The hand-engraved numbers are often hard to read correctly - especially on an old boat.
The fourth character is a letter, not a number.
CCM
B is a Hobie 16.
The next four characters are number and are the actual serial number of the boat:
6958
Then there should be an "M", then two numbers (the model year) and then a letter (A - L) that indicates the month of manufacture, starting with August of the year prior to the model year.
The extra "S" does stand for a factory second, which were common in the late 70's. The designation "A1" was also used for the same thing.
So, your "real" number (guessing) should be CCMB6958M78B S - a 1978 model made in September of 1977.
That was a time period when Hobie Cat was making thousands of boats a year and was overwhelmed by demand. It was a very giddy time at the factory. I wouldn't be surprised if the person engraving the number got "confused" when marking your hulls.
Bottom line - it's a Hobie 16 - have fun! Post some photos!