WesWorld

Thinking of building some Patrolboats

PB, Persia Patrolboat laid down 1936

Displacement:
596 t light; 629 t standard; 779 t normal; 899 t full load

Dimensions: Length overall / water x beam x draught
196,85 ft / 196,85 ft x 22,31 ft x 13,12 ft (normal load)
60,00 m / 60,00 m x 6,80 m x 4,00 m

Armament:
3 - 5,12" / 130 mm guns in single mounts, 67,03lbs / 30,40kg shells, 1936 Model
Dual purpose guns in deck mounts
on centreline ends, majority forward, 1 raised mount
6 - 0,98" / 25,0 mm guns (3x2 guns), 0,48lbs / 0,22kg shells, 1936 Model
Breech loading guns in deck mounts
on centreline ends, majority forward, 2 raised mounts - superfiring
Weight of broadside 204 lbs / 93 kg
Shells per gun, main battery: 150

Armour:
- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1,18" / 30 mm 1,18" / 30 mm -
2nd: 0,79" / 20 mm - -

- Armour deck: 0,79" / 20 mm, Conning tower: 2,36" / 60 mm

Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 12 877 shp / 9 606 Kw = 26,00 kts
Range 3 000nm at 18,00 kts
Bunker at max displacement = 270 tons

Complement:
73 - 95

Cost:
£0,441 million / $1,763 million

Distribution of weights at normal displacement:
Armament: 25 tons, 3,3 %
Armour: 62 tons, 8,0 %
- Belts: 0 tons, 0,0 %
- Torpedo bulkhead: 0 tons, 0,0 %
- Armament: 16 tons, 2,1 %
- Armour Deck: 42 tons, 5,4 %
- Conning Tower: 4 tons, 0,6 %
Machinery: 295 tons, 37,9 %
Hull, fittings & equipment: 212 tons, 27,3 %
Fuel, ammunition & stores: 183 tons, 23,5 %
Miscellaneous weights: 0 tons, 0,0 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
292 lbs / 132 Kg = 4,4 x 5,1 " / 130 mm shells or 0,2 torpedoes
Stability (Unstable if below 1.00): 1,10
Metacentric height 0,6 ft / 0,2 m
Roll period: 11,6 seconds
Steadiness - As gun platform (Average = 50 %): 76 %
- Recoil effect (Restricted arc if above 1.00): 0,91
Seaboat quality (Average = 1.00): 1,00

Hull form characteristics:
Hull has rise forward of midbreak
Block coefficient: 0,480
Length to Beam Ratio: 8,96 : 1
'Natural speed' for length: 14,03 kts
Power going to wave formation at top speed: 72 %
Trim (Max stability = 0, Max steadiness = 100): 76
Bow angle (Positive = bow angles forward): 0,00 degrees
Stern overhang: 0,00 ft / 0,00 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 14,76 ft / 4,50 m
- Forecastle (20 %): 13,12 ft / 4,00 m
- Mid (50 %): 13,12 ft / 4,00 m (9,84 ft / 3,00 m aft of break)
- Quarterdeck (15 %): 9,84 ft / 3,00 m
- Stern: 9,84 ft / 3,00 m
- Average freeboard: 11,61 ft / 3,54 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 147,8 %
- Above water (accommodation/working, high = better): 85,2 %
Waterplane Area: 2 874 Square feet or 267 Square metres
Displacement factor (Displacement / loading): 79 %
Structure weight / hull surface area: 29 lbs/sq ft or 141 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0,56
- Longitudinal: 5,75
- Overall: 0,71
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

For a patrol boat, she seems a bit too long in relation to her beam at 8.96 to 1, maybe add about 3 - 4 feet of beam.

Also I'd reconsider the 3rd 130mm, your recoil figure is 0.91, she would almost roll herself if firing broadside!!

Not bad, thought I would add a few torpedoes and some misc weight.

Try drawing her out. I'm sure you'll find that 3x5.1" will make her quite cramped (not to mention top heavy). You'll also need some misc weight for additional equipment.

With that armament its not really a patrolboat. I'd think more something along the lines of 1 x 100 or 1 x 75 forwards with 2 x 25 aft, no armour, enough power for about 20 knts and excess hull strength and seakeeping.

Looks like I will have to reconsider this concept

The vessel is actually quite close to my Gruno class Gunboats, except you added a little length and subtracted beam. You also have a great deal more machinery. The Grunos are close copies of the OTL class of that name, so they do work- but they are not intended for 'patrol' work, they are coastal and large river gunboats. To much invested for common patrols.
A single 75-105mm gun is sufficient for that, as you'll outgun any villianous types, can hole a sub, beat up a MTB, etc.

Seems like the Kaivan line is best, down rating obsolete DD, DDE & TBs

Perhaps Perisa would like to take a look at the Mexican patrolboats:
http://wesworld.jk-clan.de/thread.php?threadid=3276&sid=
Note: The pic and SS2 don't match, the pic is right, havent had time to fix the SS2.

We will have to study it closer, perhaps Mexico would accept Persian officers to study it in operation?