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Author Topic: Turning with propellers and rudder  (Read 21762 times)

Apejens

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Turning with propellers and rudder
« on: November 07, 2007, 19:54:09 »

Greetings,

I am very pleased with Ship Simulator becoming reality, let there be no question about that. However, I feel that we who are sailors should work together in making this simulator as realistic as possible.
If VStep can decide about making the game arcade-like or sim-like, then why don't they solve it in the same way as in MS Flight Simulator? That you get the choice to make it as realistic or un-realistic as you want?
Just a suggestion....

And more thing: As a mate on a medium-size twin-screw ferry, I feel that the "Twin-screw" movemnets are not good enough. The veseel I'm working on is over 130 metres long, and therefore it takes some time to turn the ship by the propellers only...so we use the rudder to help it happen a little faster.
In ShipSim this can't be done with any success because the ship (P.O.R.) behaves like it's fitted with a stern drive or an outboard engine!

So when you for example use port engine forward, starboard engine astern and full starboard rudder, the starboard mounted rudder, because of the astern thrust from its propeller,  will try to pull the ship's stern to starboard. At the same time the port rudder will, because of its propeller's forward thrust, try to move the ship's stern to port. So these to movements work against eachother, and very little happens, when it should really move the ship's stern to port (and of course, the bow to starboard).

I think I have opted this this problem in an earlier post. It seems, however, that I have to repeat myself:
ASTERN THRUST WILL NOT INFLUENCE THE RUDDER/TURNING MOVEMENT UNTIL THE SHIP MOVES BACKWARDS WITH AT LEAST THREE KNOTS! AND THEN THE SHIP WILL TURN BECAUSE OF THE SPEED, NOT BECAUSE OF THE THRUST!

I must point out that is for bigger ships mostly.
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groennegaard

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Re: Turning with propellers and rudder
« Reply #1 on: November 07, 2007, 20:30:35 »

Hi Apejens :)

Have you downloaded and installed the update?

With full ahead/full astern/full rudders I get a ROT of 102 degr/min.
With half ahead/half astern/full rudders I get a ROT of 47 degr/min.
This is without using thrusters.

These figures pretty close to those of a similar ferry I have been on. I'm not saying that the dynamics engine is perfect but it is not that bad either.

Regards
groennegaard
« Last Edit: November 07, 2007, 20:35:33 by groennegaard »
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LucAtC

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Re: Turning with propellers and rudder
« Reply #2 on: November 07, 2007, 21:28:01 »

Hello Apejens,
Like you rightly say
Quote
ASTERN THRUST WILL NOT INFLUENCE THE RUDDER/TURNING MOVEMENT UNTIL THE SHIP MOVES BACKWARDS WITH AT LEAST THREE KNOTS! AND THEN THE SHIP WILL TURN BECAUSE OF THE SPEED, NOT BECAUSE OF THE THRUST!
With the following quote, are you referring to a specific ferry with CPP, perhaps right handed propeller at starboard, left handed on the port side (when ahead)? Or was it about the handling of PoR in SS08?
Quote
So when you for example use port engine forward, starboard engine astern and full starboard rudder, the starboard mounted rudder, because of the astern thrust from its propeller,  will try to pull the ship's stern to starboard.
Regards,
Luc
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dycore

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Re: Turning with propellers and rudder
« Reply #3 on: November 08, 2007, 16:50:20 »

with the pride of rotterdam i can make a turn of 130 degr/min  ;D
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groennegaard

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Re: Turning with propellers and rudder
« Reply #4 on: November 08, 2007, 22:10:39 »

with the pride of rotterdam i can make a turn of 130 degr/min  ;D

Nice! We all can...  ;) My test involved propellers and rudders only. The bowthruster alone is 30 degr/min.

100 + 30 = 130  8)

Regards
groennegaard
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Apejens

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Re: Turning with propellers and rudder
« Reply #5 on: November 13, 2007, 13:56:31 »

Hello Apejens,
Like you rightly say With the following quote, are you referring to a specific ferry with CPP, perhaps right handed propeller at starboard, left handed on the port side (when ahead)? Or was it about the handling of PoR in SS08?Regards,
Luc


I was referring to real-life ships....

To groennegaard: what's the PoR's ROT when using propellers only compared to using rudders as well?
And what's the ROT when using both propellers (one forward, the other astern)+ rudder compared to using only one propeller forward+ rudder?

Let's say that you turn the ship to starboard by using port propeller forward and full starboard rudder.
If you now use starboard propeller astern and the ROT decreases, than there is something with the game that is not right.
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Rogier21

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Re: Turning with propellers and rudder
« Reply #6 on: November 28, 2007, 08:03:41 »

I was referring to real-life ships....

To groennegaard: what's the PoR's ROT when using propellers only compared to using rudders as well?
And what's the ROT when using both propellers (one forward, the other astern)+ rudder compared to using only one propeller forward+ rudder?

Let's say that you turn the ship to starboard by using port propeller forward and full starboard rudder.
If you now use starboard propeller astern and the ROT decreases, than there is something with the game that is not right.

What you are saying is completely right, but refering to your first post.

You mean to say if you give the port engine full ahead and the starboard engine full astern, AND you give hard port that the ship will turn slower then rudder midships?

The ship I work on (133m) cannot be done as the rudder at the propellor going astern will position itself midships all the time. But on another one I always put the rudders towards eachother to gain extra turning power during manouevring.

When the props are stopped the ships will hardly turn by just its own speed or movement by the rudder! Unless you do 17 knots.


This is irritating me off a little bit from the addon cruise ship, I find it impossible to turn this thing! Normally cruise ships have FAR over rated power onboard, CPP and diesel electric and should turn like crazy, ESPECIALLY with 2 bowthrusers. But in the game I cannot get it more then 20 degrees ROT, engines forward, reverse, rudder midship or hard, thats just wrong...

edited for language. Stu
« Last Edit: December 03, 2007, 13:22:51 by Stuart2007 »
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Kenneth E. Stacey

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Re: Turning with propellers and rudder
« Reply #7 on: November 28, 2007, 11:59:04 »

Dear Apejens,
I appreciate that this ship simulator is in its early development stage and there are plenty of tweaks required to simulate real manoeuvres. I hasten to add that at its present stage it is doing very well.
My thoughts are that the present membership will find a huge difference if tides and currents are ever introduced. There will then be consideration for berthing and unberthing times as well as calculations to be performed for underkeel clearance.
I realise that it may well be some time before the developers get to this stage but hopefully they will.
Best regards,
Ken Stacey
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LucAtC

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Re: Turning with propellers and rudder
« Reply #8 on: November 29, 2007, 00:03:06 »

Hello Rogier21,
Apejens said
Quote
...So when you ... use port engine forward, starboard engine astern and full starboard rudder, the starboard mounted rudder, because of the astern thrust from its propeller,  will try to pull the ship's stern to starboard. ...
The wash of the starboard propeller being directed forward, it will give no side thrust as long as there is not enough way astern. It is also why, like you wrote, on some ships it...
Quote
...cannot be done as the rudder at the propellor going astern will position itself midships all the time.
Dont you agree with that?
The CPP I was referring to was an improbable example, as you surely understood, the starboard pitch in forward being left-handed for this kind of propellers, right-handed for the port one.
But modern ferries being far more sophisticated than (old, alas) naval vessels, I didnt fully understand
Quote
...if you give the port engine full ahead and the starboard engine full astern, AND you give hard port that the ship will turn slower then rudder midships?
Which direction of rotation would be intended by such settings?

Also, the following quote cannot be denied, but on my pc, setting astern in these conditions increases the RoT.
Quote
Let's say that you turn the ship to starboard by using port propeller forward and full starboard rudder.
If you now use starboard propeller astern and the ROT decreases, than there is something with the game that is not right.
Do you mean on your system it decreases the RoT on your pc? Indeed, the handling in the game could depend on the system characteristics. It also could explain, about the Ocean Star, that you
Quote
cannot get it more then 20 degrees ROT, engines forward, reverse, rudder midship or hard, thats just wrong...
And that I can come on my system at a RoT of 64°/min, a perhaps too solemn pace, nevertheless 3.2 times more than on yours. Propellers at 90° (I hate  :-[ the right arrow key to set the steering to the left), max RPM, bowthruster at 100%.

Regards,
Luc
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Slowhand

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Re: Turning with propellers and rudder
« Reply #9 on: December 24, 2007, 20:14:30 »

All Vstep need to do is look up the ship handling section in a book like danton's seamnship. this is all you need to know with regards to dynamics. lets not confuse the amateurs or **** off the profesionals. I work on an anchor handling tug which has an immense amount of power, side ways and fore and aft and the fairmount sherpa doesnt cut it, nor does the towing arrangement. you need an autopilot at least, or a joystick mode. also the length of tow cannot be adjusted, plus we use wires not ropes. the tow wire should never leave the water.

Edited for language, DJM.
« Last Edit: December 24, 2007, 20:32:05 by [RWP]DJM »
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LucAtC

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Re: Turning with propellers and rudder
« Reply #10 on: December 25, 2007, 20:13:43 »

Hello Slowhand,
Welcome on the forum, as also for your suggestions, coming from an experienced professional. Surely, some more details about the AHT you are working on, and her immense amount power, could be helpful to improve the Fairmount Sherpa handling, particularly rates of turn and sideways speeds achieved under different configurations/thrust developed: To be able to realistically simulate the movements, the developers need all these figures, even if they have the valuable book you recommend. All these figures must of course be scaled, probably down, and figures are needed for that.
Be reassured, VStep knows very well the weaknesses of its models, whether about wires or bridge controls, as some other professionals already made these recommendations, and the basic data of the catenary curve equation are rather well known. Supplementary practical data will surely be of great help!
Regards,
Luc
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Tavares Junior

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Re: Turning with propellers and rudder
« Reply #11 on: January 10, 2008, 12:54:22 »

Greetings,

I am very pleased with Ship Simulator becoming reality, let there be no question about that. However, I feel

PRIDE OF ROTTERDAM Ship Simulator
Steering Effects for berth and umberth
Steering
In the case of the POR is important to mention that as she is 2 screw drive most common she have left hand for one propeller and right hand for the other propeller, this diverse handles cause an stabilization of the hydro-interaction of the vessel, with rudders at midship the vessel will be well steered. Of course as faster as she could run a faster response of the hull on the steering will be pronounced with speed lower than 5kn the response will be much slower and or nothing due to the wind angle and force of attack against to the ship’s structures and hull.

On the umberthing and or berthing maneuvering to use the propellers at different attack is very helpful for sideways slide and or 180dG turning. Is important to keep in mind that with double screw where the propellers (shafts) are turning on a different hand to use the port propeller to slow ahead and starboard propeller at slow stern and the rudder full to starboard it’s helpful as long as the interaction effects are pushing the vessel to the side to where you want to turn and not attacking the vessel from the side to where you need to turn. This method can be used without steering too. Rudder at midship.

Very important the stern force are small pronounce than the fwd force.
If do you have one propeller to ahead and other to stern the one turning ahead will pronounce it’s effects stronger than the one stern. In case of left hand port propeller the ships stern will slide to the port. With the starboard propeller handling stern and on the right handling it’s will not decrease so much the ships stern port slide due to it’s lake of power pronouncement.

Shallow waters
With a lake of under keel clearance (Shallow waters) the propellers have to present more power in order to attend the wished movement, due to the lake of water present the propellers suction gape will try to suck the bottom (Impossible) and this will reduce the ship’s performance and rudder’s performance too. At some large and width vessels this shallow water’s may cause a lake of performance up to 20% of the ship’s turning rate and or lost of maneuverability.

Banks cushion effects
Sloop banks cause a lost of performance but not more than a steep bank, the cushion effects may push the vessel against the side to where you want to handle the ship and to avoid a deviation of the course at some times you are obliged to turn the rudder on the same way where is the bank to avoid that the mass between bank and vessel push to bow to the other side of the channel, this force is well observed during narrows channel passage. With tugs connected it’s require more tugs force to avoid the deviation.

Bow and Stern Trust
The bow and stern trust are very effective with speed smaller than 4kn over this the much used power will be useless for the sideways slides and or steering.

Skin friction (Where is the break!!! I can’t stop she at all)
Is important to master to award of the ships skin friction this presence of factor cause the water friction to the hull during channel and or sea passage the vessel is carrying a significant amount of water together with her at the big mould vessels this amount of water can be up to 15% of the vessel’s displacement, this mass that slide together with the vessel extend from the bow up to abaft stern gape. This mass of water which is found sliding with the vessel behind the stern is so called as dead water, in a heavy stop of the engine this mass may push the vessel stern to an unknown side and push the vessel more ahead of the planned stop point. It’s recommend to made in practice to apply a re-direction of speed reducing it by the way points till have a safety stop speed considering shallow waters and squat effects and also channel and or sea current and wind angle of attack. This practice is common performed on width channels for anchorage and or waiting / meeting points.

Resume;
On the PRIDE OF ROTTERDAM part of the above mentioned effects are well presence and observed and same effects can be observed with the LATITUDE (Super Tanker) and VEERMAS (Container vessel).
Would be so realistic if SS team applying more effectiveness for the steering. And for the Shallow waters / Bank cushion effects / Bow and stern trust and the must important ship’s water and ship to ship interaction which today are almost pronounced.


Study and information form the Principles of the Naval architecture Part I and II, Ship Handling and Tug Use in Port.

By Juvenal Tavares Junior
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Tavares Jr
** Open Sea - Radar observer - SMCP - GPS / Chart Plotters / Certifyed yatch Master

groennegaard

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Re: Turning with propellers and rudder
« Reply #12 on: January 10, 2008, 13:30:18 »

Several members have complained about the performance of PoR after the release of v1.3. The only change I know of is a graphical adjustment of the pivot point. An adjustment to the real pivot point would of cause make a difference. I was under the impression that the PoR was tested after the adjustment, but I may be wrong. I'll check it later today.

Regards
groennegaard
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Slowhand

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Re: Turning with propellers and rudder
« Reply #13 on: April 07, 2008, 15:40:56 »

Cheers for coming back LucATC.

since this post the Fairmount Sherpa and towing wires have been modified i think. still some glitches. the pitch controls are the wrong way round. and you cant see the main deck from the aft console which is a major problem maneouvering around the rig. There is still no auto heading control or winch controls for this vessel though. Recently purchased the add on for 2008 and am very happy with Bugsier 2.






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Warrawee Tugboat

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Re: Turning with propellers and rudder
« Reply #14 on: April 12, 2008, 06:35:46 »

Why do the cables stretch?
I didn't think ropes stretch?
Is there a fix for it?
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Tuging is what I do

budbud

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Re: Turning with propellers and rudder
« Reply #15 on: April 12, 2008, 15:05:28 »

Hi Slowhand,

Quote
ince this post the Fairmount Sherpa and towing wires have been modified i think. still some glitches. the pitch controls are the wrong way round. and you cant see the main deck from the aft console which is a major problem maneouvering around the rig. There is still no auto heading control or winch controls for this vessel though

Quote
I work on an anchor handling tug which has an immense amount of power, side ways and fore and aft and the fairmount sherpa doesnt cut it, nor does the towing arrangement. you need an autopilot at least, or a joystick mode

I have been working on supply ships for 3 years now, and I had the occasion to sail on several different ones.
The first thing I have to say is: all the supply ships (compared to same types) are different. Two AHTS can have different kind of propulsion, and reactions, and also towing arrangements. The one on the sherpa doesn't shock me so much as I worked on a ship which has almost the same one.
Regarding to any kind of position or heading control, like DP systems or Auto heading, it is some bonus.
Sure it is more comfortable to have this features, but I like manoeuvring all in manual. I take parts in rig move and anchor handling several times, and sometimes we used the DP system but most of the time we made it in manual.

Third, you say you can see the main deck from the aft station? ok the aft station looks a bit strange compared to the bridge of the newer AHTS, where there is no console in front of the seat (looking aftward) but if you walk "through" the aft console, you can see the main deck very well!  :P

Finally, I agree with you on some points, like the aft commands (thrust levers) which should be corrected, and winch control which may be added, and also the RoT could be increased a little at low speed.

But I guess all of this is details and Vstep is working hard now to improve ss2008 and moreover to develop ss2009.

Budbud.

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C'est curieux ce besoin que les marins ont de faire des phrases!

Slowhand

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Re: Turning with propellers and rudder
« Reply #16 on: April 16, 2008, 11:24:36 »

Budbud

Yes it is very true about every vessel having different power and handling characteristics. I think I posted that one before vstep added the stern thruster and tweaked the handling a bit.

If you look at the real Sherpa large full height window is aft so its a case of changing the consoles around on the vstep one so that the forward console is aft so you can stand between and see the main deck.

With regards to a heading control system, yes I like to use manual all the time but if you are trying to use multiple vessels it can get a bit hectic. I assume you are familiar with Poscon Auto Fore? when you have the bow thrusters holding heding and you can use the stern thruster, pitch controls, and rudders to maneouvre.

Yeah the rate of turn at low speed could do with some tweaking.

Enough whining for one day.

Keep up the good work Vstep. looking forward to Ship sim 2009 already

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svein76@online.no

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Re: Turning with propellers and rudder
« Reply #17 on: December 15, 2008, 22:23:54 »

In real life we "split" the two rudders when manouvering with two props and two rudders. That should be possible, also in ss08
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orkneysteve

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Re: Turning with propellers and rudder
« Reply #18 on: December 24, 2008, 16:46:45 »

There is an easy way of explaining this:

Let's split the ship in two; say we want to rotate to starboard using only the props and rudders and we will start with the PORT side;

The Port Engine is put ahead, and the helm is put Hard over to Starboard - if you can immagine that the prop will "blow" a stream of water onto the Port rudder which is to starboard, hence the thrust from this prop is presently pushing ahead AND to starboard, turning the ship to Starboard.

Now the STARBOARD side;

The starboard engine is put astern but remember, the Rudder which partners the Starboard propellor has no effect on the Stream of thust from this prop, as the stream is moving away from the rudder (forwards of the rudder).

This situation is what most of us use on twin screw ships.  However, in shipsim, the STARBOARD situation is that the rudder is treated like an outboard motor in that is draws the water towards the propellor From the Starboard side and therefore contradicts the PORT situation.

Difficult to explain without a diagram (which I have tried to upload). :)
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TerryRussell

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Re: Turning with propellers and rudder
« Reply #19 on: December 24, 2008, 17:30:51 »

In real life we "split" the two rudders when manouvering with two props and two rudders. That should be possible, also in ss08

It is.

Gosh, ths is an old thread... (hint!)
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LucAtC

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Re: Turning with propellers and rudder
« Reply #20 on: December 24, 2008, 17:55:39 »

Yes indeed, and probably more related to ShipSim 2006 than 2008, at least concerning the wrong way when the rudder was working like an orientable propeller.
To implement svein76@online.no's suggestion, one would need a way to split (and un-split  ??? ) the rudders, some button to synchronize them or not. It is of course not impossible.
Regards and Merry Christmas,
Luc
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