Venice ACTV...HELP

It is not a water taxi, those are private boats that operate like taxi cabs, although it is clear from your post you are referring to the vaporettos.
Looks like the best boat is the 5.2 from Ferrovia to Ospedale. During the day, it goes every 20 minutes and takes 27 minutes to get to Ospedale. At 15, 35, and 55 past the hour.
The 4.2 goes the same route as far as Fondamente Nove, then you have to change boats at a different dock to continue to Ospedale.

Thank you Sam, you are my hero today.

If you need additional info about the vap. routes, just google "Venice vaporetto map. You will get many, many possibilities with maps -- some good, some not so good, and some great ones. By zooming in and out you will see the dotted lines that have the route number on them. Takes a bit of practice, but it does work. You can then plan your travels from place to place knowing the route you need to take.

One of the non-obvious things about the vaporetto in Venice (well, logical if you think about it), is that normal buses stop on one side of the street in one direction and the other side in the opposite direction. Not so vaporettos, they zig-zag along the canals, calling alternately at stops on opposite sides, and boats in both directions stop at the same stops (floating pontoons really).
And, one thing you cannot just do in Venice is cross a canal wherever you want, you need to find a bridge. So, you don't just want the nearest vaporetto stop, you need the nearest one on the correct side of the canal!

The official map is here: http://www.mapaplan.com/travel-map/venice-italy-top-tourist-attractions-printable-city-street-plan/high-resolution/venice-top-tourist-attractions-map-03-Water-bus-transit-lines-stations-Vaporetto-Actv-public-transport-planner-high-resolution.jpg
And yes, to get from "Ferrovia" to "Ospedale" you need a 4.2 or 5.2, which goes around the edge of Venice. The previous stop is "Fondemente Nove", which is a major interchange point. And make sure it is going in the correct direction (from right to left as you face the canal).

In addition to the bridges for crossing the Grand Canal, there are two-man gondolas called traghetti (rhymes with spaghetti). They're 2 euros to hop in and get taken to the opposite side.

If you do google searches for vaporetto maps be sure that you get a reasonably recent one as the numbers are not completely constant from year to year, and end points on some boats change seasonally. The official website has the most accuracy.