[kylania]

I really think it has to do with how many points you put into him. I just loaded up a previous save game, where there was a convoy 40km from me. My fully passive skilled sonar guy called out every ship in the convoy as he heard them. Even when I jumped to 64x TC, he'd bring me back down to 32x and call out contacts.

Then I loaded up a single mission, with a sonar guy with no skills at all. A convoy starts 34km away in that one. Within a minute of submerging a contact line appeared, but he didn't call anything out. A few minutes later he head a warship and did call that out. He than lost contacts entirely. I turned so the side of the boat would face the convoy and sped up to 64x TC. As the convoy was detected again I was dropped to 32x TC, but no call out. I sped back up to 64x and this time the other warship and some merchants were heard, I dropped to TC 32x and he called out the merchants this time.

Looking at the code for the abilities, it does look like there's a passive skill which increases detection time and range for sonar.

;SOUNDMAN - Passive abilities

[SpecialAbility 26]
ID=Ability-Boost-Sonar
NameDisplayable=Ability-Boost-Sonar-Name
Description=Ability-Boost-Sonar-Description, Ability-Boost-Sonar-Description, Ability-Boost-Sonar-Description, Ability-Boost-Sonar-Description, Ability-Boost-Sonar-Description
Levels= 5
AbilityType=SonarRange ;boosts sonar detection time and range (in percents)(nu-s sigur de ReceiveContactRate)
AbilityValue= 5, 10, 15, 20, 25

PointsRequirement= 0, 0, 0, 0, 0
AbilityRequirements= 0, 1, Ability-Boost-Sonar, 1, 1, Ability-Boost-Sonar, 2, 1, Ability-Boost-Sonar, 3, 1, Ability-Boost-Sonar, 4
LevelUpTree= 2, 3, 4, 5, 0
MoraleCost= 0, 0, 0, 0, 0
PointsCost= 1, 1, 1, 1, 1

AbylityActsIn= ALL

Duration=0, 0, 0, 0, 0
Cooldown=0, 0, 0, 0, 0

There is a mod that "corrects" this issue. It does this by setting the first level of ability to 20% (instead of 5% of stock) for hydrophone contact time and range. In my single player tests, after raising this ability, my sonar guy was calling out contacts immediately upon detecting them. He's never done that in all my tests.

[REL] Gouldjg's Crew Ability Balancing Mods