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Post by markkarj on Dec 9, 2007 7:59:46 GMT -8
Hi folks: Quite a few of BC Ferries newer single-ended ships (and the V-class) have bulbous bows. I'm pretty sure the Queen of the North had one too. So a question for all of you engineers out there: is there any reason why the QPR doesn't have one? www.pbase.com/kstapleton/image/57967078Mark
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Post by blackshadow on Dec 9, 2007 8:24:17 GMT -8
That is good question. My thoughts is because she use to go to different terminals when she was built and how deep water at these terminals. If you noticed the her bow is racked back almost like ice breakers this might support this thought. At one time bulbous bows were no required and reason for them wasn't believed as there was no figures to state the claim they were any advances. Some ship designers thought bulbous bows were bit of black magic at one time. Do some reading up on bulbous bows and you find it very interesting and including the history.
There fore only persons knowing correct answer would be the team at that time designing the QPR.
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Post by John on Dec 13, 2007 21:17:02 GMT -8
I know why the QPR doesn't have a bullbous bow. Firstly, she is a really small ship by standards today. And she transits the Hecate Strait, which is shallow. In heavy seas, I have been on it when she was rumoured to ground out in heavy water in swells.
Was on a trip from the Charlottes once, what usually takes about 6 hours, took 14. Not fun.
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Post by farout on Feb 20, 2008 13:09:27 GMT -8
The C-Class ships and I-Class ships have Propellers at both ends of the boat or can change the direction they face, How do ships like the Spirits and other ferries that only have propellers in the back end of the ship go into Reverse?
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Kam
Voyager
Posts: 926
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Post by Kam on Feb 20, 2008 13:37:34 GMT -8
The propellers are what’s called variable pitch. That is, the blade of the propeller actually changes angle and sweeps all the way over to push water in the opposite direction. This is the case on the Spirits and the C class ships as well. The propeller turns at a constant RPM, even while in dock, but to move the ship the propeller pitch is changed to essentially grab more or less water and move it in the direction required.
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Post by WettCoast on Feb 20, 2008 13:50:39 GMT -8
Single ended ships are equipped with what are called 'bow thrusters'. These push the ships out of docks such as Tsawwassen at a slow speed until they are far enough out, and then the big propellers at the stern kick in and the rudder is cranked hard to port or starboard, and then the ship is turned 180 degrees and is on its way. The bow thruster has a propeller located in a tunnel. See Kevin Stapleton's website for pictures... www.pbase.com/kstapleton/queen_of_nanaimo
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Post by DENelson83 on Feb 20, 2008 15:13:32 GMT -8
Bah! Silly me! When I saw the title "Ferries in Reverse", I thought of ferries being transported by cars. ;D
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Post by Taxman on Feb 20, 2008 17:33:04 GMT -8
Re: DENelson Osprey2000 Saltspring Queen (or was it Vesuvius Queen)
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Post by DENelson83 on Feb 20, 2008 17:48:06 GMT -8
Re: DENelson Osprey2000 Saltspring Queen (or was it Vesuvius Queen) And you didn't even mention the Kuper.
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Post by farout on Feb 20, 2008 18:47:12 GMT -8
So when the boat is docked i have noticed that the propellers are still running, when the s-class and ships of such are docked with there tail to the berth, are those used to park/hold the ship in place? what speed ruffley would anyone think they would be running at?
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Post by Ferryman on Feb 20, 2008 19:41:32 GMT -8
Yes, the propellars would still be running to hold the ship in place. Instead of "slow ahead" when the bow is in the berth, it would be "slow reverse" to pull the ship towards the dock. Even the bow thruster will be used to keep one side of the bow pressed up against the side of the dock as well. I'm not sure exactly how fast the propellars are turning in RPM. But I would say that if the ship was out in the water and had the propellars running at the same speed as it would be pushing against the dock, I'd say it would be travelling at roughly (ruffley) 2-5 knots (or 3.75km/h - 9.35 km/h).
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Nick
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Chief Engineer - Queen of Richmond
Posts: 2,078
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Post by Nick on Feb 20, 2008 22:00:36 GMT -8
Bow thrusters are used to push or pull the bow of the vessel sideways, not "astern" and "forward". For the Spirits and Cs, their propellers are always turning at the same speed (about 250 rpm for the spirits, not sure about the Cs) and in the same direction. They vary the pitch of the propellers to change direction and speed (more pitch=higher speed).
Common practice with ships that have a fast "in berth" time is to use vessel power to hold the ship in the berth. Usually they are in "slow ahead" or "slow astern" to hold the ship tight against the wingwalls, and often single enders like the Spirits or Vs use the bow thruster to hold the ship against the dolphins.
As far as the Vs go for going in reverse ("astern"), they use a gearbox and clutch system to change the direction of the propellers. The speed of the propellers (rpm) is varied using the gearboxes to change the speed of the ship.
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Post by Ferryman on Feb 20, 2008 22:10:16 GMT -8
While we're at it, we may as well go into detail about the Queen of Tsawwassens propulsion system too.
She doesn't have variable pitched propellars, but instead she has "fixed" pitch propellars. This means that the propellars themselves will turn one direction to push the vessel forward, and then will need to be stopped to turn in the opposite direction. The Tsawwassen is very old fashioned as well, and the throttle levers in the wheelhouse are actually telegraphs. When the crew member in the wheelhouse wants to change the speed/direction of the propellars, the lever will be switched to the desired speed (slow ahead/full ahead/etc) which will send a message to the engineers below decks. Now I'm not entirely sure what exactly the engineers will do at this point. So I'll leave the rest to the more educated ones.
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Post by Ferryman on Feb 20, 2008 23:10:09 GMT -8
I've compiled a short video that's a little under 3 and half minutes, that shows the vibrations encountered on the Queen of Tsawwassen. This is only when she starts to back up out of the berths. But we were at the stern of the ship in the cafeteria where most of the shaking happens. The first clip was taken as we were reversing out of Village Bay, Mayne Island. The second clip is the slightly hard landing at Long Harbour, Saltspring Island, and the disadvantage to having a fixed pitch propellar (slow response time for switching direction of propeller). Then the final scene is in the cafeteria again, focused mainly on the group (I thought it would be better to keep it focused on the group rather than the floor or other people in the cafeteria), to see the vibrations again as we start to back out of Studies Bay, Galiano Island on our way back to Tsawwassen. You will even get to see Airchime explain whats happening below decks as it's happening, and a repeat of it in the background by Mirrlees. I've posted this in another thread as well. Anyways, enjoy.
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Post by kerryssi on Feb 21, 2008 9:27:50 GMT -8
Vibration has always been a problem on that ship. I remember working on it and watching a full cup of coffee go up in the air and turn over. It is created by "cavitation" which is when the propeller grabs air as well as water and cannot run smoothly. Over the years they have tried to fix the problem then just gave up and denied it existed. When a ship using telegraphs is nearing the dock the bridge sends signals to the engine room. The second mate on the bridge records the signal and time. the engineer records the signal and time and carries out the instruction via controlls at his end. When a ship like this is put into reverse everyone on the bridge holds their breath until the engine actually re starts in reverse. One engine is kept pushing forward to provide steerage. It is the water moving over the rudder that allows the ship to be steered.
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D'Elete BC in NJ
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Dispensing gallons of useless information daily...
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Post by D'Elete BC in NJ on Feb 21, 2008 10:07:11 GMT -8
It is created by "cavitation" which is when the propeller grabs air as well as water and cannot run smoothly. Well, not exactly how cavitation is defined. Cavitation typically occurs when low pressure points occur in the turbulent water flow around the propellers. If the pressure in an area drops below the vapour pressure of water, a cavity will form and water vapour will begin to fill the cavity, forming a bubble. As the water flow transports this now formed bubble, pressure increases will overwhelm the bubble causing it to collapse explosively. This implosion causes a small amount of vibration which can sum to a considerable amount once you include all the bubbles involved.
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Quatchi
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Post by Quatchi on Feb 21, 2008 10:15:47 GMT -8
Cavitation can be defined both ways.
Is the only reason they keep the one engine going forward is to allow steering. I thought they keep one going forward in case something goes wrong and they need to go forward or stop the ship from moving at all.
Also was the shaking always that bad or has the weakening of the metal made it worse. In any case there is really nothing that can be done about it, short of rebuilding the drive system and rear end.
[Humor] Maybe when the forum buys the Tsawwassen we can address this issue to a fuller extent. ;D Might I suggest a diesel electric system. [Humor/]
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Kam
Voyager
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Post by Kam on Feb 21, 2008 10:39:57 GMT -8
While we're at it, we may as well go into detail about the Queen of Tsawwassens propulsion system too. She doesn't have variable pitched propellars, but instead she has "fixed" pitch propellars. This means that the propellars themselves will turn one direction to push the vessel forward, and then will need to be stopped to turn in the opposite direction. The Tsawwassen is very old fashioned as well, and the throttle levers in the wheelhouse are actually telegraphs. When the crew member in the wheelhouse wants to change the speed/direction of the propellars, the lever will be switched to the desired speed (slow ahead/full ahead/etc) which will send a message to the engineers below decks. Now I'm not entirely sure what exactly the engineers will do at this point. So I'll leave the rest to the more educated ones. The Tsawwassen is indeed an old design! Her configuration (as far as I’m aware) is her engines are connected only to a gear reduction box. To reverse, the engines actually completely stop and restart in reverse. (The engines actually run backwards). This is still common practice in large marine engines on freighters, etc. If you ever stand by her engine room door and watch the top of the engines, you can see them completely stop when the bridge calls for reverse, and then start up again rotating in the opposite direction. Have a look at: www.tsb.gc.ca/en/reports/marine/1994/m94l0029/m94l0029.asp
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Nick
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Chief Engineer - Queen of Richmond
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Post by Nick on Feb 21, 2008 16:42:14 GMT -8
Those Mirrlees twins must be 2-stroke diesels then.... In layman's terms, that means that instead of the pistons going up and down 4 times for one power stroke, they only go twice. That means that every time the piston goes down, it is on a power stroke. In modern diesels, like the ones used on just about every other ship in the fleet, the piston only has a power stroke half the time it is going down. These are called Four-stroke diesels, which are much more efficient and nicer to the environment since they emit far fewer emissions. When a diesel engine runs in reverse, it takes air in what would normally be the exhaust, and exhausts through what would normally be the intake. Of course, since these were designed to do that in the fist place, there are dampers and valves in place to make sure the exhaust goes out the stacks properly. Anybody else want to clarify this? I found this video on youtube that kind of shows what I mean by running in reverse.
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Kam
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Post by Kam on Feb 21, 2008 23:21:03 GMT -8
Fantastic video! nice find! :-)
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Post by oceaneer77 on Feb 23, 2008 6:37:47 GMT -8
On 2 stroke diesels.. Kam you have it not quite correct. the engine when running in the other direction does not take air in from the exhaust and exhaust from the air... this would be impossible. When running in reverse the engine operates the same was as in forward and most large 2 strokes will never know the difference. A good animation is at www.marinediesels.info/index.html shows an engine running but not reversing... will keep looking oceaneer77
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Kam
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Post by Kam on Feb 23, 2008 16:18:56 GMT -8
On 2 stroke diesels.. Kam you have it not quite correct. the engine when running in the other direction does not take air in from the exhaust and exhaust from the air... this would be impossible. When running in reverse the engine operates the same was as in forward and most large 2 strokes will never know the difference. A good animation is at www.marinediesels.info/index.html shows an engine running but not reversing... will keep looking oceaneer77 It wasn’t me who said that, and I agree, I don’t think that’s correct.
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Post by jimpilch on Feb 24, 2008 16:35:53 GMT -8
This propellor lost a blade when it hit a log backing out of Horseshoe Bay on the Queen of Tsawwassen. Lots of shaking goin' on then! The engines on this vessel are 16 cylinder Mirlees direct reversible 4 stroke. The camshafts have a double set of lobes on them and when changing rotation the camshafts drop down, move forwards (or backwards) several inches and then are pushed back up into place on the other set of cams. This is done with air cylinders. One engine is not necessarily pushing ahead all the time. Steering can be accomplished by varying the RPM of the two engines if they are both in ahead or astern.
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Post by kerryssi on Feb 24, 2008 16:55:13 GMT -8
You could never hope to dock the ship by using both engines ahead or astern. One has to be going ahead to provide water flow over the rudder. The ships are far too big to maneuver into dock any other way, even with bow thrusters. When the ships are backed out of the dock and are turning to go forward then you usually have one astern and one ahead to help the rudder make the turn, but then you have lots of sea room and are turning away from the hard stuff.
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Nick
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Chief Engineer - Queen of Richmond
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Post by Nick on Feb 24, 2008 17:28:40 GMT -8
Ok, so they have 2 separate cams for each valve. That makes sense. Thanks for the explanation jimpilch.
Oh, and BTW, if you ever get the opportunity to watch some of the old logging equipment in action, you'll see what I mean by reversing 2 strokes. If they're backed off to idle, once in a while they'll sputter and stall, and then seemingly start up again. Except there's that slight issue of tons of black smoke coming out the intakes. Most of those old line loaders and other equipment have 2 strokes in them. Pretty spectacular stuff.
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