Model Boat Mayhem
Mess Deck: General Section => Model Boating => Topic started by: Peterm on April 20, 2007, 06:54:03 pm
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Help please! If I have propellers which are not marked `left` and `right`, how can I differentiate? I have a Riva Aquarama which uses 2 unmarked 2-blade propellers and I am having steering problems which I think may be caused by incorrect props.
Pete M
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Hi Peterm,
How about this for a non tech reply.
Using only the left prop, which when viewed from behind turns anti clockwise with the motor running, place the boat in the water and see if the boat goes forwards. If it does, then this in the UK is a left hand prop. Do the same again but with the right prop, which when viewed from behind turns clockwise. Again if the boat goes forwards this is a right hand prop.
In an ideal world it is best to have the props spinning in opposite directions, or you will get prop steer making the boat turn, with the rudder straight.
There was a thread about this subject which you could look up, if you want a More tech reply.
Bob ;D
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Hi,
Look at the props from behind as if they are on the shafts, follow a blade from the rear edge to the front edge, if the forward edge is to the left of the rear edge it is a left handed blade and vice versa for right handed.
Alternatively, if the prop rotates anticlockwise to go forward its left handed and vice versa for right handed.
When 'handing' props, its usual to consider them by looking from stern to bow along the shaft.
Clear? hope so! ;D
Ian
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Thanks to you both. All is clear. Pete M
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Help please! If I have propellers which are not marked `left` and `right`, how can I differentiate? I have a Riva Aquarama which uses 2 unmarked 2-blade propellers and I am having steering problems which I think may be caused by incorrect props.
Pete M
This is an interesting one. "Left and Right" depends on where you are coming from.
In the UK a "right handed" prop means that it is turning clockwise when going ahead when viewed from aft.
In some European countries they view from the front. So a "right-handed" prop to them is a "left". Problems.
Most of the model brass props we buy from Model Shops are made in mainland Europe. Not too bad if you are building a twin scew boat but awful for a single.
If you are building a twin scew (nothing sexy, please) job, then make sure the props are turning outwards when going ahead. Inward turning props are rubbish in real life and just as bad in a model.
Just make sure the propwash impacts on the rudders, Good luck.
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Previous thread on props with pictures is:
http://www.modelboatmayhem.co.uk/forum/index.php?topic=2762.0
Richard ;)
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Then to throw the cat amongst the pidgeons, some boats have inward turning opposite handed props for either quietnes or speed, like has been said when looked at from astern with opposing props, if they turn outwards from centre and if you go backwards, you have got the English type, if you do the opposite and turn inwards, you have got the European set up. It all depends on wether or not you can tell the leading edge from the trailing edge, props are designed with a leading edge like an aerofoil type blade, the digging in side of the blade gives you the "hand" or "which way it turns" either inboard or outboard, but, this then gets confusing with different applications as said above.
A "right handed prop should turn clockwise from astern and a left handed prop anti clockwise from astern, BUT, then this is where the confusing bit comes in, ITS opposite depending on application.
I hope this helps????
Paul...
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;D ;D
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how to tell leading edge from trailing edge? Easy.
Look at the side of the prop while on the boat, the leading edge is nearer the bows!
Ian
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Cheer's Dicky D I'm with ya mate!
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Bryan,
I have done quite a lot of testing of model boats with inward or outward turning props.
Sorry for this, but you are talking rubbish.
In a full size vessel the shaft will turn up to about 250 rpm with a prop designed to run at reasonable efficiency at this speed. Obviously some low speed diesels
even less.
On a model the props usually run on a scale boat from 2500 - 9000 rpm, a vast difference.
In a twin screw single unbalanced rudder the model WILL turn much better with inward turning props as the propwash is directed together under the counter and directly over the rudder.
Outward turning props give the opposite.
Just recently a twin screw triple rudder model (a Schutze Class Minesweeper) had her turning circle greatly reduced by fitting the props inward turning.
Bob
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True about the turning circle on inward turning multiple props, this is one reason they brought in CPPs and other gizmos to help steer, "so sayeth he" who knows.
Paul...
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Chaps, I did not realise such a simple question could generate such a response, however I do appreciate all the advice. I think I was also guilty of not making things clear, like one of our other forum members, in that I did not explain that the Aquarama has no rudder, but is steered by use of the two motors. Once I have had a good read through I should be the forum expert on prop recognition, although Boatmadman has put it very succinctly. Once again, thanks to all. Pete M
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Bryan,
I have done quite a lot of testing of model boats with inward or outward turning props.
Sorry for this, but you are talking rubbish.
In a full size vessel the shaft will turn up to about 250 rpm with a prop designed to run at reasonable efficiency at this speed. Obviously some low speed diesels
even less.
On a model the props usually run on a scale boat from 2500 - 9000 rpm, a vast difference.
In a twin screw single unbalanced rudder the model WILL turn much better with inward turning props as the propwash is directed together under the counter and directly over the rudder.
Outward turning props give the opposite.
Just recently a twin screw triple rudder model (a Schutze Class Minesweeper) had her turning circle greatly reduced by fitting the props inward turning.
Bob
Tried both on mine Bob . Inward turning a lot better turning circle. Only needed one pond.
Richard ;)
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Bryan,
I have done quite a lot of testing of model boats with inward or outward turning props.
Sorry for this, but you are talking rubbish.
In a full size vessel the shaft will turn up to about 250 rpm with a prop designed to run at reasonable efficiency at this speed. Obviously some low speed diesels
even less.
On a model the props usually run on a scale boat from 2500 - 9000 rpm, a vast difference.
In a twin screw single unbalanced rudder the model WILL turn much better with inward turning props as the propwash is directed together under the counter and directly over the rudder.
Outward turning props give the opposite.
Just recently a twin screw triple rudder model (a Schutze Class Minesweeper) had her turning circle greatly reduced by fitting the props inward turning.
Bob
Sorry, I basically agree with you, but in mitigation I should have said I was thinking of twin rudders and not a single. But no matter what the set-up I have really found outward turning props makes for easier berthing and slow speed manouevring...particularly in "real ships". Not really much difference on a straight run. The outward turning set-up also allows better use of the transverse thrust imparted when berthing. But let us not get too heated up on this. Why not just swap the props around and see which the operator prefers? Cheers, BY.
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It is a bit late in the day, but I was looking at one of the mayhem listed links, `damn funny pictures`, and there was a picture of an enormous pair (of propellers) clearly showing the orientation. Pete M
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I am building a Missouri, now that has of 4 props & 2 rudders, I was assuming that they would turn as pairs - 2 stbd & 2 port,
it seemed to me unlikely that they would run in pairs - 2 inboard & 2 outboard - am I right?
Colin
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Sinjon,
It is usual to connect propshafts by side. Both Stbd and both Port.
This aids manouverability, but Missouri has 5 and 4 blade props. But I would try it this way and see.
Bob
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Thanks Bob that does sound logical.
Colin
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You can also hold your hand behind the prop' one at a time and move the throttle forward
and you should feel a draught if not its turning the wrong way
well thats how I checked it please tell me if im wrong not put my boat in the water yet .
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You can also hold your hand behind the prop' one at a time and move the throttle forward
And observe in which direction the flesh and blood is deposited.... ;D
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Yep, you were the one we were all waiting for Colin.
Richard ;)
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Colin, I thought it, but have not got your power of expression. Pete M (The idiot who started it)
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Sorry folks, couldn't resist! To be fair I do actually use this method sometimes. But it is a fine judgement between obtaining a cool breeze on the fingers and an involuntary savage manicure...
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You can tell by just looking at the prop which way is ahead, it is only a fan after all.
But if in doubt use a match, blow it out and watch the smoke.
NO DickyD not THAT closely, just ensure smoke doesn't get in your eyes!!
Bob
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??? if the result is inward turning props is better turning ability, can someone tell me WHY this should be? ???
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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.
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And if you didn't understand Colins explanation the answer is:
Because Bob say's so. ;D
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Just a bit of related interest here's a picture of ours
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Outward turning, twin rudders, Hope this helps?
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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.
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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.
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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?
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Colin are you the one with short stubby fingers ;D
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 :D
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A choir ?? ???
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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!!
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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
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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!
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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!! ;)
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;D ;D ;D ;D
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Don't get this problem with paddle wheels ! ;D ;D
MikeK
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Is that left or right handed paddle wheels ?? ???
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I will let you know when I get that far with my paddle tug. Pete M
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Is that left or right handed paddle wheels ?? ???
Depends which way up you are ;D ;D If you look between your legs they look farther away, not a lot of people know that ;) ;)
MikeK
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Bunkerbarge, question for you; of your ship in drydock: Are these the props that are held on by friction and one fell off? ;D ;D
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
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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 ;D
Paul...