(b) Long term schooling of 18 or more months.
(2) Sea Duty (Sea/Shore Type Duty Code "2"):
(a) Duty performed in commissioned vessels and deployable squadrons homeported in the U.S.(including Hawaii and Alaska).
(b) U.S. land-based activities and embarked staffs, which require members to operate away from their duty station in excess of 150 days per year.
(3) Overseas Remote Land-based Sea Duty (Sea/Shore Type Duty Code "3"): Duty performed in a land-based activity, which does not require members to be absent more than 150 days per year, but is credited as sea duty for rotational purposes only due to the relative undesirability of the geographic area.
(4) Overseas Sea Duty (Sea/Shore Type Duty Code "4"):
(a) Duty performed in commissioned vessels and deployable squadrons homeported overseas.
(b) Overseas land-based activities and embarked staffs, which require members to operate away from their duty station in excess of 150 days per year.
(5) Overseas Shore Duty (Sea/Shore Type Duty Code "6"): Duty performed in overseas land-based activities, which are credited as shore duty for rotational purposes. Members are not required to be absent from corporate limits of their duty station in excess of 150 days per year.
Wedding planning is tough on sea duty, but it can be done. Just make sure you get deployment insurance (ie, if he gets deployed, you get to reschedule at no extra cost- you'd be amazed how many vendors are willing to do this!) and have your sailor talk to his chain of command about it before you set a date. Be prepared to be frustrated and for him to not have his leave chit in hand until the last minute. We planned our wedding just over a year out and there were definitely some nerve wracking times but it all worked out.
Holiday leave period can be a GREAT time to get married- that's what all of the officers on our ship have done who got married on sea duty. We did so and were able to get 27 days of leave for it so he could help me the week before the wedding, we could get married, do our honeymoon, and have a week together before I went back to school. It is definitely not typical to get that much wedding leave, we were extremely lucky, my husband didn't take leave for 15 months prior to it in exchange for getting it and they told us the only reason we were given that much was because it was the holidays and because I don't live with my husband and they felt bad- but if you do it around the holidays, as long as they're not deployed, commands typically give a week or two of holiday leave to all the sailors so it can be a great time to get a wedding and a quick honeymoon in without fear of a short underway coming up. Christmastime is when you see the most ships in port for sure!
As far as dry dock goes- it's really expensive and a lot of ship's dry dock dates are being pushed back for money reasons. Don't count on a dry dock period being a for sure thing or the dates of it not changing. My husband's ship is due to go to dry dock after deployment but the dates they're going to be sent into dry dock have already changed four or five times! And like Anti M said, most people go to schools during dry dock, and of course school dates can change, so that's a big obstacle- and if a lot of people are in school, they may not be able to grant a leave request because someone has to be on the ship! Dry docks don't happen often for ships- they do get sent to the shipyards pretty regularly as part of their training cycle (say, once every year and a half or so) but that is not the same as being dry docked.
And yes, deployments can absolutely be longer than 8 months. I can think of two groups of ships off the top of my head, one that just finished an 11 month cruise and one that just left for a 9-11 month cruise. There is a lot of need for our navy in the world and not a lot of ships to do the job!
As far as dry docking goes, I've found the scheduling for them to be fairly accurate. My husband has now been through two dry docks (once with the Vicksburg in Florida and now with the Ike in Norfolk), and the only "problem" we've had is that it was in dry dock longer then it was supposed to be (which you didn't hear any of the guys complain about). Both times the ships were sent to dry dock almost immediatley after returning from deployment.
When they deploy they get an approximate date of return, however, be prepared for this change. I remember when my husband was deployed, the date kept changing right up to the week before. And he's a Quartermastr, so knowing the schedule was his business. So be careful when planning a wedding around a deployment return date. Always remember that with Navy, things are ALWAYS changing, so go ahead with plan A, but be prepared with plan B. The good news is that when they return from deployment, that's the perfect time to take leave. The command is a little more lax with everyone. However, this is our personal experience with my husband's ships. Deployments can be longer then 8 months, however, they very rarely are. They tend to reserve those for world tours. As for taking leave during deployment, no way. Someone in the immediate family has to die for that to happen. My best friend and her husband are expecting their first baby while he's deployed, and he has to miss it because there is no way they are going to let him leave.