IOTL, the late 19th century saw a naval arms race, with rapid improvements in both weaponry and armour. During the first decade or so armour was more effective than weaponry, rendering ships practically impossible to sink using gunnery alone, although after around 1870 or so guns came to have the upper hand.
Let's assume that, instead, naval armour manages to stay ahead for at least another couple of decades or so. Let's also assume that there are a few more naval battles than IOTL, giving admirals a chance to try out new tactics. How would naval tactics develop? The obvious would be greater reliance on ramming, which was advocated IOTL, although in the few naval battles of this period it proved difficult to get a good ramming attack in. Possibly ships would try and focus their fire on their enemies' rudders and smokestacks to try and cripple them and then ram or board them. Alternatively spar torpedoes could be used, as they wouldn't need as much speed or as good an angle to damage enemy hulls. Once self-propelled torpedoes come in they'd no doubt be rapidly adopted, perhaps even becoming the main naval armament. This in turn might spur the earlier development of torpedo nets and torpedo belts, although I'm not sure how successful these would be.
Let's assume that, instead, naval armour manages to stay ahead for at least another couple of decades or so. Let's also assume that there are a few more naval battles than IOTL, giving admirals a chance to try out new tactics. How would naval tactics develop? The obvious would be greater reliance on ramming, which was advocated IOTL, although in the few naval battles of this period it proved difficult to get a good ramming attack in. Possibly ships would try and focus their fire on their enemies' rudders and smokestacks to try and cripple them and then ram or board them. Alternatively spar torpedoes could be used, as they wouldn't need as much speed or as good an angle to damage enemy hulls. Once self-propelled torpedoes come in they'd no doubt be rapidly adopted, perhaps even becoming the main naval armament. This in turn might spur the earlier development of torpedo nets and torpedo belts, although I'm not sure how successful these would be.