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Author Topic: twin prop'd boats - which way should prop's turn?  (Read 11877 times)

RipSlider

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twin prop'd boats - which way should prop's turn?
« on: October 17, 2007, 03:36:19 PM »

Hello all.

Just a really quick question.

Currently I'm building a twin proped boat.

If I look at from the rear, so that the prop's are facing me, should the prop's turn in to each other (left prop clock wise), or away from each other ( left prop anti clock wise) ?

I have fitted L/H and R/H prop's on the respective sides.

Many thanks

Steve
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DickyD

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Re: twin prop'd boats - which way should prop's turn?
« Reply #1 on: October 17, 2007, 03:41:46 PM »

Hi RipSlider
You will get many different replies on thi probably.
On my boats the twin props turn in as we found it improves the steering.
If you are only concerned with speed have them turning out.
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Shipmate60

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Re: twin prop'd boats - which way should prop's turn?
« Reply #2 on: October 17, 2007, 03:59:11 PM »

RipSlider,
How many rudders are fitted?

Bob
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DickyD

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Re: twin prop'd boats - which way should prop's turn?
« Reply #3 on: October 17, 2007, 04:21:04 PM »

Thought you were supposed to be working Bob  :-\
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Martin [Admin]

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Re: twin prop'd boats - which way should prop's turn?
« Reply #4 on: October 17, 2007, 05:23:06 PM »

Also, what type of boat is it?
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cdsc123

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Re: twin prop'd boats - which way should prop's turn?
« Reply #5 on: October 17, 2007, 05:40:20 PM »

Type "prop rotation" up where it says "search", you'll be surprised at the wealth on knowledgeable info which has already been offered on the subject.
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RipSlider

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Re: twin prop'd boats - which way should prop's turn?
« Reply #6 on: October 17, 2007, 09:01:40 PM »

Thanks for the answers so far.

Boat is a fairly shallow draft PCF a riverine craft. Twin, fairly large rudders, located direction stern of each prop.

Sadly I don't have a working search facility on this site, so posted. Mods should free free to take down if required.

Steve
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gribeauval

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Re: twin prop'd boats - which way should prop's turn?
« Reply #7 on: October 17, 2007, 10:04:55 PM »

Have a look at this thread,


regards   Mike   ;)
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Martin [Admin]

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Re: twin prop'd boats - which way should prop's turn?
« Reply #8 on: October 17, 2007, 11:50:41 PM »

Found this if it's any use.... looks like they both turn anti-clock!  :o



You could always email them and ask...... http://pcf45.com/dedication/vumdirections.html
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Bryan Young

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Re: twin prop'd boats - which way should prop's turn?
« Reply #9 on: October 18, 2007, 07:38:25 PM »

Found this if it's any use.... looks like they both turn anti-clock!  :o



You could always email them and ask...... http://pcf45.com/dedication/vumdirections.html

Looking at the picture I would very humbly suggest that you look at again. The leading edge of the stbd. prop. is "screwing in" and so is then an "outward" turning item. Sorry to rain on your parade! BY.
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cdsc123

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Re: twin prop'd boats - which way should prop's turn?
« Reply #10 on: October 19, 2007, 08:34:04 AM »

I think....
They do both go the same way,'cept it's to the right not to the left.
So you're both kinda right.
Just like the props  :)
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portside II

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Re: twin prop'd boats - which way should prop's turn?
« Reply #11 on: October 19, 2007, 09:28:55 AM »

depends from where your looking  {-).
i supose there is a propper way of reading the direction ,either from the front or back .
daz
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Peterm

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Re: twin prop'd boats - which way should prop's turn?
« Reply #12 on: October 19, 2007, 10:28:25 AM »

Normally read from the rear.   Pete M
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Bryan Young

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Re: twin prop'd boats - which way should prop's turn?
« Reply #13 on: October 19, 2007, 07:01:58 PM »

depends from where your looking  {-).
i supose there is a propper way of reading the direction ,either from the front or back .
daz
We have been down this route before. In the UK we look at the props from aft. In many European countries they look from the front. That is why when you order a "right handed" prop from your local model shop it comes back as a "left"....'cos they are all made in some faraway country if which we know little. If you want a "right handed" prop then order a "left-handed" one!
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cdsc123

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Re: twin prop'd boats - which way should prop's turn?
« Reply #14 on: October 19, 2007, 09:40:53 PM »

We'll have to continue to agree to disagree about that, I've yet to come across the country that views from in front.

Standing to be corrected...  ;D
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Bryan Young

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Re: twin prop'd boats - which way should prop's turn?
« Reply #15 on: October 19, 2007, 10:59:20 PM »

We'll have to continue to agree to disagree about that, I've yet to come across the country that views from in front.

Standing to be corrected...  ;D
Just about all of them. Especially the Netherlands.
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funtimefrankie

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Re: twin prop'd boats - which way should prop's turn?
« Reply #16 on: October 20, 2007, 09:29:48 AM »

Does it matter if you call them, left or right hand, if you are talking twin props, after all you want one of each, you may as well call them Bob and George. ;D
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portside II

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Re: twin prop'd boats - which way should prop's turn?
« Reply #17 on: October 20, 2007, 09:40:28 AM »

here here well said
if you order a pair and the are both the same then they aint a pair whatever country your from
apart from the ones in Martins picture  O0
daz
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Mr Whoppit

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Re: twin prop'd boats - which way should prop's turn?
« Reply #18 on: October 20, 2007, 11:15:26 AM »

Ladies and Gentlemen, may I bring it to your kind attention that the rotation of propellers and the way they are viewed indeed varies.

To date, propellers are the most efficient way of moving a vessel through the water, by converting the shaft horse power into thrust.

Please see the pictures I have included below.   

One of these photographs (see picture A) is from the early 1900’s, this shows an early Cruiser. The propellers here are rotating inboard.  The blades of the propeller are long and narrow.

You will see from the photograph (see picture B) from around 1937 shows a Cruiser with ‘quad’ propellers and the forward propeller is turning outboard.  This propeller shape has changed as you will see.  It is what is classed as a wide tipped blade. (Elliptical)

The next photograph, (see picture C) shows a modern ship, propellers are in ‘pods’.  If you note that the propellers on this vessel turn inboard, and, also the propellers’ face forward to the bow of the ship, this in turn gives more efficiency from the electric drive motors in the pods.

The last photograph I have included is that of The Turbinia. (See picture D). Close examination of this, will show you that there is not one propeller on the shaft, but, there are several – of all varying designs which are again, turning outboard.

All the above are viewed from the stern, looking towards the bow.

From this we can deduct that the direction to which a propeller rotates depends upon which vessel it is fitted to and what the vessel is designed to do.

During the period of the war years a lot of our British multi-propellered small inshore vessels such as MTBs (motor torpedo boats) the propellers rotated the same way on a lot of them.  This was because there was quite a shortage of reverse gear boxes.   
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Re: twin prop'd boats - which way should prop's turn?
« Reply #19 on: October 20, 2007, 04:15:46 PM »

Nicely illustrated explanation Mr Whoppit  O0
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meridian

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Re: twin prop'd boats - which way should prop's turn?
« Reply #20 on: October 20, 2007, 07:37:41 PM »

Earlier this year I completed my first build, which was a Model Slipway kit of a  'Range Safety Craft' which I adapted it as an MOD Police Launch. The kit was supplied with two, two-bladed 'same hand' props which I used as supplied. To be honest, I have not noticed that there is any major trim required to compensate for this. To all intents and purposes the blades of two rudders lie parallel to the centreline of the boat.
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Re: twin prop'd boats - which way should prop's turn?
« Reply #21 on: October 20, 2007, 08:05:30 PM »

Hi there Meridian

I know it may make very little difference, but I feel that the props should have been handed left and right....I think it may be an oversight by the model suppliers.  But, then again, in this world who knows.

Sometimes a model can steer to one side when you have both same handed props running in the same direction.  :o

aye
John e
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Re: twin prop'd boats - which way should prop's turn?
« Reply #22 on: October 20, 2007, 08:22:54 PM »



Sometimes a model can steer to one side when you have both same handed props running in the same direction.  :o



And the swing when going astern might be even worse.

Andy
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meridian

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Re: twin prop'd boats - which way should prop's turn?
« Reply #23 on: October 20, 2007, 10:34:11 PM »

Hello Bluebird,

No it wasn't an oversight on the part of the model suppliers. The instructions clearly state, " The propellers (which are not handed) are simply screwed onto the shafts, locking them in place with the nuts provided".

However, this would not appear to be a problem as I note that PCF-104 is fitted with props of the same hand.

In view of contradicting opinions etc I intend to fit a LH and RH prop to see if I can detect any real difference. At the same time I will also try and compare the effects of inwards rotating and outwards rotating.  Will report my findings in due course.

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cdsc123

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Re: twin prop'd boats - which way should prop's turn?
« Reply #24 on: October 20, 2007, 11:13:50 PM »

Hi Meridian

The contradicting opinions are about prop rotation always being viewed from astern as an international convention and not dependent on where you happen to be in mainland Europe (I deal with Vetus NL and they certainly view from astern).

A handed pair of props, not to be confused with a pair of props, will certainly give your model better handling, of that there is no debate here.   

The kit you built, being of a relatively high performance craft, possibly supplied 2 LH props so that they wouldn't try to unscrew themselves. I believe it is also the case that 2 blade props deliver more performance and further, are not generally available in handed pairs as are 3 blade props.

As Mr woppit states, Coastal Forces craft (and RAF rescue craft) were fitted with props of the same handing, whether this was due to the cost, reliability, availability or power-robbing characteristics of handed 'boxes as opposed to simple boxes is a matter for some debate, literature I have tends to suggest the extra 2 or 3 knots achieved with same-handed props was worth the sacrifice of difficult manouvering.

Cheers,
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