A wood burning freighter?

At the risk of sounding ignorant, if the wood was first burned slowly to produce charcoal (slow pyrolysis), could it not then be used as a coal substitute?

It may be that certain hardwoods such as those used in the manufacture of lifeboats or specific tropical trees contain lower quantities of resin and burn more slowly. I know that resin can cause issues in smoke stacks and chimneys.

I bow to the advice of a suitable wood expert. I'm only brainstorming here.

Both coal and wood can be used in any firebox/boiler combination-- woodstoves too, though coal smolders endlessly without putting out much heat if it is not ventilated by a grate. Some wood burns hotter than others, but most will get up enough steam to run a piston engine.

Bottom line, wood works but it just isn't as powerful as coal.

Charcoal is made by a process that steams off moisture without incinerating the wood cellulose. It's a shortcut to fully drying firewood, and burns hotter than green wood or dried wood from water-loving species like cedar or cottonwood-- but not hotter than coals from fully dried hardwood.

Many of the old time steam railroad locos, which originally ran on wood, were converted to coal and sometimes to oil. Basically anything that will burn can be used to fire a boiler. The main advantage to coal over wood is the amount needed. Wood burns faster than coal and the fire is not so hot. It takes much more wood, by bulk, than it does coal to generate the same amount of steam. Depending on the type of wood it can take anywhere from 2 to 5 times as much wood as coal to produce the same amount of steam. You have to take into consideration the amount of fuel storage space you have. As noted above, the German raider didn't use wood, probably because they didn't have room for it.

I knew one of the men on board the Erlangen, the real ship on which this story was based. It escaped from NZ andmade it all the way across the Pacific burning wood which they cut from a remote island soon after their escape.

As noted above, most anything that'll burn will make steam, but not necessarily build as much steam pressure. WWII US Naval vessels used 600 psi superheated steam for propulsion. Pre war commercial steamships likely operated on lower pressures. It would run, but not as efficiently. A comparison might be the gas we are forced to use these days with ethanol in it. It still burns; but engines produce less power and reduced fuel efficiency.

Remember Rabbit Ears with tin foil?

Speaking of the wood, I've done some calculations.

The engineer said it would be a 14 day run to Valepariso and they'd need 30 cords of wood per day - that's 420 cords.

A cord of wood is 8x4x4 feet or 128 cubic feet.

420 cords would be 53,760 cubic feet or 1,522 cubic meters, or about 2/3rds the volume of an Olympic-sized swimming pool.

The average weight of a cord of seasoned firewood is 2,500 pounds. 420 cords would weigh about 1,050,000 pounds or 525 tons (US), or the weight of 260 2016 Ford F-150 pickup trucks.

So, those guys chopped an hauled a heckuva lot of wood!

One last trival comparison - the last coal-buring USN destroyers carried 300 tons of coal and had a range of 2,800 miles at 10 knots (12 mph).