![]() ![]() Labeling a place will give it your very own tag so you can search for it faster. This would help to confirm GPS position and the datum used on the chart.Labels are a less-known Google Maps feature that can make your life easier. Satellite imagery is not perfect, there will always by patches that are difficult to determine if there is a shadow from cloud or a shallow patch and sometimes the higher resolution satellite pictures do not give total coverage.Īlthough we found a good degree of accuracy with the satellite pictures we tried to verify the position of features by using a hand bearing compass and radar. Entering bays and through passages we’d still rely on eyeball navigation, timing our arrival so the sun was behind us. Where these tied in with the charts we had a great deal of confidence but where they didn’t we proceeded with caution. Rather than plot a route of waypoints I’d mark the position of reefs and coral outcrops on the app and add these on the chartplotter. We used Google Earth on the open CPN and the GPS MotionX, which we relied on more heavily the more we got used to it. The open CPN charting was rather out of date and not as accurate as the Navionics on our chartplotter.īefore each day’s passage we compared the Navionics on the chartplotter and satellite imagery. In harbour we’ve downloaded open-source CPN and charting, and been kindly given some satellite images. Google’s mission statement is ‘to organise the world’s information.’ This almost impossibly ambitious declaration of intent underpins the technology giant’s… Our experience There is a choice of satellite images (Google, Apple and Bing) and by switching between them you can get the best image, or even find road maps for when ashore. Using the app, you can download, at your leisure, high-resolution satellite pictures. If you use an iPhone or iPad, GPS MotionX is an app that takes out a lot of the hard work. In Fiji we were introduced to a simpler way of using satellite imagery for navigation through an app. ![]() One lovely thing about bluewater cruising is the friendliness and generosity of fellow cruisers. The Sat2Chart software will also convert from SASPlanet, another program for downloading high-resolution imagery and maps that can stay on your computer.Īll this can be quite fiddly and time-consuming for those limited in IT skills, although if I can manage it so can anyone! App images This removes any problems of the 2GB cache memory for offline work and cruisers will quite often share images that they have converted. ![]() This software takes a satellite picture of your choosing and converts it into a KAP file that’s readable on the chartplotter. One great use of the software is that you can overlay satellite pictures onto the plotter on your laptop by using GE2KAP software (what I used), which has in turn been superseded by Sat2Chart. There are many free charts you can download onto this software, as well as ones to purchase. Many cruisers use Open Source CPN, which is chartplotting software on a laptop. With the MotionX app you can switch between satellite images to find the clearest There’s also a 2GB restriction in the cache memory for use offline. That’s great when using broadband, but on a poor connection can be slow and time-consuming. Fortunately a history slide bar allows you to go back through previous pictures of the area to find the clearest view. However, some Google Earth images are affected by cloud cover, or the sun was at the wrong angle when the image was taken. We can add a GPS so that our position is seen on the image. With Google Earth, zooming in on an area where there is coral we can quite clearly see just where there are shallows and deeper areas. Using satellite imagery takes the concept of eyeball navigation a stage further. It takes a lot of practice to estimate actual depth but it is relatively easy to separate shallow from deep water. On a cloudy day it is most difficult to determine depths. Polarising sunglasses are useful, but the sun must be behind you otherwise glinting from the sun makes the depth unfathomable. Hoisting someone aloft to look down from the spreaders can aid navigation. When sailing among coral the first tactic is to use eyeball navigation: with clear water and the sun behind it is quite clear where shallows are and what needs to be avoided. We have got used to chartplotters and GPS being very accurate sometimes (I think) too accurate as we pass ever closer to obstructions, confident we’ll be safe because it shows them on a computer screen.īut when cruising further afield we need to understand that the charts may not be as accurate as we’d like them to be, and we need to sail more conservatively than we might, for example, in north-west Europe. ![]()
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