height of waves out on ocean

Question
Dear Richard,

Hello. I am writing sci-fi book and need some advice on how high the waves splash around when one is out on the ocean.

One of my characters produces an underwater containment vessel which raises from lower ocean depths to the surface (sort of like a mini submarine). This takes place about 6 miles NW from the Golden Gate Bridge, S.F., CA. Once at the surface, the containment vessel loses its top, but surrounds the open area with about a 2 foot high barrier to prevent too mush splashing from ocean waves. Then, its occupants can rise up higher and take a gander at the scenery, from out the open area.

My question is- would 2 feet be enough to prevent most waves from splashing in the containment vessel, 6 miles from shore, or am I very off base here? Should it be 3, 4 feet, or more? I went to Web sites for S.F. Bay area, looking for wave heights, but I'm not sure how to read the information they give- some of them mention 6 feet high waves, other 15 foot high! I know about tide variations, but I thought that only affects around the shore, since waves are caused more by weather( or, are they?).

I would appreciate any help you can give me on this. I figured you would know a lot, being that you have been out on the ocean many times.

Thank you,
D.W.

Answer
 I do most of my fishing off of LI NY.  But the behavior of waves are fundamentally the same most anywhere.  There are two factors to be considered when determining the height of a wave.  The true height which is measured from the highest point to the lowest. Really quite simple, or so it may seem.  The other measurement is the period.  This is how long it takes the wave to move.  The water does not move, just the force of the wave.  If the period is long, then the distance from the crest of one wave to the crest of the next is great.  These type of "flat" waves can reach heights of many feet and still have no effect of "splashing" onto the deck of a boat since the boat will rise and fall with the wave as it rides upon the surface of the water that is slowly rising and falling as the waves pass by.  Unlike the "Hollywood" wave that flipped over the liner Poseidon in the movie of the same name, a tsunami in mid ocean is generally unperceptable to a vessel encountering it because it is so spead out that even if it reaches 40, 50 or more feet in height, its period is so great that it is spread out over a great distance that may be measured in miles rather than feet.  
 What you would be concerned about in a small craft would be wind generated waves.  These are directly related to the force of the wind.  They are much steeper and often have whitecaps on their crests.  These would be anything from a ripple, to huge 50 footers as depicted in the "Perfect Storm".  Wind generated waves are the ones that would splash, crash, and generally create problems for small craft.  When the National Weather Service issues a small craft advisory, it is almost always because of wind generated waves.  There is a direct correlation between the force of the wind and the height of these waves.  
 Winds in the 15 to 20 mph range usually produce waves of at least 3 to 4 feet.  Considering the afternoon seabreezes that generally come up most days in the San Francisco area, I would say that 5 or 6 foot waves would be quite common.  Though I have never fished in that area, things I have read generally indicate that most local fishermen do their fishing in the morning and are back in port by early afternoon to avoid the afternoon seabreeze and the sea conditions resulting from them.  
 Fetch is the distance over water that the wind has been blowing from the same direction.  If this distance is relatively short, there is not enough time for a wave to build to is maximum height for the given velocity of wind.  Thus a shore breeze (one blowing from on land out to sea) will result in little or no waves near the beach with ever increasing waves furter and furter out.  But if the breeze is offshore (from sea to land) then waves of maximum height will crash along the beach.  
 I hope this will give you a general idea of what it is like on the ocean, even a few miles from shore.  If you need more detailed information about waves, I suggest you use the internet to visit the official site of NOAA(National Oceanograpic and Atmospheric Administration).