1) What is the difference between SSB & HAM? Can one use a HAM radio on a boat...they seem to be much cheaper than the equipment for a true Marine SSB
Radios that will be used on marine frequencies must be certified for marine use. Because you have to certify the radio, the cost for the unit increases. So you can use a ham radio on a boat when you operate on the ham bands. You can also modify a ham radio to work on marine frequencies. However, to do so is illegal except in an emergency. However, as others will tell you, the enforcement is lax in the US.
Outside of that, and a little operating differences, the theory is the same.