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Garmin GPSMap 451s Review


Garmin GPSMap 451s ReviewNew boat, old fish finder. The Warrior 150 came with an old Garmin combi unit on it, a GPSMap 198c to be exact and although there’s very little wrong with these units I wanted to be more up to date so a GPSMap 451s was bought.

Garmin GPSMap 451s Specs

Unit dimensions, WxHxD: 5.7″ x 5.0″ x 2.7″ (14.5 x 12.7 x 6.9 cm)
Display size, WxH: 2.4″ x 3.2″, 4.0″ diagonal (6.1 x 8.1 cm, 10.2 cm diagonal)
Display resolution, WxH: 240 x 320 pixels
Display type: QVGA display
Weight: 1.3 lb (590 g)
Waterproof: Yes (IPX7)
High-sensitivity receiver: Yes
GPS Antenna: Internal
NMEA input/output: NMEA 0183 compatible and NMEA 2000 certified
Basemap: Yes
Preloaded maps: Yes
Ability to add maps: Yes
Built-in memory: None (cannot load maps to internal memory)
Accepts data cards: SD card slot
Waypoints/favorites/locations: 3,000
Routes: 100
Track log: 10,000 points; 50 saved tracks

Why Choose Garmin?

I could come up with lots of pro’s and con’s for why we went with a Garmin fish finder, truth be told I prefer Lowrance equipment myself in general and although I didn’t want to spend that sort of money a Humminbird side imaging unit was also considered. In the end it came down to value for money and the fact that we already had a Garmin duel frequency (200/50) transducer on the boat. From what I’d read the transducer should be compatible with the 45 and 55 series Garmin’s. I’ll also let you in on a little secret, as great as the upper end Lowrance and Humminbird units are for new fangled gadgets and cutting edge technology when it comes to basic 2D sonar and GPS chart plotting functionality Garmin really does take some beating. If you’ve only got a few hundred pound to spend then I’d take a budget Garmin unit over the budget units from the other manufacturers 9 times out of 10.

The reason I wanted to update was a lot down to the charting. The 451s comes with a built in chart for the UK and Ireland whilst the old 198c relied on an old Blue Chart from 2002, on Garmin specific cards with little scope for upgrades. There was also a problem in that the old Garmin plotters don’t have saved trails/tracks, the GPSMap 451s has the ability to record a 10,000 point trail, I’m doing a lot with DrDepth and although I could have hooked the old unit up to a portable Garmin 76csx that we have via NMEA0183 to get depth information it is much easier just to use a unit like the 451s which has its SD card reader free for saving trail information due to the fact the chart is stored internally. An SD card makes PC transfer simple and with us fishing new marks in the new boat I wanted plenty of opportunities to get some detailed charts as quick as possible.

Garmin Upgrade Problems

The first issue I experienced which I hoped to avoid is with the Garmin universal plug on the back. I was hoping that the 2 units would be compatible and it would be a straight swap but it looks as though there has been some evolution over the years. The 451s features a slightly smaller plug with a full compliment of 19 pins where as the old plug for the 198C only has 18 pins. So an upgrade like this will require some basic power re-wiring, instructions do come with the 451s and it’s not a biggy to get power using the positive and negative terminals from where you removed the old wire. The same goes with NMEA0183 setup for DSC on your radio, overall it took me less than 10 minutes under the cramped dash of a Warrior 150 to have the old wire out and the new wire installed. Fortunately (as I’d hoped) the transducer connection was a straight forward swap, unplugging from the old 198C connection and going straight into the 451s transducer connecting wire.

The next problem which depending on your setup could involve a little extra cost was with the GPS antenna. The GPSMap 198C and its vintage require an external GPS antenna, model GA-29. The newer units like the 45 and 55 series have built in 12 channel-WAAS antenna’s but IF you want to use an external antenna it needs to be one of the newer GA-30 models (available here). It looks like it should work and the connections are identical but it won’t work with a GA-29. The GA-30 antennas retail for between £40 and £50, not a huge expense and one that can be avoided if you are happy to use the internal GPS as we were. A quick test shown minimal signal loss when sat at the helm and absolutely no loss when fishing.

Garmin GPSMap 451s Performance

To start with the fishfinder is excellent. A quick bottom lock was achieved and the scroll speed could be easily adjusted to paint an accurate picture. As you would expect with only a 4inch screen it’s not ideal for using split screen but the primary colour palette does show up fish well (with fish ID off, I hate fish symbols!) so that even at a glance it is clear or not whether there is anything showing in the water column. As a fishfinder I found it to be a good clutter free display. There’s not a lot of fish around at the moment but when I get the chance I’ll get some pictures so you can see just how well the sonar on these units paints fish and fish arches The other important thing I found was that the Garmin required a lot less fiddling with sonar settings than the Lowrance and Humminbirds I usually use. In terms of the dual-beam you’re obviously going to get a lot more detail from the 200 signal and so that’s what I’d recommend in depths up to 150 feet. If you’re planning on fishing much deeper than that then the limited resolution of these budget sounders may not be right for you, at a push you can zoom but when getting to depths approaching 200+ feet I prefer a unit with more vertical pixels.

If you’ve ever used any Garmin GPS/Plotter unit then you’ll know what to expect from the 451s. Signal lock even from cold is quick, the accuracy soon comes down and the 1 second updates are as smooth as you like. With WAAS we were seeing accuracy +-10ft most of the time. Unlike some other makes the slow speed <1-2mph reading is fine and you'll still get an accurate direction on the plotter when crawling along. The waypoint and route management is simple to follow with ample storage for 99.99% of users. The screen is responsive and easily visible in direct sunlight (chance would be a fine thing). Overall I have absolutely no complaints about the built-in charts or GPS plotter functionality, in fact if they could sell it to Humminbird for use in their higher end units I'd be delighted!

Garmin GPSMap 451s Conclusion

Overall I’m very happy, for less than £300 you can’t go wrong. It’s a colour sounder, reliable chart plotter and well thought out unit. It is a shame that the plugs have changed so there will be a little re-wiring if upgrading from an older Garmin GPSMap unit but that’s only a minor niggle and hoping to get away without playing with wires was just wishful thinking on my behalf. If you are after a budget colour sounder/GPS unit then you’ll be delighted with how this basic Garmin unit performs.

Our Garmin GPSMap 451s came from a reputable UK suplier on e-bay and cost less than £300, it took 3 days to arrive. More details can be found here.


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