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When we were planning our Red Sea Passage, we used the actual tracks of 2 other sailboats, one a SM, and google map images. It was easy to overlay everything using OpenCpn. It was easy to see the seabed contour as it matched up to the other boat's courses and anchorages and well as the depth indicated on the chart.
I think the method of using such data when venturing into unknown and loosely charted areas is priceless. Of course, this is time consuming and tedious work to cover an area as large as the Red Sea, but all of that effort filled days at anchor that were well in advance of the planned trip. We used this information to plan our course and potential anchorages.
I fully back Ken in his OpenCPN support and use.
It is done brilliantly by sailors and it is FREE! Like most things, there is a learning curve to it.
Jean-Pierre Germain, Eleuthera, SM007, Opua, NZ
On 5 Oct 2020, at 08:46, Ken Powers SV Aquarius <ken@...> wrote:
Google overlays is not difficult to read, and is sometimes the only option for a map. In some places the maps are a 100 meters off. Take a look at the entrance to Maupiha'a in the French Polynesia. The entrance is a 30 meter wide channel, and only one place to get in and out. Most maps are 100 meters off. You can see the entrance clearly on google maps, and all the shallow areas in the middle of the atoll once inside. It's nice having a moving map showing the entrance. For this entrance the Navionics Maps were correct, but at the time I didn't have the google overlay, and I didn't know which map was correct. I had several maps, but which is correct? If I had the google overlays then I wouldn't have had to wait 4 hours outside until someone informed me over VHF which map was correct.
The wind was 35kts and kind of rough when we entered Maupiha'a. Google Maps are just another tool that sailors can use to make sailing around the world a MUCH safer proposition. Many boats that ended up on a reef could have been saved with a quick look at a google map while doing the planning. And, please don't think it's like reading tea leaves, because it's more like a walk in the park.
I also use a Mac for OpenCPN. I have never made a .kap file, I just go on line and search for .kap maps for the area I will be going. And, I have found most of the maps I was looking for. Currently I have 9GB of maps in my OpenCPN Folder. And I have 3 or 4 maps for each area.
One more thing about OpenCPN. It's got a great Climatology tool. Shows all the paths of hurricanes, and typhoons over the past 30 years, and how strong and location each day of the year. It also shows the normal winds for each day of the year, which is great for planning ocean crossings! It also shows the currents, but have found this feature to be useless. I do all my crossing planning using these tools on OpenCPN. I encourage everyone to do a deep dive into the capabilities of this very helpful tool.