Explain to me how the 'contact influence' works

[BooBooLovesAll]

I launch a torpedo at a ship with a draft of 24.6 feet. I set the torpedo to 25ish feet for depth setting.

I make sure that contact influence is set.. and launch.

I then watch to see that it just harmlessly swims under the ship with no explosion?

Time of year is 1942.. I know they had some problems, but with all of them?:o

[Von Manteuffel]

They had major problems almost throughout the entire War. Certainly from 1941 well into 1943 ( around August ). It's become known as "The Great Torpedo Scandal." The Mark 14 had notorious problems with depth-keeping and with both contact and magnetic influence triggers. The "scandal" was that commanders in the field experienced and reported the problems - by the score - but the U.S. BuOrd refused to do anything about it.

Mark 10s and Mark 14s were acknowledged to run around 4 feet deeper than setting, but, even when this was included in a firing solution, still there were too many misses. In desperation, in June 1942, the field command carried out their own tests at Frenchman's Bay in Australia. They fired a sequence of Mark 14 torpedoes at fishing nets and discovered that the average deep-running was eleven feet over the set depth. One of the main reasons for deep-running was that the depth-keeping mechanism in a Mark 14 relied on the torpedo sensing the exterior water pressure and altering its depth until the sensed pressure matched its depth-setting. They tested the depth-keeping pressure sensors by lowering torpedoes into water. Sure enough the indicated depth, matched the actual depth BUT, they didn't take into account that the water pressure around the surface skin of a torpedo running at speed is different. It's much greater than the actual hydrostatic pressure at the nose and tail, but much less around the cylindrical centre-section. That's where the depth-keeping pressure sensor was. So the sensor was sensing a lower water pressure ( and to it a shallower depth ) than was actually the case. This caused the torpedo's fins to operate to send the torpedo deeper - until the sensor was happy that it was at the set depth according to depth = pressure calculations. After a lot of arguing, further, official testing discovered that a Mark 14 torpedo, on average, ran at 10 feet deeper than the actual set depth. The problem was finally solved, 18 months into the U.S. War by moving the torpedo's pressure sensor inside the free-flooding body of the torpedo, where the water pressure was much closer to the actual outside pressure. These "fixed" torpedoes were given the suffix "A" e.g. Mk 14 Type 3A. The Mark 14 also suffered from big calibration problems.

It looks as though deep-running may have been modelled into SH IV. ( but not, I think a 10 feet error ). I've found the best thing is to set a torpedo to run at keel depth, or slightly shallower. That way, if the track is true, you stand a good chance of an effective hit. Either as a contact, deep enough to do real underwater damage, or as a sub-keel explosion using the magnetic trigger which can break a ship's back.

The state of the sea also effects torpedoes. Depending on the how deep the surface turbulence goes, a torpedo can be lifted and dropped several feet by wave action. I set torpedoes shallower for bad weather. Add to this the fact that the target is also rising and falling and the chances are that any shot set at below keel depth which does hit is more down to luck than judgement.

For your example of a ship with a 24,6 feet keel-depth, I'd set at 22, or 23 feet in calm water and around 18 feet in rough conditions.

Good hunting.