@neauoire @cathos You don't really need any fancy antenna to receive wefax on HF. On a boat you're supposed not to have too much noise. You just put up a small wire dipole on the mast and you're good. As others said, just use fldigi and an old HF receiver. I just received this map on 11MHz with my kiwiSDR.
Here you find the schedules:
https://www.weather.gov/media/marine/rfax.pdf