What do you call...?

[Jib]

Recently I was reading about a type of weapon used to deter pirates boarding a ship. A smaller canon ball is wrapped in oil soaked cloth, ignited, and hurled on the ships attempting to board. I can't recall which book it was in and the name of the weapon seems familiar but now I can't place it.

[Jas. Hook]

Jib -

I'm a blank on this one but having a tossed aboard iron ball wrapped in a lit oil soaked rag rolling across the deck would distract my attention away from the task at hand. Sounds almost like an improvised grenado or firepot.

Jas. Hook

[Jib]

I guess the concept is that it would start a fire and be very difficult to pick up and toss overboard. Anyone?

[Mission]

It sounds like you're talking about hot shots. I read about this somewhere, although I don't think it would be done the way you mention. The point of hot shot was to get the cannon ball red-hot so that it would set fire to the ship when it hit. To do that, you'd have to have more than oil-soaked rags, you'd have to have the constant, intense heat created by a furnace. (Oil soaked rags would burn out long before heating small pieces of metal red-hot, let alone cannon balls. Plus there would be extraordinary danger in setting oil-soaked rags on fire on the wooden deck.)

Stolen from the wiki on cannon projectiles:

Heated (or Hot) Shot

A process where a solid iron cannonball is heated red hot in a specially-designed wood- or coal-fired furnace and then is loaded in a muzzle-loading cannon, cushioned by a substantial thickness of wet wads, and is then fired while still red hot, at flammable targets with the intention of setting them on fire. This was a much advocated tactic (and many times a very successful one) for shore based forts defending against attacks by wooden warships. Examples of these small brick furnaces may still be seen at permanently constructed pre-1860 forts in Europe and the United States. The adoption by most navies of iron hulled ships generally made these obsolete. The shot was carried on a specially-designed iron barrow or 2-man litter and, in the era of blackpowder cannon charges contained in cloth bags, occasioned much fanfare and notice as it was conveyed to the cannon muzzle as the red-hot projectile would easily ignite any carelessly handled loose powder. Any reckless or somewhat dangerous individual who seemed to draw trouble to themselves and those around them was referred to as a "Hot Shot", giving rise to the term in common use to this day.

I doubt they would be used aboard a ship because of the problem of having the furnace 1) close enough to the cannon to load and fire the shot before it cooled and 2) protected enough to avoid setting the ship on fire. (Imagine a cannon ball smashing into your cannon-ball furnace and spewing hot coals all over your deck and into your sails. Bad idea.)

I've read that even the cooking fires were often put out during rough weather, long travel and battle. So this idea was probably not used by pirates - at least not more than once or twice.