It would help if you gave a bit more information regarding what kind of refrigeration system you're looking for as well as the specifics of the boat and engine you're looking to install them on. More information, rather than less will get you better answers.
Are you looking for a 12 VDC based system, an engine powered system or a 110 VAC system?
Are you looking for an integrated unit, or one that you can install in an existing icebox?
Are you looking for a water cooled or air cooled unit?
I would also recommend you read the POST in my signature, since it would probably help you.