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Author Topic: LH & RH Propellers  (Read 578 times)

silverfern

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LH & RH Propellers
« on: August 23, 2018, 05:15:34 AM »

Hi Guys,
I'm scratch building a scale model of a commercial type LCT (landing craft 45m scaled to 140cm) and it will have twin high torque low speed motors. I don't understand why there are a LH & RH drive propellers available.


On a twin drive is it normal to fit LH & RH drive propellers? What is the effect v's say twin drive RH propellers?


I would like to purchase the drive lines including the motors from the UK before I start the build in order to fit the prop shafts early into the build before  the hull covering begins.


As I'm in Brisbane, Aust I would like to have a clear understanding before committing to an order.


Thank you in advance.





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Peter Fitness

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Re: LH & RH Propellers
« Reply #1 on: August 23, 2018, 05:56:26 AM »

This has been discussed on numerous occasions here on the forum, and a quick search may provide you with some answers. It is usual for twin screw vessels to have their props rotating in opposite directions, although there is much debate as to whether they should rotate outwards or inwards, viewed from the stern. Type propeller rotation into the search box, and be prepared to be totally confused :}


Peter.
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BarryM

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Re: LH & RH Propellers
« Reply #2 on: August 23, 2018, 08:25:29 AM »


Propellers not only drive a vessel forwards or backwards but also create a side force. This is inherent in the design of all props and, although designers try to minimise the effect, it cannot be eliminated.  Thus, if props are like-handed, there will always be a need for opposite helm to counteract the side thrust. This adversely effects speed and fuel consumption.
Set-ups employing RH and LH props running on separate shafts at the same speed will cancel each other out as far as side thrust is concerned. Similarly, LH and RH props that are mounted on a single shaft in tandem formation.
Whether you have inward or outward turning props is another question and plenty of info can be found by searching on this forum.
Barry M
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silverfern

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Re: LH & RH Propellers
« Reply #3 on: August 23, 2018, 08:34:14 AM »

Thanks Barry, good info for me.
Bob
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Allnightin

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Re: LH & RH Propellers
« Reply #4 on: August 23, 2018, 09:21:59 AM »

Can you be more specific about the LCT you are building please?  I'm a bit confused about any LCT being described as Commercial as the business of landing large armoured fighting vehicles is usually reserved for the armed forces!

In fact some of the types of LCT used in WW2 were built as simply and cheaply as possible so would have had all propellers turning the same way rather than have had to allow for different gearboxes and props.
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CGAux26

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Re: LH & RH Propellers
« Reply #5 on: August 23, 2018, 04:12:32 PM »

I am also scratch building a commercial landing craft/ferry.  The Henry Island ferry runs among the San Juan Islands in Washington State, carrying fuel trucks, utility trucks and all sorts of things.  It is twin screw, so my model will be, too.


A twin screw boat needs to have opposite handed props, for the reasons stated above.  I call this side thrust "prop walk" since it resembles a tire on the road-bottom of prop or tire moving left, side thrust is to the right.  That side thrust moves the stern of the boat, more so in reverse.  With props that turn outward going ahead you can use the prop walk to help spin the boat on its own length going ahead on one engine and astern on the other.  This can be done with "tank steering," with the port motor on the left stick and the starboard motor on the right stick of your TX.  Or with a motor mixer, such as the Action P40. 
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silverfern

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Re: LH & RH Propellers
« Reply #6 on: August 23, 2018, 11:26:29 PM »

Thank you CGAux26. A good reply with useful information for me.  :-))


Allnightin, if you go to www.ratson.com your questions will be answered.
Downunder these vessels are known with several different
reference titles such as:


LCT is a landing barge used around the Pacific Islands, Indonesia, Philippines and north Australia. They can also be referred to as simply a barge. These vessels are very different to a military LCT, in fact some LCT's also carry passengers but are mostly used to transport freight and cars to outer lying islands due to no ports being available.



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Allnightin

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Re: LH & RH Propellers
« Reply #7 on: August 24, 2018, 01:26:36 PM »

Thank you CGAux26. A good reply with useful information for me.  :-))


Allnightin, if you go to www.ratson.com your questions will be answered.
Downunder these vessels are known with several different
reference titles such as:


LCT is a landing barge used around the Pacific Islands, Indonesia, Philippines and north Australia. They can also be referred to as simply a barge. These vessels are very different to a military LCT, in fact some LCT's also carry passengers but are mostly used to transport freight and cars to outer lying islands due to no ports being available.





Thanks - obviously they use the word "tank".  I presume the vessels aren't actually built to take a 70 ton main battle tank onboard though!
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