What ever you buy, don't buy the cheapest one. It doesn't matter if youre just hanging in the bay or not. Cheap antennas bare cheap for a reason the elements are made from inferior conductors like aluminum. They can break internally and you wouldn't know it. I dropped like $240 or something on my Shakespeare with gold and silver internal elements, stainless ferrule and beefed up fiberglass shell . You can buy off brand boat soap, cheap cushions , cheap dock line even, but going cheap equipment that could save your life , well that's where I draw the line. I destroyed my antenna docking at Fort Jefferson as there is an overhead lift thingy at the guest dock. Took it right out. Forgot the antenna was up. When I got back to the Keys a few days later I bought a new one at West Marine in Key Largo .
Doc is point on in the radio theory there.