There is nothing fancy, special of different between an antenna marketed as HD and any regular old-school UHF antenna. Most of the HD spectrum is broadcast in the old UHF frequencies.
When you say rail mount, are you talking line temporarily mounting the antenna to your stern rail and then stowing it when you cast off lines? Know height is key to good reception. I see your sig and notice you are in Chicago, so it is likely you will not have a height issue but you might. An antenna at the masthead is going to work better than the same antenna down low at the rail.
I have used Shakespeare and Glomex amplified antennas with good success. They can be spendy compared with a non-powered antenna but they do work.
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