For receiving weather maps etc, any metal conductor on the
boat at all will
work for an antenna, and a ground will not be required.
For transmitting, a helical whip will be complete rubbish. You will hear things strongly, but dangerously, you will assume they can hear you just as well, which will be untrue. In fact, if you heard a recording of yourself at their station you would be utterly horrified.
The 4/6/8 MHz bands are most useful, and for those bands you should hoist a good long piece of antenna wire, and for a "ground" you should drop about the same amount of wire
overboard in a
single long length.
It will take you a long time to get to grips with what frequency to use during what season, at what time of the day, and at what range. These vary immensely, and also these bands just love to play tricks on you - like randomly dumping you instantly without warning - it's great fun and great comms, but you need your wits about you.
If you use HF and you really enjoy it, then get your ham ticket and get on the air and learn the ropes. HF is a blast if you're into it, and a puzzling mess if you're not. My suggestion is to pick one band and learn it, usually the 6 or 8MHz band which works quite well during the summer. Lower bands are kinda "night" or "winter" bands.