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[derekwarner]

Kiyo.......there appears   to be a prop locknut on the port side prop?....so how    did you did you loose the stdb side prop [with a locknut?].... Derek

[Backerther]

Derek
Sorry to say, I do not understand exactly what you mean with my English reading comprehension ...
I used the lock-nuts on both sides. She returned as it was in the pic.

[Allen A]

Hi Derek, in reversing the polarity of the motor to get correct contra rotation, I think that's what I forgot to do, ie; tighten the lock nut against the prop .. duh .. !!??

[Circlip]

Ever heard of "Gasket Goo?" A touch on the shaft end before screwing the locknut and prop on.


 Regards  Ian.

[Allen A]

Thread lock ... superglue ..?? ... .. hindsight's a wonderful thing isn't it 


In reality though and in having a contrarotation system I would have thought that it would be practical to have the right hand prop and prop shaft fitted with a reverse thread to counter the problem of the prop unscrewing ..??

[derekwarner]

Morning Allen.......yes, it is easy sitting back after the event, however my comment was intended only to be a belt & braces thought


Using any Grade of Loctite [even 'Loctite Threadlok'] with a nylon/plastic bodied prop is not a good idea, as even the moderate flame-heat needed to break the Loctite bond will distort the nylon from the brass hub & render the prop useless


Quite a number of Folk, trial different lower cost plastic/nylon props in different sizes/blade numbers, until an optimum size/performance is found, then substitute full brass props of that selected size/style etc


From this, Loctite 'Threadlok' together with a locknut can be used without any concern  

Derek

[Circlip]

That's why I said "Gasket Goo". 'Spose it is a mixture of red Lead and oil. When we had the ability to service and repair our own motor bikes and cars, it was a necessity in the toolbox. Ahhhh, the good old days.


 Regards  Ian.


 PS. Allen, my Sea Hornet used to go a bit quicker than 4mph on my dinner time forays as an apprentice at Andertons.

[dodgy geezer]

I see from your picture that you have two locknuts on your shaft, followed by a prop. Are you tightening one locknut against another? You would normally have one locknut, and tighten it against the prop, to hold the prop securely on the shaft.


If you run a motor with standard clockwise rotation viewed from the rear, a standard prop with a standard screw thread  will try to tighten itself up when running, and will be in no danger of falling off. However, if you reverse the moror rotation, the standard screw thread will now try to undo itself.  That seems to be what has happened.


The cure is either to get a left hand prop with a left hand screw thread,  and have a corresponding left hand thread on the shaft,  or to use a locknut AGAINST THE PROP to hold it on securely.


Locknuts are commonly used for most boats, since going into reverse can cause the same problem. The only time you don't need to worry is when your motor can only go one way, like an I/C one...

[Allen A]

The cure is either to get a left hand prop with a left hand screw thread,  and have a corresponding left hand thread on the shaft,  or to use a locknut AGAINST THE PROP to hold it on securely.

As I suggested in a previous post, I would have thought it would be logical to have matching left hand threads on the prop and prop shaft as a matter of course in order to perhaps counter the potential problem of losing a prop from the right hand side ... ??

[dodgy geezer]

As I suggested in a previous post, I would have thought it would be logical to have matching left hand threads on the prop and prop shaft as a matter of course in order to perhaps counter the potential problem of losing a prop from the right hand side ... ??

Easy enough to do if you are cutting the threads, but it may be harder to buy prop shafts and props like this?  And you would still need locknuts if you expect to run in reverse...Props with a dog connector tapped and soldered onto the shaft would also address the problem...

[Allen A]

That's my point ... in making and supplying reverse props as they do, albeit it with right hand thread, I would have thought that they would also make the prop shaft with a left hand thread and have a left hand thread on the reverse prop ??


I acknowledge the fact that in reversing a boat lock nuts would still be needed, the reality there perhaps being that as its a minimal, and slow, operation for most it wouldn't cause that much of a problem ..  question then ... on a double motor craft, would it hurt to have two standard props on it, wouldn't a boat still work OK like that or is it better and/or necessary to have contra rotating props ??

[Circlip]

How many pitches and diameters and blade configurations do you want to stock with a LH thread?? And how much do you want to PAY for the pleasure? The road to Hell and all that.


 Regards  Ian.

[John W E]

Talk about opening the gates to hell - with wanting to produce left and right handed threaded props and prop shafts - We had a late dear friend on here who is now on the other side, bless him - I can hear his screams of fright and anger, like many a time the telephone calls I used to receive when his customers couldn't even wire up a battery the correct way in their models - and consequently burned out umpteen speed controllers and sent them back to him, wondering why they didn't work.   So, if the average modeller cannot understand simple things like positive and negative what chance have we got of them understanding left and right handed threads     - we do know for a fact we would get 'me propeller won't fit on the shaft; there is something wrong with the threads'


   so keep well away from that idea.


A lock nut secured properly onto the back face of the propeller boss is the simplest way, to stop the prop falling off.


John

[Geoff]

Curiously, if I have the picture right, when viewing from the stern a right hand prop will screw on in a clockwise direction and if rotated in a clockwise direction will actually have a tendency, because of the thrust on the blades, to unwind and fall off. A left hand prop will do the reverse so will tend to tighten up on the shaft. Either way a simple lock nut on the shaft will hold the prop on securely irrespective of the direction of rotation. I've never lost a prop yet!


The lock nut also serves another important purpose as depending on the direction of rotation the prop can screw up the shaft and lock itself solid.



We should also reflect where the thrust goes. Between the lock nut and the end of the outer prop shaft tube you should have one or two small washers as these act as thrust bearings together with say 1mm of endwise float fore and aft such that the thrust is taken by the tube and not the engine bearings which will cause premature wear and overheating of the motor and increased current consumption (unless brushless as I believe they have different bearings).


Cheers


Geoff

[Allen A]

Hi guys ... whoa there ..    ...  the logistics of it all aside it was just a 'Spock' question re; a logical thought .. does beggar the question though, why make a reverse prop ?? ... and I notice there has been no answer to my question about a boat operating correctly with two matching props .. ie both spin the same way for fwd or reverse .. is it necessary to have contrarotation on a twin engine craft ..?


I received the replacement 35mm prop today but in talking about being confused I ordered a 'right hand ' one in as much as from the rear it is for the right hand motor but have in fact received a standard prop for fwd movement, now I could use it and reverse the motor again so both spin anticlockwise for fwd operation, but I also ordered two opposite 40mm props and have fitted them for now, and yes locked the new one in place so it doesn't unscrew. .. so another new to RC 'dumb' question, when talking  left and right re props are we talking about prop shape or its position on the boat ... looking from the stern, the No 2 boat has the left hand motor etc configured for anticlockwise fwd direction and the right hand one configured for clockwise fwd direction, ...  right or wrong, or doesnt it matter .. ??

[John W E]

Hi there Allen


Your basic question about prop rotation and so forth can become a very complex subject.   There are a lot of governing factors involved to the extent that it may sometimes stove ones brain in - leaving one looking for a bottle of whisky    .    But, have a search on this Forum there are a lot of very good topics detailing this subject and it could possibly answer all of your queries.


I have put a link on just of two  topics I found using a quick search


Prop rotation direction (modelboatmayhem.co.uk)
Propeller Rotation & Configuration (modelboatmayhem.co.uk)


Now here is something to put a cat amongst the pigeons for you.    Many moons ago I built an RTTL model.   The build is somewhere on this forum if you want to look it up.


It was built with a lot of information from the builders of the original vessels.    Originally, the vessels began with triple shafts and engines and then some of them were converted to a twin engine twin shaft configuration.    Now, here is the thing, the props both turned the same direction - because, it was found, during World War II , they could achieve a bit more speed from the craft that way for the given horse power and revs of the engines.


The other deciding fact was the shortage of reversing gearboxes.


A pic of my RTTL props .....


John

[Circlip]

And we haven't even broached (    ) metric and him perryall threads.


 Regards  Ian.

[Allen A]

And we haven't even broached (    ) metric and him perryall threads.

 Regards  Ian.

... say what ... ???    ... yes lets not go there then ... T M I for one thing at the level I'm at in all of this and not something I think that will affect my operating my boats ..??




John


many thanks for that post and the links therein, very interesting reading and yes something of a can of worms I feel making me wonder if it was a good idea asking the question I did .. ??


In short my No 1 boat has a single prop so until I got the No 2 boat and the problems arose where it wouldn't reverse that I realised, with help on the forum here, it was down to the props being opposites yet turning the same direction ... Having corrected that led to my losing the stbd prop as posted, the solution there being as I say to buying two more and fitting them, quite by accident I admit, as outward turning configuration and it has yet to be tested but from all that is said should be OK .. interesting point re WWII settings to use a word that they found with props both turning in the same direction it gave more speed, an answer then to my question about a boat operating Ok with both props in the same direction and a back up too if I lose the stbd prop again (despite the lock nut) as I have two standard props spare now.


I will admit to one thing that hadn't occurred to me, I had, have, always assumed a boat turned in answer to the rudder due to the directional motion it was going, now I know this will make a few smile or even roll their eyes, but I had no idea the prop wash assisted in all of that but does make sense after reading about it all .. and there was me at one point wondering if my props were too close to my rudders ...     sigh !!

[Backerther]

My setup of screw props for 1/32 Pt-109 are like these.

1;35mm dia props with three blades.  Major difference with yours I feel is just the pitch. Mine seems more positive.
   
2;With these props, she has sailed at high speed many times so far successfully except the latest one in which I lost stb prop
    due to my poor maintenance.
3; The props were CCW and CW, both rotate outboard each other, by which she leaves nice wakes to me as in pic2 at a bit          high speed. A combination of twin Mabuchi 540 motors and a lipo 2S 5000mAh has made an awesome job to me.
   I think you had better reconsider these precedent data for your setting as mine is the evidence to go through to the good sailing,
   although much useful argumentation has been done so far for seeking the best/better solutions.

[Allen A]

Took the No 2 boat for a sail tonight, went reasonably well, didn't lose the stbd prop so all good there and has a good turn of speed too, but a canal is perhaps not an ideal spot as it kept slowing occasionally due to minor  clogging of props. ... one thing tho', despite rudders being centered it has a tendency top drift to port, wondering if props are balanced right in as much as not bought as a pair but singles ??

Pics attached then, grabs from very short videos so apologies for quality, it is hard to control boat and try to take video and stills at the same time, but they serve perhaps to illustrate performance ??

[Backerther]

I checked briefly and previously the balance of both motors concerning their revolutions in the manners as seen in the pics below at a piece of 1.3V Nimh battery. The test was done to know how many rotation may be the starting point, by which I could know the smoothness or silence of the motors mainly.　In other words, the rotations will be so-called "idling status" for these motors.
Moreover, I could confirm how smooth and well the connections among the motors, couplings and screw shafts were at a higher
voltages.
The result was...so silent, so smooth and so slow enough to be able to see the coupling as its original still shape while
rotating in around 1900 RPM.   I regarded these setups as serviceable for a RC boat to operate on our lake,
where noisy RC boats have been strictly prohibited to sail for many years.
Needless to say, both stern tubes were filled with grease completely and the 1900-2000RPM idling was achieved at 1.3V.
This MTB has run well later on subsequently as seen in my previous video.   1900 and 2000RPM were acceptable to me in balance test and subsequent performance of maneuverabilities on the water.

1;stern tubes were filled with grease and tachometer was set. Let's go the test....expecting a stable rotation...
2;Left motor ..1900RPM rotating stably enabling the coupling in nearly in its still mode at 1.3 V battery.
3;Right 2000RPM

The motors were getting a bit warmer in several minutes test like high and low speed and then finished.

[Allen A]

You cant photo/video and control a boat at the same time ...!!


Ive said that a few times now I think, shame I didn't learn from it as I took the No 1 boat for a run tonight and had a wake up call ... set the boat running, (and mind you this thing is f a s t ) but must have knocked the rudder control as I picked up my camera and it was heading straight for a concrete edge on the canal .. yes I panicked somewhat but managed to stop it before it hit, only in trying to move the control to stop it went a little further and hit reverse .. the result being as in the pictures attached .. as well as disintegrating the coupling I managed to also bend the end of the prop shaft ... of course without power now she was drifting along the canal and out of reach, a lighter moment occurring when a couple on a narrow boat put an RC duck .. (yes a duck) .. in the water to try and guide my boat back to the bank .. unfortunately, or perhaps fortunately, it wasn't working, (would have made a bit of a funny and perhaps embarrassing video though) and they helped me salvage my boat using their narrow boat.


I'm beginning to realise that the skill involved in making these boats, especially scratch built ones, isn't just limited to being about the build but also very much in the the handling, sailing and controlling of them and if there's a 'driving test' for model boats I maybe need to take it ? 

[Backerther]

Oh,,,You really had so severe experience ,but lucky that a certain couple was near your boat...
You had better carry a kind of rescuing method in case of such emergency unless you are confident in the model boating
on the field or unexpected mishaps.   I lost a small tugboat in such a similar situation in the past after drifting a mile or so
in this lake.

One of my mottos empirically is "A RC boat/ship be judged finally/properly by and on the water whether or not she is well built"   For this point of view, it is ideal if the suitable(larger) water is available nearby for repeated testings...
       IF POSSIBLE,though...

1; Ideal couplings in most my RC boats of middle-size. Silent and tough!
2; Ideal water for testing and normal sailing, instead, rescue methods must be always considered...
A larger lake/pond is better for a fast PT boat to enjoy her peculiar high-speed feeling, isn't it? Wow-!
3: A happy sailing on the large water for me and her at high speed. !?

You had better ask your son or grandchild or wife for a help to take a video for your precious boat and better postings on here.!    Simultaneous one-man operation is so risky to do, needless to say.

[Circlip]

Is (was) the motor and shaft in line with each other in both axis? Grease is adequate as a seal, rubber washer (O-Ring?) not necessary. Lot to be said for ball and socket drive couplings rather than hewko rubbish.


  Regards  Ian.

[Allen A]

Hi Ian, not sure if its me or Backerther you're referring to ... in my case yes it was in line well and very slightly low to be honest but ran well and fairly smoothly, I did manage to get a very short video of it and in fact I didn't try to simply stop it but unwittingly hit reverse hard and you can hear the 'clunk' that resulted from that which caused the damage as in the pictures.


Will be ordering a new prop shaft and coupler too but a little puzzled by your comment on those to be honest, aren't they standard item then ??