Why charcoal is only an emergency substitute for marine coal

Could charcoal replace mineral coal as fuel for ships?

Only in an emergency over a short distance; it could raise steam, but would not provide the range, power density, or boiler performance needed for normal naval use.

Charcoal is considered a possible emergency fuel when no other option is available and the ship only needs to travel a short distance. The objection to regular use is inadequate range and useful power density. Heating wood or other organic material in a low-oxygen environment removes water and volatile constituents to produce a more consistent heating fuel. A further concern raised is sulfur and its effect on steam machinery, although no fuel analysis or boiler trial is supplied.