In addition to "type acceptance", there are real differences between ham radios and marine radios. The differences are not just in type acceptance, spectral purity (reduced "splatter"), and cost. Anyone who tells you different is either trying to make the case for spending less money, or they simply don't know what they're talking about.
Some of these differences include:
1. ability to operate effectively at lower input voltages
(as often is the case on a sailboat with partially depleted batteries), without either severe FM-ing (distortion) or simply cutting out (as some ham radios do);
2. ease of operation
....fewer controls, channelized operation, etc. This makes it far easier for a non-radio person to operate the radio in an emergency; and
3. marine radios tend to have superb audio quality
, both on receive and on transmit. Typically, they easily surpass many/most ham rigs in this department.
Coupled with their spectral purity and frequency stability, this package of "features" makes most marine radios come in a cut above most ham radios for SSB operation on the marine bands.
However, they are typically less well suited for ham operation, because they :
1. have less frequency agility
(yes, even the Icom M-802 isn't as easy to use on the ham bands);
2. lack many of the controls and features
hams like to have (RF gain, CW keyers built-in, dual VFOs, notch filters, etc., etc.).
I sell and install both marine and ham radios on boats and have some 25 HF radios in stock at the moment...ham radios, marine radios, military radios, land mobile radios, aircraft radios. Many of these are connected and are operational during the workday...listening on ham, marine, aircraft HF frequencies. By the way, HF/SSB radio is not just the principal means of communication between ground controllers and long-distance aircraft in Africa as was mentioned above, but WORLDWIDE. Still.
I have two favorite radios which I operate daily on various ham and marine nets: a Kenwood TKM-707 marine SSB and a Yaesu FT-920 ham radio. The TKM-707 is a very, very simple radio....or so it would appear from the very few controls. But, it is a very sophisticated radio, with excellent performance. Alongside it is the FT-920 -- a very complicated radio. There are almost 80 knobs and buttons on the front panel, compared to 14 on the TKM-707, plus a keypad behind a little door.
They're both great radios. Both are technically capable of operating on the ham bands and the marine bands. Only one can be legally operated on the marine bands (the marine type-accepted TKM-707), provided you have the necessary marine station and operator licenses.
Both can be legally operated on the ham bands, provided you have a ham license.
As the previous post indicated, there's often not much difference in cost between ham and marine radios, particularly used ones. I have used ham and marine radios beginning at under $500. In any event, the difference in cost between marine and ham radios is a very small portion of the total cost of installation, counting the antenna tuner, the antenna system, the ground system, and the materials and labor for a proper installation aboard ship.
One strategy, which I use on my boat, is to install BOTH a ham rig and a marine rig. That way, you can have the best of all possible worlds, and be perfectly legal. And, if you choose quality used radios, you can do it for the cost of a single new marine SSB.
Here's a pic of my boat, with a Yaesu FT-900CAT ham radio on the left and a Yaesu System 600 marine radio on the right (the one with very few knobs). And, further to the right is a PTC-IIe SCS Pactor modem which will work with either radio. NavStn_0140