I have a question, it may sound silly but, could you use regular wood to stoke the fires in a coal furnace to power a battleship like the ones during WW1 and WW2, that had coal and fuel furnaces? How much would you think the efficiency would suffer? Imagine a battleship has 10 oil furnaces, and 10 for coal. Could regular wood be used in the coal ones? Even if the fuel density is lower? AND could you convert the fuel ones to run on wood?
Skoops
As long as you have a furnace, you could theoretically get a coal engine going with wood for a while, until your pipes clog up with soot and you've got more ash than hot coals in there. The major bottleneck is just that coal burns hotter than wood, full stop. You're never going to get the same output even if you're correcting for the efficiency differential and have a small forest on deck ready to burn. I think you could maybe get a WWI Destroyer moving, but if we're talking about anything heavier (like a battleship), you might have a problem producing enough force to get those propellers spinning at any speed that could fight the tides. Can't say I've been at liberty to try it myself though, so hey, who knows.
As for converting an oil burner engine to a wood engine, that's a bit less possible. WWI oil burner engines were essentially big flamethrowers bolted to the floor, pointed into a boiler. There's no place for wood to go. Note that WWII warships were nearly all running on relatively advanced oil, diesel or gasoline engines; you're in a whole other ballpark by that point.
Sevi
Thank you, this is helpful, basically a lot of trouble for it to barely work, if at all. Might make more sense to outfit a turn of the century battleship with sails, and use what little fuel you have left to operate the hydraulic systems.