Another interesting design concept of the transitional period was the so-called "Flatiron" or Rendel gunboat. The concept envisioned a very small vessel carrying a single large-caliber gun, intended to operate in coastal waters or in defense of harbors. While the type was built in substantial numbers their combat record proved very disappointing. More information can be found
here.
-----
TBD, TBD Coastal Gunboat laid down 1881
Displacement: 237 t light; 261 t standard; 265 t normal; 268 t full load
Dimensions: Length overall / water x beam x draught
89.17 ft / 87.27 ft x 26.12 ft x 6.50 ft (normal load) [27.18 m / 26.60 m x 7.96 m x 1.98 m]
Armament:
1 - 9.45" / 240 mm guns in single mounts, 364.85lbs / 165.49kg shells, 1881 Model Breech loading gun in deck mount on centreline forward
Weight of broadside 365 lbs / 165 kg
Shells per gun, main battery: 90
Armour:
Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1.97" / 50 mm 0.98" / 25 mm -
Armour deck: 0.98" / 25 mm, Conning tower: 1.97" / 50 mm
Machinery:
Coal fired boilers, simple reciprocating steam engines, Direct drive, 2 shafts, 127 ihp / 94 Kw = 8.50 kts
Range 600nm at 5.00 kts
Bunker at max displacement = 8 tons (100% coal)
Complement: 32 - 42
Cost: £0.049 million / $0.195 million
Distribution of weights at normal displacement:
Armament: 46 tons, 17.2 %
Armour: 44 tons, 16.6 %
- Belts: 0 tons, 0.0 %
- Torpedo bulkhead: 0 tons, 0.0 %
- Armament: 11 tons, 4.2 %
- Armour Deck: 31 tons, 11.7 %
- Conning Tower: 2 tons, 0.7 %
Machinery: 16 tons, 6.0 %
Hull, fittings & equipment: 132 tons, 49.7 %
Fuel, ammunition & stores: 28 tons, 10.5 %
Miscellaneous weights: 0 tons, 0.0 %
Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship): 149 lbs / 68 Kg = 0.4 x 9.4 " / 240 mm shells or 0.2 torpedoes
Stability (Unstable if below 1.00): 1.38
Metacentric height 1.2 ft / 0.4 m
Roll period: 10.1 seconds
Steadiness - As gun platform (Average = 50 %): 100 %
- Recoil effect (Restricted arc if above 1.00): 0.81
Seaboat quality (Average = 1.00): 2.00
Hull form characteristics:
Hull has raised quarterdeck
Block coefficient: 0.626
Length to Beam Ratio: 3.34 : 1
'Natural speed' for length: 9.34 kts
Power going to wave formation at top speed: 52 %
Trim (Max stability = 0, Max steadiness = 100): 50
Bow angle (Positive = bow angles forward): 2.25 degrees
Stern overhang: 1.64 ft / 0.50 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 6.56 ft / 2.00 m
- Forecastle (20 %): 7.38 ft / 2.25 m
- Mid (50 %): 7.38 ft / 2.25 m
- Quarterdeck (22 %): 9.84 ft / 3.00 m (7.38 ft / 2.25 m before break)
- Stern: 9.84 ft / 3.00 m
- Average freeboard: 7.86 ft / 2.40 m
Ship tends to be wet forward
Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 145.8 %
- Above water (accommodation/working, high = better): 75.1 %
Waterplane Area: 1,708 Square feet or 159 Square metres
Displacement factor (Displacement / loading): 58 %
Structure weight / hull surface area: 54 lbs/sq ft or 263 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.80
- Longitudinal: 7.41
- Overall: 1.00
Hull space for machinery, storage, compartmentation is cramped
Room for accommodation and workspaces is cramped
Ship has slow, easy roll, a good, steady gun platform
Excellent seaboat, comfortable, can fire her guns in the heaviest weather