Albatross IV handling

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[LucAtC]

Hello Yaw,

The trial that you describe is to create a clockwise torque while countering it with 20° left rudder. Doing this trial resulted in a 8 to 10° port swing on my pc. Pc's are indeed sometimes weird. Even so, I don't fully understand how you came to the conclusion about the ferry reaction.
Also, the propeller efficiency astern is lower than ahead, and the ferry will slowly make way ahead with the shaft settings that you described. By the way, the slip ratio of the propellers is also taken into account for the thrust and consequently the rudder forces for all propeller powered ships.

Regards,
Luc

[LucAtC]

Hello Apejens,

I don't fully understand the conditions where your manoeuver didn't work, there is indeed an important rudder lift due to the propeller flow, as the rudders are behind the propellers. Pivoting with no speed ahead is due to the rudder lift, prop walk and shaft eccentricity, what else could it be?
Certainly berthing was bow first, against or at a very short distance to the linkspan that you set both sides 75% ahead, full right rudder. Although I can only guess what you meant by not losing the bow, did the ship refuse to turn and to come alongside the quay? Could it not be an underwater obstacle that prevented it or did you try it also in an open place with no luck? I cannot anyway reproduce it, perhaps a description of the place where it happened could help clear the issue.

Regards,
Luc

[Apejens]

Hi Luc,

By "losing" the bow I mean that it would move sideways.
When docking a ferry, I'll generally dock her gently into the linkspan, then apply plenty of propeller thrust and a moderate rudder angle to bring the stern alongside. This will keep the bow pushed into the linkspan with such high power that the bow keeps in place and doesn't move away from the linkspan.
If I'd use full rudder and a more moderate amount of propeller thrust to bring the stern alongside,
the bow would not be pushed so hard into the linkspan, and it will in most cases then swing out from the linkspan.
These examples are without use of mooring lines, of course.
I apologize for my appaling abilities to explain in English, but it's the best I can do.

About the "Albatros IV" 's dynamics, there may be something with my computer that's causing the weird behaviour,
but in general she doesn't respond to the rudder except when making speed ahead...this is where I feel the dynamics should be tweaked a bit.
As I said, I brought her bow gently into the linkspan at Cowes, then applied forward thrust and st'b rudder to bring her stern alongside. Nothing happened at all, her stern stood still, until I tried the stern thruster, which brought her stern alongside. I would say she has the dynamics of a twin-screwed ship with a single rudder placed in the ship's center line.

I have to say that I don't understand why she should have a stern thruster either, as she didn't have it in the first place. A powerful, twin screwed vessel would not be needing such things.

Please note, Luc, that I am absolutely in love with the "Albatros IV" - I think the Papenburg sisters are some of the most handsome ships ever bulid, and VStep has captured that beauty magnificently.
I do not wish to be a moaning, complaining fool about these things.
I also really like the PoR, which has great dynamics too - as I said, I think the "Albatros IV" should behave like a smaller sister.

[LucAtC]

Hello Apejens,

What you meant by "losing the bow" is quite clear, and if I can easily imagine that there is enough fendering at the bow in reality, I don't know how the virtual linkspan is made, particularly its friction coefficient or reaction to collisions.

I made similar tests at this "Trinity Wharf" linkspan. Once in the linkspan, I had the same result that you describe while pushing both sides ahead, but having starboard set slightly astern was enough to liberate the bow so that the stern could be brought alongside.
It was as if there was an all or nothing process about the bow rubbing the linkspan. Under a certain value of the thrust there is no friction at all and the "bow is lost", above this threshold the bow becomes locked and prevents pivoting. I have no idea of the reason, nor what to do about this place. Still, it is possible to get along, and the next patch will include less propeller turning astern action on the corresponding rudder.

There are various ways to show the rudder-propeller action at zero speed, be it simply by turning on the spot without use of the thrusters.
Still easier, there is a quay downstream at one ship length, where I made a similar trial, pushing against this solid wall and changing the rudder angle from one side to the other. The ferry pivoted, following faithfully the rudder thrust, with the bow sliding accordingly at a reasonably very slow speed. Certainly something that a single rudder between two propellers wouldn't allow.

Regards,
Luc

[MokMok]

@Apejens:

By "losing" the bow I mean that it would move sideways.
When docking a ferry, I'll generally dock her gently into the linkspan, then apply plenty of propeller thrust and a moderate rudder angle to bring the stern alongside. This will keep the bow pushed into the linkspan with such high power that the bow keeps in place and doesn't move away from the linkspan.

Can this cause damage like dents and holes to the bow?

[Third Mate]

@Apejens:
Can this cause damage like dents and holes to the bow?

There's no damage model like in Ship Sim 2008

[MokMok]

I mean in the real world with locking the bow into the linkspan.

[Third Mate]

I mean in the real world with locking the bow into the linkspan.

Oh yes, I've seen it happen 

[clanky]

I mean in the real world with locking the bow into the linkspan.

If it's done properly it shouldn't, the most likely time for damage to occur is when the bow actually contacts the linkspan, if this is done slowly then just pushing the bow into the linkspan shouldn't really do damge unless more too much force is applied, but obviously in real life it's hard to have the speed just right at the exacvt moment of impact and sea conditions also have an effect.

[Stuart2007]

A certain well known cruiseferry that used to run to Bilbao had a very experienced Cpt named "Robert Ross". I've never seen ANY ship approach a linkspan so accurately- especially not Bilbao- under any other Captain. I reckon that you could balance an egg between the linkspan and the stern and he wouldn't have broken it.

Other Captains on the other hand were a little more unsteady- either you would "feel" the bump or the ship would come to full stop and then edge backwards again (one time it took 4 times to line up (no wind- maybe bad tide?)

Sorry for the digression.

[Apejens]

I'm sure I'm beginning to get on Luc's/VStep's nerves here, but I haven't found myself reassured by any answers here. In order to prove this, I took the ferry for a spin at Bora Bora, docked with her port side alongside(which was, at best, difficult without stern thruster use), moored the ferry with a spring line, and put on full speed ahead and hard st'b rudder to bring her stern alongside.

Nothing happened, instead she swung her stern out from the quay with a speed of 1,2 knots.
To test the realisticness of her dynamics, I then applied hard port rudder without changing engine speed.
Surprisingly, this reduced her athwartship's speed to 1,0 knots. Is this realistic..?!

When this was done, she was docked stern against the quay.
On departure she was given hard port rudder, thereafter full speed ahead.
As the attached screenshot shows, at a SOG of 2,4 knots, she only has 0,3 knots speed athwartships.
As the SOG rises, her ROT increases and she eventually reach an athwartship speed of 4,8 knots at 8,1 knots forward.

This proves, in my view, that she is indeed configured to swing by her speed ahead, and not by the thrust made by her propellers. You may call it sailship-like dynamics, or, as I wrote further up this topic, that she behaves like a twin-screwed vessel with a single, centre-mounted rudder.

I do believe that a only a full revision of the ship's dynamics will do her justice.


Attached are some screenshots of my aforementioned points.

[clanky]

Putting a forward spring ashore and going ahead on the engines is used to move the stern away from the quay when leaving the berth, it is not a way to bring the stern along side when approaching the berth, but even then only with dead slow ahead as full ahead on the engines will snap ropes in real life.

If you want to bring the stern in (when going port side to the quay) try using the starboard engine astern with full port rudder if the ship is stopped or moving astern and with no rudder if she is still moving ahead. 

[Ballast]

You sure would piss off the guys on the forecastle 

[clanky]

The ship moored ahead wouldn't be best pleased either

PING, CRUNCH/

[Apejens]

What kind of ropes have you been using then - made of paper, perhaps? 
On almost every ship I've been on, we've always been fastening a spring line going from the forecastle and astern-wards when docking, then swinging the ship in by going forward i the spring line and applying rudder. I must add, these were coasters without a stern thruster, and only with a pretty dismal bow thruster. This method was even taught as "the way of doing it" in the "Ship Handling" study when I took my nautical education.

Please don't think I'd be using full power in real life - that would've annoyed the guys on the forecastle, surely, perhaps even beheading them  On the pictures above, I applied full power only to prove my point.

[captcj]

I have also noticed these perculiarities with the handling characteristics of the Albatross.  Her steering is definitely responding to speed over ground rather than thrust from the propellers.  I even tried shoving her bow into a "solid wall" full ahead with both engines, but could not get any turning response from either a port full rudder nor a starboard full rudder.  In my opinion, she handles just like a twin screw boat with a single rudder.  In order for her rudders to to have an effect, you have got to be making way either ahead or astern. 

For example, try backing her out of a berth at about 4-5 kts astern.  When clear, come full ahead on both engines.  Wait till the engines reach 200 rpms, then apply right full rudder.  You will notice the bow start turning to the port up to about 12degrees/min.  This rate of turn will eventually correct when the Albatross starts making headway.  Vice versa with same trial applying left full rudder.   

[Ballast]

What kind of ropes have you been using then - made of paper, perhaps? 

We use a double polyrep spring with a total MBL of 54 tonnes as described by the OCIMF mooring guidelines 

Ofcourse this is the way to get a single prop vessel off the quay - i'm really happy that it's possible in SSE! - but not full ahead as you say 

[The Ferry Man]

OK, pulling into the green field port of Portsmouth, coming in at about 7 knots

I put the port engine at 60rpm forward , and the starboard engine at 65rpm astern - this should start me turning, however I found that I just am currently slowing down only - no sign at all of any turning...

Will keep you posted...

Edit: 4.5 knots - still no rotation and approaching the berth area rapidly...

Edit 2: 4 knots, and currently slicing through Portsmouth, and no turning either

Edit 3: 3 knots, fast approaching the M275... still no signs of turning... :/

Edit 4: 2 knots now, passed the M275, have a RoT now! 1' per minute...  :/

Edit 5: OK at about 1.2 knots it appears to have stopper decelerating at all :/

[Third Mate]

This is why VSTEP should add under each boat the following:

Speed:
Tonnage:
Passagers load max:
Crew:
Fuel inboard capacity:
Fresh Water:
Supplies:
Engine Type:
Fuel Consumption:
Fuel Type:
Twin screw, triple screw?
Range(miles):

All there is, is the pointless information no one bother's to read I bet, then is the important information which is left out plus should have a medium sized photo of the ship in real life as you click on it. And if someone comments on this and say's oh sorry this is not ship sim pro excuse than that you are have no soul.

[Ballast]

Except for the propulsion, the rest of the info is kinda useless for manoeuvering  

I'd rather see info like turning circle, left or right handed vessel, zig zag test and so on  

Edit: added a real wheelhouse poster.

[clanky]

As it's a simulator you get to find out the info like that yourself and unlike in real life if you get it wrong you can go back and try again.

[Traddles]

If you want to carry out this particular move it can be done very well indeed in SS 20008. virtually all the ships there can be "sprung off" or, very carefully, sprung onto  the quayside. The only comment I would make is for the Mate on the foc'sle head to be certain that he and all the men up there do NOT stand within the bight of the rope, but well clear of it. A Mate I knew was killed when a roller fairlead carried away and the bight of the rope snapped back and severed both his legs in an instant. He bled to death in a matter of a few minutes. Not funny at all.
What clanky says is worth its weight in gold.

Angus.

[LucAtC]

Hello,
Clearly, having read captcj post that adds to Apejen's one, we don't use the same Albatross IV dynamic files. It is not impossible, but I cannot check that unless I receive a copy of the file itself to do a comparison. My mail address can be found in my profile, it is the file
C:\Program Files\Vstep\ShipSimExtremes\Projects\ShipSimExtremes\Data\Entities\Dynamics\Coromuel.act

TFM, do you have an idea of the yaw torque made by the propellers in your test conditions, ship speed 6 to 7 kts, and 60/65 RPM propellers having a pitch +/- 3 m, at 5.84 m distance from each other? I guess you don't. It is an impressive (or not) 14.5 tm, or a 0.3 t (3 kN) force exerted laterally at the stern. As you designed screw propellers, you can partly use a very interesting program, Javaprop, Design and Analysis of Propellers that can be used, changing the blade form and the air parameters into water, to get an idea.

Regards,
Luc

[The Ferry Man]

TFM, do you have an idea of the yaw torque made by the propellers in your test conditions, ship speed 6 to 7 kts, and 60/65 RPM propellers having a pitch +/- 3 m, at 5.84 m distance from each other? I guess you don't. It is an impressive (or not) 14.5 tm, or a 0.3 t (3 kN) force exerted laterally at the stern. As you designed screw propellers, you can partly use a very interesting program, Javaprop, Design and Analysis of Propellers that can be used, changing the blade form and the air parameters into water, to get an idea.

Regards,
Luc

I see....

So this means it won't produce a turn? I would have thought a 3kN force on the stern would have priduced some Rotation, even if its not much...?

Thanks,

TFM

[LucAtC]

You are right, pulling during 2 minutes could let the ship turn at 10°/min, disregarding hydrodynamic resistance, ie ship stopped. It wouldn't even break a 5 mm nylon rope. But once the ship is making way, the sway resistance and the yaw resisting torque increase strongly.
Anyway, the files that you have are certainly wrong, as the test made by captcj succeeds easily as it should do, in the 2 versions that I have. Do you still have a Steam version?
Regards,
Luc