I was also using the PC version before buying
a new MacBook Pro.
A little further down the page at the Apple Logo is the old release candidate for Mac. file name is openCPN-1.3.6-mac-rc.zip.
Actually that's a link to the download. It's from here as you know. http://opencpn.org/download
This is not as nice as the newer PC release. Has quirky behavior as well. I'm waiting for the new version. Many thanks to those who are working to get it ready.
Also try PolarView and MacENC.
PolarView and PolarCom are needed, not freeware but very reasonably priced. That and NOAA charts
are good to go for me right now.
MacENC is a bit more costly. It's a little cluttered looking to me until I turn off place names.
I'm new to the lifestyle, so discount my opinion accordingly.