OK, AIS, that makes more sense than what I was assuming.
At 327 feet, you should get some great coverage.
Since all your targets will be sitting at the horizon, or lower, you should really consider your antenna pattern carefully. Something with a bit of down tilt might be more productive.
The losses in 1/2" heliax should be fine if you are using a good receiver and an antenna with some gain. If feedline losses were still a concern, a tower top amplifier might be a good option.
I work at a site that's at about 800 feet above sea level and looking out over the Pacific Ocean. I don't have any AIS gear to try out, but I do have an ADS-B receiver here. Even at 1.09gHz, I regularly pick up aircraft 300+ miles out. Of course they are at 38,000 feet, but still, pretty good coverage. I've got a remote controlled receiver that covers 40kHz to 3.5gHz at one of our tower sites, and the coverage is pretty good.
Should be really interesting to see not only how well the AIS system works, but how well the SDR works. It's a lot of fun when you have access to these sites and can set up your own projects.