Cutting and pasting from my message to the big gun forum: (photos coming soon!) I'm currently at home on spring break, so yesterday I built a target that holds a small sheet of balsa wood as a target, to test if a shot will penetrate. The target is 12" long and 3" tall overall. It is designed to simulate the ribs of a ship from both sides, so there are ribs sandwiching the balsa on both sides every three inches. It is is the equivalent of three panels with 3/8" ribs in between, a 3/8" subdeck and deck, and has a 3/8" strip along the bottom to simulate the impenetrable bottom of a ship. Since the targets used in Gunnery and Maneuvering events are tennis balls and water bottles and such, which float so shallow you only get practice hitting well above the waterline and in the superstructure of a real ship. I want to know if I can hit the hull of a ship at or below the waterline and cause a hole, which is why I made this new target. Of course, now that I have this target, I couldn't wait until the next G&M, so I ran a test. I loaded Cadorna's torpedoes with a single 1/4" ball in each barrel and determined the new safe pressure to be 75 PSI (normally torpedoes are loaded with two balls per barrel). I then loaded the target with 1/8" balsa with silkspan on both sides but no paint. I proceeded to test the direct penetration of the 1/4" shot on the 1/8" armor out to a 30 foot range on a flat trajectory (target and cannon were at the same level). Next, I rotated the target 45* to the side and began testing again, but it became too late to finish the test. The testing revealed several interesting tidbits. Because the torpedo cannon for Cadorna doesn't rotate, it has no wobble, so it provides a very repeatable pattern. Even despite the sloppy tolerance barrels, I was able to achieve excellent accuracy out to 20 feet (I only began to miss the target after 15 feet). I had to break for dinner and continue from 15 feet after dark, so that may also be the cause of the inaccuracy (I was sighting down the barrel by eye). The actual hits revealed that after about 20 feet the holes changed slightly. The balls did not knock out as much balsa as a closer ranges. Also, the holes were slightly smaller in diameter. All the holes were clean, round holes, and all were smaller than 1/4", which suggests that the balsa closes back in behind the shot, unless it is torn away. The silkspan helped to hold the balsa together, and in most cases, I could push the balsa back in place to form a near-perfect patch with minimal effort. Importantly, even at a 30 foot range, the cannon caused holes to appear on the flat armor. When the target was rotated 45 degrees, I scored one good hit, which left a large dent, which bulged the balsa on the back of the target and would have started a minor leak had it been in water. At 25 foot range, I was unable to score a hit on the balsa after 5 shots, though I was able to hit the impenetrable ribs three times. At that point, it was 10:30, and time to pack up for the night. The test was very limited in scope, covering only 1/8" armor and 1/4" shot perpendicular to each other and began to investigate 45 degrees. Unfortunately, the weather report calls for rain tomorrow and I have lots of other things to do before heading back to Davis, so I don't think I will be able to continue for a while. At the next G&M even, I'd like to modify it so it floats in the water with 1" of penetrable area below the water, mark a 1/2" boot, and leave the rest as grey. I want to use a single Arizona cannon, with the barrel securely mounted so that it can be adjusted, but won't wiggle, to provide the best repeatable accuracy. I'll then be able to test penetrability below the water line. In other good news, I built a motor mount for Spahkreuzer's new motors, and the boat is ready for sea trials. I was worried for a while, but now it seems certain that Spahkreuzer will be back to terrorize the pond!
OK guys, I ran another test tonight. This time, I took the target to the bathtub. The objective was to identify damage patterns from both mine and my brother's torpedo-cruisers, as well as determining maximum depth of possible penetration, with both single- and double-shot torpedo cannons against 1/8" balsa armor plating silkspanned on both sides. Tests were performed at torpedo-cruiser ranges, varying from 1 inch to six inches horizontal distance. All cannons were foam-tested before use on the balsa target. The first test was my Spahkreuzer's triple torpedoes, firing two balls from each barrel as per WWCC rules, at 1 inch range into the target, aiming to hit above the water. The objective was to duplicate previously observed patterns of massive chunking, and removing large sections of balsa with a single shot. The result was mostly as predicted, with one surprise. As expected, the blast removed a large section of balsa, approximately 1/2 inch tall and 2 inches wide. The unexpected part was that the silkspan stayed behind and did not follow the balsa, so the overall waterflow was equivalent to two 1/4" by 1/2" rips and one 1/4" hole. Guys in the WWCC take note, if you're facing the Spahkreuzer then silkspan the outside of your boat. The second test was similar to the first, except that the range was expanded to about 5 inches and the torpedoes were expected to hit at or below the waterline. Since there were two balls in each barrel, I expected the second ball from each barrel to closely follow the first. The experiment proved that this is not always the case. I fired the cannon (the splash soaked my brother's head ) and inspected the results. The target had six beautiful new holes, all varying from 1/4 inch to 1 inch below the waterline. I was unable to get any sort of chunking to occur throughout the underwater testing, despite firing multiple balls per barrel. The third test was again similar to the first, except again the range was expanded to about 6 inches, and the ship was listed somewhat to aim for about 2 to 3 inches below the waterline. The target was also specifically held deeper in the water for this test. The cannon was fired, and three holes appeared. Inspection of the damage revealed two clean holes and one shot embedded in the balsa. What happened with the other rounds, I do not know. I suspect that in this case, the second round from each barrel DID follow the first round from each barrel, although that does not explain the shot lodged in the balsa. The fourth test was run with my brother's Giussano-class cruiser, the Luigi Cadorna. Cadorna has less depression on its torpedoes, so the fourth test was run at about 4 inches range, aimed above the waterline. The cannon blast left two clean holes right where predicted. The Cadorna is much heavier and more stable than my Spahkreuzer, so it rocked less during firing and the two balls from each barrel did not spread out at all. This behavior has also been observed often during battle. The fifth test was also run with the Cadorna, this time aiming for about 1 inch below the waterline. To achieve this, the range was opened to 5 inches and the ship was re-ballasted to represent the farthest it can rock. This time the shots spread out a little more, and while one hole was clean, the other was taller, as though a second ball had passed partway above the first. The sixth test was run with Cadorna, loading only one ball per barrel and aiming as deep as it could go. The ship was listed until the barrels were literally touching the water, and the target was held with the very top of the penetrable as the waterline. The shots hit about 1.5 inches below the waterline, one clean hole and the other a legal hole but the shot itself did not pass through. The partial penetration was enough to break the balsa and let water in, but indicates that this was near the maximum possible depth of penetration. While I did not test this, I would bet that a similar test aimed for 2 inches or deeper would not penetrate balsa. In other news, I pond-tested the Spahkreuzer and tested current draw in water. The ship easily gets up to speed, and in fact goes fast enough at 100% throttle to ship water over the bow, which it has never done before. Current draw while motionless in water was a little under 3 amps, and stall current was 6 amps even. Eric's Cadorna tested in at 2 and 4 amps respectively. Since Spahkreuzer runs 3 motors and Cadorna runs 2, that suggests that the motors are approximately equal. Next time I'm around good power tools, I will sharpen up the bow of both boats to cut the water better.
