WesWorld

I have attempted a second cruiser project, and find that SS has handed me a design failure. I'm not worried about that because that's how one learns. I've appended it below and I am looking for some theory on sim mechanics to address

What drove the failure - lack of overall hull size, too much freeboard, or something else?

What parameters impact relative hull strength?

What parameters impact survivability?

Thanks in advance for all answers/comments/suggestions.

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Project 11, TBD Light Cruiser laid down 1938
DESIGN FAILURE: Overall load weight too much for hull

Displacement:
7,966 t light; 8,313 t standard; 8,969 t normal; 9,493 t full load

Dimensions: Length overall / water x beam x draught
577.09 ft / 570.87 ft x 59.06 ft x 18.04 ft (normal load)
175.90 m / 174.00 m x 18.00 m x 5.50 m

Armament:
9 - 5.98" / 152 mm guns (3x3 guns), 107.15lbs / 48.60kg shells, 1930 Model
Breech loading guns in turrets (on barbettes)
on centreline ends, majority forward, all raised mounts - superfiring
8 - 4.72" / 120 mm guns (4x2 guns), 52.72lbs / 23.92kg shells, 1934 Model
Dual purpose guns in deck mounts with hoists
on side, all amidships, all raised mounts - superfiring
8 - 1.57" / 40.0 mm guns (4x2 guns), 1.95lbs / 0.89kg shells, 1936 Model
Anti-aircraft guns in deck mounts
on side, evenly spread, 3 raised mounts
12 - 0.79" / 20.0 mm guns (6x2 guns), 0.24lbs / 0.11kg shells, 1930 Model
Breech loading guns in deck mounts
on side, evenly spread, all raised mounts
Weight of broadside 1,405 lbs / 637 kg
Shells per gun, main battery: 200
6 - 20.9" / 530 mm above water torpedoes

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 3.94" / 100 mm 433.07 ft / 132.00 m 26.25 ft / 8.00 m
Ends: Unarmoured
Main Belt covers 117 % of normal length

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 3.94" / 100 mm 1.97" / 50 mm 3.94" / 100 mm
2nd: 0.98" / 25 mm 0.39" / 10 mm -
3rd: 0.79" / 20 mm - -

- Armour deck: 1.97" / 50 mm, Conning tower: 3.94" / 100 mm

Machinery:
Oil fired boilers, steam turbines,
Geared drive, 2 shafts, 100,598 shp / 75,046 Kw = 35.00 kts
Range 6,000nm at 15.00 kts
Bunker at max displacement = 1,180 tons

Complement:
460 - 599

Cost:
£4.576 million / $18.306 million

Distribution of weights at normal displacement:
Armament: 176 tons, 2.0 %
Armour: 3,036 tons, 33.9 %
- Belts: 1,826 tons, 20.4 %
- Torpedo bulkhead: 0 tons, 0.0 %
- Armament: 310 tons, 3.5 %
- Armour Deck: 864 tons, 9.6 %
- Conning Tower: 37 tons, 0.4 %
Machinery: 2,755 tons, 30.7 %
Hull, fittings & equipment: 1,950 tons, 21.7 %
Fuel, ammunition & stores: 1,003 tons, 11.2 %
Miscellaneous weights: 50 tons, 0.6 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
4,557 lbs / 2,067 Kg = 42.5 x 6.0 " / 152 mm shells or 1.1 torpedoes
Stability (Unstable if below 1.00): 1.23
Metacentric height 3.3 ft / 1.0 m
Roll period: 13.6 seconds
Steadiness - As gun platform (Average = 50 %): 52 %
- Recoil effect (Restricted arc if above 1.00): 0.45
Seaboat quality (Average = 1.00): 1.04

Hull form characteristics:
Hull has a flush deck
and transom stern
Block coefficient: 0.516
Length to Beam Ratio: 9.67 : 1
'Natural speed' for length: 27.29 kts
Power going to wave formation at top speed: 62 %
Trim (Max stability = 0, Max steadiness = 100): 50
Bow angle (Positive = bow angles forward): 9.00 degrees
Stern overhang: 2.46 ft / 0.75 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 23.75 ft / 7.24 m
- Forecastle (17 %): 20.64 ft / 6.29 m
- Mid (50 %): 20.64 ft / 6.29 m
- Quarterdeck (19 %): 20.64 ft / 6.29 m
- Stern: 30.97 ft / 9.44 m
- Average freeboard: 21.83 ft / 6.65 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 116.1 %
- Above water (accommodation/working, high = better): 178.1 %
Waterplane Area: 23,712 Square feet or 2,203 Square metres
Displacement factor (Displacement / loading): 90 %
Structure weight / hull surface area: 51 lbs/sq ft or 247 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.45
- Longitudinal: 0.84
- Overall: 0.48
Hull space for machinery, storage, compartmentation is cramped
Room for accommodation and workspaces is excellent

Main armament based on Bofors 152mm 55cal M1930
Secondary armament based on Bofors 120mm 50cal M1934/36
Tertiary AA armament 40mm 60cal Bofors M1936 and 20mm Oerlikon
Miscellaneous Weight - 50 tons reserved for A/C, handling equipment, RDF

Likely the speed. Above 32 knots, speed "costs" more than anything else you can add.

Think of Hull Strength as a somewhat odd sort of "budget" for a given displacement. Let's say that you have the blank chassis of a car, and want to build something that's drivable on it. You can add a body, an engine, drive train, etc. At some point, the weight you add will start over-stressing the frame you're adding it to. Alternately, you could have a fantastic chassis, add a tiny little engine and seat, and have a frame that really is overkill for your car. That's one of the ways to look at hull strength: it's your budget to know when you've overloaded your hull with too much stuff.

Speed is part of the quirks of Springsharp. You'll note that most of Wesworld's destroyers run about 33 to 35 knots, and that's mostly because Springsharp is not designed to calculate lighter destroyer machinery nor the semi-planing hull forms many of them featured. There are any number of other quirks where you occasionally need to "trick" Springsharp into doing what you need, rather than what it thinks you need. (Carriers, submarines, cargo ships, sailing ships, and such are all examples.)

Looking at your posted design, I'm guessing that it's almost certainly the speed which drove the HS of the design down. Try it with a 32 knot speed and I bet it'll come pretty close to working.

One of the ways to increase hull strength is to redesign and add displacement. This basically can be interpreted as buying a bigger, more expensive chassis to stack your stuff on when you realize the chassis of Mini Cooper isn't going to handle the engine and body of a big heavy BMW (as an example).

Quoted

Originally posted by Brockpaine
Likely the speed. Above 32 knots, speed "costs" more than anything else you can add.

Speed is part of the quirks of Springsharp. You'll note that most of Wesworld's destroyers run about 33 to 35 knots, and that's mostly because Springsharp is not designed to calculate lighter destroyer machinery nor the semi-planing hull forms many of them featured. There are any number of other quirks where you occasionally need to "trick" Springsharp into doing what you need, rather than what it thinks you need. (Carriers, submarines, cargo ships, sailing ships, and such are all examples.)

Looking at your posted design, I'm guessing that it's almost certainly the speed which drove the HS of the design down. Try it with a 32 knot speed and I bet it'll come pretty close to working.

Brock, thank you for the excellent advice. As an aid to my learning process, I've tried to keep track of the design changes in the notes. Of course, one of the first errors I found was the height of the armor belt. Eight *meters* is much more than eight *feet*. Fixing that had the most significant impact.

---------
Project 11, TBD Light Cruiser laid down 1938

Displacement:
7,966 t light; 8,313 t standard; 8,969 t normal; 9,493 t full load

Dimensions: Length overall / water x beam x draught
577.09 ft / 570.87 ft x 59.06 ft x 18.04 ft (normal load)
175.90 m / 174.00 m x 18.00 m x 5.50 m

Armament:
9 - 5.98" / 152 mm guns (3x3 guns), 107.15lbs / 48.60kg shells, 1930 Model
Breech loading guns in turrets (on barbettes)
on centreline ends, majority forward, all raised mounts - superfiring
8 - 4.72" / 120 mm guns (4x2 guns), 52.72lbs / 23.91kg shells, 1934 Model
Dual purpose guns in deck mounts with hoists
on side, all amidships, all raised mounts - superfiring
8 - 1.57" / 40.0 mm guns (4x2 guns), 1.95lbs / 0.88kg shells, 1936 Model
Anti-aircraft guns in deck mounts
on side, evenly spread, 3 raised mounts
12 - 0.79" / 20.0 mm guns (6x2 guns), 0.24lbs / 0.11kg shells, 1930 Model
Breech loading guns in deck mounts
on side, evenly spread, all raised mounts
Weight of broadside 1,405 lbs / 637 kg
Shells per gun, main battery: 200
6 - 20.9" / 530 mm above water torpedoes

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 3.94" / 100 mm 328.08 ft / 100.00 m 11.48 ft / 3.50 m
Ends: Unarmoured
Main Belt covers 88 % of normal length

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 3.94" / 100 mm 1.97" / 50 mm 3.94" / 100 mm
2nd: 0.98" / 25 mm 0.39" / 10 mm -
3rd: 0.79" / 20 mm - -

- Armour deck: 1.97" / 50 mm, Conning tower: 3.94" / 100 mm

Machinery:
Oil fired boilers, steam turbines,
Geared drive, 2 shafts, 70,358 shp / 52,487 Kw = 32.00 kts
Range 6,000nm at 15.00 kts
Bunker at max displacement = 1,180 tons

Complement:
460 - 599

Cost:
£3.923 million / $15.692 million

Distribution of weights at normal displacement:
Armament: 176 tons, 2.0 %
Armour: 1,843 tons, 20.5 %
- Belts: 632 tons, 7.0 %
- Torpedo bulkhead: 0 tons, 0.0 %
- Armament: 310 tons, 3.5 %
- Armour Deck: 864 tons, 9.6 %
- Conning Tower: 37 tons, 0.4 %
Machinery: 1,927 tons, 21.5 %
Hull, fittings & equipment: 3,971 tons, 44.3 %
Fuel, ammunition & stores: 1,003 tons, 11.2 %
Miscellaneous weights: 50 tons, 0.6 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
13,899 lbs / 6,305 Kg = 129.7 x 6.0 " / 152 mm shells or 1.8 torpedoes
Stability (Unstable if below 1.00): 1.10
Metacentric height 2.7 ft / 0.8 m
Roll period: 15.0 seconds
Steadiness - As gun platform (Average = 50 %): 62 %
- Recoil effect (Restricted arc if above 1.00): 0.55
Seaboat quality (Average = 1.00): 1.24

Hull form characteristics:
Hull has a flush deck
and transom stern
Block coefficient: 0.516
Length to Beam Ratio: 9.67 : 1
'Natural speed' for length: 27.29 kts
Power going to wave formation at top speed: 58 %
Trim (Max stability = 0, Max steadiness = 100): 50
Bow angle (Positive = bow angles forward): 9.00 degrees
Stern overhang: 2.46 ft / 0.75 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 23.75 ft / 7.24 m
- Forecastle (17 %): 20.64 ft / 6.29 m
- Mid (50 %): 20.64 ft / 6.29 m
- Quarterdeck (19 %): 20.64 ft / 6.29 m
- Stern: 30.97 ft / 9.44 m
- Average freeboard: 21.83 ft / 6.65 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 86.6 %
- Above water (accommodation/working, high = better): 178.1 %
Waterplane Area: 23,712 Square feet or 2,203 Square metres
Displacement factor (Displacement / loading): 125 %
Structure weight / hull surface area: 103 lbs/sq ft or 504 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.94
- Longitudinal: 1.79
- Overall: 1.01
Hull space for machinery, storage, compartmentation is adequate
Room for accommodation and workspaces is excellent
Good seaboat, rides out heavy weather easily

Main armament based on Bofors 152mm 55cal M1930
Secondary armament based on Bofors 120mm 50cal M1934/36
Tertiary AA armament 40mm 60cal Bofors M1936 and 20mm Oerlikon
Miscellaneous Weight - 50 tons reserved for A/C, handling equipment, RDF

Rev B Adjustments

Corrected belt height from 8m to 4m, removed design failure
Reduced speed to 32 knots - Machinery savings 828 tons, increased overall hull strength to 0.94
Smaller machinery plant reduced minimum belt requirements from 130m to 98.9 m; reduced belt to 100m, increased overall hull strength to 0.98
Reduced armor belt height to 3.5m - increased overall hull strength to 1.01
Net survivability increased to 1.8 torpedoes - improvement over Project 10 RevC

Quoted

Originally posted by BruceDuncan
Brock, thank you for the excellent advice. As an aid to my learning process, I've tried to keep track of the design changes in the notes. Of course, one of the first errors I found was the height of the armor belt. Eight *meters* is much more than eight *feet*. Fixing that had the most significant impact.

Whoa, yeah. That'd do it - and I missed that, too.

Quoted

Originally posted by Brockpaine

Quoted

Originally posted by BruceDuncan
Brock, thank you for the excellent advice. As an aid to my learning process, I've tried to keep track of the design changes in the notes. Of course, one of the first errors I found was the height of the armor belt. Eight *meters* is much more than eight *feet*. Fixing that had the most significant impact.

Whoa, yeah. That'd do it - and I missed that, too.

It came to me while I was in the shower <sound of palm striking head>.

But more seriously, is there a rule of thumb for the height of an armor belt. Most reference works seem to record only the length and thickness.

Quoted

Originally posted by BruceDuncan

Quoted

Originally posted by Brockpaine

Quoted

Originally posted by BruceDuncan
Brock, thank you for the excellent advice. As an aid to my learning process, I've tried to keep track of the design changes in the notes. Of course, one of the first errors I found was the height of the armor belt. Eight *meters* is much more than eight *feet*. Fixing that had the most significant impact.

Whoa, yeah. That'd do it - and I missed that, too.

It came to me while I was in the shower <sound of palm striking head>.

But more seriously, is there a rule of thumb for the height of an armor belt. Most reference works seem to record only the length and thickness.

To start with, generally take what SS gives you for height. Then you can increase it if you have spare strength and don't want to shrink the ship.

Something else you could try is setting up your guns. You've got all your 152s as "raised" as well as all your 120s (weird combo BTW. IMHO, why not go for 140mm DP all around). Having all these weapons 'raised' adds top weight, which hurts stability and steadiness and cuts into your hull strength. Also, I'd add hoist/below deck armor to your 120s as this will be greatly appreciated by those in the magazines and the rest of the ship if you're hit.

As to belt height I shoot for at least 1 full deck, so it depends on your deck height. Springsharp also assumes that the belt is split evenly above and below water, so a 12' belt will get you plenty of protection underwater, by only 6' above.

Quoted

Originally posted by Sachmle
Something else you could try is setting up your guns. You've got all your 152s as "raised" as well as all your 120s (weird combo BTW. IMHO, why not go for 140mm DP all around). Having all these weapons 'raised' adds top weight, which hurts stability and steadiness and cuts into your hull strength. Also, I'd add hoist/below deck armor to your 120s as this will be greatly appreciated by those in the magazines and the rest of the ship if you're hit.

As to belt height I shoot for at least 1 full deck, so it depends on your deck height. Springsharp also assumes that the belt is split evenly above and below water, so a 12' belt will get you plenty of protection underwater, by only 6' above.

Thank you for the pointer on the raised mounts; I will have to investigate the impact of correcting that oversight; thanks also for the rule of thumb on belt heights - I will file that away.

As the ordnance choice, I was looking to sim historical ordnance of the period, as cited in the notes. The Wesworld tech timeline diverges from the OTL (something else I need to investigate) but historically a 140mm DP was not available in 1938, hence the choice of a 152mm main and 120mm DP secondary. As to weirdness, it's no more strange than the 6in main and 5in secondary of a Brooklyn - designed in the same time frame.

A bit of a gravedig here... sorry, but I felt compelled to post as part of my learning curve.

Quoted

Freeboard (% = measuring location as a percentage of overall length):
- Stem: 23.75 ft / 7.24 m
- Forecastle (17 %): 20.64 ft / 6.29 m
- Mid (50 %): 20.64 ft / 6.29 m
- Quarterdeck (19 %): 20.64 ft / 6.29 m
- Stern: 30.97 ft / 9.44 m
- Average freeboard: 21.83 ft / 6.65 m
Ship tends to be wet forward

I'd flip those two values around (as it is, the 'back' is taller than the 'front'). I believe that would improve steadiness and seaboat ratings, and keep the her from being wet forward.

Quoted

8 - 1.57" / 40.0 mm guns (4x2 guns), 1.95lbs / 0.88kg shells, 1936 Model
Anti-aircraft guns in deck mounts
on side, evenly spread, 3 raised mounts

Four mounts of which three are raised. A typo?

Quoted

Originally posted by Eidolon
A bit of a gravedig here... sorry, but I felt compelled to post as part of my learning curve.

Quoted

Freeboard (% = measuring location as a percentage of overall length):
- Stem: 23.75 ft / 7.24 m
- Forecastle (17 %): 20.64 ft / 6.29 m
- Mid (50 %): 20.64 ft / 6.29 m
- Quarterdeck (19 %): 20.64 ft / 6.29 m
- Stern: 30.97 ft / 9.44 m
- Average freeboard: 21.83 ft / 6.65 m
Ship tends to be wet forward

I'd flip those two values around (as it is, the 'back' is taller than the 'front'). I believe that would improve steadiness and seaboat ratings, and keep the her from being wet forward.

Quoted

8 - 1.57" / 40.0 mm guns (4x2 guns), 1.95lbs / 0.88kg shells, 1936 Model
Anti-aircraft guns in deck mounts
on side, evenly spread, 3 raised mounts

Four mounts of which three are raised. A typo?

Yes indeed, several typos along the way - so bad I abandoned the entire concept. But I still find tracking the changes from revision to revision useful, as you'll see in the Project 39 and Project 40 schemes I've done.