Rudder / shaft anodes?

Hi there,

Our go-to guy, the PO's son, is out of town right now and we could use a little advice.

From the photo's below, does it look like there was a second smaller round clamp-on anode on the rudder which would cover the hole in the rudder, or just one big one in the top corner?

Second question; there is only 2 inches of prop shaft (1 1/4" diameter) for an anode, and all the 'streamlined' anodes available here are over 2 inches long. What do you think was used before?

As you can tell, the boat hadn't been hauled for a while, and the prop shaft anode was totally gone.......

Aha! A "collar anode" for the shaft...maybe I can find 1" thick collar anodes and stack them?

The rudder only ever had the one zinc. Probably an "R-3" (certainly nothing smaller)



You need a limited-clearance collar for the shaft

Thanks

fstbttms said:

The rudder only ever had the one zinc. Probably an "R-3" (certainly nothing smaller)

You need a limited-clearance collar for the shaft

Click to expand...

You could cut file the collars down to fit as zinc is solft.

Isn't the hole in the rudder there to facilitate shaft removal?

I was not aware a zinc would be fitted through it. Or am I looking at the wrong location on the rudder?

CPseudonym said:

Isn't the hole in the rudder there to facilitate shaft removal?

I was not aware a zinc would be fitted through it. Or am I looking at the wrong location on the rudder?

Click to expand...

The large hole is not for a zinc. You can see the mounting screw for the zinc in the upper left portion of the rudder.

Phil Fill said:

You could cut file the collars down to fit as zinc is solft.

Click to expand...

That was plan 'B'

Murray,
Take a run down to Rupert and get one of these. Perhaps that's what you meant by "streamlined" anode. I only have about 1" shaft showing ahead of the prop.

I think the experts say that the short nut should go on first and the larger "big" nut on top of the short nut. Seems bass akwards and I can't remember why .... hopefully someone else will help out. Has to do w the nut loading .. I think.
I'll bet fstbttms knows the real stuff.

manyboats said:

Murray,
Take a run down to Rupert and get one of these. Perhaps that's what you meant by "streamlined" anode. I only have about 1" shaft showing ahead of the prop.

I think the experts say that the short nut should go on first and the larger "big" nut on top of the short nut. Seems bass akwards and I can't remember why .... hopefully someone else will help out. Has to do w the nut loading .. I think.
I'll bet fstbttms knows the real stuff.

Click to expand...

I use the same thing prop zinc. I add some Loctite 242 (blue) to the allen head screw, as the tensile force holding it on goes away if you let it go to long. I think the new ones already have it on though.

I have posted this before on another electronic trawlering media...

The thin nut goes on first.

I spent 11 years wrenching on submarines. When I reflect back, I am still amazed at the amount of useful technical training that the Navy provided me. One of my favourite technical manuals to this day is NavShipsTechManual Chapter 75, Fasteners. I still use it all the time.

To quote:

075-5.3.4 JAM NUTS (LOCK NUTS). Jam nuts are an older variation of the prevailing torque concept. They are not usually recommended for new installations due to the tendency to use an improper thickness for the jam nut and to install them in the wrong relative positions.

075-5.3.4.1 Jam Nut Assembly. The jam nut assembly requires a regular or main nut and a thin jam nut, as shown in Figure 075-5-5. The assembly is installed with the thinner nut between the thick nut and the bearing surface. The main nut has to be as thick as if no jam nut were being used, because the main nut carries all the working load. The jam nut is usually about 2/3 as thick as the main nut. If the jam nut is too thin, however, the threads in the jam nut area will be damaged as the main nut will pull the bolt threads partially through the jam nut. Conversely, if the jam nut is too thick, the main nut cannot distort the threads enough.

075-5.3.4.2 Tightening the Jam Nut. At assembly, first tighten the jam nut to the same or slightly less percentage of the preload torque specified for the main nut, based on the relation the jam nut thickness bears to the thickness of the main nut. Then hold it in position with a wrench while you tighten the main nut. For example, if the jam nut is 2/3 as thick as the nut, tighten the jam nut to 1/2 to 2/3 of the torque used for the main nut. Then, when the main nut is tightened to the preload torque specified for the bolt, it stretches the bolt (stud), thereby tending to pull it through the jam nut. Any vibration or load that tends to loosen the bolted joint will allow the bolt to shrink back to its original length, leaving the jam nut tight against the main nut. This creates the necessary prevailing torque to prevent the jam or main nut assembly from rotating on the bolt.


Link to Chapter 75

The instructions say;

"If the jam nut is too thin, however, the threads in the jam nut area will be damaged as the main nut will pull the bolt threads partially through the jam nut. Conversely, if the jam nut is too thick, the main nut cannot distort the threads enough."

So what they're saying is that the bolt, shaft, stud or whatever stretches so that the small nut (jam nut) "jams" because it becomes ..... ???

Furthermore,

" Then, when the main nut is tightened to the preload torque specified for the bolt, it stretches the bolt (stud), thereby tending to pull it through the jam nut."

I "sense" that that would tend to unload the threads in the Jam nut. The main nut is pulling on the shaft and pushing on the jam nut and the propeller hub. The jam nut is doing the same so it would seem that the main nut would unload the jam nut.

I think I should quit while I'm ahead ... but I'm not ahead .. I think?????

If the jam nut becomes less loaded how can it's threads become "distorted"?

You pretty much have it right.

The jam nut goes on first with SAY 1/3 the full torque spec. Higher preload higher torque, lower prleoad, lower torque. Hold the jam nut in place with a (thin, if need be) wrench. The main nut then goes on to full torque value. The main nut carries the axial clamping force of the load by stretching the fastener. The jam nut clamps to the main nut by pulling the other way (with less axial force) and as it has less thread engagement it tends to distort the threads. If you can imagine, the threads are engaged on opposite sides of the pitch for the two nuts. Less threads on the thinner nut, means less engagement. The frictional forces on the faces (and on the threads) keep the two nuts from rotating.

So why is it usually wrong (in just about all cases) to put the thin one on second? To get to the proper torque required for fastener preload, you risk stripping the threads, as there is less of them engaged.

...and I thought it was a simple question...sometimes it feels better to be blissfully unawares!

Northern Spy said:

Link to Chapter 75

Click to expand...

Egad.

You Navy guys really know your nuts!!!

MAybe this is a less complicated explanation:

Post #17


http://www.trawlerforum.com/forums/s6/propeller-shaft-prep-prop-2460.html

While we are getting into a bit of "thread creep", I will start by saying that the big hole on the rudder is for removing the shaft without having to drop the rudder... Ok, so now I will say this about the "new" topic the thread has created...

I just learned about the jam nut config a few weeks ago when I was researching what we need to look for when we replace or straighten our current shaft. I have been meaning to find a pic of it to confirm because I don't remember the way ours is. So I just did a search and it appears that Skinny Dippin's nuts are backwards too. Sooooo, adding it to the list of stuff to correct when we are workking out the shaft issue.

This is a pic from out bottom job over the last winter


P1020043 by GonzoF1, on Flickr

Here's a thread that Rick posted about 3 years ago that is so good I'm posting it here suspecting many others aren't clear about the jam nut. Thinking of it as a washer and a jam nut to keep the big nut from turning helped for me.

Two of Ricks posts (I sure hope you're OK w me doing this Rick)

"The thin nut is a jam nut. It purpose in life is to prevent the larger load bearing nut from backing off. It goes on first.

The way it works with props is the large nut is used to push the prop tightly on the taper. It is then removed and the thin jam nut is torqued to about half of its rated torque. This is just to ensure that the nut is hard against the prop hub and its threads are loaded. The jam nut is held with a wrench and the large nut is then tightened against it.

What happens is the threads on the jam nut are at first in contact with the loaded or working side of the threads, picture the nut pulling itself down the shaft by gripping one side of the threads. A nut works because torque on the threads creates a tensile load on the shaft or bolt, it stretches it. The parts are held together because the shaft or bolt wants to spring back and whatever is between the nut and the shaft gets squeezed and held by that tension. The torque figure you use or how much umph you twist the nut or bolt depends on how much load the fastener can take before it breaks in tension, or breaks across the threads because of torsional failure or thread stripping. The figure for tension or elongation is calculated by the loads imposed on the shaft or bolt by the machinery it is holding together.

Head bolts must withstand the forces of compression and combustion that want to separate the head from the block. The bolts are tightened so that the force holding the head on is several times higher than those trying to lift it off. If the tension is not high enough, the forces will stretch the bolt each time the cylinder fires and then when that pressure is relieved, the bolt is actually loose for a moment and vibration will loosen the bolt. The best way to prevent firing pressure from stretching the bolt is to pre-stretch it more than the engine can.

Anyway, back to the jam nut. When the jam nut is in place it is applying a force toward the propeller. That force comes from the contact of its "forward" thread surface on the "aft" thread surface (we can use those terms because the shaft is horizontal and we are moving the prop forward) of the shaft. Most of us know that there just aren't enough threads on the jam nut to hold the prop on without strippiing and this is where the controversy comes from. The job of the jam nut is not to hold the propeller on, it is to prevent the prop nut from loosening.

The prop is held securely because when the prop nut is torqued fully it pushes the thread contact area of the jam nut off the "aft" threads of the shaft and unloads the jam nut threads completely. Torgue applied to the prop nut stretches the shaft by pushing against the jam nut which in turn pushes against the prop hub until the jam nut threads contact the "forward" thread face of the shaft. This jams the two nuts together preventing any movement between them.

It's not religion, it's mechanics.

That was post #17. Here's a followup post #21.

Rick B. Wrote "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.


Well there it is. I posted the old threads so a maximum number of people would see it. I thought many would not bother to look at the old thread unless it was right here. Now that it's right here ... and extensive as it is ... I wonder how many will read it. Well if you are interested you should learn why it's done w the small nut first.

My prop to keel clearance is about the same as Tom B.s I use the zinc "nut cap" or "streamlined" style of zinc to protect the stern "cutlass" bearing. Some clearance is necessary to allow a good flow of water through the rubber cutlass bearing to insure it's lubrication. The first one I used fell off but I've had good luck since.

There seems to be some confusion about what a "streamlined" anode is:

Streamlined collar


Limited-clearance collar


Prop nut or "cap"

Tom.B said:

While we are getting into a bit of "thread creep", I will start by saying that the big hole on the rudder is for removing the shaft without having to drop the rudder... Ok, so now I will say this about the "new" topic the thread has created...

I just learned about the jam nut config a few weeks ago when I was researching what we need to look for when we replace or straighten our current shaft. I have been meaning to find a pic of it to confirm because I don't remember the way ours is. So I just did a search and it appears that Skinny Dippin's nuts are backwards too. Sooooo, adding it to the list of stuff to correct when we are workking out the shaft issue.

This is a pic from out bottom job over the last winter

http://www.flickr.com/photos/22889131@N05/8193813447/
P1020043 by GonzoF1, on Flickr

Click to expand...

Not too worry too much...one famous NA has written more than once in addressing the nit issue that probably 90+ percent (or some other high number) of all boats have them backwards and hardly any really have issues...especially on slow turning shafts....living in one and visiting hundreds of marinas more a year, I have to agree.

Whenever I try and tell boaters of "little nut on first"...few believe me even after handing them written articles on the subject...they just look around and shrug their shoulders. Inertia is hard to overcome.

Yup I "learned" about the little nut first some time ago but only a few years ago started doing it "right".

HaHa and our TF nuts will prolly mostly remain the same. But w most mechanics I lean toward doing things the best way I know how depending on how much trouble it is and how much there is to gain. In this case it's no trouble at all to do it right .... so why not.

An observation that may be worth mentioning is that w the "prop nut and cap" there is no lock/jam nut so it would seem the security of the nut (and basically the propeller) is dependent on the cotter pin. And in my opinion it's difficult to install it properly and is usually only fairly secure. If I had shaft clearance I'd go back to double nutting and having the shaft zinc ahead of the prop. However I like the prop close to the stern bearing for stability and shaft rigidity.

or use a shaft brush to a transom zinc/bonding system instead........

Scout came with the big nut first and a castellated nut outside. Shaft drilled for cotter key in the perfect place. I put it back the way it was and am still sleeping well at night.

Anode said:

Scout came with the big nut first and a castellated nut outside. Shaft drilled for cotter key in the perfect place. I put it back the way it was and am still sleeping well at night.

Click to expand...

While I see that as a good setup to keep from losing a prop...not sure if it's the right engineering setup to keep the assembly very tight.

Probably works fine but sure isn't the industry standard.

psneeld said:

or use a shaft brush to a transom zinc/bonding system instead........

Click to expand...

Yep... I have that too.

1) How much room do you leave between the prop shaft zinc and the cutlass bearing?

2) We have a shaft brush a bit forward of the stuffing box connected to a transom plate zinc...would this 'double protect' the prop shaft if a zinc is also put on the shaft just forward of the prop?

psneeld said:

or use a shaft brush to a transom zinc/bonding system instead........

Click to expand...

That is what we have, it has works great. No zincs on the prop or shaft.

rochepoint said:

That is what we have, it has works great. No zincs on the prop or shaft

Click to expand...

Our transom plate bolts are 6 3/4 inches apart...how big is your set-up?

Found this bit about shaft brushes;

"The Shaft Brush will provide a low resistance connection between the bonding system and the shaft. This connection should allow a properly sized and installed zinc corrosion control system to provide an adequate protection to the shaft and propeller.

An additional benefit is that zinc installed onto the shaft, will last somewhat longer. After the propeller shaft zinc is consumed, additional protection is then provided by the vessels main zinc corrosion control scheme."

We have two Z3 zincs mounted on the transom, I drill 2 holes in the metal straps and bolt them on 1/2" studs mounted in the transom. The bonding wires attach to these studs on the inside of the transom.

Thanks for the fast reply, Mike.

Ours is similar, but have only one.

This is our first haul out, so we weren't very organized. Problem with living in a little city perched on the edge of Paradise is that shopping options are dismal. Nobody in Kitimat, or Terrace, has a collar zinc for a 1 1/4" prop shaft, Prince Rupert is a 6 hour round trip, and I have that pesky job thing that keeps getting in the way.

Considering cutting down a streamlined one, but won't until I can confirm safe distance between zinc and cutlass bearing. So far I've read from 1/4" to 1" which is quite a big difference.

Want to be in the water tomorrow!!!!