I have had this happen to me only to later realize that the other torpedoes were electric and thus only capable of the slow speed so setting a spread and selecting fast will only change the speed setting on torpedoes that are capable of the higher speed setting.
try this:
when I'm in port, I always go to the upgrade screen where you choose your torpedo load out. once im there i will load steam torpedoes in tubes one and four, and electric torpedoes in tubes two and three. (i rarely choose to use electric torpedoes in the bow tubes)
This way when you are out at sea if you choose to spread shots one and four for example; you know that both torpedoes will be of the same type and thus have the same capabilities.
also upon leaving port, i always set my pistols to impact, and set running speeds to fast long before i ever reach enemy waters.
edit: dont figure out a firing solutiong only to then change running speed settings - you will miss by a fair margin... if you change torpedo speed after solution input you will have to adjust the solution to account for torpedo speed
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