Topic: Propeller recognition (Read 11336 times)

Peterm · « **on:** April 20, 2007, 06:54:03 pm »

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

BobF · « **Reply #1 on:** April 20, 2007, 07:21:10 pm »

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

boatmadman · « **Reply #2 on:** April 20, 2007, 07:24:12 pm »

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!

Ian

Peterm · « **Reply #3 on:** April 20, 2007, 08:10:10 pm »

Thanks to you both. All is clear. Pete M

Bryan Young · « **Reply #4 on:** April 20, 2007, 09:03:13 pm »

Quote from: Peterm on April 20, 2007, 06:54:03 pm

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.

DickyD · « **Reply #5 on:** April 20, 2007, 10:20:29 pm »

Previous thread on props with pictures is:

http://www.modelboatmayhem.co.uk/forum/index.php?topic=2762.0

Richard

PSSHIPS · « **Reply #6 on:** April 20, 2007, 10:26:52 pm »

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...

DickyD · « **Reply #7 on:** April 20, 2007, 10:33:18 pm »

boatmadman · « **Reply #8 on:** April 20, 2007, 10:42:32 pm »

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

PSSHIPS · « **Reply #9 on:** April 20, 2007, 10:45:55 pm »

Cheer's Dicky D I'm with ya mate!

Shipmate60 · « **Reply #10 on:** April 20, 2007, 10:52:59 pm »

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

PSSHIPS · « **Reply #11 on:** April 20, 2007, 11:07:14 pm »

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...

Peterm · « **Reply #12 on:** April 21, 2007, 08:56:27 am »

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

DickyD · « **Reply #13 on:** April 21, 2007, 09:43:07 am »

Quote from: shipmate60 on April 20, 2007, 10:52:59 pm

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

Bryan Young · « **Reply #14 on:** April 21, 2007, 02:23:33 pm »

Quote from: shipmate60 on April 20, 2007, 10:52:59 pm

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.

Peterm · « **Reply #15 on:** April 21, 2007, 06:24:51 pm »

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

sinjon · « **Reply #16 on:** April 23, 2007, 12:18:33 pm »

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

Shipmate60 · « **Reply #17 on:** April 23, 2007, 12:48:29 pm »

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

sinjon · « **Reply #18 on:** April 23, 2007, 01:11:21 pm »

Thanks Bob that does sound logical.

Colin

MCAT · « **Reply #19 on:** April 23, 2007, 01:40:28 pm »

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 .

Colin Bishop · « **Reply #20 on:** April 23, 2007, 06:03:22 pm »

Quote

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....

DickyD · « **Reply #21 on:** April 23, 2007, 06:10:08 pm »

Yep, you were the one we were all waiting for Colin.

Richard

Peterm · « **Reply #22 on:** April 23, 2007, 06:52:58 pm »

Colin, I thought it, but have not got your power of expression. Pete M (The idiot who started it)

Colin Bishop · « **Reply #23 on:** April 23, 2007, 07:01:37 pm »

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...

Shipmate60 · « **Reply #24 on:** April 23, 2007, 07:10:03 pm »

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

News:

Author Topic: Propeller recognition (Read 11336 times)

PSSHIPS

PSSHIPS

PSSHIPS