We have aircraft, tanks, why not ships? This also has the advantage of a longer period to look at. So, here are some...
Napoleonic War:
Nuestra Senora de la Santisima Trinidad- the ridiculous four-decker 140-gun Spanish ship of the line (aka El Ponderoso), which was so slow and unwieldy that the British neglected to take possession the first time it surrendered, and scuttled it the second time!
Ironclad period:
Popoffkas. Circular battleships. Why? Just, why?
HMS Captain- Masts and turrets don't mix. Pity they had to lose 480 sailors to find that one out...
Defence-class ironclads. OK, so you build the Warrior, then you build a class of ships that are cheaper but worse in every way, and too slow to catch the French ship they're built to defend against.
CSS Hunley- sinks 3 times, sinks 1 enemy ship. Kills more Confederate sailors than Union ones.
Pre-dreadnoughts:
Victoria-class battleships. Ludicrously overgunned- the recoil buckled the deckplates, and the barrel actually drooped!
Late US pre-dreadnoughts: obsolete on commissioning, especially the Mississippi-class.
I'll leave WW1 and WW2 surface combatants to those who know more about such things, with a dishonorable mention for the Hyuga/Ise conversions (neither fish nor fowl) and the British "large light cruisers", especially Furious- 2 18-inch guns and no armour!
Interwar cruiser-sub ideas turned out to be wrong, but perhaps the worst were the British ones. M2 sank, killing its crew, while the K-class were a bad idea from the start- who builds an oil-fired steam-powered submarine? Seas were known to eneter the funnel and put out boiler fires- oh, and
this happened.
Cold War:
Kiev-class CV. Same problem as the Ise. There's a reason why the Indians are taking off the ridiculous levels of missile armament.
US nuclear-powered surface combatants- no real reason for these, which is why they don't build them any more.
Type 21 frigate. A cheap private design, with an aluminium superstructure. Bad idea. Before they got Exocet, they were effectively armed only for self-defence.