Royal Navy and Lobster Pots

[mobeydick]

Surely they need to fit a couple of rope cutters ....

BTW it was said that the 'lobster pot' caused the prop blade to shift, due to the blade/seal not being installed correctly. This inbalance caused the thrust block to crack. (I would not have thought welding the thrust block would have been a sufficient repair, but what do I know?)

The thrust block fastenings were undersized due to an incorrect calculation from 'several years ago', which meant it could not take the shaft vibration - as you would have thought it should do battle? So, on that ONE prop installation, we have two manufactures faults - incorrectly installed prop blade, and undersized thrust block. Either of which could have had catastrophic consequences if not found due to a freak lobster pot.

Does make you wonder what other faults are hidden. That is why you have sea trials and shake downs I guess....

 

[harry potter]

Watched a programme about HMS Queen Elizabeth tonight. Much head scratching by marine engineers over vibration in Stbd prop shaft causing thrust block crack and assorted "issues".
One engineer said likely cause might be a lobster pot and rope.......seriously....and that a six ton prop blade on a capital ship was buggered by a lobster pot!!
Someone should tell them about the RYA pot campaign?

Actually in fairness, the marks on the shaft did look like a seriously thick (I.e. Not a pot marker) rope had been picked up and wrenched a blade. (Are they variable pitch props?)

Passing Horse Sand Fort last Friday noticed two lobster pots strategically placed at 50.44.953N 1.04.385W, directly in shipping lane. ? Russians ?

 

[lpdsn]

Perhaps they mean dangerous to everything else? ... a broadside on Harlepool?

They could probably get an EU Regional Development Fund grant for that.

 

[harry potter]

!

 

[Champagne Murphy]

Personally, I thought it a shame that they weren’t able to pin the blame on a pot. It might have encouraged the Government to do something about unmarked pots.

 

[newtothis]

Personally, I thought it a shame that they weren’t able to pin the blame on a pot. It might have encouraged the Government to do something about unmarked pots.

Could be a job for any minesweepers not involved in a hot war at the moment, which I'm pretty sure is all of them.

 

[jac]

Forgive my ignorance on macroeconomics, but what is "the deficit" that is falling?

Pete

The one we've had since about 2002 - that was up around the £150bn p.a. and is now down to about £50bn p.a. On current projections it's due to be eliminated in about 5 years and then we start paying back the national debt - currently about £1.9 TRILLION pounds.

Big scary numbers but without wishing to teach grandmothers, the current deficit is not the issue as it's only about 2% of GDP ( 3% is considered the limit by the Eurozone for example) - it's the size of the total debt now - it's about 80% of national income ( GDP) ( compared to 60% for the Eurozone countries.) As the deficit is now relatively small and the economy growing the Debt to GDP ratio is getting better each year.

Latest estimates show deficit projections slightly ahead of plan but of course still plenty of scope for it to go wrong.

SO we should start to increase spending ( and on other things as well) as the finances become slightly less stretched.

 

[wotayottie]

are there other reasons to have special kit?

You dont really expect the MoD to order standard off the shelf bitr rather than specials 10 times more expensive do you?

 

[Daydream believer]

Surely they need to fit a couple of rope cutters ....

BTW it was said that the 'lobster pot' caused the prop blade to shift, due to the blade/seal not being installed correctly. This inbalance caused the thrust block to crack. (I would not have thought welding the thrust block would have been a sufficient repair, but what do I know?)

The thrust block fastenings were undersized due to an incorrect calculation from 'several years ago', which meant it could not take the shaft vibration - as you would have thought it should do battle? So, on that ONE prop installation, we have two manufactures faults - incorrectly installed prop blade, and undersized thrust block. Either of which could have had catastrophic consequences if not found due to a freak lobster pot.

Does make you wonder what other faults are hidden. That is why you have sea trials and shake downs I guess....

3 slight errors there
First they did not weld the thrust block but welded an additional chock behind the thrust block
Secondly the thrust block was not undersized it was the sizing of the bolts that was at fault
Finally the blade itself was installed correctly but moved because the bolts were not torqued up correctly due to a misaligned seal
But as you rightly suggest these do seem errors that should not have happened. Perhaps they were made because we have lost the ability & some of the skills to build ships in the way we did in the past

 

[dom]

Big scary numbers but without wishing to teach grandmothers, the current deficit is not the issue as it's only about 2% of GDP ( 3% is considered the limit by the Eurozone for example) - it's the size of the total debt now - it's about 80% of national income ( GDP) ( compared to 60% for the Eurozone countries.) As the deficit is now relatively small and the economy growing the Debt to GDP ratio is getting better each year.

Interestingly, despite their rules, Euroarea Debt-to-GDP is in fact 88.1%, almost exactly the same as the UK's. France's is higher at 96.5%. That said the falling deficit prognosis is based on some fairly optimistic productivity growth and a faster rate of Govt spending cuts, which probably won't happen.

Still, some kind of rope cutter should certainly not be a problem :ambivalence:

 

[Daydream believer]

I’m not sure that they are particularly susceptible to damage.

A commercial vessel is invariably designed to operate efficiently at one speed. It’s got a design cruising speed and that’s that. A military vessel is usually designed to be able to sprint or jog along slowly and to manoeuvre as rapidly as possible. The design requiremt is very different and although compromises will be made, off the shelf propulsion systems are not going to be suitable.

But when one takes into account that the Bismark built for WW2 could do 30Kts & was over 800ft long & about 60,000 tonnes against the QE's 900 ft & 70,000 tonnes approx values then technology has not exactly advanced much further. The Japanese had even larger battleships I understand.
So for a simple thing like the thrust block & propellor installation to fail it does seem like a serious failing in our ability to build good ships anymore.

 

[Daydream believer]

Perhaps they mean dangerous to everything else? A few run down boats, the odd missile randomly fired off, a broadside on Harlepool?

Hartlepool is perfectly safe - Unless the Spanish send another armada full of monkeys that is!!
She is not fitted with any weapons other than small arms for local defence. That is to be supplied by surrounding task force.
However, as we have no proper long range radar surveillance system other than helicopters with limited air time the ship is vunerable to missile attack. It does not have any catapults so it cannot carry long range surveillance aircraft. It really has little more than line of sight radar.
The Russians have already found out how to jam our intership communication & defence systems so the carrier will be dead easy to knock out. It does not have any inbuilt missile defence & early warning system suitable for warning of much beyond the horizon other than aircraft- of which there are none. Even when it does have them their range is limited due to the fact that the jump jet capabilities limit the weapon carrying ability & they are poor in dogfight scenarios.
Why on earth did we scrap the Harrier so soon?

When fully equipped it will be OK for local support of isolated battle zones such as blowing up the odd defenseless building in Syria. However, in a full blown war it would be next to useless.
Just drop a nuclear warhead on the task force.- Or string a few lobster pots out!!!!!!!!

 

[Neil_Y]

Nearly every year I come across (large) fishing boats with big props that have caught pot rope and in many cases the forces can pull the gearbox off the engine, breaking the bolts. The forces pulling the shaft aft are huge as the debris winds on gradually, just like a winch drum.

The force is caused by the power of the engine, fishing boats often do more damage as they have a bigger reduction so more torque. This can all be done with 12mm poly prop

 

[Daydream believer]

Can I ask a question of those that may have been connected with the navy in their past lives?

When i watched the TV programme some of the recruits looked totally lost as though they had not got a clue. Now that is not to say that eventually they might not become quite good at what ever it is they are assigned to do.

However, they are going to have leave or depart from the force altogether & there will be the inevitable rotation of ratings.
In the past when the navy had a much larger pool of trained ratings & officers I can imagine that the powers that be would send a proportion of new recruits but always ensure that some experienced people would come from other ships. They would, I imagine, keep up a rotation so that every ship had some experienced pool on every ship.
But in the current climate we have a far lower staffing level "in the field" & fewer skilled people to rotate around with the newbies. So does that create a problem for the officers on ships like the QE as every so often it has a ship load of totally unskilled people with no idea of how the ship runs & very little experience of working on other ships beforehand.
If that is the case it would put the operation of the ship at extreme disadvantage.
Or have I got it all wrong & everyone who goes on the ship already knows about ship life & what to do within their particular field of operation

 

[East Cardinal]

Yes they are variable pitch and each with a total weight of 30+ tonnes according to last weeks programme when they showed the hub and flukes being fitted to the shafts by divers underwater.

I thought they were fixed pitch props. The markers on the shaft/blades are an aid to fixing in correct position, not an indicator of variable pitch.

 

[Corribee72]

But when one takes into account that the Bismark built for WW2 could do 30Kts & was over 800ft long & about 60,000 tonnes against the QE's 900 ft & 70,000 tonnes approx values then technology has not exactly advanced much further. The Japanese had even larger battleships I understand.
So for a simple thing like the thrust block & propellor installation to fail it does seem like a serious failing in our ability to build good ships anymore.

The Yamato class battleship, they did see some action but spent a fair time in port as the Japanese were worried about losing the iconic ships to subs, some things don't change! Big assets make big targets I guess.

 

[Giblets]

I thought they were fixed pitch props. The markers on the shaft/blades are an aid to fixing in correct position, not an indicator of variable pitch.

My apologies - my source has been slapped round the head with a wet cod!

 

[East Cardinal]

The controllable pitch propellers were fitted to propulsion systems that were constantly turning once engaged. For example the Type 42's (see how old I am!) had gas turbine power driving through reduction gearboxes. Once the engines were connected to drive the shaft, the shaft would turn. The propellor blade pitch was controlled to give slow speed manoevring or no propulsion.
That differs from a steam propulsion plant where the steam through the turbine can be redirected and the shaft stopped.
In the case of QE the drive is indirect from gas turbine and diesel motors via electric motors so the shafts can be stopped if reqiured.
Why the props turn the same way, I don't know. I guess that confined turns in harbour will be aided by tugs, and keeping both shaft designs the same would reduce spares required to be carried.
The speed of the ship will be designed to give enough airspeed over the deck to allow the embarked aircraft to take off.
25 kn or so must be adequate for the proposed aircraft.

 

[Pete7]

Why the props turn the same way, I don't know. I guess that confined turns in harbour will be aided by tugs, and keeping both shaft designs the same would reduce spares required to be carried.
.

The props do turn in opposite directions its just they are mounted so looking from the stern the port prop turns clockwise and the starboard prop turns anticlockwise. I thought twin propped boats had props that turned the otherway.

 

[mobeydick]

3 slight errors there
First they did not weld the thrust block but welded an additional chock behind the thrust block
Secondly the thrust block was not undersized it was the sizing of the bolts that was at fault
Finally the blade itself was installed correctly but moved because the bolts were not torqued up correctly due to a misaligned seal
But as you rightly suggest these do seem errors that should not have happened. Perhaps they were made because we have lost the ability & some of the skills to build ships in the way we did in the past

3 slight errors there:
Firsty they said they welded the block, then welded some additional support to the block. Still seems a bit makeshift
Secondly I wrote that the thrust block FASTENINGS were undersized
Finally, if the seal is not installed correctly, the blade is not installed correctly.