Karl Heidenreich wrote:1. When the navies changed the adopted fuel from coal to oil?
Britain started trials with oil in 1898.
In 1908 it was decided that all future destroyers were to be oil fired exclusively.
2. Which was the first capital ship that used the new fuel?
In 1912 the Queen E and USS Nevada were started, the first exclusively oil burning capital ships.
3. Apart from the logical advantages regarding consumption which are the overall advantages of the oil over coal: weight, power output?
Here's a comparison between two RN destroyers built at the same time the coal fired Beagle and the oil fired Defender:
Boiler room weight: Coal 187 tons, Oil 142 tons
Boiler room length: Coal 92', Oil 61'
Fuel required for same endurance: Coal 225 tons, Oil 175 tons
Engine room complement: Coal 58 men, Oil 24 men
The cost of the oil powered ship was also about 20% less than it's coal fired contemporary.
The disadvantages of oil include the lack of ballistic protection provided by the coal
Of the 3 main disadvantages advanced against oil it was eventually realized that 2 could be discounted:
1) In the absence of oxygen oil was not significantly more of a fire hazard that coal.
2) Any ballistic protection coal might have provided was mute when the weight saved could be reinvested in actual protective elements that would be much more effective: armor plate, more bulkheads, smaller machinery spaces, etc
The #1 liability of oil then, as it is now, is the quantity and the location of it's sources and their vulnerability to foreign influence.