The South Coast Battle Group has experimented with several different torpedo designs in it's history. I'll try to detail our findings and conclusions here.
In the beginning, torpedoes were developed specifically to give small ships such as destroyers, a weapon they could carry into combat that had a reasonable chance of hurting a larger vessel such as a battleship. The first torpedoes were single-shot non-reloading affairs made from brass tubing and fittings. They were loaded with .243 caliber rifle bullets. Cotton wadding was used to hold the bullets in their tubes and to provide a gas check. These torpedoes worked very well and proved to be extremely effective. basically, in the hands of experienced skippers they became one-shot ship killers. The reason for this was that, because of the low muzzle velocity, the torpedoes would immediately begin to tumble in flight. This caused large holes when three projectiles would hit a ship. Holes 2" x 2" to 2" x 4" were not uncommon when using these type of torpedoes.
As soon as these torpedoes proved themselves in the destroyers, other larger ships wanted them too. Eventually a reloading version of this torpedo was developed for installation on larger ships. battles were always decided by torpedo hits and not by gun fire. being a newbie (many years ago) I immediately wanted a Prinz Eugen with all 12 torpedo tubes. I couldn't have cared less if it even had guns as long as I could have all the torpedoes. because of the construction of this ship coupled with the excessive destructiveness of the then current .243 systems, it was decided to abandon this style of torpedo and attempt to return to a game dominated by gun fire. All the existing systems were adapted to fire two ¼" ball bearings per salvo.
During this time, John White had developed a reloading torpedo system small and light enough to fit into a destroyer with the associated regulators etc. Although these systems were not very effective due to their small accumulator tanks, they were soon up-sized to fit into larger ships. These ships had the volume and displacement to handle reloading torpedoes and could carry larger accumulator tanks. It soon became apparent that the destroyer reloading systems were ineffective. Destroyers now uses single-shot non-reloading systems (one ball per tube) with large accumulator tanks. Since the onboard regulator and CO2 supplies are eliminated, the little ships are much more stable and can carry the larger and more effective accumulator tanks. The larger ships of course were able to carry large accumulator tanks and sufficient CO2 to fire many salvos (originally 6, later 12) per tube.
Torpedoes, although not as effective as before, still to a great extent decided who sinks and who does not. After reviewing all of our many years of experience it was decided this year to restrict torpedoes to (single ball) non-reloading systems only. Skippers can now arm as many tubes as the ship had, however they can only fire once per sortie and must return to port in order to reload. We believe that this will return the "game" to it's original intention and make gunfire the deciding factor in most if not all battles.
Underwater torpedoes have mostly consisted of the systems described above with their barrels mounted to fire from the scale underwater locations. This reduces the effective range of the torpedo and usually results in a nice, clean hole below the waterline. The best way we found to increase the effective range of underwater torpedoes was to take a ¼" ball bearing and super glue a ¼" diameter, 3" long piece of K&S brass tubing to the ballbearing. This reduces the hydrodynamic drag on the ballbearing and allows the torpedo to travel further. The really cool thing is that CO2 fills up the brass tube and makes the torpedo buoyant as it streaks to the target. This "automatic depth control" feature makes it very easy to hit ships from 6' to 10' away near the waterline. When the torpedo broaches or loses forward motion, the CO2 leaks out the back and the torpedo sinks straight to the bottom.
This system was installed in a transport ship under R&D and fired many times in combat. Several ships were hit below the water line. The torpedoes would usually only penetrate ¼" to ½" and very little water entered the ship because the torpedo would plug it's own hole. The biggest "problem" or fear we had was that if you had one of these torpedoes hanging in your hull and another ship rammed or side swiped the hanging torpedo, it would likely rip a big hole in the side of your boat because of the side-swiping action of the ram. We abandoned this successful R&D and returned to using only ballbearing torpedoes. If someone wanted to try this again using a flexible material (in place of the brass tube) for the afterboby of the torpedo, I think it would be found to be acceptable for general combat use.
If you have a torpedo system with at least a 3" long barrel you can try experimenting in the swimming pool. be careful regarding holding the barrel level when you fire the torpedo. I fired one with slight elevation and it left the pool and traveled 20', over the fence and into the neighbor's yard. It also important to have a well constructed gun system to fire the torpedoes with. Remember that water is incompressible, and if something has to give, it will be the weakest part of your system (not the water). Always wear safety glasses when firing any CO2 cannon.
Dave Merriman of the Subcommittee has developed 1/96th scale gas-powered torpedoes which he fires out of his submerged submarines. These work well and are fun to watch. The problem with adapting these to our hobby is that they do not have enough energy to penetrate a ship's hull at a reasonable distance. Just like the real torpedoes, they would need an explosive warhead to be successfull. Sufficient velocity could be obtained by using higher pressure gas to propel the torpedo at a higher speed. but you then run the risk of the torpedo broaching the surface, flying out of control and injuring people on shore. Safety must come first.
Usually this "solution" is "discovered" by every new member who joins our club. They are usually amazed that we haven't thought of these ideas before. Estes (and bottle) rockets are very dangerous and can cause great injury. Their flight paths are very unpredictable. It only takes a few minutes for rational person to think of the "worst case scenario" and to visualized the army of lawyers waiting for this scenario to occur. I do not want to loose my house and live in a shopping cart, no thanks. Explosives fall into the same area. We have tried them though. The biggest problems were associated with the detonating mechanism. If made the "safe way", i.e. difficult to detonate, then you get a lot of duds when the torpedo doesn't strike the hull hard enough. This usually causes the developer to go with the "hair trigger" approach. This has resulted in the torpedo exploding in it's own ship, on the bench or in the captain's hands when loading it. It doesn't take a rocket scientist to figure out that these are bad ideas.
Usually the people that want to develope these ideas have never had to repair a damaged ship. Their fantasies usually never include having these weapons fired at their ship, only the ships of others. Lets put our energy into something useful like a truly watertight box or improved, cheaper cannons, etc.