Gemini Experimental Sub, Denmark Submarine laid down 1936

Displacement:

550 t light; 563 t standard; 600 t normal; 631 t full load

Dimensions: Length overall / water x beam x draught

160.00 ft / 160.00 ft x 20.00 ft (Bulges 24.00 ft) x 12.00 ft (normal load)

48.77 m / 48.77 m x 6.10 m (Bulges 7.32 m) x 3.66 m

Armament:

2 - 0.79" / 20.0 mm guns (1x2 guns), 0.24lbs / 0.11kg shells, 1936 Model

Anti-aircraft guns in deck mount

on centreline amidships, all raised guns - superfiring

2 - 0.51" / 13.0 mm guns in single mounts, 0.07lbs / 0.03kg shells, 1936 Model

Machine guns in deck mounts

on side, all amidships, all raised mounts - superfiring

Weight of broadside 1 lbs / 0 kg

Shells per gun, main battery: 1,000

6 - 17.7" / 450 mm submerged torpedo tubes

Armour:

- Conning tower: 0.59" / 15 mm

Machinery:

Diesel Internal combustion generators plus batteries,

Electric motors, 2 shafts, 1,612 shp / 1,203 Kw = 16.00 kts

Range 4,000nm at 10.00 kts

Bunker at max displacement = 68 tons

Complement:

59 - 78

Cost:

£0.135 million / $0.541 million

Distribution of weights at normal displacement:

Armament: 0 tons, 0.0 %

Armour: 1 tons, 0.2 %

- Belts: 0 tons, 0.0 %

- Torpedo bulkhead: 0 tons, 0.0 %

- Armament: 0 tons, 0.0 %

- Armour Deck: 0 tons, 0.0 %

- Conning Tower: 1 tons, 0.2 %

Machinery: 45 tons, 7.5 %

Hull, fittings & equipment: 354 tons, 58.9 %

Fuel, ammunition & stores: 50 tons, 8.4 %

Miscellaneous weights: 150 tons, 25.0 %

Overall survivability and seakeeping ability:

Survivability (Non-critical penetrating hits needed to sink ship):

223 lbs / 101 Kg = 915.6 x 0.8 " / 20 mm shells or 0.3 torpedoes

Stability (Unstable if below 1.00): 1.10

Metacentric height 0.5 ft / 0.2 m

Roll period: 13.8 seconds

Steadiness - As gun platform (Average = 50 %): 0 %

- Recoil effect (Restricted arc if above 1.00): 0.00

Seaboat quality (Average = 1.00): 0.00

Hull form characteristics:

Hull has a flush deck

Block coefficient: 0.456

Length to Beam Ratio: 6.67 : 1

'Natural speed' for length: 12.65 kts

Power going to wave formation at top speed: 57 %

Trim (Max stability = 0, Max steadiness = 100): 50

Bow angle (Positive = bow angles forward): 1.00 degrees

Stern overhang: 0.00 ft / 0.00 m

Freeboard (% = measuring location as a percentage of overall length):

- Stem: 0.00 ft / 0.00 m

- Forecastle (20 %): 0.00 ft / 0.00 m

- Mid (50 %): 0.00 ft / 0.00 m

- Quarterdeck (20 %): 0.00 ft / 0.00 m

- Stern: 0.00 ft / 0.00 m

- Average freeboard: 0.00 ft / 0.00 m

Ship tends to be wet forward

Ship space, strength and comments:

Space - Hull below water (magazines/engines, low = better): 118.6 %

- Above water (accommodation/working, high = better): 0.0 %

Waterplane Area: 2,051 Square feet or 191 Square metres

Displacement factor (Displacement / loading): 248 %

Structure weight / hull surface area: 112 lbs/sq ft or 548 Kg/sq metre

Hull strength (Relative):

- Cross-sectional: 3.86

- Longitudinal: 2.82

- Overall: 3.05

Hull space for machinery, storage, compartmentation is cramped

Room for accommodation and workspaces is extremely poor

Ship has quick, lively roll, not a steady gun platform

Caution: Lacks seaworthiness - very limited seakeeping ability

Diving depths

-Normal = 305 ft

-Emergency = 488 ft

-Crush = 762 ft

Designed to be able to make better use of the shallow waters of the Kattegat, Baltic and North Sea, the Gemini has a twin pressure hull layout; 2 tubes side by side, with connecting hatches between the two, allowing alternate routes fore and aft.

(Drawing to follow!)

Displacement:

550 t light; 563 t standard; 600 t normal; 631 t full load

Dimensions: Length overall / water x beam x draught

160.00 ft / 160.00 ft x 20.00 ft (Bulges 24.00 ft) x 12.00 ft (normal load)

48.77 m / 48.77 m x 6.10 m (Bulges 7.32 m) x 3.66 m

Armament:

2 - 0.79" / 20.0 mm guns (1x2 guns), 0.24lbs / 0.11kg shells, 1936 Model

Anti-aircraft guns in deck mount

on centreline amidships, all raised guns - superfiring

2 - 0.51" / 13.0 mm guns in single mounts, 0.07lbs / 0.03kg shells, 1936 Model

Machine guns in deck mounts

on side, all amidships, all raised mounts - superfiring

Weight of broadside 1 lbs / 0 kg

Shells per gun, main battery: 1,000

6 - 17.7" / 450 mm submerged torpedo tubes

Armour:

- Conning tower: 0.59" / 15 mm

Machinery:

Diesel Internal combustion generators plus batteries,

Electric motors, 2 shafts, 1,612 shp / 1,203 Kw = 16.00 kts

Range 4,000nm at 10.00 kts

Bunker at max displacement = 68 tons

Complement:

59 - 78

Cost:

£0.135 million / $0.541 million

Distribution of weights at normal displacement:

Armament: 0 tons, 0.0 %

Armour: 1 tons, 0.2 %

- Belts: 0 tons, 0.0 %

- Torpedo bulkhead: 0 tons, 0.0 %

- Armament: 0 tons, 0.0 %

- Armour Deck: 0 tons, 0.0 %

- Conning Tower: 1 tons, 0.2 %

Machinery: 45 tons, 7.5 %

Hull, fittings & equipment: 354 tons, 58.9 %

Fuel, ammunition & stores: 50 tons, 8.4 %

Miscellaneous weights: 150 tons, 25.0 %

Overall survivability and seakeeping ability:

Survivability (Non-critical penetrating hits needed to sink ship):

223 lbs / 101 Kg = 915.6 x 0.8 " / 20 mm shells or 0.3 torpedoes

Stability (Unstable if below 1.00): 1.10

Metacentric height 0.5 ft / 0.2 m

Roll period: 13.8 seconds

Steadiness - As gun platform (Average = 50 %): 0 %

- Recoil effect (Restricted arc if above 1.00): 0.00

Seaboat quality (Average = 1.00): 0.00

Hull form characteristics:

Hull has a flush deck

Block coefficient: 0.456

Length to Beam Ratio: 6.67 : 1

'Natural speed' for length: 12.65 kts

Power going to wave formation at top speed: 57 %

Trim (Max stability = 0, Max steadiness = 100): 50

Bow angle (Positive = bow angles forward): 1.00 degrees

Stern overhang: 0.00 ft / 0.00 m

Freeboard (% = measuring location as a percentage of overall length):

- Stem: 0.00 ft / 0.00 m

- Forecastle (20 %): 0.00 ft / 0.00 m

- Mid (50 %): 0.00 ft / 0.00 m

- Quarterdeck (20 %): 0.00 ft / 0.00 m

- Stern: 0.00 ft / 0.00 m

- Average freeboard: 0.00 ft / 0.00 m

Ship tends to be wet forward

Ship space, strength and comments:

Space - Hull below water (magazines/engines, low = better): 118.6 %

- Above water (accommodation/working, high = better): 0.0 %

Waterplane Area: 2,051 Square feet or 191 Square metres

Displacement factor (Displacement / loading): 248 %

Structure weight / hull surface area: 112 lbs/sq ft or 548 Kg/sq metre

Hull strength (Relative):

- Cross-sectional: 3.86

- Longitudinal: 2.82

- Overall: 3.05

Hull space for machinery, storage, compartmentation is cramped

Room for accommodation and workspaces is extremely poor

Ship has quick, lively roll, not a steady gun platform

Caution: Lacks seaworthiness - very limited seakeeping ability

Diving depths

-Normal = 305 ft

-Emergency = 488 ft

-Crush = 762 ft

Designed to be able to make better use of the shallow waters of the Kattegat, Baltic and North Sea, the Gemini has a twin pressure hull layout; 2 tubes side by side, with connecting hatches between the two, allowing alternate routes fore and aft.

(Drawing to follow!)

I can't see any other obvious benefits myself.

Does each tube have two forward and one aft torpedo tube?

## Quoted

Originally posted by Hood

I can see it would aid survivabilty but what happens if one side floods and the other stays dry? You won't surface again for sure. I don't know why but in my mind for five years time is some kind of 'Oscar' SSGN sized sub in WW. Is that where Denmark will ultimately end up?

I doubt if any sub would come back up with half of it flooded, so it's kind of a moot point....

The ballast tank arrangement is one each side plus two smaller ones above and below the centerline...

I don't know about nuclear power yet........

## Quoted

I can't see any other obvious benefits myself.

Shorter hull (160ft versus 320ft), built on smaller slips, but with the advantage of greater internal volume.

## Quoted

Does each tube have two forward and one aft torpedo tube?

Yes

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