Doesn't seem to add up ??

[Roughasguts]

Just looking at the spec's on the QM 2 and she weighs 150,000 tons
Okay big, and her 6 motors produce 157, 000 HP.

Now thats 1 HP per ton, according to logic ain't now way she would move.
what am I missing here.

[Noelm]

there is a lot more to this than weight to HP, it all comes into things like waterline length and lots of stuff! very very complicated and there is lots of scientific stuff available about propulsion from Naval designers and so on.

[kingcobe]

Just looking at the spec's on the QM 2 and she weighs 150,000 tons
Okay big, and her 6 motors produce 157, 000 HP.

Now thats 1 HP per ton, according to logic ain't now way she would move.
what am I missing here.

Archimedes Principle which i'm learning at school may have something to do with it. The water is supporting the weight so that the engines don't have to work as hard as they would if they were pushing opr pulling something on dry land. i may be wrong though:-/

jj

[FNQCairns]

Gut's need WOT RPM and GPS speed with full tanks and compliment or it is just a waste of time and space, you should know that! :)

Wonder what the prop surface area per 1K HP is? She is a displacement vessel so the rules change greatly, imagine how many HP needed to plane the thing!!

cheers fnq

[triman]

Unfortunately most fishos and boatowners are fixated on horsepower. The modern marine diesel engine, especially the long-stroke type, produce huge amounts of torque and in matters maritime this is what counts, not horsepower.

[Roughasguts]

Thank's guys, yeah there is something here I can't get me head around.
I notice these big things idle past at 8-10 knots and not a ripple behind the boat. When you consider there moving thousands of tons of water, seems a lot has to do with shape of the hull, got me buggered.
Can't imagine how the hold course in a cross wind at low speeds either.

I know if you fly through the wake of a 747 on take off your dead, doesn't seem to be the same with the wake with a huge ship.

[Roughasguts]

Ahh but Triman two of the QM 2 motors are gas turbines, ain't no long stroke motors there, just big Rev boxes.

[FNQCairns]

I am not even going to pretend I understand displacement vessel rules, the ultimate displacement vessel is a sub when underwater, suspect this big ship would throw a HUGE wake at cruise when viewed from a small boats persective.

It's interesting when pushing up a tight creek at dead slow speed how much the water level rises on the bank even from a 16 footer.

cheers fnq

[triman]

Roughasguts, ship hull design has slowly improved over the years to such an extent that at low speeds they are extremely efficient, and one of the major reasons for the low wake at slow speeds has been the use of the bulbous bow. I don't claim to know the theory, practice or mathematics behind it but designing a bulbous bow into a dispalcement hull somehow minimises the bow wave. Energy going into producing a bow wave is energy lost in the propulsion of a ship so the vessel can either go faster on installed horsepower/torque or use a smaller propulsion plant for given speed if bow waves are eliminated or at least lessened.
Regarding the LM2500 gas turbines they are serious fuel-guzzlers and would only be used when absolutely needed, but their power output versus unit size is huge, giving great output from a small package.

[Roo]

how do these extra engines couple to the prop shaft(s)?? surely a gearbox isn't used or is it a hydraulic coupling?

[Roughasguts]

Not sure here guy's the tech info isn't great, but i'm thinking the gas turbine engines which are housed just under the stack are hooked up to electric motors.

Thank's Triman thought that boulbous bow was for added bouyancy, learn something every day.

Now you got to be a ships captain right.

[FNQCairns]

Think this ship is stopping over at Cairns soon, anyone know it's draft? Suspect that once it reaches the reef, it will be truly unsinkable, would make for a great platform to cast toward green zones:)

They must be going to anchor it outside the reef and transport people, I dunno.

The other world's largest ship or whatever anchored 5km off yorkys and transported passengers in their enclosed 25ft tenders, rough day, many sick bags and green people -was funny!:)

cheers fnq

[Kerry]

You might do a search for CODAG as QM2 proplusion is dual.

As for the HP? Sounds about right relative to the displacement.

[Kerry]

FNQ, Draft is only 10 metres, just a shallow draft punt compared to some of the coal boats :)

[Roughasguts]

Yeah CODAG big two strokes, backed up with Gas turbines.

[Stuie]

Apparently she can do 19 knots - backwards!

[triman]

Roughasguts, yes I was at sea for 30+ years and commanded quite a few large vessels in my time.
The QM2 propulsion system is CODAG with 4 diesel and 2 gas turbine engines, all turning generators.
The propellors are driven by electric motors in azimuthing pods.

[cbs]

I'm not sure on the exact figures on it, but using some very simplified figures, I'ss take a quick stab at it.

A large ship traveling at 30 knots in open water and operating in the displacement range is considered a slow vessel in terms of its length (Froude scaling).

For a given length, the resistance of a vessel increases exponentially with increase in speed up to the point of planing. (ie at displacements speeds, to double your speed, you need four times the power), hence QM2 is very low on the curve even if she is doing 25 knots or so, compared to a 10m boat at the same speed which would equate in relative terms to a low HP/ton requirement.

The designers/engineers of these large projects have R&D budgets of many $millions to answer these questions using a multidude of techniques so one would think they get it right. There was a documentarty on the building of the QM2 which showed some of the model testing done. Been on TV once or twice.

Make sense?


Somebody above also commented that Torque is more important than power for these vessels. It's not, though the two are related.

Simply,

A vessel is traveling at speed V (m/s)
Its total drag at that Speed is R (N)

Then the effective (note the term effective) power requirement P (eff) = R x V (watts) - (SI unit for power)

Then take a propulsive efficiency of the shafts/propellers/gearbox et as (%)

thus the installed power required is then P = P(eff) / %

Divide by 1000 to get kW then divide by 0.746 to get Horsepower requirement.

ie the Installed power is greater than the power required to push the vessel due to losses in the transmission and propellers.



the Power/Torque relationship is P=2(Pi) x n x T
P= Power (watts)
Where 2 x (Pi) = 2*3.14
N = shaft Revolutions /sec
T = Torque (Nm)

ie for a given power an increase in torque coincides with a decrease in shaft revolutions.

Make even more sense.

[Roughasguts]

Roughasguts, yes I was at sea for 30+ years and commanded quite a few large vessels in my time.
The QM2 propulsion system is CODAG with 4 diesel and 2 gas turbine engines, all turning generators.
The propellors are driven by electric motors in azimuthing pods.

Thought so Triman, On another site we where helping some one out with basic navigation questions.
Was good to explain something that we both took for granted, and pretty much forgoten about.

[Roughasguts]

Thanks CBS, kinda makes sence, hopfully i'll wake up one morning and understand the basics of it.

So there must be a formula, for lengh, width, and displacement, to get these really efficient figures for HP/ per ton.

Trying to work out how many tons my Signature should be so I can bring down the HP required to push it. I'm guessing 85 ton at the moment.

[Roughasguts]

I am not even going to pretend I understand displacement vessel rules, the ultimate displacement vessel is a sub when underwater, suspect this big ship would throw a HUGE wake at cruise when viewed from a small boats persective.

It's interesting when pushing up a tight creek at dead slow speed how much the water level rises on the bank even from a 16 footer.

cheers fnq

Hi FNQ, you raise an interesting point. Is displacement the key to effiecientcy,
Does any one know if a submarine can go faster under water, than above the water using the same method of propulsion ??

[insideout]

all the talk about propulsion is very interesting to me, but the one thing that really astounds me is how does she stay upright,when she only has a 10 mtr draft, when it is so many storeys high? Say she carries 5000 people at (for argument sake)100 kg per person ,and they all ran to one side, could this affect the ship in any detrimental way? Or is 2/3 rds of the weight of the ship under the waterline?

[cbs]

Hi FNQ, you raise an interesting point. Is displacement the key to effiecientcy,
Does any one know if a submarine can go faster under water, than above the water using the same method of propulsion ??


When a submarine travels on the surface its total resistance isa sum of skin friction and wave making resistance (plus a few other bits but lets ignore that)

Wave resistance is evidenced by the creation of surface waves as do most normal vessels. This wave will only occur near the air water interface. A deeply submerged submarine will not have this component of resistance.

Even with the increase in wetted surface, the total resistance (drag is less) thus they will travel faster.

[Roughasguts]

Good stuff there cbs, strangely I follow that, but looks like they have eliminated the shafts and gearboxes and use electric motors to over come all the losses.

Same principle as the Locomotive I guess.

[Roughasguts]

Thanks for the Submarine explanation, cbs, I thought it might be better under the water.

[cbs]

all the talk about propulsion is very interesting to me, but the one thing that really astounds me is how does she stay upright,when she only has a 10 mtr draft, when it is so many storeys high? Say she carries 5000 people at (for argument sake)100 kg per person ,and they all ran to one side, could this affect the ship in any detrimental way? Or is 2/3 rds of the weight of the ship under the waterline?

It isn't necessary to have the centre of gravity (CG) below waterlevel (or the vertical centre of buoyancy for that matter.

99% of boats including runabouts have a centre of gravity that is much higher than the centre of buoyancy. Don't believe me, Skech your boat and plot the CB below the waterline, then take a guess where all the major weights on board would be. The 1% of boats that do have CG below CB would mostly be racing yachts with heavy bulbs on their keels eg Americas Cup.

Now CB acts upwards, CG downwards, CG is above CB Sounds Unstable? Not necessarily, beacuse as a vessels heels due to a movement of weight (CG) the centre of buoyancy will move in the same direcion due to change in immersed volume. The key to positive stability is that the CB will move outboard with increase in heel. To maintain equilibrioum, CG and CB must be one above each other.

This is much easier to explain with a few sketches, but hopefully you get the jist.


To answer your other question, the movement of passengers is a very real possibility on most charter vessel (Ooh, a whale on the port side - Everybody runs) This effect is easily calculated and is a requirement to do so, along with wind and turning for nearly all commercial vessels, and had prescribed maximum limits, so don't be afraid to go with the crowd (except in dodgy 3rd would countries which don't have such rules in place)


cbs

[wessel]

I saw the program on the building of this ship, and there has been a few pictures in the papers here of them in Sydney harbour. One question I had then when watching the building of this ship, is how on earth do you service those azimuth pods?
An awesome idea and they make her go like the clappers, but the drive unit is contained inside of a box, effectively, that is sitting outside of the hull of the ship?

It gives a total new meaning to the term outboards.....

Wessel

[cbs]

Good stuff there cbs, strangely I follow that, but looks like they have eliminated the shafts and gearboxes and use electric motors to over come all the losses.

Same principle as the Locomotive I guess.

Most of the loss is in the prop. (maybe 65% efficient)

Shafts and Gearboxes lose very little (maybe 98% efficient)

[Roughasguts]

Wessel, I think they replace the whole unit for servicing.
Apparently there are four units stored some where up front out of sight.
Guess there ready to go and some how put in place with divers??

[Roughasguts]

Cbs, yeah maybe your right considering the low Revolutions.
I was considering the big drain with a turbo prop engine 2500 HP at the spool, drops to 800 HP through the gearbox then the prop.

[Roughasguts]

So is the weight and associated huge amount of inertia got a lot to do with all this efficientcy.
I guess once you have 150,000 tons finally moving you could back of the throttle and let inertia do all the work.

So my next question two cargo ships exactly the same one fully loaded one empty.

Which one is faster ? or more economical ? is there a differance in there performance.

[cbs]

So is the weight and associated huge amount of inertia got a lot to do with all this efficientcy.
I guess once you have 150,000 tons finally moving you could back of the throttle and let inertia do all the work.


doesn't work like that, a constantly moving ship still requires a power input to maintain a constant speed. the low power/weigh ratio will mean slow accelleration and deacelleration however when the power is applied/removed.




So my next question two cargo ships exactly the same one fully loaded one empty.

Which one is faster ? or more economical ? is there a differance in there performance.

The lighter one would be faster. Displacement is still displacemnt.

On a planing vessel, Weight is possibly the single most important factor to consider when making a boat get up and go though a little less significant imo for a displacement vessel. Still a factor in all cases.

[Greg P]

Heading to Cairns hey ---- You guys have left out the most important question :-X

Will it handle the NQ 2ft chop;D :P8-)

[Roughasguts]

Thank's cbs, now I won't do my head in thinking about that all night.

Greg, I think if the Qm 2 drops the stern motors 16 feet it should give a reasonable ride in the 2 foot chop.

But the captain should consider moving 5000 pax to the port stern quarter just to maintain balance.

[Dicko]

That thing probably has a pool big enough to develop it's own 2 foot chop in a 10 to 15 s/easter ;D

[insideout]

thanks cbs for clearing that up for me! Sounds like you have a lot of knowledge in this area, are you a engineer ? Or boat crazy like the rest of us?

[Luc]

Alowing for good design, displacement speed depends on the lenght to width ratio.

On some African documentaries, you see dugout canoes (very heavy crafts) move along at surprising speeds just powered by a 40 hp engine.

I have experienced it with Roscoe canoes where, given a 2hp engine, the 21 feet canoe moves faster then the 18 which is faster than the 16 etc...

A point with nuclear subs is that they can move much faster under the water than on the surface.

Luc

[Roughasguts]

Yeah still got me thinking one of dad's boats 1930 something clawson 19 foot in fibreglass, with a 4 cylinder prefect motor had only 8 HP yes 8 HP yet pushed the displacement hull along at 17-19 knots.

Now you couldn't put a 10 HP Honda on the back and do the same.
I also know some guys eventually put in there same type boat, a Holden 6, made no differance. Once the hull it terminal velocity that was it, just a waste of fuel.

I notice in me Baby Signature, it's very arse heavy, and 2 foot of the keel line is out of the water, at rest. So thinking I should be moving weight forward Eg: my 80 litre fuel tank, battery and me esky full of Beer.

Sure increases the water line, but will decrease the actual size, or depth of the hole the boat is trying to get out of.
Or am I barking up the wrong tree here.

[PinHead]

Displacement:101,000 to 104,000 tons full loadLength:Overall: 1,092 ft (333 m)
Waterline: 1,040 ft (317 m)Beam:Overall: 252 ft (76.8 m)
Waterline: 134 ft (40.8 m)Draft:Maximum navigational: 37 ft (11.3 m)
Limit: 41 ft (12.5 m)Propulsion:2 × Westinghouse (http://en.wikipedia.org/wiki/Westinghouse_Electric_Company) A4W nuclear reactors (http://en.wikipedia.org/wiki/A4W_nuclear_reactor)
4 × steam turbines (http://en.wikipedia.org/wiki/Steam_turbine)
4 × shafts
260,000 shp (194 MW)Speed:30+ knots (56+ km/h)Range:Essentially unlimitedComplement:Ship's company: 3,200
Air wing: 2,480
























you wouldn't want to get in the way of this one...101,000 tons at 30 knots

[Roughasguts]

Cool pinhead, where can I get me one of those little Westinghouse motors with the great fuel economy.

[honda900]

Is that all, Check out the new inboard..

http://people.bath.ac.uk/ccsshb/12cyl/

and a massive 102 rpm..

[Wayne_Red]

I had a conversation with a fellow years ago. He told me he was on a destroyer escorting the original QM during the war during a trip when it had troops on board. He said one day they got an alert there was submarine activity in the area.
To his amazement and mine he told me when they got the alert they increased to full speed, were doing 34knots flat out in the destroyer and the QM left them for dead and steamed over the horizon like they were standing still.

True story, first hand account. Makes you wonder what those ships were capable of. They were built with wars and troops in mind. It must have been doing 50 knots plus that day to leave the destroyer behind like that.
Wayne

[PinHead]

The original:



Queen Mary Statistics


Overall Length: 1,019.5 ft. (310.74 m.)
Overall Length: 1,019.5 ft. (310.74 m.)
Gross Tonnage: 81,237 gross tons (230,039 cu. m.)
Constructed by: John Brown & Co., LTD., Clydebank, Scotland
Commissioned by: Cunard Steamship Co., LTD.
Keel Laid: December 1, 1930
Date Launched: September 26, 1934
Maiden Voyage: May 27, 1936
Portholes: Over 2,000
Rivets: Over 10 million
Hull Plates: 8 ft. (2.44 m) to 30 ft. (9.14 m.) in length; up to 1.25 in. (3.2 cm.) thick
Moulded Breadth: 118 ft. (35.97 m.)
Height from Keel to Forward Smokestack Top: 181 ft. (55.17 m.)
Height from Keel to Promenade Deck: 92.5 ft. (28.19 m.)
Height from Keel to Top of Foremast: 237 ft. (72.24 m.)
Number of Decks: 12
Height from Keel to Top of Foremast: 237 ft. (72.24 m.)
Passenger Capacity: 1,957
Officers and Crew: 1,174
Horsepower: 160,000
Cruising Speed: 28.5 knots (55.17 km./hr.)
Rudder: 140 tons
Whistles: 3 - Steam type. Two on forward funnel, one on middle funnel. Each over 6 ft,. (1.83 m.) long, weighing 2,205 LB. (1,002 kg.)
Lifeboat Capacity: 145 persons
Smokestacks: 3 - Elliptical in shape; 36 ft. (10.97 m.) fore and aft, 23.3 ft. (7.1 m.) wide
Smokestack Height: Forward:</STRONG> 70.5 ft. (21.49 m.)
Middle: 67.5 ft. (20.57 m.) Aft:</STRONG> 62.25 ft. (18.97 m.)
Boilers: 27
Fuel Consumption: 13 ft./gal (1 m./l.)
Draft: 39 ft. 4-9/16 in. (12.00 m.)
Bow Anchors: 2 @ 16 tons (16,291 kg.)
Anchor Height: 18 ft. (5.48 m.)
Length of Promenade Deck: 724 ft. (220.68 m.)
Length of Anchor Chain: 990 ft.
Weight of Anchor Chain: 45 tons (45.818 kg.)
Anchor Chain Link: 2 ft. (61 cm.) long, weighing 224 LB. (101.8 kg.)

[Wayne_Red]

They were amazing feats of engineering then and they still are today.
Wouldn't you love to have a day to look over the engine rooms in the QM2 or QE2
Wayne