"Coal as Protection" Topic

Protected Cruisers and Armored Cruisers of the Pre-Dreadnought era were designed so that their coal stocks were considered part of their protection factor (in effect, they added armor protection). Since the protection value was greatly affected by how much coal was currently stocked, a ship low on coal received less protection.

First, how much protection did the coal add to these vessels?

Second, I have not seen any rules that account for this factor (at least actively- it may have been baked into armor factors by designers). Does anyone know of rules that account for this?

The "Battleship" Maine blew up in Havana harbor, giving the yellow journalists a good reason to trumpet a war with Spain.
Later investigations blamed the explosion on "spontaneous combustion" of coal dust.
Doubtful protection, I would think.

In any event, coal was stored way below, convenient to the boilers which were generally below the water line. Placing coal where it would serve as additional armor would involve a rather tortuous path to the boilers.

Hey John,

That sounds very counter intuitive to us in the modern world, but yep, they absolutely did this in design and practice.

The grey areas in the following diagram show where the coal was placed using this procedure.

link

I personally had the chance to explore all over the USS Olympia (a protected cruiser) to see this first hand. There are coal loading doors all over the gun deck (!) where they would shovel the coal down into the coal bunkers to spread out the protection. All the major navies did this in practice at the time and it was accepted standard design practice as well.

It seems to me that this practice would certainly increase the coal dust in the air.
I wonder how many sailors suffered from Black Lung?
And the mania for clean decks must have kept the other sailors busy.

Don't forget that fuel oil formed a key element in the side protection systems in battleships in the 30s and 40s, so it was a practice that lasted in one form or another for quite some time

True, that.

But do any rules take this into account? I've played a lot of rules, but have never seen it.

Bunkering used as protection on otherwise unarmoured vessels was common to many nations designs. The more specific case here is where it is used below the armoured deck to protect the ships vitals.

Against ships carrying similar armament it was thought to add a significant degree of protection in that it exploded shells in the bunkerage rather than in the 'vital' spaces of engine room or boilers.

It was recognised that against larger calibre shells it would be of little use and also that the risk of fire was considerably increased – hence the fitting of flooding and sprinkler systems in some ships.

Considering the few times such protection was tested I doubt that there would be enough evidence to say whether or not it worked. Fires at Tushima were reputedly due to wooden panelling and flooring but coal may have played a part. Fires happened by spontaneous combustion of coal in a number of ships so it was a potential danger wherever it was kept.

Coal dust explosions are very violent but you need a deal of space in which to reach the optimum conditions for explosion and full or nearly full bunkers would not have that space.

I'm not aware of any that split it out as a consideration. When I wrote "Fire When Ready" I just assumed that it was inherent in the relevant armour factors rather than applying any modifiers.

The rule of thumb used at the time was that 6 feet deep of a full coal bunker equals one inch of wrought iron armor, or about 1/2 inch of WWI era steel. This was before modern terminal ballistics, I have no idea how well it holds up. Good enough for game purposes, though. Now to find those ship plans…

FYI Coal dust is really only a problem when bunkers are nearly empty. Same as with gasoline…a full tank of gasoline isn't half the problem that a near empty tank is. Hollywood movies always get it wrong.