting a partial view of the sky afforded by the field of view of the window.
No GPS antenna will ever operate as effectively as one that is placed outside with full sky-dome visibility.
Fixed-mount
These are usually the best quality GPS units available, and they almost always cost more. The antenna’s surface area is greater and its design will often be more sophisticated, making them more sensitive to weak satellite signals. Additionally, they are mounted topsides on a mast, pole, radar arch or, less often, deck mounted. The combination of a larger and more sensitive antenna, having a clear and unobstructed view of the sky and more sophisticated electronics are the primary factors that makes these GPS systems work better and cost more.
This class of GPS can often come with other benefits. For example: there is a class of device called a satellite compass. These are comprised of 2 or more GPS antennas. This allows them to not only provide standard GPS data (position, course and speed being primary for use aboard a seagoing vessel) but also heading, and often rate-of-turn. While this type of instrument comes in a wide range of prices and capabilities, generally they are the best. Commercial vessels, particularly inland vessels, get the most benefit from an accurate HDG (heading) and ROT (rate-of-turn), especially in conjunction with features in Rose Point ECS (our commercial navigation software) that can predict the future locations of the vessel when it is actively turning, which is extremely useful when operating on narrow inland waterways. However, these units generally sit at the top end of the fixed-mount GPS price range.
Fixed-mount GPS units are typically made of higher quality components and have higher R&D costs for hardware and software design, justifying their higher retail prices. They also tend to be more complicated to install. You must find a good mounting location for the antenna, then cables must be routed through the vessel between the antenna and where the sensor data is used. Many GPS’ of this type will have a case containing electronics that is separate from the actual antenna. It is also common for them have a small screen where important data from the GPS can be displayed. You will also find data ports for connecting the GPS system to other devices that can use that data, including devices running navigation software like Coastal Explorer or Rose Point ECS.
Getting this data to the computer, so it’s accessible to the navigation software can be accomplished many different ways.
The simplest, and least reliable, method is to use a USB to Serial adapter of the RS-232 variety. While these devices are certainly inexpensive, they are definitely not the best way to interface this class of device to a computer system, nor are they compliant with best-practices for marine electronics installations. The next step up are USB/RS-422 adapters, which at least use the correct electronics standard for most NMEA 0183 compatible GPS units and other marine electronic sensors. The next step up are opto-isolated USB/RS-422 adapters. These will allow for a truly conformant marine electronics installation, but they are still only “the top of the bottom of the heap” in terms of reliability, since they are still hamstrung by the weakness inherent to USB port connections, meaning it can be pulled out very easily, either intentionally, accidentally, or over time from vibration.
Much better are interfaces that don’t rely on USB ports. The Rose Point Nemo Gateway, for example, uses Ethernet to transmit data to one or more computers or other devices. When only a single computer needs to access the data, one can simply connect the locking Ethernet cable between the Nemo’s RJ45 port and the computer’s. If more than one computer needs access, the cable can be connected to a router instead of the computer, so any system connected to that router can access the data. If the router is a WiFi capable router, several computers, and even cell-phones, can connect wirelessly to gain access to the data if needed. There is still nothing better than a cable for reliability, though. It is highly recommended to connect the most critical computers with cable, such as Ethernet.
It is also becoming more common for GPS systems to support NMEA 2000. This is a more modern and flexible marine networking standard that can support many different marine electronics devices interconnected to each other on the NMEA 2000 network. Computers will need a suitable interface to the NMEA 2000 backbone. The Nemo Gateway supports both the older NMEA 0183 and the newer NMEA 2000 standards.
Portable USB
This class of GPS has three distinct advantages and, of course, other significant disadvantages.
The advantages are portability, not needing to run cables through the boat to where the antenna is mounted and, of course, price. These are the least expensive options for providing GPS data to a computer for PC-based navigation software to access it.
The disadvantages are that these units typically contain a very small patch antenna that cannot be as sensitive to relatively weak satellite signals as the larger fixed-mount antennas. This means they can be greatly affected by how and where they are placed and other environmental factors, such as inclement weather. Additionally, they are usually not intended for use on a boat and are often not watertight. They also give you no options on how you connect them to your computer. You must plug it into a USB port and deal with the vagaries of the USB plug itself and the accompanying driver software. If you don’t have enough USB ports for all the devices you intend to connect, it may then be necessary to use a USB hub, which can also create problems.
Portable Bluetooth
Bluetooth GPS antennas have one primary advantage. They can be connected to your computer wirelessly via a Bluetooth signal.
The disadvantages of using this technique are many:
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“Pairing” the device with your computer can be tricky.
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Be prepared to deal with pairing problems, or re-establishing the connection should it fail, at the worst time.
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You must recharge its batteries when they are low.
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You must contend with the limited range of wireless Bluetooth signal, which may or may not be a problem depending on how far away the computer is from where the GPS antenna is placed.
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There are potentially radio interference problems, which is true of any wireless technology.
Conclusion
Your GPS system is one of the most important systems on your boat, since it tells you where you are located, what direction you are moving, and how fast you are doing so. If you happen to have a satellite compass, it will also tell you your HDG (heading) and probably your ROT (rate-of-turn).
It becomes even more important if you are offshore, or in foul weather such as fog, where both place you out of sight of land. Unfortunately, recreational and commercial boaters often spend more money on dock lines than on their GPS antenna and other equipment. While good lines are certainly critical when docked or at anchor, navigation equipment is critical when underway, unless you always use the vessel under circumstances where knowing your precise position is optional.
When choosing any marine electronics equipment, it’s generally best to consult with an NMEA certified marine electronics installer. They will take your budget and requirements into consideration, suggest products that fit those criteria, then install them using marine electronics best practices.