Sea Div will teach you this:
Rope work- more in depth knowledge of knots and their uses
Rig upper deck equipment- how to erect awnings, deploy accommodation ladders and jumping ladders, maintaining upper decks
Lifting appliances-cranes and davits
Hand Sewing- learn how to operate and maintain a heavy duty sewing machine
Fire Small Arms- Sig Sauer, C7, C6,C7, C8, C9 .50 Cal HMG, LTG (line throwing gun)
Ships Boats- operating and navigating small boats
RAS- learn how to work in the dump (gear and stores handling area) during a replenishment at sea
Demolitions-learn how to rig and set a basic demolitions charge
Seamanship - learn how to rig the equipment for towing, mooring, and anchoring
When you are posted to a ship and you are alongside your typical day will start at 0750 and end at 1600. You will conduct daily cleaning stations, departmental maintenance and what ever job the Buffer and DeckO will think up for you.
At sea you will be on a 1 in 2 watch rotation and you will do the same as above and in addition you will stand watch on the bridge wings, lifebuoy sentry, helmsman and Boatswain mate. You'll fire the .50 cal, maybe be a member of the NBP, be a worker bee for RAS, Seamanship, Rigging of equipment and what ever other job the Buffer will think up for you.
On top of this you will have to learn the entire layout and arrangement of the ship you are on and learn an entire new language.
Have fun and I hope this helps.