Reading this very interesting USNI article, I was thinking in something similar to this for a new damage point calculation based in the named "Navy’s Survivability Instruction 9070.1A are taken into account in designing U.S. Navy surface ships to three survivability standards", affecting mostly auxiliary and low-value ships (analogy can be applied to other navies/ships), as for me many civilian/merchant ships (also in other time periods) receive too many damage/hit points:

 

Level 3: CVN, CG, DDG (and decommisioned BB, CV, CVN, CG/CGN, DD/DDG, FF/FFG?).

I think this Level 3 can keep 100% hit points derived from her standard displacement, as usual (previously to construction type and build year considerations: aluminium, wood, etc.).

 

Level "2.5": LPD-17 San Antonio-class.

I think this Level "2.5" can keep 75% hit points, as usual (previously to construction type considerations: aluminium, wood, etc.), as has a dock well, but is apparently stronger than other LPDs.

 

Level 2: Some underway replenishment ships and rest of amphibious (LHD-1 Wasp-class, LHA-6 America-class, LSD-41 Whidbey Island-class and LSD-49 Harper's Ferry-class).

I think this Level 2 can keep 75% hit points, as usual (previously to construction type and build year considerations: aluminium, wood, etc.), except those classes with aft dock well, probably reduced to 62,5% hit points.

 

Level 1: LCS, others underway replenishment ships, mine warfare ships, patrol crafts and support ships/ancilliaries.

I think this Level 1 should receive only 50% hit points of those derived from her standard displacement (previously to construction type and build year considerations: aluminium, wood, etc.).

 

Level "0": navy vessels build to mercantile standards.

I think this Level "0" should receive only 25% hit points of those derived from her standard displacement (previously to construction type and build year considerations: aluminium, wood, etc.).

 

Level "-1": pure civilian/merchant ships.

I think this Level "-1" should receive only 12.5% hit points of those derived from her standard displacement (previously to construction type and build year considerations: aluminium, wood, etc.).

 

Source:

http://news.usni.org/2016/02/04/essay-when-in-comes-to-ship-survivability-prayer-isnt-enough

It would make for an interesting experiment, if anyone wants to try it in their own DB dabbling.

One of my motivations was to do the system capable to sunk merchant ships with surfaced submarine guns (I need to retrieve historical data on it, perhaps this summer. i.e. how many gun shell were used by surfaced submarines in WWI and WWII to sink a merchant, and perhaps Q-ships. Also I want to revise battles of auxiliry cruisers, as that between Carmania and Cap Trafalgar).

Observe Level 3-100% and Level 2-75% coincides with the damage of ordinary warships the first and amphibious the second.

 

As consequence, not major alterations in true warships combat.

I think I would need to see this in pretty graphs . The combination of modifiers sounds scary and extreme when I read it in words only.