Navy ships off Plymouth

[Mick F]

PS:
If a ship was going round in circles under its own power, it wouldn't be for compass calibration, but some sort of navigation training, or possibly for testing the rudder system.

To do a "compass swing" to check the compasses, the ship is tied to a buoy and is turned round and round by a tug.
Meanwhile, the compasses are calibrated using visual references ashore.

Gyro compasses and magnetic ones too.

Gyro compasses need to know the latitude on Earth to correct for Earth's rotational speed.
Magnetic compasses have correction balls port and starboard of the unit to correct for the length of the ship, and bars beneath to correct for the height of the ship. These need to be regularly calibrated.

Gyro compasses are very sophisticated instruments, and the frigates I've served on had two each. Not only do they feed heading info to the compass repeaters, but they also stabilise the weapon systems. Point your weapon at a target, and you want the ship's movement to be removed from the point of aim. This is subtracted for pitch, yaw and roll, as well as heading.

[KTHSullivan]

Could have been knitting

[philvantwo]

Says on wikipedia your Falklands ship was sold to Pakistan and is still in service Mick F. For both ships you mentioned, it says they're powered by gas turbines, I always thought ships ran on diesel? How do they work? Tell me more please Mick F.

[mumbojumbo]

Gas is a little combustible,making for a risky journey.There was a decent grey diesel market in 50s Portsmouth.

[halfpenny]

Gas turbines seldom are fuelled by gas - think avgas (paraffin) for planes, diesel for gensets

[Jdsk]

Marine propulsion:
https://en.wikipedia.org/wiki/Marine_propulsion#Gas_turbines

NB the very interesting use of different engines in the same ship.

There's been enormous effort within NATO to consolidate on as few types of fuel as possible. One amusing effect of that was the use of Diesel engined motorbikes.

Jonathan

[Mick F]

Says on wikipedia your Falklands ship was sold to Pakistan and is still in service Mick F. For both ships you mentioned, it says they're powered by gas turbines, I always thought ships ran on diesel? How do they work? Tell me more please Mick F.

HMS Ambuscade and yes, still in service with the Pakistan Navy.

The Type 21's were diesel powered.
Two Rolls Royce Tyne engines and two Rolls Royce Olympus engines.
Tynes powered jet aircraft, notably Vickers Vanguard, and Olympus famous for Concorde of course.
Two shafts with variable pitch propellors and both shafts could be powered from all four engines.
One heck of a torque and one heck of a performance. Speed boat performance.

The ships could accelerate in a standing start with all four engines on full power and you could feel the power like in a car on the road. The ships could go into reverse at the flick of the lever from full ahead to full astern and the front end of the ship would dig in and 3,000 tons of ship could stop dead in the water in almost its own length. One captain of one of them, was on water-skis behind one just to prove it could be done.

[philvantwo]

How do the gas turbine engines work and how many miles can they run for? How do they refuel if they're at sea?

[nirakaro]

... even with electronic (rather than mechanical) magnetic compasses.

How does an electronic compass work? I imagine it to be a standard magnetic compass, scaled down to integrated circuit dimensions? In which case it would be subject the same distortions as any other compass?

[Brucey]

there is more than one sort but this is the most commonly used on ships

https://en.wikipedia.org/wiki/Fluxgate_compass

cheers

[Mick F]

All this is beyond my expertise.
I was an electronics engineer specialising in radars and comms and computers and guided weapon systems and gunnery direction systems too.

Gas turbines are rotating fans, and they suck in air and burn refined diesel ......... not your diesel you shove in your cars ........... and the fans rotate at phenomenal speed and gearboxes to reduce the speed to a max of low hundreds of RPM with the consequential increase in torque for the drive shafts.

Dunno about electronic compasses.
Electro/mechanical gyro compasses have a compressed air supported bearing and the gyro spinning at a very fast rate and they are then gyro-stabilised by dint of normal physics. Viz a bicycle wheel spinning whilst holding the axle and trying to turn it sideways.

Clever alignment gets them in the right orientation, and the ship can pitch this way and that and the gyro will remain stable within the spherical housing.
Electro pickups see the alignments and send that to the system. The ship then knows its pitch, yaw and roll, as well as its heading.

Beyond my ken, as gyro compasses were in a different section of the department to mine, and gas turbines and propulsion systems were in a different department entirely.

[Jdsk]

How do the gas turbine engines work and how many miles can they run for? How do they refuel if they're at sea?

In general or in marine applications?

They refuel by pumping liquid in from shore or other ships. As above the fuel specs are standardised at NATO level.

And range is crucial to what warships can achieve. Other than in the nuclear-powered vessels it's often limited by fuel. A large part of the debate about what the Royal Navy is and should be able to do revolves around the capacity for independent operation, both in logistics and the problem of unprotected carriers.

Jonathan

[Mick F]

Two points here.

Go back years, and some ships had diesel engines. Big reciprocating things.
Some of the RN frigates could circumnavigate the globe without refuelling if they kept to best economical speed. Can't remember the class of ship but they were in service early in my career.

Type 21 frigates were gas turbine propelled but they didn't have separators. This meant as they got low on fuel, they became unstable.
Later gas ships - and earlier ones too - had separators and the fuel tanks could be flooded with sea water, as the diesel fuel would float on the water to some degree in the tanks and the separators would "separate" the contaminated fuel for the pure stuff.

Type 21 frigates were thirsty, but unstable if they didn't have lots of fuel, so needed refuelling every week.

Edit:
Leopard Class. Mate of mine was in Jaguar.
https://en.wikipedia.org/wiki/Leopard-class_frigate
There were more ships propelled like that. Salisbury Class and the like.

[Jdsk]

Go back years, and some ships had diesel engines. Big reciprocating things.

Our new carriers have Diesel engines: four each along with two gas turbines.

Jonathan

[philvantwo]

I've just been reading about the latest aircraft carrier, 4million litres of fuel for the ship and then it holds another 3million litres of fuel for the aircraft!
Fascinating stuff!