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Old 12-26-2010, 02:36 PM   #21
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Propeller shaft prep for prop

Quote:
nomadwilly wrote:

So the jam nut just sit's there jamming the two nuts and keeping the load on the big nut that is capable of holding the prop on YES! If the jam nut is installed last the big nut transfers part of it's load to the jam nut but if the big nut goes on last the jam nut transfers it's load to the big nut so the big nut holds the prop on AND carries the jam nut load as well.
Did I get it?
Sort of ... think of the jam nut as a spacer that transfers the force created by the prop nut onto the prop hub. It is sort of a a washer that pushes back at the nut at the same time.

Because the jam nut doesn't have enough thread to push the prop nut forward without stripping, all you have done is tighten a jam nut against the prop nut with a few threads, not enough to stretch the shaft between them and produce a force that will hold the two of them together.

*


-- Edited by RickB on Sunday 26th of December 2010 03:45:14 PM
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Old 12-26-2010, 03:08 PM   #22
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RE: Propeller shaft prep for prop

Rick--- I understand (I think) your explanation of why the thin nut goes on next to the prop and the heavy nut after that.

But I'm curious--- if the purpose of the thin nut is to jam the large nut in place and keep it from backing off, thus holding the prop in position, why wouldn't this work if the jam nut was put on behind the main nut?

Is it because tightening the jam nut would "unseat" the main nut from the forward face of the shaft threads and so allow it to succumb to vibration and eventually loosen everything?
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Old 12-26-2010, 03:39 PM   #23
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RE: Propeller shaft prep for prop

If the jam nut was capable of pushing the prop nut forward enough to shift the thread contact to the aft face of the shaft threads then it would work. But since the thin jam nut has only a few threads it will (probably) strip before it can produce enough force.

If you have enough threads then a second prop nut would jam the first one but then you risk exerting more torsion or elongation than the shaft could withstand in way of the thread roots..

It's easy to demonstrate the effect if you take a bolt in a vice and put two identical nuts on the threaded portion. Tighten them together as hard as you can then put a wrench on the inside nut. You will easily unscrew both nuts togther just by turning the inside nut.

That happens because the bolt is not stretched to produce tension to hold the nuts together.
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Old 12-27-2010, 01:24 PM   #24
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RE: Propeller shaft prep for prop

Thanks for the explanation. I can understand the logic.
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Old 12-27-2010, 03:26 PM   #25
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RE: Propeller shaft prep for prop

RickB* Your explanation is good, but the part that has always flustered me in boating, not other applications where a cotter pin is not used, is the one Eric raises. Why after tightening properly,*then turn the nut to fit the cotter key/pin?
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Old 12-27-2010, 03:49 PM   #26
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RE: Propeller shaft prep for prop

Quote:
sunchaser wrote:

RickB* Your explanation is good, but the part that has always flustered me in boating, not other applications where a cotter pin is not used, is the one Eric raises. Why after tightening properly,*then turn the nut to fit the cotter key/pin?

Is not the cotter pin solely to ensure that a nut cannot back completely off the shaft? It seems to me that the pin has nothing to do with the nuts and their order of placement and torquing?
*
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Old 12-27-2010, 05:15 PM   #27
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RE: Propeller shaft prep for prop

Quote:
sunchaser wrote:Why after tightening properly,*then turn the nut to fit the cotter key/pin?
In an ideal world, the shaft is drilled to match the notch (crenula?) in the castle nut. If torquing a bit more won't line up a notch with a hole then a shim or washer is called for to move them in line. Backing off unloads the whole assembly.

Considering how infrequently props fall off or shear the key, it shows how well a tapered fit holds the prop on the shaft since a lot of other people probably also back off the nut just a hair to get the pin to fit.
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Old 12-27-2010, 08:03 PM   #28
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RE: Propeller shaft prep for prop

Quote:
Mike wrote:I have never owned, or even seen, a prop nut that has a hole drilled thru it for a cotter key.
There's all sorts out there. Castellated nuts are very common, as are plain nuts like the one in your picture. I have seen plain nuts with a hole drilled through them and even nylock or fiberlock nuts on smaller shafts.

Not all shafts are machined on the end to provide a section of reduced diameter that provides a place to drill a hole for a pin. When I mentioned drilling the hole, it was in reference to a new undrilled shaft with a castle nut tightened in place. The hole is drilled through the shaft in a notch so the castle nut does what castle nuts do.

If you can imagine a way to secure a prop to a shaft, it is being done that way somewhere.

Let me know if you can figure how this one is attached ...* 8-)
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Old 12-27-2010, 08:34 PM   #29
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RE: Propeller shaft prep for prop

The prop nut has holes around the outer circumference that are spaced a little wider (or narrower) than the holes on the prop face. This gives you a chance of alignment between the holes in the nut and prop ( one of the two will be threaded to hold a lock pin) at almost any position that you determine is the appropriate torque ?
A guess.
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Old 12-27-2010, 08:56 PM   #30
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Propeller shaft prep for prop

Quote:
Forkliftt wrote:The prop nut has holes around the outer circumference that are spaced a little wider (or narrower) than the holes on the prop face.*
Nope, good guess though ... here's a view from another angle.



*


-- Edited by RickB on Monday 27th of December 2010 10:05:15 PM
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Old 12-27-2010, 09:21 PM   #31
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RE: Propeller shaft prep for prop

Hiya,
** Stub sitting in strut screws onto shaft and is bolted in place to prop.* Once assembled now "solid" propshaft is supported by strut aft of prop unlike smaller vessels where shaft is supported by strut forward of prop.
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Old 12-27-2010, 09:42 PM   #32
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Propeller shaft prep for prop

OK this is like a fun game.
My guess.
The flange (just below the guys left collar(in the pic)) has holes that match the drilled and taped holes in the prop hub. One simply tightens the ss nut to the correct torque and then rotates a bit to the closest holes that align and then install and torque the hex head machine screws through the flange and into the propeller hub.
Power went out and my msg is still here wow.
RT, that should'nt work. As the power is applied the engine, gearbox, shaft and prop needs to move fwd a bit against the engine mounts. That taper on the nut would introduce a lot of slop but of course one could have a Aqua Drive or Python Drive or some other thrust bearing but even the hull flexing could unload a tapered bearing there.





-- Edited by nomadwilly on Monday 27th of December 2010 11:20:36 PM
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Old 12-27-2010, 09:54 PM   #33
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RE: Propeller shaft prep for prop

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RT Firefly wrote:

Hiya,
Stub sitting in strut screws onto shaft and is bolted in place to prop.* Once assembled now "solid" propshaft is supported by strut aft of prop unlike smaller vessels where shaft is supported by strut forward of prop.
RTF wins the ceegar!* It really is an unusual arrangement. It was designed to provide a cleaner inflow to the propeller. How much difference that bit of an efficiency increase makes I don't know ... the boat is powered with a pair of 12V149TAs that scare the water into movement anyway.

Here's a picture of the completed installation showing the rudder installed.



*
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Old 12-27-2010, 09:55 PM   #34
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RE: Propeller shaft prep for prop

In a similar setup (non prop) with a sheave or pinion gear,*it is called a pillow block bearing.
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Old 12-27-2010, 10:13 PM   #35
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Propeller shaft prep for prop

Rick,
What kind of bearing is in that strut and how does it fit onto the propeller nut?

Also:
What do you think of plastic prop to shaft sleeves? I've heard of them but never seen one. If they work at all they should be good on my Willy w only 37hp on a 1 1/4" shaft.

-- Edited by nomadwilly on Monday 27th of December 2010 11:18:43 PM
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Old 12-28-2010, 05:49 AM   #36
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RE: Propeller shaft prep for prop

Quote:
nomadwilly wrote:What kind of bearing is in that strut and how does it fit onto the propeller nut?



What do you think of plastic prop to shaft sleeves? I've heard of them but never seen one.*
The bearing is a standard cutless bearing. The "prop nut" is actually a stub shaft with the free end the same diameter as the main shaft and it fits in the bearing exactly the same as the shaft would if it were in a normal strut.

Re the sleeves, do you mean like the drive sleeves used on some outboard props? I have never seen or heard of using a plastic sleeve between the prop and shaft on a conventional drive so can't really comment, other than saying plastic is both a noun and an adjective and that can bring a lot of interesting issues into play on a drive train.
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Old 12-28-2010, 06:02 AM   #37
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RE: Propeller shaft prep for prop

Quote:
nomadwilly wrote:
What do you think of plastic prop to shaft sleeves? I've heard of them but never seen one. If they work at all they should be good on my Willy w only 37hp on a 1 1/4" shaft.

-- Edited by nomadwilly on Monday 27th of December 2010 11:18:43 PM
I had a prop on a sailboat that used a plastic sleeve.* But it was used*by the PO*as a cheap way of fitting a used prop to a shaft that was to small for the prop.* I removed it and put a proper fitted prop on.* When we took it off the plastic sleeve looked all beat up and I'm not sure that the prop was ever really on the shaft correctly.*Looked a bit to*Mickey Mouse to me.*

*
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Old 12-28-2010, 08:50 AM   #38
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RE: Propeller shaft prep for prop

"Plastic" sleeves/spacers are common on IO drives - I*have one that was used on*a 300 hp Bravo One.
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