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[AlisterL]

Not sure if this is a silly question or not, but I need to move the prop further in towards the fore end of a kort nozzle.
With the nut in the "normal" place the prop is too close to the end of the nozzle:



So will the alternative arrangement work ok?



I can't think why it would be a problem, but thought I'd check with the brains-trust...

And no the nozzle can't be made longer :)

[pettyofficernick]

I do not think that would work as the prop and nut would unscrew its self, have you thought of shortening the shaft and tube, assuming you have access to a die of the correct thread it would e a relatively easy job to slip out the bush, shorten tube and extend the thread by the appropriate amount. You would then be able to fit a nut, the prop, and a locknut to hold it all together.
Regards,
Nick.

[AlisterL]

I new there was a reason... Thanks Nick. Unfortunately the problem is not with the length of the shaft, but the position of the prop relative to the end of the nozzle. The washer and the nut (mostly the nut) push the prop an un-scale distance away from the end of the shaft. I might try filing the nut down a bit.

[derekwarner]

Guys.....just thinking.......the principal of using a lock nut is simple

1. a nut can be positioned at any given point on a threaded shaft
2. we introduce a second nut and apply a torsional moment between the two nuts [holding each nut with a close fitting spanner] and tightening toward each other
3. in effect we are stretching the threaded shaft....however we must not exceed the yield point value of the shaft material as if that happened the shaft would fracture & split
4. placing Loctite is a form of insurance, however it is the induced torque applied between the two components that locks them to the shaft
5. we can consider the propeller tapping to be one nut....the other component is the lock nut
6. the difference in the length between the propeller tapping to the nut length has no influence ...again it is the induced tension between the two components
7. in an extreme overkill...if each component were tightened against each other beyond the shaft materials yield point..........the component with the shortest thread form length [the nut] would have caused the yield failure

Now the alternate to this is locking the propeller against a shoulder on the prop shaft & installing a lock nut.........however the same principals apply.......stretch the shaft thread

As I am sure many would understand cylinder heads on large marine diesel engines are secured by hand and without a lock nut   as the cylinder head studs [160 diameter?] are hydraulically stretched....the nut engaged to seat & the hydraulic tension on the stud released   ....same principal

For my money...........if you install the prop & locknut as per the points above ...they will never move........ .....Derek

[AlisterL]

And that, Derek, was what I based the original question on - if the prop and the lock-nut are tightened to each other then it should be secure. Maybe I should have said it that way to start with.

TYVM!

[chingdevil]

For piece of mind could you fit a spring washer between the nut and prop, or is there enough thread to fit a nyloc nut?

Brian

[derekwarner]

Brian & Alister....some of the principals applied to both small & large diameter screwed/bolted applications are...  

1. having close toleranced male & female threadforms
2. having square shoulder faces of the components relative to their shaft axis
3. a spring washer when compressed is only a spacer........it does not contribute to shaft thread stretch & the induced torque applied between components
4. a spring washer [when tightened] will also attempt to alter the axial alignment of the components via the male to female thread tolerance
5. a result of this is out of balance alignment
6. a Nyloc nut when correctly torqued/tightened offers no greater resistance to loosening other than the friction offered by the nylon insert to the shaft thread within the nut

.....Derek  

[hopeitfloats]

could the torque on the  prop eventually loosen them though. i know i have had the odd prop come off (usually only in the middle of the pond though ) and thats what i have put it down to. possibly going astern a bit quick.

[derekwarner]

mmmmmm ... this is an interesting subject  

1. the anti rotational torque [acting] on the propeller blade surface is the resultant of the applied input power - this applies equally to FWD or ASTERN rotation
2. these are complex calculations.......
3. if the resultant applied power [torque] exceeds the induced mechanical tension [torque] applied between the two components .....then   yes something else will fail in the drive line
4. however this does not include the loss of induced tension/torque between the propeller & the lock nut
5. if you have experienced...  'the odd prop come off (usually only in the middle of the pond though)'   ...please re-read & consider the points offered   ....Derek


  

[ooyah/2]

Not sure if this is a silly question or not, but I need to move the prop further in towards the fore end of a kort nozzle.
With the nut in the "normal" place the prop is too close to the end of the nozzle:



So will the alternative arrangement work ok?



I can't think why it would be a problem, but thought I'd check with the brains-trust...

And no the nozzle can't be made longer :)

Alister,
Put the thrust washer onto the shaft, smear the thread with Loctite 243 thread lock, screw on the prop, a little more thread lock onto the shaft and lock up your lock nut, leave to cure overnight and It will last for ever.
If you don't want it to come of again use Loctite 603.

I have been doing this  for years and no mater what the rotation of the shaft or the speed  (up to 15,000 rpm Flash Steam  and on fast electric with brushless and Lipo's up to 30,000 rpm ) and I have never lost a prop yet.
I really don't know why all this technical book stuff  on so simple a solution.
George.

[AlisterL]

Thanks Derek, Brian and George for your comments. Two things I will do:
- File a flat on two side of the centre portion of the prop so I can torque it on properly and
- Get some Loctite

[Shipmate60]

ON the previous pics the prop will be fine either way.
the prop/locknut combination will provide the mechanical locking required as it is the reaction of the 2 nuts slightly stretching the threads on the nut(s) that lock the prop to the shaft.
My only concern was I thought in the written description you wanted to put the washer between the locknuts which would negate most of the locking properties.

Bob

[john s 2]

With Locktite,if locknut is used ive found it ok to undo. But stronger mixes  sutch as studstick Bearingfit etc do require heat to break. They are made to hold and thats what they do. Actually oxcy act with the correct jet does give you a very accurate hot flame. At least my set does. I use it to silver soider. John.

[HS93 (RIP)]

so do you use Loctite product's on your shafts when you sail ? and which side do you put your nuts on ?

Peter

[AlisterL]

For what it's worth, what Derek wrote was of interest to me and I thank him for his contribution, as I do all the others who contributed.
Bob - no way will the washer be in-between the prop and the nut - but thanks for checking :)

Usually I tend not to get involved when threads get a little heated as this one seems to be - perhaps we should all call it quits on this one as I have the answer I needed.

Thanks again to all.

[dave301bounty]

Honestly ,,Being a retired Ship.s /Marine ,Engineer ,with a B O T Ticket ,what I myself does is ,get the prop lock nuts on a surface plate and put a good flat finnish to them ,so when you lock/up with the proper size spanner/s ,no need for big stuff they only wreck ,you just lock up as proper and them nuts /props will not come loose ,if you wish a drop of the pink loctite will give you a bit of peace of mind ,but this method does me ,pure engineering .learned over time and lots too.

[John W E]

Hi all

Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft.  Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent.   This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet 
Aye
john

[AlisterL]

Hi all

Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft.  Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent.   This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet 
Aye
john

Very clever John! And I like the idea with the pin too :)

[RaaArtyGunner]

Honestly ,,Being a retired Ship.s /Marine ,Engineer ,with a B O T Ticket ,what I myself does is ,get the prop lock nuts on a surface plate and put a good flat finnish to them ,so when you lock/up with the proper size spanner/s ,no need for big stuff they only wreck ,you just lock up as proper and them nuts /props will not come loose ,if you wish a drop of the pink loctite will give you a bit of peace of mind ,but this method does me ,pure engineering .learned over time and lots too.

Good tip 

[RaaArtyGunner]

Hi all

Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft.  Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent.   This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet 
Aye
john

John, Good idea, will now replace the split pins with brass as the split pins always rust off and unbalance the shaft,

[Patternmaker]

Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.
Just hold the prop with a thick glove or rag and tighten a stainless lock nut, I have always used this method on all
my sports boats with flexishafts and a shaft saver, never lost a prop in over 50 years. 

[John W E]

Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.

Hum    A good engineer would have the sense to remove the prop and shaft from the model and secure the prop in a vice or on a V block so the hub of the prop was secure enough to knock the pin out without distorting the shaft 

aye
john

[Patternmaker]

Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.

Hum    A good engineer would have the sense to remove the prop and shaft from the model and secure the prop in a vice or on a V block so the hub of the prop was secure enough to knock the pin out without distorting the shaft 

aye
john

Hum, A lot of models you can only remove the shaft from the inside, by removing the rudder and its linkages therefore having to remove the prop first, (example)























 

[John W E]

Hum, A lot of models you can only remove the shaft from the inside, by removing the rudder and its linkages therefore having to remove the prop first, (example)























 

Hummmmmmm that indicates a lack of for-thought on behaif of the designer and modeller if you have to go to so much truble to remove all the rudder linkages to get the rudder off   

Looks a nice model mate 

aye
john

[Colin Bishop]

I'm amazed at this thread!

Surely, just put the prop where you need it, screw up a locknut to lock it (use loctite if you want) and then a spacer plus a sealing washer between the locknut and the end of the tube to keep it in position. Then another washer and set of spacer, locknut and coupling at the inboard end to complete the installation. hardly rocket science!

Colin