WesWorld

It's just dawned on me that Nordmark has a disproportionate amount of sea ice but no icebreakers. A quick forum search shows that past ships have had significant full-power endurance and significant hull armour to reflect thickened shell plating, and that some - but not all - have excess hull strength. Does anyone know what rules of thumb we've been using to design them?

I've built mine with 40-50mm belts on the sides going the full depth of the draft, and 90-100mm forward, concentrated at the stem. Range is massive, to reflect the requirement of going full power for long periods of time. A TDS helps if the hull gets breached or partially crushed. Overall hull strength is 1.50

mine are built to a very strenuous requirement, keeping the Northern Sea Route open as long as possible to support the economic development of the Far North. You may not need quite so much.

For Chile I've done roughly the same sort of things as AdmK, but on smaller and less specialized ships; but Chile doesn't have a high requirement for icebreaking ships. I've got a converted sealing vessel as an antarctic expeditionary ship (40mm TDS and assigned weight), and a converted Canadian-built icecutter bought from the Merchant Marine. The icecutter's a bit of an odd duck design-wise.

Cheers: I'm looking into probably five smallish ships (about 2k-4k tons) to keep one in South Georgia and one off Greenland, mostly for maintaining access to odd little garrisons and rescuing whalecatchers which have gone and got themselves frozen in.

*shrugs* I can help, if you'd like.

Argentina is going down this route too. A little 4k design is suitable for most things without being too expensive.

This is what I'm looking at. Nothing terribly large or expensive, but good for about two weeks on station 1,000 miles from base.

AGB 40, Nordmark Icebreaker laid down 1940

Displacement:
2,572 t light; 2,637 t standard; 3,152 t normal; 3,564 t full load

Dimensions: Length overall / water x beam x draught
284.41 ft / 280.00 ft x 54.00 ft x 12.00 ft (normal load)
86.69 m / 85.34 m x 16.46 m x 3.66 m

Armament:
1 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1940 Model
Dual purpose gun in a deck mount with hoist
on centreline forward
2 - 1.46" / 37.0 mm guns (1x2 guns), 1.55lbs / 0.70kg shells, 1940 Model
Anti-aircraft guns in deck mount
on centreline aft
Weight of broadside 17 lbs / 8 kg
Shells per gun, main battery: 200

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 2.00" / 51 mm 190.00 ft / 57.91 m 25.00 ft / 7.62 m
Ends: 3.00" / 76 mm 90.00 ft / 27.43 m 25.00 ft / 7.62 m
Main Belt covers 104 % of normal length

- Torpedo Bulkhead:
1.50" / 38 mm 150.00 ft / 45.72 m 12.00 ft / 3.66 m

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1.00" / 25 mm 0.50" / 13 mm -
2nd: 0.50" / 13 mm 0.25" / 6 mm -

Machinery:
Diesel Internal combustion generators,
Electric motors, 2 shafts, 3,000 shp / 2,238 Kw = 14.80 kts
Range 8,071nm at 14.80 kts
Bunker at max displacement = 927 tons

Complement:
209 - 273

Cost:
£0.618 million / $2.472 million

Distribution of weights at normal displacement:
Armament: 2 tons, 0.1 %
Armour: 773 tons, 24.5 %
- Belts: 671 tons, 21.3 %
- Torpedo bulkhead: 100 tons, 3.2 %
- Armament: 2 tons, 0.1 %
- Armour Deck: 0 tons, 0.0 %
- Conning Tower: 0 tons, 0.0 %
Machinery: 80 tons, 2.5 %
Hull, fittings & equipment: 1,382 tons, 43.8 %
Fuel, ammunition & stores: 580 tons, 18.4 %
Miscellaneous weights: 335 tons, 10.6 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
18,446 lbs / 8,367 Kg = 1,366.4 x 3.0 " / 76 mm shells or 8.5 torpedoes
Stability (Unstable if below 1.00): 1.16
Metacentric height 2.6 ft / 0.8 m
Roll period: 14.1 seconds
Steadiness - As gun platform (Average = 50 %): 100 %
- Recoil effect (Restricted arc if above 1.00): 0.01
Seaboat quality (Average = 1.00): 2.00

Hull form characteristics:
Hull has rise forward of midbreak
Block coefficient: 0.608
Length to Beam Ratio: 5.19 : 1
'Natural speed' for length: 16.73 kts
Power going to wave formation at top speed: 45 %
Trim (Max stability = 0, Max steadiness = 100): 60
Bow angle (Positive = bow angles forward): 10.00 degrees
Stern overhang: 0.00 ft / 0.00 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 25.00 ft / 7.62 m
- Forecastle (35 %): 22.00 ft / 6.71 m
- Mid (40 %): 22.00 ft / 6.71 m (13.00 ft / 3.96 m aft of break)
- Quarterdeck (15 %): 13.00 ft / 3.96 m
- Stern: 13.00 ft / 3.96 m
- Average freeboard: 17.02 ft / 5.19 m

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 35.1 %
- Above water (accommodation/working, high = better): 141.1 %
Waterplane Area: 11,141 Square feet or 1,035 Square metres
Displacement factor (Displacement / loading): 245 %
Structure weight / hull surface area: 87 lbs/sq ft or 425 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 1.37
- Longitudinal: 3.23
- Overall: 1.50
Hull space for machinery, storage, compartmentation is excellent
Room for accommodation and workspaces is excellent
Ship has slow, easy roll, a good, steady gun platform
Excellent seaboat, comfortable, can fire her guns in the heaviest weather

Misc. Wt. is:
100 tons polarization
100 tons for hospital facilities
100 tons for heated catapult, hangar and two aircraft

Interesting design. Compared to historical icebreakers she doesn't displace much for her size, though.

I'm thinking that in this case I'd go for a steam plant instead of diesel - I think that was preferred because they could reuse the steam to help heat the ship.

Quoted

Originally posted by Brockpaine
Interesting design. Compared to historical icebreakers she doesn't displace much for her size, though.

Not especially, she's just quite shallow-draught by icebreaker standards, which might pose problems for propeller protection in thicker ice - although she doesn't really have the power for that anyway.

Quoted

I'm thinking that in this case I'd go for a steam plant instead of diesel - I think that was preferred because they could reuse the steam to help heat the ship.

Maybe; the USCG Wind class had diesel-electric drive, though, and seem to have been quite well thought of.

I installed both steam and an auxiliary diesel on the Piloto Pardo - but as I've noted, as an icecutter she's hardly a normal icebreaker.