Going backwards

Welcome, Guest. Please login or register.

[Stinky]

Hello all shipfreaks,


I bought the ship sim about 2 weeks ago and now, in all my free time, I am sailing as much as I can. Yesterday, I was  navigating the Pride of Rotterdam away from the ferryterminal in Rotterdam and going backwards. Then I figured out (I think so) that the ship is reacting wrong to rudder positions. Immagine you turn the steeringwheel to the left. So the rudder rotate to the left side of the ship. If you are going backwards, then the nose must turn to the right but in the sim it doesn't. The ship turns as if you would go forward (the nose goes to the left). I first thought I was making some mistake but before I post this, I tested it again somewhere in open sea and with calm weather to have no influences. I first went forward and turned the steering wheel to the left. Indeed, the ship turns to the left. Then I went backwards and turned the wheel again to the left which then, you expect the ship to turn the other way (because the stream of the water over the rudder is the opposite) but no, the ship turned again to the left.

I know that you have some Technical Forum to post such a things. I tried to go there but I get some error. So that's why I posted it here.

And then some other question. I tried the mission where you have to load 4 containers on the Vermaas. I really don't know what I do there wrong but this doesn't go. The only thing I can move is the crane to go left/right and front/back and then also if you press 'i' the big crane lever. But I cannot take the containers and put them on the ship. So if I press the buttons 't', 'y' and 'u' nothing happens. I saw on Youtube a movie of this mission but if I open it, it doesn't look like on the Youtube movie.

Thanks for any reply.

[Lanedre]

I know that you have some Technical Forum to post such a things. I tried to go there but I get some error. So that's why I posted it here.

to access the technical forum you must register your license key in your profile
If you don't know how to do that you must read the FAQ or PM a Moderator or ask somebody who is good in explanations
And for the first part of your post I haven't noticed that yet so I am on my way to the PoR now    

[Stuart2007]

Hello Stinky. What an unusual name... never mind, welcome to the forum. As Lanedre says, it's best to enter your licence key as you will miss a lot of features otherwise.

On the subject of rudder action, in this case you are quite wrong. That was a viewpoint I held until I learned otherwise from one or two professional mariners here. I will try and find the posts about it.

Basically, the rudder has so little effect in reverse that it is more or less irrelevant (that is conventional prop/rudder combination).

No doubt one of the aforementioned professionals will give a more scientific explanation

Stu

[LucAtC]

Hello Stu,
Our friend is not at all wrong, in the simulation or not.
In the simulation, having 8 kts way backwards and full rudder, the rate of turn remains null, that is plainly wrong.
Making way backwards, the rudder action is significantly diminished (against forward way) for different reasons.
First, the center of rotation of the ship is closer to the rudder than in forward. (It comes to the rear of midships). Secondly, the more way you do backwards, the closer they come to each other, unlike going forward.
Moreover, but it has been frequently evoked, the rudder stays out of the wash of the screw (the accelerated flow, correct word?), and there is no gain from the screw.
Finally, as the turning moment of the ship remains small, the relative effect of the wind becomes more significant, and there is no possibility to change that, save to reverse the rudder and give a forward kick (keeping way backwards).
Also, one keeps in mind that the rudder forces stay the same than going forward if the rudder installation has been well designed, with the difference that they tend to push the rudder full, instead of bringing the rudder midships when going forward.

Basically, the rudder has so little effect in reverse that it is more or less irrelevant (that is conventional prop/rudder combination).

So Stu, you are also quite right!
Regards,
Luc

[Stuart2007]

That is the reason I came to my original conclusion that theoretically it should, but in reality it doesn't.

Do you remember, Luc, that I made the same comment in a Titanic post about running the engines astern and switching the steering the opposite way to your target direction?

In THEORY it should, but reality is always such a pain

Cheers Luc.

Stu

[LucAtC]

Hello Stu,
Yes, indeed, but I think it remains worth to be reminded that it all depends of hull and rudder design, weather, speed. Well, even sailships can be manoeuvered going backwards, sometimes like you told, at great pain, of course.
Having checked PoR (1.1), I was surprised that the rudder had strangely no action when backing? I dont remember that before the patch/add-on. I wonder if it is only on my system?
Vermaas, to the contrary, seems to have correct handling characteristics, even if the transverse effect of the screw is small, but in the correct direction (rotation clockwise when backing).
Regards,
Luc
Horresco referens, edit: transverse effetc of the screw, not rudder!

[mvsmith]

And then some other question. I tried the mission where you have to load 4 containers on the Vermaas. I really don't know what I do there wrong but this doesn't go. The only thing I can move is the crane to go left/right and front/back and then also if you press 'i' the big crane lever. But I cannot take the containers and put them on the ship. So if I press the buttons 't', 'y' and 'u' nothing happens. I saw on Youtube a movie of this mission but if I open it, it doesn't look like on the Youtube movie.

http://www.shipsim.com/ShipSimForum/index.php/topic,2635.msg26931.html#msg26931 (http://www.shipsim.com/ShipSimForum/index.php/topic,2635.msg26931.html#msg26931)

[groennegaard]

When going astern with both engines on this type of vessel, the rudders won't have any effect worth mentioning until you reach approx. 5-6 knots.

LucAtc mentions most of the reasons. The pivot point is moves aft when going astern so I recommend that you use the bow thrusters to steer the ship - the greater the distance between the pivot point and the transverse force is, the greater turning effect.

Regards
groennegaard

[[RWP]DJM]

Hiya all

I'm far from an expert on ship controls, but I use thrusters and rudder control when reversing, is this a recommended procedure?  More to the point, does it have any more effect than just using thrusters on their own?

Excuse my ignorance

Regards.

DJM.

[groennegaard]

When going astern you would rarely use the rudders as they would just block the waterflow to the propellors rather than turning the ship. You'll always use the bowthusters as they are far more effective when going astern and you can still have some effect when reversing with 10 knots! This would typically be around 15% of the normal thruster output.

Regards
groennegaard

[[RWP]DJM]

Ah, I see

What I usually do is this:

If I wanted to go Port-Astern (not sure if that's the right phrase ), using a vessel with fore and aft thrusters, I would set the fore thruster to full starboard and aft thruster to full port.

Then set engines to full astern and rudder to full port.  Based on what you just said, am I wasting my time then, or am I just a danger on the seas?

Regards.

DJM.

[groennegaard]

I think you're just a danger on the seas... 

My recommendation was for going astern with both engines and then I wouldn't use the rudders at all as they are slowing the vessel without helping me turning the vessel. If you have stern thrusters, you could use them as well, but they will not be that effective when going astern.

The attached table shows the effectiveness of thrusters when going ahead. It's roughly the opposite when going astern. I think the table is for a containership but it shows a general tendency.

Regards
groennegaard

[[RWP]DJM]

I think you're just a danger on the seas... 

LOL, I have suspected that for a while now

I guess I should stop playing racing games maybe, I can reverse a car at full reversing speed, perform a quick 'flick' of the wheel and spin the car 180 degrees.  Then continue in that direction in forward, with little or no loss of speed

I guess applying this technique doesn't work so well with ships eh

Thanks for the info, I will have to try that out

Regards.

DJM.

[LucAtC]

... most of the reasons. ...

Indeed, I forgot to say that while having way backwards, the efficiency of rudder profiles is reduced vs forward, more heavily for high lift rudder profiles than simpler ones.
Also, but it is more debatable, the stern forms are optimized for forward, not backing.
Finally, one must not forget than the stall angles of the rudder are smaller than in forward, as is the angle of maximum lift, and that sometimes people could stall the rudder, the more that rudder movements are today quick.
Setting rudder angles above the angle of maximum lift before the ship rotates is counterproductive, of course. Well, it is the same when making way forward, with or without screw thrust, but it is than less remarkable.
I wonder if my explanations are understandable? 
Regards,
Luc

[LucAtC]

Hello [RWP]DJM,
You put the finger where it hurts!
I think indeed that the physics engine of the simulation is quite well adapted for cars, even tire pressures can be adjusted, as drift angles, etc...
Problem, there is nothing about hydrodynamics in it, so it has to be mocked up at great pain.
Regards,
Luc

[[RWP]DJM]

I wonder if my explanations are understandable? 

I believe they are

The problem I have with most of this technical data is, my complete inexperience of sailing anything other than a rowing boat

I have no idea what 'draft' or 'screws' are relating to, or most other shipping terms to be honest

I guess it's time for some reading to be done eh.....now where did I put that Wiki link

Hello [RWP]DJM,
You put the finger where it hurts!
I think indeed that the physics engine of the simulation is quite well adapted for cars, even tire pressures can be adjusted, as drift angles, etc...
Problem, there is nothing about hydrodynamics in it, so it has to be mocked up at great pain.
Regards,
Luc

I see Luc, of course I stumbled on that one purely by accident

Regards.

DJM.

[Stuart2007]

I have made a decision. When I go on this damned ferry on Tuesday... I shall let the captain 'drive'. I will quite happily sit in my cabin playing ship sim instead.
Stu

[LucAtC]

  Better so, Stu! Even with the relative lack of realism of today, shipsim gives good hints about handling ships, without wind or streams. Surely enough to be able to appreciate the ability of the 'driver'.
Also, you surely made the link with aerodynamics. After all, an aircraft is some kind of a 3D ship?
About the tires, I had a look at the procedures, and I was exagerating, the parameters about tires are more general (steering angle, lateral speed, slide coefficient, etc...).
As well, [RWP]DJM, I have no doubt (already heard this expression many times somewhere) you also exagerate by telling

  I have no idea what 'draft' or 'screws' are relating to, ...

Is a draft not some kind of an essay for a document? Is there a link with an open window, a chimney?
A link with draught?
And a screw, is it not some kind of a rotating nail?
English vocabular and grammar are often difficult to be understood.
Regards,
Luc


 

[[RWP]DJM]

Is a draft not some kind of an essay for a document? Is there a link with an open window, a chimney?
A link with draught?
And a screw, is it not some kind of a rotating nail?
English vocabular and grammar are often difficult to be understood.
Regards,
Luc

I can understand your reasoning here Luc, apparently the English language is one of the hardest to learn because of the variations in spelling/meaning of similar sounding words.

For example 'There', 'Their' and 'They're' all sound the same when spoken, but are obviously spelled differently and have different meanings.  I admire anyone who can speak more than language fluently, I can manage a little French, a little German and understand certain words from a few other languages, but can't speak any of them fluently, although I do pride myself on my use of the English language

Regards.

DJM.

[Traddles]

In light of the foregoing comments, when I was a seafarer on right handed, single screw ships with no bow thrusters, when going astern we made use of the fact that the ships head would fall off to the starboard side due to the lower blades of the prop being in deeper and thus more dense water. The effect was always quite remarkable, and occurred when the helm was amidships. Just thought this might add to the confusion!!! in previous posts.

[[RWP]DJM]

Just thought this might add to the confusion!!! in previous posts.

Well, you definitely added to mine

I need to go for a lie down now

If anyone needs me, I'll be over there ---------------->

[LucAtC]

Hello Traddle,
You are right  , and some of us insisted heavily many times last year. I was also given the English expressions for this screw effect: Corkscrew, paddlewheel effect, transverse thrust or lateral screw effect, etc...
It was examined at length, I think, so you surely didnt add to the confusion, quite the contrary.
The developers tried to implement it, and succeeded more or less with some of the add-ons ships, although not enough "decisively" (strong?). Hopefully, it will be implemented when the add-on will be converted and published.
Vermaas (the ship  , not the developer) shows yet this transverse screw effect, not strongly  enough in my opinion, and that is also why I hope there will be a possibility to tweak the parameters of the ships.
Stopping distance tests under full power of VLCCs give a clear estimation of the effect. The transfer (lateral displacement) to starboard and the heading change (while no rudder command) are as interesting as the distance (IMO compulsory under 15 lengths?).
On a more modest scale, whether small or big, mooring along port side is always much easier than starboard for 'standard' propellers (righthanded fwd).
It also explains  why commonly the starboard CPP propeller of a ship with 2 screws (RPA12, PoR?), is left-handed, and the port one right-handed (in ahead): Quite the contrary of fixed blades screws. So, the transverse thrust effect of the screw is added to the eccentricity, instead of being substracted.
Let us hope for the future 
Regards,
Luc

[Stuart2007]

Luc, just to add to your earlier comments about comparison with aerodynamics of a plane. IMHO whilst you are technically/ scientifically correct, I would be confident that handling an aircraft is comparatively easy.

I am sure some pilots would disagree. But I know that I could (if money were no object) progress to captain of wide body multi jets much quicker than I could become a bridge officer of a ship!

Stu

[Stinky]

Thanks for all the comments. Some were technically quite deep. I just based myself on my sailing experiance with small sailing boats (Laser and 420 if some would know those types). If we went backwards, a simple trick to steer the boat was to push the stick of the rudder in the direction that you wanted to steer the nose or bow. And with those small boats, it was very effective. But indeed, with a big ship like the Pride of Rotterdam (which is a bit my favourite ship to sail with) there are maybe other effects with bigger influence. By the way, yesterday I did the mission with the Vermaas in Marseille and with the small tug boat, the effect of the rudder when going backwards really works good!

Now some explanation about my (indeed) strange name. It comes from my girlfriend. She cannot stand the smoke of cigarettes. Me and her brother went once in the very beginning that I started to date with her, to a pub to have a drink and play some pool. But in the pub, many people were smoking, so the smell was in my clothes. And when we came back home (way too late because we played too much pool), she was mad because we were later then we told. And then she suddenly said with a mad face: "You STINK". And then, "Stinky" was born