WesWorld

Something a lot different;

An Oceanic Tug/Repair ship. The Meditterenean is becoming increasingly crowded with larger and larger ships (merchant as well as naval units). The current largest tugs are approx 500tons shown here. This vessel(s) is considerably larger with more power. This makes it more suitable for towing larger vessels. In its secondary role, it'll serve as a repair ship, having materials onboard for effecting temporary repairs.

The design itself is heavily built with extensive subdivision inboard and thicker than usual outer hull plates (in addition to fenders). There are extensive accomodations onboard in case crew need to be taken off.

Machinery includes 2x2000hp marine diesels from the Gabbiano class of escorts. In addition to this are 2x5000hp Fiat-Guidoni diesels with clutches that can be engaged to the propellor shafts to transmit additional power if needed.


Tug/Repair ship, laid down 1935

Displacement:
1,899 t light; 1,966 t standard; 2,656 t normal; 3,208 t full load

Dimensions: Length overall / water x beam x draught
304.05 ft / 295.28 ft x 49.21 ft x 9.84 ft (normal load)
92.68 m / 90.00 m x 15.00 m x 3.00 m

Armament:
4 - 0.98" / 25.0 mm guns (2x2 guns), 0.55lbs / 0.25kg shells, 1935 Model
Anti-aircraft guns in deck mounts
on side, all forward
4 - 1.85" / 47.0 mm guns (1x4 guns), 3.86lbs / 1.75kg shells, 1935 Model
Anti-aircraft guns in deck mount
on centreline aft
Weight of broadside 18 lbs / 8 kg
Shells per gun, main battery: 1,000

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Ends: Unarmoured

- Torpedo Bulkhead:
0.39" / 10 mm 213.25 ft / 65.00 m 16.40 ft / 5.00 m

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
2nd: 0.39" / 10 mm 0.39" / 10 mm -

Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 4,000 shp / 2,984 Kw = 17.00 kts
Range 10,440nm at 16.00 kts
Bunker at max displacement = 1,242 tons

Complement:
184 - 240

Cost:
£0.427 million / $1.708 million

Distribution of weights at normal displacement:
Armament: 2 tons, 0.1 %
Armour: 52 tons, 2.0 %
- Belts: 0 tons, 0.0 %
- Torpedo bulkhead: 51 tons, 1.9 %
- Armament: 1 tons, 0.0 %
- Armour Deck: 0 tons, 0.0 %
- Conning Tower: 0 tons, 0.0 %
Machinery: 114 tons, 4.3 %
Hull, fittings & equipment: 1,181 tons, 44.5 %
Fuel, ammunition & stores: 758 tons, 28.5 %
Miscellaneous weights: 550 tons, 20.7 %

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
13,437 lbs / 6,095 Kg = 28,185.2 x 1.0 " / 25 mm shells or 4.0 torpedoes
Stability (Unstable if below 1.00): 1.10
Metacentric height 2.1 ft / 0.6 m
Roll period: 14.3 seconds
Steadiness - As gun platform (Average = 50 %): 94 %
- Recoil effect (Restricted arc if above 1.00): 0.01
Seaboat quality (Average = 1.00): 2.00

Hull form characteristics:
Hull has rise forward of midbreak
and transom stern
Block coefficient: 0.650
Length to Beam Ratio: 6.00 : 1
'Natural speed' for length: 20.13 kts
Power going to wave formation at top speed: 49 %
Trim (Max stability = 0, Max steadiness = 100): 47
Bow angle (Positive = bow angles forward): 10.00 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 %): 26.25 ft / 8.00 m
- Mid (60 %): 24.61 ft / 7.50 m (16.40 ft / 5.00 m aft of break)
- Quarterdeck (15 %): 16.40 ft / 5.00 m
- Stern: 16.40 ft / 5.00 m
- Average freeboard: 22.38 ft / 6.82 m

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 65.5 %
- Above water (accommodation/working, high = better): 264.0 %
Waterplane Area: 11,614 Square feet or 1,079 Square metres
Displacement factor (Displacement / loading): 315 %
Structure weight / hull surface area: 60 lbs/sq ft or 293 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.89
- Longitudinal: 7.06
- Overall: 1.10
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

5000miles at 80% power = 337tons main engines
2x5000hp Fiat-Guidoni Diesels + auxiliaries = 100tons
5000miles at 80% power = 1.6tons/hour
Speed with both engines at 80% = 22.6knts
Time to cover 5000nm=221hrs = 353tons fuel for Fiat diesels
Total fuel = 337+353 = 690tons

450tons = supplies/cranes/gensets etc.

Built to 1.10hull strength with thicker hull plates.

A very interesting ship but why aren´t her main diesel the more powerful pair?!?!

Am I right to assume this vessel may also be a good tender for subs or small vessels if need be?

Quoted

A very interesting ship but why aren´t her main diesel the more powerful pair?!?!

The 2x2000hp diesels are medium speed, more reliable and more fuel efficient. The 5000hp pair are high speed turbodiesels and less reliable. (They're only just starting to be reliable after help from Danish technical centre. -See news)

She'd probably make a reasonable tender for small vessels. Leaving the quarterdeck free would make it possible to hoist some MAS onboard for repairs.

Not sure why you placed guns on her at all...?!

I wanted some limited anti-aircraft and anti-small craft capability. The mountings don't greatly impact the vessel.

Quoted

Originally posted by HoOmAn
Not sure why you placed guns on her at all...?!

Next thing you know they'll start exploding.

Isn´t her draught a bit low for such a vessel and those screws look awefully tiny......?! At least compared to her 7-deck--upper-hull....?!

Have to say, Gavin, that the screws want to be several times that size. Even oceanic tugs finish up with relatively huge props for high thrust at a low speed. Having said that, the salvage tug is something that needed to be invented sooner or later.

Of course, like most tugs, she has all the aesthetic qualities of half a breeze block, but that can't be helped. Since she's going to be ugly anyway, why not go with a straight sheer rather than a parabolic sheer forwards. The yard workers will thank you greatly.

I'd be interested to know the effects of those cranes on stability: when cargo is being lifted, the loads effectively act at the head of the crane. I suspect the crane may have a practical capacity rather less than its' theoretical capacity. Especially with that massive superstructure. However, without knowing KG, I can't begin to estimate what might happen.

A standard American Fleet tug of World War II can make 10 knots....towing or not. But it has an increadible range, as they could in theory tow the modern U.S.S, Enterprise halfway around the world (at 10 knots) if they had to do so. While the specs say I believe 14 knots, anything over 10 knots makes the ship rattle loudly.

Not sure about the draught. I think it just seems that way because of the massive freeboard (for space and seakeeping).

I've updated the pic with some larger props. Too early for Kort nozzles.

Shes definitely ugly, but that was the intention in drawing her.

Having a look at other floating cranes, they've got rather large counterweights. It'll add quite some weight to the crane but its better than capsizing. Maybe some large retractable fin stabilisers. Not the current generation of ones that change attitude but fixed to reduce roll. Then there are problems in coming alongside other ships. Maybe fit anti-roll tanks instead?

The Germans had some "floatplane recovery vessels" or whatever they were and those had quite large cranes (compared to their size) so I doubt it´s much of a problem...

Funnily enough, I did think of Kort nozzles. The leap to come up with them isn't terribly great, and 1934 is when the theoretical work was historically done. Not too clever over 10 knots or so, though.

The problem with the cranes isn't one of balancing, but one of topweight. At risk of preaching to the converted, metacentric height (GM) is a measure of stability, and indicative of the righting moment.

A 20 ton load at deck level may be fairly benign, and not do an awful lot to harm stability. If the weight is then fully supported by the crane, even with no lifting done, the force effectively acts at the head of the crane. For a 2,000 ton ship, that would raise the height of the centre of gravity (KG) by about 15 centimetres. If GM is only 60 centimetres with the weight on deck, it will be 45 centimetres when the crane takes the full load. That's not a trivial shift, and ballasting down is the only reasonable way to counter it.

Adding a counterweight will probably help stability of the crane, for the same reasons as on a land-based crane. It involves adding topweight, though, which will be detrimental to ship stability. Time for more ballast. That may not be a bad thing in a tug, though, as they tend to be fairly heavily ballasted when towing anyway. Stability again.

Quoted

Funnily enough, I did think of Kort nozzles. The leap to come up with them isn't terribly great, and 1934 is when the theoretical work was historically done. Not too clever over 10 knots or so, though.

I just looked at this. Besides Mr. Kort the other notable person was Lugi Stipa. Stipa also experimented with aircraft producing a flying prototype and numerous design studies. These use a similar principal to waterborne Kort nozzles but the additional drag in air isn't as great a factor. I didn't know that he'd experimented with waterborne applications as well. It shouldn't be overly difficult to fit them in a couple of years.