WesWorld

Gentlemen,

I have little information about river monitors in my books. No line drawings and no real stats. Can you provide such data?

Below is a sim for what could be a small river monitor. I envision a single 15cm fore and aft - I have seen something similar on a photo somewhere. Four 2cm guns provide close-range cover (against infantry or planes).

What do you think?

RM36A, South African River Monitor laid down 1936

Displacement:
173 t light; 198 t standard; 205 t normal; 211 t full load

Dimensions: Length overall / water x beam x draught
139,30 ft / 137,80 ft x 26,25 ft x 3,61 ft (normal load)
42,46 m / 42,00 m x 8,00 m x 1,10 m

Armament:
2 - 5,91" / 150 mm guns in single mounts, 102,98lbs / 46,71kg shells, 1932 Model
Breech loading guns in deck mounts
on centreline ends, evenly spread
4 - 0,79" / 20,0 mm guns in single mounts, 0,24lbs / 0,11kg shells, 1930 Model
Machine guns in deck mounts
on side, evenly spread, all raised mounts
Weight of broadside 207 lbs / 94 kg
Shells per gun, main battery: 180

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 0,79" / 20 mm 100,07 ft / 30,50 m 3,94 ft / 1,20 m
Ends: Unarmoured
Main Belt covers 112% of normal length

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1,97" / 50 mm 1,97" / 50 mm -
2nd: 0,59" / 15 mm - -

- Armour deck: 0,79" / 20 mm, Conning tower: 1,97" / 50 mm

Machinery:
Diesel Internal combustion motors,
Geared drive, 1 shaft, 135 shp / 100 Kw = 9,48 kts
Range 2.000nm at 8,00 kts
Bunker at max displacement = 13 tons

Complement:
26 - 35

Cost:
£0,149 million / $0,594 million

Distribution of weights at normal displacement:
Armament: 26 tons, 12,6%
Armour: 70 tons, 34,2%
- Belts: 13 tons, 6,5%
- Torpedo bulkhead: 0 tons, 0,0%
- Armament: 20 tons, 9,6%
- Armour Deck: 36 tons, 17,4%
- Conning Tower: 1 tons, 0,7%
Machinery: 3 tons, 1,4%
Hull, fittings & equipment: 69 tons, 33,8%
Fuel, ammunition & stores: 32 tons, 15,6%
Miscellaneous weights: 5 tons, 2,4%

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
209 lbs / 95 Kg = 2,0 x 5,9 " / 150 mm shells or 0,3 torpedoes
Stability (Unstable if below 1.00): 1,75
Metacentric height 1,7 ft / 0,5 m
Roll period: 8,5 seconds
Steadiness - As gun platform (Average = 50 %): 70 %
- Recoil effect (Restricted arc if above 1.00): 0,21
Seaboat quality (Average = 1.00): 1,30

Hull form characteristics:
Hull has a flush deck
Block coefficient: 0,550
Length to Beam Ratio: 5,25 : 1
'Natural speed' for length: 11,74 kts
Power going to wave formation at top speed: 34 %
Trim (Max stability = 0, Max steadiness = 100): 54
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: 8,53 ft / 2,60 m
- Forecastle (20%): 5,91 ft / 1,80 m
- Mid (50%): 4,92 ft / 1,50 m
- Quarterdeck (15%): 4,92 ft / 1,50 m
- Stern: 5,25 ft / 1,60 m
- Average freeboard: 5,50 ft / 1,68 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 105,7%
- Above water (accommodation/working, high = better): 92,3%
Waterplane Area: 2.448 Square feet or 227 Square metres
Displacement factor (Displacement / loading): 71%
Structure weight / hull surface area: 23 lbs/sq ft or 112 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0,58
- Longitudinal: 1,25
- Overall: 0,62
Caution: Hull subject to strain in open-sea
Hull space for machinery, storage, compartmentation is adequate
Room for accommodation and workspaces is adequate
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily

Looks nice. The one thing that popped out to me was the range - is that necessary for a river monitor?

Is the 15cm gun a howitzer, a field gun, or an actual naval gun? The 15cm guns on Bulgaria's Danube monitors are howitzers, reason I ask...

Isn't hull strength a bit too low, though?

Looks pretty good, other than the low strength. It's about the same size as the German Habordansky class river gunboats, but better armed and armored, but only half as fast.

Thats my only nitpick, speed is abit low. You might have to fight river currents. Its funny you should bring this design up as I've been recently reading "Soviet warship developement: Volume 1, 1917-1937" In it there is a nice river patrol boat design, the Udardnyy, which is quite similar albeit slightly larger. She is capable of 13 knots on 262 tons.

Thanks for your input. As I said, I have little information about such vessels in general.

So why would her speed be a real problem? She is not meant to fight prolonged battles with other surface combatants? 9,5kn seems suffice for a river vessel. Most merchants of that era were even slower.

Range might be excessive, don´t know. She should carry enough for deployment. She should also carry enough to have some reserve in case she is with the army and supply is cut off for a relatively short period of time (surely she cannot kept active for a long time).

What hull strength do she needs? 1.0?

I don´t know if her guns should be howitzers. I thought of them as high angled guns, capable to shoot over trees on river banks ans some hills. Won´t a 15cm/L40 naval gun do the job? Which is better?

Would you add a high tripost or something similar for spotting or would such a unit work with army spotters anyway?

With reguards to speed I would expect that if the opertunity presented itself the ship could use the additional speed to persue its target, or on the flipside get itself out of harms way.

The aformentioned Russian patrol boat Udarnyy (Richard Worth classes her as a monitor which seems correct) is slightly larger than your preposed design and mounts 2x130mm/55 guns.

Hull strength wise you could likely up her BC as she's clearly not going to be creating any large wakes with her sleak lines.

I'd give her a telescopic mast with an observation post for spotting. It might also help her clear the underside of bridges on any river you may put her on.

Germany chose to use Heer howitzers on it's river monitors, vs naval guns, for a couple reasons: 1, the river monitors will more likely work with the Heer vs the KM, so commonality of supply is useful; 2, the howitzers, with their variable propellant charges and higher elevations, can fire on targets that are masked by terrain from higher-velocity naval guns; 3, by using the standard Heer howitzers, a Heer fire direction center can command the monitor's guns without needing a whole set of naval fire control tables; 4, the lower-velocity howitzer shells will have more explosive fill than the higher-velocity naval gun shells because the shell walls can be thinner; 5, using the howitzer allows the monitor to use any specialist rounds that the Heer has developed that the KM might not have (such as smoke, concrete piercing, rocket assist, etc).

How much speed you want is, of course, up to you, but consider that you might be going upstream against, say, a 3 knot current.

Bulgaria's issue with the Danube currents, incidentally enough, forced me to select a very high speed for my monitors. There are spots on the Danube - the Iron Gates in particular - where the current is running in excess of eleven knots.

As I purchased the designs for the German monitors and patrol boats, I decided to go along with Hrolf's line of thinking regarding the 15cm howitzers; I agree that it provides the best army-support firepower. Of course, there are additional 88mm AA guns aboard which can cover the angle of anti-ship (if it comes up) and anti-air.

http://www.warshipsww2.eu/lode.php?langu…od=&idtrida=933

Seems pretty much what you want. Its more like a proper boat than the moving pontoons of some river monitors.

The same one I ran across when looking for something similar to the RM36A. It is more than three times bigger though than the RM36A... which is probably why the hull strength ended up rather low...

So this one is better (HS 1,0):

RM36A, South African River Monitor laid down 1936

Displacement:
216 t light; 242 t standard; 250 t normal; 256 t full load

Dimensions: Length overall / water x beam x draught
139,30 ft / 137,80 ft x 26,25 ft x 4,40 ft (normal load)
42,46 m / 42,00 m x 8,00 m x 1,34 m

Armament:
2 - 5,91" / 150 mm guns in single mounts, 102,98lbs / 46,71kg shells, 1932 Model
Breech loading guns in deck mounts
on centreline ends, evenly spread
4 - 0,79" / 20,0 mm guns in single mounts, 0,24lbs / 0,11kg shells, 1930 Model
Machine guns in deck mounts
on side, evenly spread, all raised mounts
Weight of broadside 207 lbs / 94 kg
Shells per gun, main battery: 180

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 0,79" / 20 mm 91,86 ft / 28,00 m 3,94 ft / 1,20 m
Ends: Unarmoured
Main Belt covers 103% of normal length

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1,97" / 50 mm 1,97" / 50 mm -
2nd: 0,59" / 15 mm - -

- Armour deck: 0,79" / 20 mm, Conning tower: 1,97" / 50 mm

Machinery:
Diesel Internal combustion motors,
Geared drive, 1 shaft, 178 shp / 133 Kw = 10,00 kts
Range 2.000nm at 8,00 kts
Bunker at max displacement = 14 tons

Complement:
30 - 40

Cost:
£0,158 million / $0,631 million

Distribution of weights at normal displacement:
Armament: 26 tons, 10,4%
Armour: 70 tons, 27,9%
- Belts: 13 tons, 5,0%
- Torpedo bulkhead: 0 tons, 0,0%
- Armament: 20 tons, 7,9%
- Armour Deck: 36 tons, 14,3%
- Conning Tower: 2 tons, 0,7%
Machinery: 4 tons, 1,7%
Hull, fittings & equipment: 111 tons, 44,6%
Fuel, ammunition & stores: 34 tons, 13,4%
Miscellaneous weights: 5 tons, 2,0%

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
429 lbs / 195 Kg = 4,2 x 5,9 " / 150 mm shells or 0,4 torpedoes
Stability (Unstable if below 1.00): 1,58
Metacentric height 1,5 ft / 0,4 m
Roll period: 9,1 seconds
Steadiness - As gun platform (Average = 50 %): 72 %
- Recoil effect (Restricted arc if above 1.00): 0,22
Seaboat quality (Average = 1.00): 1,34

Hull form characteristics:
Hull has a flush deck
Block coefficient: 0,550
Length to Beam Ratio: 5,25 : 1
'Natural speed' for length: 11,74 kts
Power going to wave formation at top speed: 38 %
Trim (Max stability = 0, Max steadiness = 100): 54
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: 8,53 ft / 2,60 m
- Forecastle (20%): 5,91 ft / 1,80 m
- Mid (50%): 4,92 ft / 1,50 m
- Quarterdeck (15%): 4,92 ft / 1,50 m
- Stern: 5,25 ft / 1,60 m
- Average freeboard: 5,50 ft / 1,68 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 89,2%
- Above water (accommodation/working, high = better): 80,0%
Waterplane Area: 2.448 Square feet or 227 Square metres
Displacement factor (Displacement / loading): 86%
Structure weight / hull surface area: 36 lbs/sq ft or 175 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0,92
- Longitudinal: 1,95
- Overall: 1,00
Hull space for machinery, storage, compartmentation is adequate
Room for accommodation and workspaces is cramped
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily

I would say that yes, it is better.

The ABS war told RSAN high ranks they completely missed river warfare in their plans and doctrines. Learning the hard war the RSAN is now interested in having some river/coastal gun boats.

Below is one of the proposed designs. What do you think?

RGB37A, South African River Gun Boat laid down 1937

Displacement:
460 t light; 490 t standard; 552 t normal; 602 t full load

Dimensions: Length overall / water x beam x draught
219,31 ft / 213,25 ft x 25,59 ft x 5,91 ft (normal load)
66,85 m / 65,00 m x 7,80 m x 1,80 m

Armament:
4 - 4,13" / 105 mm guns (2x2 guns), 35,32lbs / 16,02kg shells, 1937 Model
Breech loading guns in deck mounts
on centreline ends, evenly spread
4 - 1,57" / 40,0 mm guns (2x2 guns), 1,95lbs / 0,88kg shells, 1937 Model
Anti-aircraft guns in deck mounts
on side, all amidships, all raised mounts - superfiring
4 - 0,79" / 20,0 mm guns (2x2 guns), 0,24lbs / 0,11kg shells, 1937 Model
Anti-aircraft guns in deck mounts
on centreline ends, evenly spread
Weight of broadside 150 lbs / 68 kg
Shells per gun, main battery: 220

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 0,79" / 20 mm 98,43 ft / 30,00 m 6,56 ft / 2,00 m
Ends: Unarmoured
Main Belt covers 71% of normal length
Main belt does not fully cover magazines and engineering spaces

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1,18" / 30 mm 0,79" / 20 mm -
2nd: 0,59" / 15 mm - -
3rd: 0,39" / 10 mm - -

Machinery:
Coal fired boilers, complex reciprocating steam engines,
Geared drive, 2 shafts, 2.500 ihp / 1.865 Kw = 18,38 kts
Range 2.500nm at 12,00 kts
Bunker at max displacement = 112 tons (100% coal)

Complement:
56 - 74

Cost:
£0,291 million / $1,162 million

Distribution of weights at normal displacement:
Armament: 19 tons, 3,4%
Armour: 34 tons, 6,1%
- Belts: 23 tons, 4,2%
- Torpedo bulkhead: 0 tons, 0,0%
- Armament: 11 tons, 1,9%
- Armour Deck: 0 tons, 0,0%
- Conning Tower: 0 tons, 0,0%
Machinery: 153 tons, 27,7%
Hull, fittings & equipment: 205 tons, 37,0%
Fuel, ammunition & stores: 92 tons, 16,7%
Miscellaneous weights: 50 tons, 9,1%

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
488 lbs / 222 Kg = 13,8 x 4,1 " / 105 mm shells or 0,3 torpedoes
Stability (Unstable if below 1.00): 1,24
Metacentric height 1,0 ft / 0,3 m
Roll period: 11,0 seconds
Steadiness - As gun platform (Average = 50 %): 70 %
- Recoil effect (Restricted arc if above 1.00): 0,25
Seaboat quality (Average = 1.00): 1,00

Hull form characteristics:
Hull has a flush deck
Block coefficient: 0,600
Length to Beam Ratio: 8,33 : 1
'Natural speed' for length: 14,60 kts
Power going to wave formation at top speed: 55 %
Trim (Max stability = 0, Max steadiness = 100): 70
Bow angle (Positive = bow angles forward): 20,00 degrees
Stern overhang: 1,64 ft / 0,50 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 12,14 ft / 3,70 m
- Forecastle (20%): 7,55 ft / 2,30 m
- Mid (44%): 7,55 ft / 2,30 m
- Quarterdeck (15%): 7,55 ft / 2,30 m
- Stern: 7,55 ft / 2,30 m
- Average freeboard: 7,91 ft / 2,41 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 126,9%
- Above water (accommodation/working, high = better): 102,4%
Waterplane Area: 3.991 Square feet or 371 Square metres
Displacement factor (Displacement / loading): 102%
Structure weight / hull surface area: 36 lbs/sq ft or 175 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0,97
- Longitudinal: 1,32
- Overall: 1,00
Hull space for machinery, storage, compartmentation is cramped
Room for accommodation and workspaces is adequate
Ship has slow, easy roll, a good, steady gun platform

NOTE: Armor is meant to protect magazines and boilers only.

I think it depends very much on what exactly you want to do. I'm not sure I see the value of armouring anything apart from the gunhouses and the con. There's very limited hull space so there will be large superstructure for accommodation etc. which makes a large target and easy to hit.

Armament would drive things quite a lot. 150mm is a nice size for shooting things on the shore but rate of fire quite low. 75mm still gives a reasonable bang but with a higher rate of fire and much easier to locate on the boat.

I think I might go with two 75mm forwards, one superfiring the other, and a 150mm aft. Then a twin 40mm on the superstructure aft the funnel and few machine guns on the beam.

For the ships themselves, low draught, high Cb.

I'm no expert, but what about freeboard? Since you are on a river with such a ship, I would think that a lower freeboard would mean a smaller target for those on shore who want to take out the river boat. Considering that you are on a RIVER, I doubt you have to keep an eye on the SEAboat quality of the ship.

I'm not sure of the reasoning behind the switch from two 15cm guns to four 11.5cm guns is, but I'd think you'd want more ammunition for the smaller guns than you provided for the larger guns. If it were me, I'd probably stick with the 15cm guns and see if I could fit in a few mid-range guns (7.5-9cm) to support them. The use of coal fuel is interesting, but..... I think it's probably, by this point, unnecessary for the RSAN, and it's very bulky compared to diesel or bunker oil. RA's right, too, on the draught issue: the deeper you are, the more restricted you are on where you can go and the more vulnerable you are to shoals and general issues of running aground.

Maybe the idea is to be able to cut down trees and use that as fuel for the boat?

Coal makes sense as its readily available in most places, and if it's not you use trees. Fuel oil is a bit harder to find in the back of beyond.

I'm guessing that might be the idea, but..... that seems more appropriate for a less developed power than the RSAN. For Peruvian boats on the Amazon, that makes sense, where it's hard to get more modern fuel to the location. But where is the RSAN going to be that cut off?

No doubt he is planning another campaign in South America.