Elan calculations:

Suppose a hypothetical battleship has a mass of a thousand metric tons. It must be capable of ascent at high speed to be worth anything, BUT since pressurization does not exist, the max altitude is around 8000 feet and unless the crew wants really nasty baurotrama (too rapid depressurization), the ship must rise at a rate no faster than 2.53 meters per second (Research into cabin altitude pressure rate of change gives 500 FPM as industry standard). 

My research and calculations yielded very interesting results:

1. Gaining alttitude becomes essentially no problem for Elan equipped ships assuming Elan counteracts gravity 100%. In order to accelerate at 0.14 m/s^2 at sea level, a 1000000 kilogram ship only needs an 14 meter radius sphere of helium. My original calculations called for a situation in which the sphere was carried externally, so that factors in the weight if the bottom half of the sphere was armored in one inch of steel.
2. On the other hand, steering is an ENORMOUS engineering challenge. There are essentially no good ways to generate thrust in the 1870s. So suppose our gigagram ship is basically a Pearl Class cruiser in the air. I couldn't find its height, but it sufficiently illustrates my purposes to use its draft (waterline to keel) times its length as though it were a rectangle in cross section. That gives it a windward cross section of about 1060 m^2. 

According to this website:
http://www.engineeringtoolbox.com/wind-load-d_1775.html

A 62.8 mph wind would exert 710200 newtons per second. That means you would have to fire one BL 12 main gun round every 2.5 seconds to counter the momentum change wrought by the wind. Meaning, ships should be spherical to reduce the impact of the wind. 

I am thinking of other means by which to mitigate the problem posed by winds. Nothing is forthcoming, however. No way to sail against the wind.