Hello Guest June 15, 2024, 18:38:31 *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
 
Pages: [1]   Go Down

Author Topic: A possibly stupid question about boats...  (Read 3275 times)

Ifful

  • Forum member
  • Posts: 11
A possibly stupid question about boats...
« on: February 06, 2008, 01:02:29 »

I'm not very knowledgeable about real life boats, rarely even riding them and never piloting them, so I may be entirely wrong about this, but something strikes me as strange in how ship sim handles rudder turns.

With the exception of outboard motors, most boats make turns using rudders placed at the back.  Does the engine really need to be running for the rudder to affect the boat's heading?  It would seem to me that if you cut the engine at high speed and let it glide, the rudder should still turn the boat so long as it is in forward motion.  In ship sim, as soon as you cut the engine (either setting rpm to 0 or turning it off), the rudder no longer has any effect: it is as if it has been set to neutral position.  It this what happens on real boats?
Logged

trains

  • Forum member
  • Posts: 1541
Re: A possibly stupid question about boats...
« Reply #1 on: February 06, 2008, 01:08:37 »

it depends what kind of boat, how heavy, and long.  ;)
Logged

thanks to TJK for this awsome sig :D

Radeon HD 6850; AMD FX 4100 3.62 Ghz; 4 GB Ram

Mad_Fred

  • Administrator
  • Posts: 8689
  • ✝ In Memoriam
Re: A possibly stupid question about boats...
« Reply #2 on: February 06, 2008, 01:21:18 »

Rudders do have an effect when the screw(s) are not running. And it will indeed depend on the size of the ship, the speed you travel at too, and so on..

But If you take the Arie Visser for example, it has waterjets. you can turn the nozzles but without propulsion it wont steer. so it only applies to the vessels with conventional rudders.

Regards,
Fred

Logged

LucAtC

  • Ship Simulator Developer
  • Global Moderator
  • Posts: 2219
Re: A possibly stupid question about boats...
« Reply #3 on: February 06, 2008, 01:25:30 »

Hello Ifful,
Of course that ships do turn due to their rudder, even when the engine is stopped. In fact, it was already known before engines were invented...
Now, the waterflow, the wash of the propeller on the rudder increases the speed of the water, and as a consequence the rudder force, in drag and in lift. So, stopping a propeller in front of a rudder decreases the rudder effect, the more the area of the screw shadows the rudder.
If you search the forum, or perhaps look at these extracts of a book, you will have a better idea of the forces involved. Googling "ship rudder action handling manoeuvring" or any other words will give you excellent links describing the rudder action, in so far the ship has rudders.
Good reading,
Luc
Logged

budbud

  • Forum member
  • Posts: 292
Re: A possibly stupid question about boats...
« Reply #4 on: February 06, 2008, 01:44:13 »

Hi,
I know it's a little bit away from the point but I would like to precise one thing about waterjets:
Quote
But If you take the Arie Visser for example, it has waterjets. you can turn the nozzles but without propulsion it wont steer

This statement is right when the ship makes her way through water, but when the ship is stopped, you can turn her without any thrust. Ship sim doesn' take into account this fact.
Logged
C'est curieux ce besoin que les marins ont de faire des phrases!

mvsmith

  • Guest
Re: A possibly stupid question about boats...
« Reply #5 on: February 06, 2008, 01:51:36 »

budbud,
If there is no thrust on the boat, what turns her?
Logged

budbud

  • Forum member
  • Posts: 292
Re: A possibly stupid question about boats...
« Reply #6 on: February 06, 2008, 02:08:27 »

Ok,
Actually, when you put the handles to zero on waterjet boat, the screws keep turning in the nozzles, but as the reverse gate is in middle position, half of the flow is ejected forward, and the other half backward. So your right you keep having thrust.
I simply meant that if your put your handles to zero with no speed you go on turning your ship.

(Sorry for my english, a little approximate...)  ;)
Logged
C'est curieux ce besoin que les marins ont de faire des phrases!

Ifful

  • Forum member
  • Posts: 11
Re: A possibly stupid question about boats...
« Reply #7 on: February 06, 2008, 05:07:44 »

Hello Ifful,
Of course that ships do turn due to their rudder, even when the engine is stopped. In fact, it was already known before engines were invented...
Now, the waterflow, the wash of the propeller on the rudder increases the speed of the water, and as a consequence the rudder force, in drag and in lift. So, stopping a propeller in front of a rudder decreases the rudder effect, the more the area of the screw shadows the rudder.
If you search the forum, or perhaps look at these extracts of a book, you will have a better idea of the forces involved. Googling "ship rudder action handling manoeuvring" or any other words will give you excellent links describing the rudder action, in so far the ship has rudders.
Good reading,
Luc


I've had a read through, and so I wonder why the ships in ship sim do not behave like that.  In ship sim, when the engines are set to neutral, the rudder no longer affects the turning of any of the ships even when the ship is still moving forward by inertia.  Is this a bug?
Logged

Sam

  • Forum member
  • Posts: 1041
Re: A possibly stupid question about boats...
« Reply #8 on: February 06, 2008, 11:30:15 »

The ships do turn very slowly, just look at you ROT.

The Fairmount Sherpa clearly turns with zero throttle.

I think it isn't a bug, it is realistic.


I have experience on manouveing a 10m sailingyacht, and that turns very well at speed.
But a sailingyacht has a verry large rudder compared to a big ship.
Logged

Ifful

  • Forum member
  • Posts: 11
Re: A possibly stupid question about boats...
« Reply #9 on: February 06, 2008, 15:25:32 »

The ships do turn very slowly, just look at you ROT.

The Fairmount Sherpa clearly turns with zero throttle.

I think it isn't a bug, it is realistic.


I have experience on manouveing a 10m sailingyacht, and that turns very well at speed.
But a sailingyacht has a verry large rudder compared to a big ship.


Ah, I see it now.  It seems all of the boats that I was using were the ones that don't or don't noticeably turn with engines off.  The P6 seems to turn in glide mode too.
Logged

jjkabel

  • Guest
Re: A possibly stupid question about boats...
« Reply #10 on: February 18, 2008, 17:49:00 »

I don't know which commercial Personal Watercraft was used for the PWC model in ShipSim, but there is steering without thrust on some newer PWCs. Bomardier (Sea-Doo) has a steering feature on its newer and larger PWCs where even without thrust through the jetdrive nozzle you get some steering action. This overcomes a major safety defect of PWCs. There have been some terrible accidents here in Canada involving younger people riding them. In one case, a girl turned towards a rock wall at fairly high speed, then let off the throttle to try to prevent collision. Of course, the steering was disabled, so she ran into it head on.

We now have rules to prevent operation by anyone under 16, but no mandatory on-the-water training to prevent this. I belong to a volunteer boating safety education group which tries to train people off the water as much as possible. Ship Sim may have some usefulness in this regard.

I am just getting started with Ship Sim 2008, so will let you know more about my impressions of the PWC model handling.

Cheers.

Jan Kabel
Logged

TerryRussell

  • Guest
Re: A possibly stupid question about boats...
« Reply #11 on: February 18, 2008, 18:37:37 »

I have some experence of small and medium sized vessels (2.4 metres up to about 25 metres). None of these had rudders, only outboards or outdrive legs.

I currently have a 12 metre boat with twin screws and steerable outdrives. With no thrust it doesn't turn much at any speed.

I also have an 8 metre boat with single screw (goes like a rocket!). With no thrust but with forward or reverse motion ("gliding"), it is still moderately steerable due to the geometry of the outdrive leg (Thank you, Volvo!). With thrust it turns very tightly.

But until recently I had a third boat of about the same size which had virtually no steerage when there was no thrust (had an older style of Volvo outdrive).

So, for anyone who may be tempted to say "this isn't realistic", it depends on the vessel and assorted bits dangling in the water. Even apparently very similar vessels will handle differently.
Logged

Eemspoort

  • Forum member
  • Posts: 372
Re: A possibly stupid question about boats...
« Reply #12 on: February 18, 2008, 22:57:16 »

I don't have much to add to what is said allready. But i can give an excample that isn't mentioned yet.
I have an inland-ship myself (see avater and sig) and it still steers pretty well in "glide-mode".
Only below 3 km/h the effect fades away. In reverse, with or without the screw in work, the steering-effect is only very minimal, not enough to manouvre with. In that case i use my 360 degree turnable bow-thruster for steering the ship where i want her.
Logged
m/s "Eemspoort"
1961, Hilgers A.G.-Rheinbröhl
76,2 x 8,20 x 2,72 mtr, 1085 ton
Deutz RBV 6 M 545, 800 HP @ 380 rpm
Daf KMD 250.2, 250 HP @ 1800 rpm, bowthruster
Pages: [1]   Go Up
 
 


SMF 2.0.14 | SMF © 2017, Simple Machines