WesWorld

A new class of escort vessels, with 3 ships to be laid down in 1933. Intended to supplement and eventually replace the aging A and B classes from 1916 and 1917. The class follows on from the Vespa and Gabbiano classes of 1930 and 1932 but with greater size and capability.

The Vespa class have been reasonably succesful in their role, but their turbine powerplant has caused some problems. It has been considered to refit them with either reciprocating or diesel engines. They are large, strong, seaworthy and cheap.

The Gabbiano class laid down last year are smaller vessels of 600tons and are more regarded as 2nd line units for short Meditterenean voyages. It is felt that they are overly specialised for ASW. In the Med. it is quite likely to encounter surface forces and their single 100mm gun is viewed as inadequate, as is their AA armament. Again, they are strong, seaworthy and cheap.

This class, the Dianas, try to provide a proper Ocean-going escort in order to honour Italy's commitments elsewhere. They are larger at 1600tons and much more heavily armed. They are more akin to slow destroyers, hence their designation of Avviso Veloce or Scorta.

Hull is 110x12x3.5 with quite a full hull in comparison to contemporary destroyers. The freeboard is large, making for excellent seakeeping. A forecastle is used, limiting forwards fire but serving to keep the open bridge drier and more effective. Two bridges are provided, a closed bridge and an open one above. The varying climates and need to safe navigation in close waters have shown this to be essential.

Machinery. The main propulsion is from 4x2000hp Fiat diesel engines. Essentially doubling the powerplant of the Gabbianos for ease and cheapness. These are grouped in two engine rooms. 250hp electric "creeping" motors are included for low-speed maneuvering. There was quite some indecision over the powerplant of steam vs. diesels, but the shorter start up time of the diesels won over SuperMarina. In addtion to the low-speed diesels are 4x5000hp high speed units. Manufactured by Fiat for the Aliscafo, they can provide a much needed boost in power for emergencies. This came about from their percieved role as fleet escorts. There are two main engine rooms with 2x1000hp diesels, 1x125hp electric motor and 1x5000hp diesel in each. Aft of the gearing room is another room housing the remaining two 5000hp diesels. The range provided by the diesels is excellent and is indicative of their role.

Armament. Particular was paid to surface gunfire with the standard destroyer armament of 4x135/45 used [lined down to 130] arranged fore and aft with hoists and magazines below. These are LA weapons, there being insufficient space, weight and funds for DP [ and the absence of a DP 135mm gun]. The AA armament is excellent, with one quadruple 47/62 mounting aft and ten duple BredaMadsen 25mm mountings. ASW fit remains broadly similar to Vespa and Gabbiano. Two scaricabombe gattescho dischargers are carried aft on the quarterdeck with 48 depth charges and a single towed torpedo. Fore is a D2bis sonar set with retractable dome instead of the fixed set used in Vespa and Gabbiano. Just in front of the bridge is one of the mutiple launchers from Vespa. A grouping of 4x430mm projectors together, each double loaded with 2x50kg depth charges with variable sink rates. The experiments with short range rockets in one of the Soldati class destroyers have not been satisfactory with uneven burn times, and explosions eroding morale and eventually causing the program to be abandoned in favour of the safer 430mm projectors. Four 325mm torpedoes are carried in duple launchers on either beam.

The class are expected to be effective open-ocean escort vessels and the three examples ordered in late 1932 will probably be expanded on, with more batches ordered in 1934 and onwards.

NB. Their speed and torpedo carriage means they rate as type B destroyers. But Italy has plenty of tonnage to spare in this category. I think I covered everything...


Diana, Italian Avviso Veloce laid down 1933

Displacement:
1,538 t light; 1,646 t standard; 2,331 t normal; 2,879 t full load

Dimensions: Length overall / water x beam x draught
375.52 ft / 360.89 ft x 39.37 ft x 11.48 ft (normal load)
114.46 m / 110.00 m x 12.00 m x 3.50 m

Armament:
4 - 5.31" / 135 mm guns (2x2 guns), 79.37lbs / 36.00kg shells, 1933 Model
Breech loading guns in deck mounts with hoists
on centreline ends, evenly spread
4 - 1.85" / 47.0 mm guns (1x4 guns), 3.86lbs / 1.75kg shells, 1933 Model
Anti-aircraft guns in deck mount
on centreline aft
24 - 0.98" / 25.0 mm guns (6x4 guns), 0.53lbs / 0.24kg shells, 1933 Model
Anti-aircraft guns in deck mounts
on side, evenly spread
Weight of broadside 346 lbs / 157 kg
Shells per gun, main battery: 300
4 - 12.8" / 325 mm above water torpedoes

Armour:
- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 0.79" / 20 mm 0.39" / 10 mm -
2nd: 0.39" / 10 mm 0.39" / 10 mm -
3rd: 0.39" / 10 mm - -

- Conning tower: 0.79" / 20 mm

Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 8,000 shp / 5,968 Kw = 21.75 kts
Range 14,200nm at 15.00 kts
Bunker at max displacement = 1,233 tons

Complement:
167 - 218

Cost:
£0.570 million / $2.279 million

Distribution of weights at normal displacement:
Armament: 41 tons, 1.7 %
Armour: 13 tons, 0.5 %
- Belts: 0 tons, 0.0 %
- Torpedo bulkhead: 0 tons, 0.0 %
- Armament: 10 tons, 0.4 %
- Armour Deck: 0 tons, 0.0 %
- Conning Tower: 3 tons, 0.1 %
Machinery: 233 tons, 10.0 %
Hull, fittings & equipment: 1,142 tons, 49.0 %
Fuel, ammunition & stores: 793 tons, 34.0 %
Miscellaneous weights: 110 tons, 4.7 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
7,585 lbs / 3,441 Kg = 101.0 x 5.3 " / 135 mm shells or 2.0 torpedoes
Stability (Unstable if below 1.00): 1.21
Metacentric height 1.8 ft / 0.5 m
Roll period: 12.5 seconds
Steadiness - As gun platform (Average = 50 %): 70 %
- Recoil effect (Restricted arc if above 1.00): 0.44
Seaboat quality (Average = 1.00): 2.00

Hull form characteristics:
Hull has raised forecastle, low quarterdeck
and transom stern
Block coefficient: 0.500
Length to Beam Ratio: 9.17 : 1
'Natural speed' for length: 21.83 kts
Power going to wave formation at top speed: 48 %
Trim (Max stability = 0, Max steadiness = 100): 35
Bow angle (Positive = bow angles forward): 20.00 degrees
Stern overhang: 3.28 ft / 1.00 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 31.17 ft / 9.50 m
- Forecastle (20 %): 22.97 ft / 7.00 m (18.04 ft / 5.50 m aft of break)
- Mid (50 %): 18.04 ft / 5.50 m
- Quarterdeck (13 %): 9.84 ft / 3.00 m (18.04 ft / 5.50 m before break)
- Stern: 9.84 ft / 3.00 m
- Average freeboard: 18.62 ft / 5.68 m

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 53.7 %
- Above water (accommodation/working, high = better): 188.0 %
Waterplane Area: 9,845 Square feet or 915 Square metres
Displacement factor (Displacement / loading): 255 %
Structure weight / hull surface area: 59 lbs/sq ft or 290 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.85
- Longitudinal: 4.50
- Overall: 1.01
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

15t = quad 47mm
9t=sonar
7t=scaricabombe
10t=asw mortar
250hp creeping motors = 9t 28hp/ton
=50t

20,000shp diesels
40tons + 20tons design factor

Speed with electric motors = 8 knts
Speed with Diesels = 29.95knts

13" torpedoes? What for? Scrap them and you have an unlimited ship.

12.8", same caliber as the torps on the Current Iroquois class Destroyers as well as many other modern DD's.

The forward 5.31" has a poor firing arc with the bow sheer as is.

Kind of a long range for just the Mediterreanian don't you think?

325mm torpedoes seems...odd for the time period. If I recall modern smaller torpedoes are designed to attack submarines, not surface ships. I'm not sure what the 100 or so pounds of explosives will do to a ship if fired in the conventional way.

I wonder if the hull is possible to build with 1930's technology (the pictured vessel, not the SS form). She looks top heavy for rivited steel construction.

I'd be as bold to say 325mm is rediculous in an era when most navy's are finding the 18" torpedo's left over from WW1 inadequate and moving to larger, more powerfull torpedo's.

The only use for such small torpedo's would as you say be against submarines but this is completely unrealistic for the time period. Depth charges are still the best and cheapest solution to subs.

I suspect these are something other than the conventional torpedo.

The firing arc of the forward 135/45 isn't too bad. Limited to 5° - 10° min elevation so a 6000-8000yd dead zone right over the bow. I don't think this a problem when you could turn by a couple of degrees and start hitting a target with 4x135mm and 4x47mm.

Opening up the debate on the 325mm torpedoes again after they've been used since 1928/29. They are electrically powered and are short range, high speed devices. Roughly 1000-1500m at 50knts. The batteries just make them easier and safer to use than normal torpedoes. Less maintenance, which would mostly involve topping up the lead-acid batteries with distilled water. They really need to be preheated to get them to go the required range. Its relatively simple to get around this by going to an AC motor and dumping about 3 times the overload through it for the first couple of seconds. [AC motors will take this] The batteries surrounding will soon get very warm. They are designed for use against submarines on the surface and for sinking merchantmen and the like. Speed of about 28m/s means they'll cover a 1000m range in 36s or so, less than diving time - and they run below the surface which helps more.

The range would be long for the Med. if they were designed with the Med. in mind.

I don't think it would be that hard to build the hull. Maybe getting a little tall but the beam and bilge keels compensate.

2 points on the torpedoes: first, it's a bit early for an battery-powered torpedo, and second, 50 knots is WAY, WAY too fast for a battery-powered torpedo in the 1930s, you're looking at the 1980-1990s before that was acheived (with Stingray, A-290, DM2A4, etc) in production weapons. The fastest production battery-powered torpedo of the 1940s I can find was able to move at 30 knots or so.

Not to be really sticky on dates but the earliest I can find the 325mm "torpedo" being used was the refit for Quarto in 1930.

The Vespa merely mentions "towed torpedos" and also uses them in 1930. RMI weapons list also doesn't state a date of first use.

The other issue I'd have with this design is the pattern-throwing ahead-thrown weapons. That's at least a year or two of anti-submarine warfare ahead of time. Technically, it's certainly doable, doctrinally, though, there's no reason for such a thing (as shown by the production dates for Hedgehog and Squid of late 1942 and 1943 respectively). A single launcher, firing single projectiles, fine. Multiple weapons firing multiple projectiles in a pattern, that's an anachronism.

The main issue I have is...this ship is some kind of ugly.

Nice work on her design history, Gavin. That´s much better than just posting a SS-file, you know. :o)

Is that a radar device at her main masts top?

The machinery layout seems rather complex for A) such a small and b) meant-to-be-cheap vessel that is to be build in larger numbers.

I also second some other points but hey, it´s an italian vessel, you know?! ;o)

I'm not sure on speed. The range and warhead is very small to compensate. These have definitely been mentioned before and iirc both Wes and Stephan showed considerable interest in them.

It was standard Italian practise to fire two DCs from the same projector. I'll look out a picture I have.

Radar - yes Gufo, I tore the mast straight from a Capitani Romani drawing and didn't change it. Not carried anytime soon.

Machinery is a bit complicated but at least its all diesel. Oil fired boilers don't go well with electric motors. Running quiet and slow on the motors yes, but you'd still have boiler and turbine noise if you kept up pressure in the system - and if you don't keep the pressure up them you can't suddenly go to flank and chase. I still think its a relatively cheap method.

On the torpedo, the earliest torpedo of this size and propulsion type that I can find is the US Mk 43 Mod 0 of 1950. It had a warhead of 60 pounds, and a speed of only 20 knots (over a range of 4300 yards). The 10" Mk 43 Mod 1 was even smaller, with a warhead of only 54 pounds and a speed of 15 knots over a range of 4500 yards.

On armament- I presume the 15t for the 47mm is to sim the stabilized mount you’ve developed? I’ve been trying to decide how to proceed in that matter. I’d prefer to add the weight to the mount so it’s at the right ‘place’ on the ship, and also not eating up hull volume.

On miscellaneous weights- shouldn't you have a couple tons for ammunition for the ASW & torp mounts?

On the machinery,

A question - With the higher efficiency of the high speed diesels, why not go to electric drive, where the diesels can run at the most efficient speed, then you could dispense with the low speed plant ?

And a concern :
You have the basic propulsion modeled as 8,000 hp for 233 tons in what you characterize as low speed diesels.

Then you have under miscellaneous weight the 20,000 HP diesels, at an additional 60 (40+20) tons?

I realize there's the OTL reality of better Italian machinery, but that’s a 9.7:1 improvement in HP/Ton. That’s a huge difference. How flexible are we with accommodating OTL within the Wesworld SIM framework? Can we expect CanisD to start reducing USN power plant displacements to account for the improved steam plants? Heck if Italy's diesels are so good, the Dutch should start buying those.

My only contention with the small torpedo is its usefulness in this time period. 60-100 pounds of explosives isn't going to do enough damage to most warships to warrent mounting them in small numbers on an escort vessel. Another question is why would anyone think of torpedoing a submarine when a shell from the main guns will be enough to sink most subs, assuming it hits the hull rather than the sail. Also batteries in the 1930s are huge and expensive. While having a conventional torpedo this size is possible (I know of at least 14" torpedoes in the early days) but gyroscopic air driven torpedoes still need a certian volume, right? It is a matter of it being technically possible, but also logical I suppose.

And I don't remember the torpedoes being mentioned before, but we were probably going off on something else and didn't really notice. It is not a major deal, so long as the torpedoes don't start doing things that are quite impossible using even the slightly ahead technology we have avalible to us. (like the homing torpedoes these are based on).

I hadnt noticed the machinery, we must start stealing Italian technology.

The torpedoes are useless. Any Sub Skipper who is caught by a such a small short legged torpedo deserves getting sunk for his stupidity. The warheads of the torpedoes are no better than that of the 130mm shells, I doubt you can sink a merchant with them. The guns can fire faster, have much better range, better accuracy, similar impact, have reloads, and can be brought into action faster. But keep the torpedes, that way Italy gets less Type B Destroyers.

As for the foward firing full size DCs, a wrong decision could have the Escort Ship over them when they blow, not a good thing for it.

Edit: That reminds me, since SS2 doesnt sim British hulls adequately, does that mean I can consider Tiger to be capable of 33kts?

While I agree with folks on the anachronistic concerns being raised, I don't take issue with the concept of the torpedo if the technology did exist.

A submarine travelling at ~ 10 knots might travel about 200 metres in the torpedo's run time. That's about three times the hull length of an ocean-going sub, giving - if the depth setting is right - a good chance of a hit. And a single hit, even from such a small fish, ought to real mess up that sub. The operational criticism I'd have is that you'd probably want a spread of three to five little fish to improve the odds of a hit.

You (Foxy) can say that sub captains deserve to get sunk if caught at such short range, but consider how many short-range actions there were between subs and escorts, some of which did end with the sub getting away. Think night convoy actions, where a sub will almost certainly try to breach the convoy perimeter on surface.

It could work for scuttling merchies too. Remember that the important thing is to make a hole underwater. A single small torpedo may do that more effectively than a couple of guns that'll be hard-pressed to hit below the waterline at close range.

I think what we have here is the opposite to Janes' Fighting Ships.

Janes' lists very little information, when all is said and done, and what there is lacks some in accuracy. That depends on what the navy in question wants you to know - the same applies to most shipping publications, actually, whether civil or military. Most numbers are kept under wraps, and the public ones are fairly vague.

The RM is bombarding us with information, listing more or less everything they can think of about the ship, and hoping nobody can figure out what's going on. For instance, I see no less than three speeds, with corresponding horsepower, and at least two machinery weights.

The machinery layout looks interesting; uptakes for the high-speed diesels might prove interesting if that's them abreast the after superstructure. I wouldn't like to be on the quarterdeck at speed. Not so sure about the diesel weights, though. To put it in context, the present-day Wärtsilä 9L20 medium-speed diesel develops 1,800 kW (about 2,400 horsepower) from 23.8 tonnes. These Italian engines, apparently, have a power to weight ratio of over 300 horsepower/tonne, whereas the modern engine (1992 design, 60 years after this ship) has only 100 horsepower/tonne. That's a really rather dramatic step back. I would be grateful to see some historical examples to support this degree of engine performance

I can see the utility in the small torpedo, although the speed seems optimistic. Running underwater, perhaps ten to fifteen feet down, gives a much better chance of hitting a diving submarine than a steeply diving shell does. Against merchantmen, too, it should be more than adequate; if you can get it into a hold, which seems likely, you'll get a fairly large hole even with a 60-100 pound warhead, and I doubt whether that will be survivable. The main issue with it is whether the speed (perhaps closer to 40 knots) will allow an interception of a diving submarine before it is out of depth.

The hull does appear to be rather deep for its' draught, but the diesels may well benefit her in that regard, as their weight low down should offset some of the topweight. Even so, I think it might be prudent to trim down above decks. Lower the after weapons some, which will cost seakeeping but not so much as capsizing would, and use aluminium extensively. It does have some disadvantages, like fatiguing rapidly and burning more readily than steel, but it is lightweight.

Foxy, until SS can handle hulls done with Froude's work, I'm sticking with Holtrop as coded in SS. Partly because I can't be bothered doing anything more difficult. If you want to, you could see what effect the Froude, Haslar and Denny-Mumford formulae for wetted surface area have. I leave finding them as an exercise for the reader.

And yes, I do have answers.

Given the data on 1950s vintage torpedoes, I'd expect a 325mm electric torpedo of 1930 vintage of have MAYBE a top speed of 30 knots. The problem is volume: the torp doesn't have room for the fairly hefty (relative to the volume of the torpedo) motor, the battery pack, and the warhead for anything faster. Larger 21" electric torps of somewhat later vintage (like the G7e of 1939) were 8-10 times heavier and no faster (though longer ranged at 5,000m initially and 7500m by the end of the war).

Yeah, it does sound like there's something a little dubious with the engines. I can't see any reason to do anything unusual with the engines: just use a diesel plant that's big enough to go as fast as you want it, leave the breakdown of any cruise engines vs flank speed engines (VERY unusual for this period, and as far as I've seen deployed on separate shafts when used at all) to the text.

In order,

Yes 15tons for stabilised 47mm mount. SS really underestimates the weight of light AA even if the mounting wasn't stabilised.

Good point on misc weight for the projectors. Maybe carry 24-36 extra in the forward magazine.

Higher efficiency of the high speed diesels? No, they are quite hungry in comparison.

The low speed diesels are for cruising for long periods of time. They are reliable, heavy duty types. SS still overestimates their weight by over 100%

The high speed diesels are lighter weight types that may be used for a few hours at most. They are not for continuous use for days/weeks. They are a conservative design compared to their contemporary Isotta Fraschini and CRM diesels I looked at. 0,5hp/kg is a conservative figure. Even more so with the design factor [which could be increased] getting down to 0,33hp/kg. With looking at today's diesels you have to be careful about turbos and EMC - these don't exist. Uptakes for 2 of them are aft. Might cause some problems. Later vessels may use underwater uptakes (or downtakes?)

The torpedo is eminently doable I think, and is useful for scuttling/sinking merchantmen as well. Speed would depend more on the physical size of the motors. 325mm might be a bit too small.

Definitely not going to use aluminium. Really awful stuff when the outer oxide layer is removed, such as in a fire. look at Sir Galahad. The above decks space is useful for the crew.

As for an overload of information. I could just say nothing like others, but am used to having to justify every engineering decision I make.