From the old forums.
Once you find the number on the hull, you need the secret decoder ring to pick the hull number out of it. My number is:
Which translates to:
TPS = manufacturer (Tillotson Pearson or TPI in my case)
50 = model number, 50 standing for J35.
257 = hull number, the piece you're looking for.
C = month of the year it was built, A = January.
9 = certification year, last digit only (so 1989 in my case)
89 = year of manufacture, also 1989 in my case.