Vulnerability assessment, wooden splinters from ship side

FOI has, on behalf of the Vasa Museum friends association "Vasamuseets vänner" studied the effects of wooden splinters from the hull of a ship under fire from a replica of Vasa's 24-pound cannons. There are numerous descriptions in the literature of the inferno of splinters that were created on board a wooden ship when hit by heavy fire. Being hit by splinters from the hull side is mentioned as one of the major causes for injury during sea battle. A scientific basis for these descriptions is less easy to find and the aim of this report was to analyze the effects of splinters and assess their lethality for the crew on board a ship that was hit by one of Vasa's 24 pound cannons. During the fall of 2014 live fire testing with a newly cast 24-pound cannon made of bronze was performed by Vasamuseets vänner at Bofors Test Center (BTC). FOI was assigned to take responsibility for those parts of the design of the experimental set-up and analysis that considered the vulnerability and lethality assessment. The risk of serious injuries or incapacitation due to splinters was considered to be caused primarily by splinters that penetrated the skin or eyes, but also due to crush injuries from large blunt wooden fragments. The penetrability of the splinters was studied using witness material consisting of sheets of aluminum and ballistic soap covered with wadmal-like cloth, placed behind the ship side as it was hit by 24-pound cannonballs. For later analysis of splinter lethality, splinter distribution and velocity was registered using a high speed video camera. Splinter velocities in the front of the splinter cloud emerging from the impact, equaled or exceeded the residual speed of the cannonball after perforation. From the shot with the highest splinter velocities, exceeding 300 m/s, splinters penetrated both the aluminum sheets and the ballistic soap through the wadmal cloth. In this case the probability of incapacitation was higher than 75 % for crew members located in the proximity of line of fire. The rest of the shots fired had splinter velocities below 180 m/s. At these velocities severe injuries were limited to distances of a few meters from the hull. The fabric covering the ballistic soap showed no signs of penetration, implicating that it effectively stopped splinters. However, the risk of eye injuries and severe bruising was evident for all shots fired. In some cases large pieces of wood were torn from the hull. Although they did not travel far before falling to the ground, they had enough kinetic energy to result in fractures to the head if hit. The live fire tests performed at BTC gave a fair implication of the environment under which the crew operated aboard cannon deck, as well as the type of injuries they sustained. In order to make assumptions about the influence of impact velocity on splinter lethality, the experimental set-up and number of shots need to be expanded. However, the live fire tests gave a glimpse of what it was like during the era of the wooden ships