WesWorld

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!)

Its an interesting concept, but the stacked arrangement is most likely better, offering less drag for one.

I wanted to avoid a tall hull, hence the side by side arrangement. The drag would only be an issue on the surface, once your under there shouldn't be any difference.

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 can't see any other obvious benefits myself.

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

Quoted

I don't know why but in my mind for five years time is some kind of 'Oscar' SSGN sized sub in WW

Well, with the Sen-Toku class, Japan will be well on the way to that size.

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