Could you elaborate on this please?
On most technical/advanced wreck courses, you will learn the same basic protocols as per full cave. Drills like lost line, lost buddy, entanglement etc. You will learn team diving, roles and responsibilities. You will learn guideline deployment and retrieval. You will practice specific drills, contingencies and skills without visibility (black mask) etc.
Wrecks tend to be considerably more confined/restricted than most caves (
at least at entry-cave experience levels). There is more risk of structural collapse in many wrecks, silt is almost inevitable, there are many sharp objects (
risk to guidelines), there can be multiple entanglement hazards (
beyond your own guideline), such as electrical wiring and other floating debris. Areas such as engine rooms can be very disorientating and restricted - full of pipes/equipment etc with no 'clean surfaces' - making contingency searches very difficult. Protocols for staging tanks / deco aren't as clear-cut and require a decision-making process and some careful planning/consideration. Ascent from the overhead-to-surface can be more complex and have other (
open water) environmental conditions - these can sometimes conflict with priorities for the actual overhead phase. There are issues with currents, tides etc - these can differ from simple 'flow' planning in a cave. Wrecks can contain hazardous materials, including liquid pollutants. There can also be hazardous marine life in/around wrecks (
i.e. stonefish/scorpionfish in the tropics).
Wreck penetration does not tend usually to be as lengthy (
in distance from open-water/ascent) as cave diving, but there is greater risk of entanglement/entrapment. Many wrecks offer multiple entrance/egress points - often favoring traverse dive approaches. Or, at least, identification and planning for contingency exits. There may also be issues in running guidelines from outside the wreck, should the wreck site be shared with other/recreational divers etc...
So.... even if the core approach is the same.... there are a hundred 'little differences' that could trip you up. Avoiding those trip ups...and the consequences they sometimes bring...is why we train.