Better than a Monitor

[AnchorSteam]

THREE of them, and all of them can always be assumed to have 2-4 x B=class MTB with them or nearby.

One of the best designs I have seen...[/color]

Ok, so you indicated the Norse Monitor might be a bit more than you were looking for.
So I modified a Parthian gunboat design I had.

The Norse was 2,996 tons, this is 3000, so same budget 'cost'.

This has 180mm guns fore and aft for a fair amount of HE power.
Superimposed over the aft gun is a shielded 118mm Howitzer for arcing shots.
The main belt is +1 /-1 of facehardened armor along the waterline, while a 65mm belt carries to freeboard, rendering the ship fully armored.
at 3.9m, the draft is shallow for inshore work.  Torpedo nets are fitted so it can sit offshore and conduct bombardment safely.

The ship is very beamy, which makes it a steady platform. It also gives it the amidships deckspace to stack ships' boats.
These can be motor launches for marines, or MTBs.  There is room for both Marines, and large numbers of torpedoes or mines.

Ethiopian export, Parthian Coastal Gunboat laid down 1903

Displacement:
   2,991 t light; 3,128 t standard; 3,444 t normal; 3,697 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (294.98 ft / 291.99 ft) x 54.13 ft x (12.80 / 13.56 ft)
   (89.91 m / 89.00 m) x 16.50 m  x (3.90 / 4.13 m)

Armament:
      2 - 7.09" / 180 mm 45.0 cal guns - 176.37lbs / 80.00kg shells, 300 per gun
     Quick firing guns in deck and hoist mounts, 1899 Model
     2 x Single mounts on centreline ends, evenly spread
      1 - 4.65" / 118 mm 20.0 cal gun - 50.71lbs / 23.00kg shells, 300 per gun
     Breech loading gun in deck mount, 1899 Model
     1 x Single mount on centreline, aft deck centre
      1 raised mount
      4 - 0.30" / 7.5 mm 45.0 cal guns - 0.01lbs / 0.01kg shells, 1,500 per gun
     Machine guns in deck mounts, 1899 Model
     4 x Single mounts on side ends, evenly spread
      4 raised mounts
      Weight of broadside 404 lbs / 183 kg

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   3.54" / 90 mm   189.80 ft / 57.85 m   6.56 ft / 2.00 m
   Ends:   0.98" / 25 mm   102.17 ft / 31.14 m   6.56 ft / 2.00 m
   Upper:   2.56" / 65 mm   189.80 ft / 57.85 m   8.01 ft / 2.44 m
     Main Belt covers 100 % of normal length

   - Hull void:
      0.00" / 0 mm     0.00 ft / 0.00 m   0.00 ft / 0.00 m

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   3.54" / 90 mm   0.98" / 25 mm      0.98" / 25 mm
   2nd:   0.98" / 25 mm         -               -
   3rd:   0.31" / 8 mm         -               -

   - Armoured deck - single deck:
   For and Aft decks: 1.18" / 30 mm
   Forecastle: 0.79" / 20 mm  Quarter deck: 0.79" / 20 mm

   - Conning towers: Forward 3.54" / 90 mm, Aft 0.00" / 0 mm

Machinery:
   Coal and oil fired boilers, complex reciprocating steam engines,
   Direct drive, 2 shafts, 4,163 ihp / 3,105 Kw = 16.00 kts
   Range 4,600nm at 10.00 kts
   Bunker at max displacement = 570 tons (90% coal)

Complement:
   224 - 292

Cost:
   £0.226 million / $0.902 million

Distribution of weights at normal displacement:
   Armament: 97 tons, 2.8 %
      - Guns: 97 tons, 2.8 %
   Armour: 682 tons, 19.8 %
      - Belts: 397 tons, 11.5 %
      - Armament: 29 tons, 0.8 %
      - Armour Deck: 238 tons, 6.9 %
      - Conning Tower: 17 tons, 0.5 %
   Machinery: 615 tons, 17.9 %
   Hull, fittings & equipment: 955 tons, 27.7 %
   Fuel, ammunition & stores: 453 tons, 13.1 %
   Miscellaneous weights: 642 tons, 18.6 %
      - Hull below water: 190 tons
      - Hull void weights: 25 tons
      - Hull above water: 132 tons
      - On freeboard deck: 255 tons
      - Above deck: 40 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     5,639 lbs / 2,558 Kg = 31.7 x 7.1 " / 180 mm shells or 1.4 torpedoes
   Stability (Unstable if below 1.00): 1.58
   Metacentric height 4.3 ft / 1.3 m
   Roll period: 11.0 seconds
   Steadiness   - As gun platform (Average = 50 %): 77 %
         - Recoil effect (Restricted arc if above 1.00): 0.09
   Seaboat quality  (Average = 1.00): 1.57

Hull form characteristics:
   Hull has a flush deck,
     a ram bow and a round stern
   Block coefficient (normal/deep): 0.596 / 0.604
   Length to Beam Ratio: 5.39 : 1
   'Natural speed' for length: 17.09 kts
   Power going to wave formation at top speed: 47 %
   Trim (Max stability = 0, Max steadiness = 100): 49
   Bow angle (Positive = bow angles forward): 15.00 degrees
   Stern overhang: -1.50 ft / -0.46 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   20.00 %,  11.15 ft / 3.40 m,  11.15 ft / 3.40 m
      - Forward deck:   30.00 %,  11.15 ft / 3.40 m,  11.15 ft / 3.40 m
      - Aft deck:   35.00 %,  11.15 ft / 3.40 m,  11.15 ft / 3.40 m
      - Quarter deck:   15.00 %,  11.15 ft / 3.40 m,  11.98 ft / 3.65 m
      - Average freeboard:      11.22 ft / 3.42 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 79.3 %
      - Above water (accommodation/working, high = better): 109.3 %
   Waterplane Area: 11,518 Square feet or 1,070 Square metres
   Displacement factor (Displacement / loading): 119 %
   Structure weight / hull surface area: 67 lbs/sq ft or 327 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.95
      - Longitudinal: 1.60
      - Overall: 1.00
   Excellent machinery, storage, compartmentation space
   Adequate accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform
   Excellent seaboat, comfortable, can fire her guns in the heaviest weather

Warning: Beam between bulkheads too wide

Misc weight

Void
25t - Construction Reserve

Above deck
25 - LR radio
10 - FC

On Deck Amidships

240 - provisions for 2 x 60t TB / MTB / MGB (will fit 4x MTB-B)

Above Water
12 - Tender services for 120tons TB/MTB/MGB
100t - Marines
20t - brig

two mine rails exit through hatches above the stern here.

Below Water
90t - Torpedo nets.
100t - Mine/Torpedo Storage Space, chilled, with cargo lift to deck.