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[Ghost in the shell]

 ??? if the result is inward turning props is better turning ability, can someone tell me WHY this should be?  ???

[Colin Bishop]

if the result is inward turning props is better turning ability, can someone tell me WHY this should be?

I think that this has been referred to before, but if you have a single rudder then the full force of the prop on the inner side of the turn (which is tending to throw water against the keel area) will hit the inclined rudder blade and help push the stern in the desired direction. Without "propwash" it is only the lesser pressure exerted by the forward motion of the boat through the water which will be applied to the rudder. You can see this in action if you put the helm hard over when the boat is stopped and then apply a burst of ahead power. The stern will kick round before the boat starts moving ahead. When the props are outward turning the propwash is thrown away from the side of the hull and there is less pressure on the rudder and therefore less turning force.

Incidentally, I was once told that the traditional practice was for merchant ships to have inward turning screws and warships outward ones.

[DickyD]

And if you didn't understand Colins explanation the answer is:

Because Bob say's so.

[Bunkerbarge]

Just a bit of related interest here's a picture of ours

[PSSHIPS]

Outward turning, twin rudders, Hope this helps?

[Colin Bishop]

Outward turning, twin rudders, Hope this helps?

In this case the rudder is situated immediately aft of the prop on each side so it doesn't matter quite so much which way the props turn. In fact this is probably the most effective steering setup for a conventional prop/rudder combination.

[Bunkerbarge]

Added to this the rudders are of a high lift Becker type so in conjunction with three bow thrusters and two stern thrusters you have a very manoeuvreable vessel.

[Colin Bishop]

Bunkerbarge, when turning the ship in a mooring situation do you use the screws to assist the thrusters or are the thrusters sufficient on their own?

[MCAT]

Colin  are you the one with short stubby fingers 

good point I did say behind the props not in them. I should have put in a warning
will be more carefull in the future

But two of my fingers are shorter than the rest makes typing a choir

[DickyD]

A choir ?? ???

[Bunkerbarge]

Bunkerbarge, when turning the ship in a mooring situation do you use the screws to assist the thrusters or are the thrusters sufficient on their own?

Both shafts and thier rudders can be controlled seperately from the thrusters and any combination of them can be used for manoeuvring the ship.  When the joystick is used it links all of them together for positioning and manoeuvring.

When the rudders are hard over the tail flap is at 90 deg to the centre line so the main shafts are generating a significant amount of side thrust and quite often one will be used in this way to balance out windage while the other shaft is used to move the ship ahead or astern.  The original design philosophy was that the thrusters should be used to support the main shafts at the back end and not provide the primary motive force.

An interesting fact is that not only can the ship turn in it's own length but the Master can also decide about which point on the hull he wants it to rotate!!

[Peterm]

This has been an enjoyable thread.   I started off with a model Aquarama and we finished with real merchant and warships.   Not bad going, thanks, all.   Pete M

[Bryan Young]

This has been an enjoyable thread.   I started off with a model Aquarama and we finished with real merchant and warships.   Not bad going, thanks, all.   Pete M

Just to throw more cats amongst the pigeons......The original Mauretania had the 2 forward props turning in the opposite direction to the 2 after ones!

[Bunkerbarge]

This has been an enjoyable thread.   I started off with a model Aquarama and we finished with real merchant and warships.   Not bad going, thanks, all.   Pete M

Just to throw more cats amongst the pigeons......The original Mauretania had the 2 forward props turning in the opposite direction to the 2 after ones!

There you have the advantage on me Bryan, I never sailed on her!! 

[DickyD]

 

[MikeK]

Don't get this problem with paddle wheels ! 

MikeK

[DickyD]

Is that left or right handed paddle wheels ?? ???

[Peterm]

I will let you know when I get that far with my paddle tug.   Pete M

[MikeK]

Is that left or right handed paddle wheels ?? ???

Depends which way up you are  If you look between your legs they look farther away, not a lot of people know that 

MikeK

[John W E]

Bunkerbarge, question for you; of your ship in drydock: Are these the props that are held on by friction and one fell off? 

Here's one for the experts, modern war ships use gas turbines of variable pitch props instead of reversing gear, which way did the shafts turn (the prop shafts that is).

aye
john e
bluebird

[PSSHIPS]

Bit rusty now John, but, after having some very close encounters with the type22 Coventry's shafts on several occasions, I seem to remember they turned outwards, but, like I say memory fades over time. But, then it depends on wether I was in the bilge looking aft or fwd and wether or not I was hanging upside down, LOL
 Paul...