There really is no standard for a cable called RG-8X. As a result, there are many inferior products labeled with RG-8X. Be careful in buying
any cable marked as RG-8X as that marking does not really designate any official cable specification.
If your transmission line length is 17-meters (56-feet), and you use a small-diameter transmission line like RG-58C/U (a Mil-Spec cable version of what is found attached to most boat antennas), at 150-MHz the loss will be more than 3-dB, or half of your transmitter power will be lost
in the transmission line.
Designing an antenna and transmission line system in which more than half of the power is lost
in the transmission line is not an acceptable practice for most installation, but it may be just great for some boaters. It seems to me that the purpose of installing an AIS transceiver is to let other boats receive your signal. The notion that it does not matter how little signal you emit seems inappropriate. If you are installing a Class-B AIS transceiver, you will already be operating at reduced power (2-watts) relative to the other Class-A devices.