If you're interested in looking at the code itself, go to the WMO site and use it's code document [here].
Page 9 is where the FM 13–XIV SHIP code, (usually know as ship SYNOP code) begins. Section 2 of the code allows the reporting of water temperature and the direction, period and height of several sets of waves/swell. The details are in "12.3 Section 2" a few pages down.
When you look through this, you'll see why it's desirable to let a computer do the work for you. I use the program Digital Atmosphere, and a description of how to use it is on my site [here]
while the DA program writer's home page is [here]