There are some gems and some very misleading statements in several of the above posts. And, some red herrings.
1. As Rick said, there are good reasons for having BOTH a ham and a marine SSB
aboard these days. I won't elaborate here, for sake of brevity; there are posts on the SSCA board which make the case.
2. Virtually ALL SSB
radios aboard small vessels these days -- ham or marine
-- are powered by 12 volts. The discussion about 115VAC power supplies and generators is a red herring. It's almost never involved.
3. Marine rigs, in general, are more tolerant of low input voltages than are, e.g., many ham rigs. Once input voltage drops -- for whatever reason -- below a threshold level for that particular radio
it begins to behave erratically or to just quit. Typically, an HF set will begin "FM-ing", or distorting the voice signal. Most ham rigs are designed to operate at voltages normally found in cars, i.e., 13.6 or 13.8 volts (with the motor
running); they're happy with voltages plus or minus 10%, but not much more. Marine rigs generally have 15% or more tolerance.
4. Some ham rigs are very good in this respect, and will operate down to voltages as low as will marine rigs. And, there are good solutions, like the W4RRY booster which delivers 13.6 volts to the radio
voltages as low as about 11 VDC. I've used this wonderful little device on my boat for a couple of years now. See, e.g., Gallery :: W4RRY Leo's Battery Booster
5. The discussion about voltage drop is interesting, but not complete. Yes, quality fuses
have lower voltage drops than do bi-metal circuit breakers. And, fuses
provide better protection for the radio than do circuit breakers. And, they are more reliable (less prone to failure). Still, circuit breakers may be OK in addition to fuses, since the amount of voltage drop at the typical loads presented by a SSB radio are very small. Usually, the prime culprits in voltage drop occurrences is inadequate size wiring
and poor connections, not fuses and circuit breakers.
6. As Rick said, fuses or circuit breakers belong NEAR THE BATTERY
. And, contrary to what Rick said, one isn't enough. You need to fuse BOTH the positive and the negative leads to a SSB radio.
7. The discussion re: fixed and variable PEP levels is ...well...misleading (I'm trying to be nice). Both marine and ham radios use similar PEP levels...generally between 100 and 150 watts...and in most cases the user can choose to reduce the output power (many commercial
radios have a LOW-MED-HIGH power setting, while many ham rigs have a continuously variable RF power level adjustment). Mostly, users don't touch these....the radios operate at their rated output levels most of the time.