Royal Navy and Lobster Pots

Habebty

Habebty

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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?)
 
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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 was shocked about how vulnerable the ship is to that sort of damage. I would have thought that propulsion plant would be almost off the shelf as used on commercial ships of a similar size and speed and hence utterly reliable. (Perhaps with added redundancy to survive damage.)
Is she much faster than comparable commercial vessels, or are there other reasons to have special kit?
 
DJE said:
I was shocked about how vulnerable the ship is to that sort of damage. I would have thought that propulsion plant would be almost off the shelf as used on commercial ships of a similar size and speed and hence utterly reliable. (Perhaps with added redundancy to survive damage.)
Is she much faster than comparable commercial vessels, or are there other reasons to have special kit?
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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.
 
I thought the lobster pot idea was a bit of folklore to cover red faces at the builders as one of the propellor blades had not been fixed on properly, which is what they said towards the end. Something about a seal that was not placed properly and stopped the bolts being tightened fully. The wobbly blade then caused vibration that damaged the thrust block and shaft brake, both of which looked pretty under spec. to an armchair sailor like me.
 
I watched the programme last night with interest & thought that all the enemy has to do is stream a few wires or multiplaits about just under the surface & the whole thing would be disabled.. Almost undetectable, unless picked up by mine sweepers that would be in front.

The technology involved has been about for years & it seems pretty poor design that they made such a basic error in the construction of the thrust block.

Although the ship cost billions I somehow wonder if it has been built "on the cheap". Why not nuclear powered? Surely a range of 10,000 miles is rather low, or is it that in a war situation they do not expect it to last that long anyway.
 
john_morris_uk said:
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.
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Thanks for that. My cynicism needs reining in every now and again.
 
I didn't see the programme, I was put off by the description of sea trials in the North Sea as dangerous. Sure there's a risk a few things will go wrong, but dangerous? It's a warship FFS; if a trundle round the North Sea is dangerous I want my money back!

I would have expected a twin screw ship to have one left hand and one right hand prop to balance out prop walk, or is that something that only affects our wee boats?
 
Stemar said:
I didn't see the programme, I was put off by the description of sea trials in the North Sea as dangerous. Sure there's a risk a few things will go wrong, but dangerous? It's a warship FFS; if a trundle round the North Sea is dangerous I want my money back!

I would have expected a twin screw ship to have one left hand and one right hand prop to balance out prop walk, or is that something that only affects our wee boats?
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Perhaps they mean dangerous to everything else? A few run down boats, the odd missile randomly fired off, a broadside on Harlepool?
 
'I would have expected a twin screw ship to have one left hand and one right hand prop to balance out prop walk, or is that something that only affects our wee boats?'

I would expect prop noise reduction to be on the agenda.
 
Daydream believer said:
Although the ship cost billions I somehow wonder if it has been built "on the cheap". Why not nuclear powered? Surely a range of 10,000 miles is rather low, or is it that in a war situation they do not expect it to last that long anyway.
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Cheap being a relative term! £6.2bn for the pair.

AIUI the rationale behind avoiding nuclear was not just cost.

Whilst the range would be to all intents and purposes infinite, she would still need support. She can't carry infinite food, the F35Bs need fuel, she needs weapons and her escorts need fuel anyway so going nuclear doesn't avoid a long logistics tail.

Nuclear is more expensive, carries risks that stretch long after the lifetime of the nuclear plant and IIRC the "usual" lifetime of a nuclear plant is in the 25-30 year span - the QE carriers have a 50 year planned lifespan so you face a very expensive mid life upgrade.

Finally - many states object to the presence of nuclear powered vessels. That could cause issues for example if Egypt closed the Suez canal to them in a couple of decades.

That said - the whole package is short of money.

She carries no point defence missiles ( assuming that CIWS will be fitted at some stage) and relies on her escorts. We have too few escorts 13 T23 and 6 T45 - assuming 1/3 are fully available and not under refit / training then at any one time then that's 2 T45 and maybe 4-5 T23 to undertake all of the standing tasks and escort the carrier. Even when the F35's are ready we will only have 2 squadrons of them available. They may be able to contain up to 50 F35s in surge conditions and 36 in normal use but ignoring the OCU and OEU planes we will only have 24 combat ready operational up till at least 2030.

If we're going to do carrier strike ( and personally I think we should) then we need to pay for it. IMHO that means increasing the size of the defence budget to circa 3% of GDP over the next 5 years as the deficit falls and using the extra money to 1) bring in sufficient manpower to crew the existing ships, 2) cover the costs of existing planned unfunded purchases, 3) increase the escort fleet to minimum 30 ships, 4) stand up an additional 4 squadrons of F35. ( In addition to the 3 needed to replace the existing tornado fleet)
 
mainsail1 said:
I thought the lobster pot idea was a bit of folklore to cover red faces at the builders as one of the propellor blades had not been fixed on properly, which is what they said towards the end. Something about a seal that was not placed properly and stopped the bolts being tightened fully. The wobbly blade then caused vibration that damaged the thrust block and shaft brake, both of which looked pretty under spec. to an armchair sailor like me.
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Almost exactly as was stated later in the programme. They even showed the the seal that had failed.
 
Stemar said:
I didn't see the programme, I was put off by the description of sea trials in the North Sea as dangerous. Sure there's a risk a few things will go wrong, but dangerous? It's a warship FFS; if a trundle round the North Sea is dangerous I want my money back!
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Television always has to manufacture drama.

Pete
 
jac said:
AIUI the rationale behind avoiding nuclear was not just cost.
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Indeed - as well as everything you listed, there would probably be huge political backlash of the "noocular = bad" variety.

jac said:
IMHO that means increasing the size of the defence budget to circa 3% of GDP over the next 5 years as the deficit falls
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Forgive my ignorance on macroeconomics, but what is "the deficit" that is falling?

Pete
 
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