Complex sentence: Fire had taken hold on the surrendered "Alcide" in the foretop, probably due to the detonation of a grenade, and by 14:15 it had spread out of control, sweeping the ship from end to end.
Split into simpler sentences: Fire had taken hold on the surrendered "Alcide" in the foretop, probably due to the detonation of a grenade. By 14:15 it had spread out of control, sweeping the ship from end to end.