You and I believe they bounce off the atmosphere because you and I are told they bounce off the atmosphere. You and I do not know this experientially because you and I do not have the physical ability to know if it is bouncing off the ionosphere....or what many claim to be the firmament, but that being said, we can know for certain about different radio types and their abilities.

CB radios are limited to 4 watts and are not bouncing off the ionosphere anyway...they are straight line comms like GMRS and are limited to antenna height and interference with buildings and ground terrain. GMRS can be up to 10 watts like my Revetis NR30, but still line of sight and without a ground repeater station to link to, the GMRS is typically no more than 10-12miles on high power.

The Marine radios are VHF. The range of VHF radios is dependent on many factors, the most limiting of these is that VHF is basically line of sight radio. Simply put, the transmitting and receiving antennas must be able to see each other in order to establish communications, therefore as the original poster commented, the ships must have line of sight via antenna heights to be able to communicate. Using the earth curvature, CB/GMRS/VHF cannot round a curve or bounce off the ionosphere or firmament...whichever you choose to believe, therefore we are left to discuss how those comms were able to work with 24 miles of curvature....that is the discussion...those are the maths given to us by science that needs to be discussed here, because all those comms used are straight line ONLY.

True, we cannot literally embody a short wave radio signal and feel ourselves bounce off the atmosphere. But this doesn’t mean the ionosphere or the firmament (or a giant turtle shell or a group of interdimensional gnomes or any other random explanation) are equally valid explanations for the observable over-horizon communication of short wave radio, right?

I explained how maritime radios work....they are LINE OF SIGHT ONLY and instead of recognizing you were WRONG, you come back with some other unrelated gibberish...just like you have done elsewhere in these comment sections.