Topic: Seriously, how dare you... (Read 25665 times)

ACR · « **Reply #75 on:** October 16, 2012, 22:00:59 »

Quote from: clanky on October 16, 2012, 20:38:02

If you are on a ship like Vermas and you are stopped and put the engine control lever to the full ahead (100%) position then the pitch / rpm should increase to about 40% over a period of around 30 seconds then to 60%over the next 30 seconds and then slowly increase to 100% over the following 20 minutes or so.

clanky, ships like the vermaas have no variable pitch propellers . further no gearing, no clutch, so prop rpm is equal to engine rpm and usually very low about 100-120 rpm.

so having the engine control lever at full stop means the engine is also stopped. pushing it forward means to initially start the engine at all- going from forward to astern means initially fully stop it, then reverse it and then start it again. i think this will take more than 30 seconds.

the load curve you described seems right to me.

and compare it to the "simulator" here...

zilverenmist · « **Reply #76 on:** October 16, 2012, 22:37:19 »

Quote from: saltydog on October 16, 2012, 21:30:35

To put in my 2 cents, the picture that Traddles posted seems to indicate that she does not have contra-rotating props (judging by the angles of the blades)..

You are right. Ingame they both move the same direction.

danny · « **Reply #77 on:** October 16, 2012, 22:51:38 »

The real world version of the "fairmount class" does have counter-rotating screws, along with almost every other twin screw ship in operation. (I got contra and counter rotating props mixed up

)

Also - The single screw sherpa bug appears to be rather odd... When I load the sherpa in "ship preview" I have 2 propellers, when I load into free roam and apply power I still have 2 screws. If I change views from the orbital cam however my 2 screws merge into 1.

LucAtC · « **Reply #78 on:** October 17, 2012, 00:15:07 »

Hello Saltydog and gentlemen,

Sherpa propellers? You probably meant outward turning, and so you are right, the Sherpa model of the game is designed indeed with inward turning propellers. Contra-rotating is something else. Nevertheless, I think it is indeed a pity that the screw models don't represent pitch really, and also they don't rotate as we would have liked it.

To come back to the issue about the pitch settings of Sherpa, danny is indeed right: the times are not realistic, but then very far from his friend's 3.5 seconds. The time from full pitch, while at full load (not far from maximum torque), to full pitch in the other direction is 65 seconds (ahead to astern) and 78 seconds (astern to ahead). But from astern at full load to 0 degree blade angle, the delay is only 22 seconds. I am sure that an expert engineer like Clanky can explain why to us, but it is not possible to take into account the propeller load in a game, and that is why it was assumed that the no load time of 15 seconds from max to 0 pitch was a reasonable guess for Sherpa. There is no doubt that clanky knows better than anyone else here that big container ships have fixed pitch propellers, evt contra-rotating, and has seen and heard more than enough of them.

Reason for this choice is that the game is about handling ships in or around harbours, and so I am not ashamed of the thrust buildup of most ships, although errare humanum est. Well, I think also many if not most interested players are aware of the time it takes to accelerate the engines.
Vermaas startup was set at around 10 seconds from bridge order to deadslow (set at 34 RPM), another 20 to get to 104 RPM, too fast certainly, but also not at full load, as the propeller is not at its best efficiency at full RPM and harbour speed.
If somebody wants to play more realistically, he can replace the PLCs at the bridge or the engineers dowwn there, by pushing the controls slooower? Eventually, asking to change some settings will certainly be answered, and done if it is sensible and can be done.

Regards,
Luc

saltydog · « **Reply #79 on:** October 17, 2012, 00:15:37 »

As far as I could discover, the Fairmount Sherpa does not have contra-rotating props.
She does however have controllable pitch props, but that option is not in the game..

zilverenmist · « **Reply #80 on:** October 17, 2012, 01:50:30 »

Doubleprop ships with variable pitch control usually do turn counterwise.

saltydog · « **Reply #81 on:** October 17, 2012, 02:08:15 »

I think I was confused with counter-rotation propellers, such as on the Titanic..

zilverenmist · « **Reply #82 on:** October 17, 2012, 02:38:11 »

Quote from: saltydog on October 17, 2012, 02:08:15

I think I was confused with counter-rotation propellers, such as on the Titanic..

The picture you show is either the Olympic or Brittanic, Titanic had a 3 blade centrepropeller with a little larger diameter than the 4 blade centreprop of the Olympic. At least this is the case as far as I studied Titanic.

If the Titanic is made for simulation with a 4 blade centreprop, I can tell people did not do their homework.

saltydog · « **Reply #83 on:** October 17, 2012, 03:49:30 »

Whether or not Titanic's central propeller was 3 or 4 bladed is a matter of debate..
It is not the question here..

clanky · « **Reply #84 on:** October 17, 2012, 10:33:18 »

She has controllable pitch propellers so the angle can be set to whatever you want, but yes, if those are both set to the ahead direction then they are not contra-rotating. They also look nothing like real propellers.

danny · « **Reply #85 on:** October 17, 2012, 14:04:02 »

Sorry - I got contra-rotating and counter-rotating mixed up

zilverenmist · « **Reply #86 on:** October 17, 2012, 16:14:36 »

Quote from: saltydog on October 17, 2012, 03:49:30

Whether or not Titanic's central propeller was 3 or 4 bladed is a matter of debate..
It is not the question here..

How dare you write that! In terms of how accurate SSE is (see 2 clockwise turning props on the Fairmount) on ships, it is actually a good question here!

http://www.encyclopedia-titanica.org/mystery-titanic-central-propeller.html (http://www.encyclopedia-titanica.org/mystery-titanic-central-propeller.html)

Why? It is kind of obvious that the found papers at Harland and Wolff may tell the truth.

Danny could try to look in his game how many blades and props the Titanic has

Quote from: clanky on October 17, 2012, 10:33:18

She has controllable pitch propellers so the angle can be set to whatever you want, but yes, if those are both set to the ahead direction then they are not contra-rotating. They also look nothing like real propellers.

Who is "she" in your comments? if Titannic its a NO, if it is Fairmount Sherpa also no, and they do look like a solid prop from a little distance

I rest my case.

Quote from: danny on October 17, 2012, 14:04:02

Sorry - I got contra-rotating and counter-rotating mixed up

Nevermind, we understand what you mean

zilverenmist · « **Reply #87 on:** October 17, 2012, 16:20:29 »

Quote from: clanky on October 17, 2012, 10:33:18

She has controllable pitch propellers so the angle can be set to whatever you want, but yes, if those are both set to the ahead direction then they are not contra-rotating. They also look nothing like real propellers.

Forgot to add this to previous post, but 2 prop ships with pitchcontrol are supposed to contra rotate, or it would stationary drift left or right depending on the rotation.

danny · « **Reply #88 on:** October 17, 2012, 16:32:53 »

Further to clankys' point about the screws not looking "correct" - The leading edge should have a much shallower curve, with a sharp tip.

zilverenmist · « **Reply #89 on:** October 17, 2012, 16:43:10 »

Controlable or not, it is obvious these props will (have to) turn counterwise. These props are mirrored, as the wingprops of Titanic, Olympic and Brittanic are also.
Even with azipods if there are 2, they are mirrored, and work counterwise.

clanky · « **Reply #90 on:** October 17, 2012, 19:13:07 »

Quote from: ACR on October 16, 2012, 22:00:59

clanky, ships like the vermaas have no variable pitch propellers . further no gearing, no clutch, so prop rpm is equal to engine rpm and usually very low about 100-120 rpm.

so having the engine control lever at full stop means the engine is also stopped. pushing it forward means to initially start the engine at all- going from forward to astern means initially fully stop it, then reverse it and then start it again. i think this will take more than 30 seconds.

the load curve you described seems right to me.

and compare it to the "simulator" here...

There are ships in service with large 2 stroke diesels and controllable pitch propellers, granted it is unlikely in the case of something like Vermass, but it is not that unusual for other ships.

sydmichel · « **Reply #91 on:** October 17, 2012, 19:29:39 »

Quote from: danny on October 16, 2012, 22:51:38

The real world version of the "fairmount class" does have counter-rotating screws, along with almost every other twin screw ship in operation. (I got contra and counter rotating props mixed up )

I think contra rotating propellers are 2 screws on the same shaft turning in opposite directions. most Torpedoes use this set-up to stop the weapon from spinning in the water.

clanky · « **Reply #92 on:** October 17, 2012, 19:59:04 »

Syd, you are correct, contra rotating describes 2 propellers on the same shaft, counter roatating is what Sherpa is supposed to be, although I have to admit that I had to google it!

zilverenmist · « **Reply #93 on:** October 17, 2012, 21:43:51 »

Counter and contra rotating means the same. It are props on the same shaft or in some occasions in one line.
In ships with double propellors it is said as the prop turn clockwise or anticlockwise or counterwise. I think there is no special expression for twinscrews, it is however from before the Titanic a fact that a starboard and port propellor have opposite work direction.

LucAtC · « **Reply #94 on:** October 17, 2012, 23:07:57 »

Hello,
It is only semantics, of course, and I am not English speaking, but I'll try to explain what I think to know about the terminology used for propellers, with the caveat of the language.

Counter-rotating propellers are just that, propellers turning in opposite directions on parallel shafts, vertical like CH47 Chinook or KA-31, horizontal like twin engine aircraft, or for ships with pairs of propellers turning in opposite directions, like most but not all twin screw ships. Indeed, some modern ASD tugs, or towboats, have the same propulsion units at both sides, an interesting feature to steer on large bends on rivers.

Such counter-rotating propellers can be outward turning, like Sherpa, or inward turning like RPA12 or many other but not all CPP propulsions.
Outward turning propellers mean that the starboard propeller is right-handed, the port prop is left-handed.
Inward turning sees a left-handed one at starboard and a right-handed one at port side.
A right handed propeller turns ahead clockwise when seen from astern, the screw is right-hand. Left-handed etc.

Screw propellers like Volvo Penta Aquamatic Duoprop, or Wartsila Lips for large marine propellers have pairs of coaxial propellers, in view of increasing the efficiency of the propulsion. The turboprops of Tu-114 or the rotors of some helicopters are flying examples of the same. They have since a long time been named contra-rotating propellers.
The main goal of such an arrangement is more the increase in efficiency of the propellers, not so much canceling opposing torques. The propeller shafts are coaxial.

There are also propellers in tandem on the same shaft, with the same pitch direction, for instance at both ends of the main shaft in a pod. These propellers are of course not contra-rotating nor counter-rotating propellers.

Perhaps could an English speaking check and correct this.

Regards,
Luc

zilverenmist · « **Reply #95 on:** October 18, 2012, 00:18:08 »

Think it does not need much correction.

The marinewiki only shows contra-rotating propellers
http://www.marinewiki.org/index.php/Contra-rotating_Propellers (http://www.marinewiki.org/index.php/Contra-rotating_Propellers)
Counterwise just means the opposite. So it is not completely wrong to name them counterwise propeller.
Counterwise is often the opposite of clockwise, so if clockwise is right, counterwise is the general name for left turning things.

It seem contra-rotating propellers is the right expression.

As you are French, I am Dutch, we may have the same language gap.

Quote

Indeed, some modern ASD tugs, or towboats, have the same propulsion units at both sides, an interesting feature to steer on large bends on rivers.

I am not that sure if some tugs have this setting, rivers have many bends, and on the "countertrip" it would not help at all.

saltydog · « **Reply #96 on:** October 18, 2012, 04:25:35 »

Quote from: zilverenmist on October 17, 2012, 16:14:36

Who is "she" in your comments? if Titannic its a NO, if it is Fairmount Sherpa also no, and they do look like a solid prop from a little distance

If you look at this (http://www.fairmount.nl/index.php/fleet/ship/14) description of the Fairmount Sherpa, you will see she has 2 cp propellers. I think that means controllable pitch..

ps; the opposite of clockwise is counterclockwise..

clanky · « **Reply #97 on:** October 18, 2012, 09:19:23 »

Luc, I think you have nailed it. No need for correction.

zilverenmist · « **Reply #98 on:** October 18, 2012, 17:07:18 »

Indeed it is counterclockwise or anticlockwise. Counterwise has in fact nothing to do with rotational movement, but it is as far as I recall commonly used to express a left rotation.

Quote from: saltydog on October 18, 2012, 04:25:35

If you look at this (http://www.fairmount.nl/index.php/fleet/ship/14) description of the Fairmount Sherpa, you will see she has 2 cp propellers. I think that means controllable pitch..

ps; the opposite of clockwise is counterclockwise..

Sherpa has controlable pitch and clockwise and anticlockwise propeller.

Stuart2007 · « **Reply #99 on:** December 05, 2012, 13:00:57 »

duplicate comment. deleted

Author Topic: Seriously, how dare you... (Read 25665 times)