To lube or not to lube….that is the question.

[Luvboats]

Greetings fellow mariners,

A recent dockside conversation resulted in a few differing ideas and opinions on prop installation.

The short version is some insisted that a waterproof grease or anti seize compound should be used to assist in future removal.

Others were adamant that no lube or compound of any kind should be used for a dry friction fit.

(We can leave the idea of lapping shaft to prop and whether or not the big or little prop nut should be against the prop hub for another conversation unless you wish to opine on these issues as well.). You can see we we had a lot of time and a few extra beers to drink so our dock conversations took us down a few rabbit holes.

The above questions pertain to a tapered shaft and traditional prop with a jam and king nut followed by a cotter pin for security.

If this was an outboard leg or a saildrive with a splined shaft would your recommendation differ?

I have witnessed boat yards and others I believe to be very knowledgeable folks use grease, anti seize, and in some cases nothing so I am unsure what is best practice and why?

In reading the manual for my Yamaha outboard it recommends greasing the splined shaft prior to prop installation for whatever that is worth in this conversation.

Curious as to your thoughts, ideas, wisdom and wild ass guesses if all else fails.

Safe Journeys,
~Jeb

[kapnd]

Grease or anti seize is commonly used, but doesn’t last very long.
In a couple of years it will wash out, and the prop will be welded to the shaft by corrosion between the metals and marine growth.
I’ve seen commercial fishing boats use gasket sealer or even 5200 in the bore to seal out the salt water that creates the havoc.
They lap the prop to the shaft first, till the fit is perfect, then fine tune the key, warm up the propeller, apply a thin coating of sealant, slip everything together, torque the nut, wait 5 minutes and torque it again, finished.
It will require heat to remove it, but it will be in pristine condition!
I wouldn’t recommend this process for your outboard…

[fstbttms]

You should never, EVER put any kind of lubricant on the prop bore or shaft taper. This is not a matter of opinion and anybody who does it or advocates for it doesn't know what they are talking about.

The reason is simple- the tolerances in the prop/shaft connection are so close that putting anything in between them will keep the prop from setting correctly. They are 100% not designed for it. Further, the prop is not supposed to be easy to remove. It's supposed to want to stay where it is.

BTW- boatyards and especially commercial fishermen should not be looked upon as the be-all and end-all of boat maintenance wisdom.

[Pauls]

As you have already observed, there are people who swear both for and against using a grease/antiseize on taper fitted props. The ones who oppose grease will typically say that props fitted with grease are very hard to remove. Why would this be? Wouldn't grease make the prop come off easier?

The reason is this. When installing a prop onto the shaft taper the prop nut has to apply enough force to drive the prop onto the taper firmly enough that it will not shift during operation. With a dry prop and shaft there is a lot of friction and therefore the nut needs to have a significant amount of torque applied.

When the prop/shaft is greased the friction between the two is greatly reduced. So less torque needs to be put on the nut to achieve the same level of compression force in the prop/shaft joint.

People who use the same level of torque to install a greased prop that they would use on a dry joint (and there are a lot of them) are creating much higher forces on that joint because of the reduction in friction. They are way overpressuring the joint and then they find the prop is hard to remove.

I am in the greased joint camp because the protection from corrosion is a clear advantage of having grease in the joint. If you do not overtorque the nut the prop will come off easily and reliably, more reliably in my opinion due to the protection from corrosion.

[japawil]

Originally Posted by fstbttms

You should never, EVER put any kind of lubricant on the prop bore or shaft taper. This is not a matter of opinion and anybody who does it or advocates for it doesn't know what they are taking about.

The reason is simple- the tolerances in the prop/shaft connection are so close that putting anything in between them will keep the prop from setting correctly. Further, the prop is not supposed to be easy to remove. It's supposed to want to stay where it is.

BTW- boatyards and especially commercial fishermen should not be looked upon as the be-all and end-all of boat maintenance wisdom.

I was going to ask why, rather than just the declarative statement in your first paragraph which was all that showed up.
When I went to reply in order to ask, the quote showed all three paragraphs……

Very interesting; both the reasoning and the fact that only part of your post showed up on my feed. (Viewing on an iPhone)

[fstbttms]

Originally Posted by japawil

I was going to ask why, rather than just the declarative statement in your first paragraph which was all that showed up.
When I went to reply in order to ask, the quote showed all three paragraphs……

Very interesting; both the reasoning and the fact that only part of your post showed up on my feed. (Viewing on an iPhone)

I edited my post with the reasoning shortly after the initial post, That's why you didn't see my rant in its entirety at first.

[Luvboats]

Fastbottoms, curious what, if anything, you use or suggest for splined shafts such as sail drives, outboards, etc.

[fstbttms]

Originally Posted by Luvboats

Fastbottoms, curious what, if anything, you use or suggest for splined shafts such as sail drives, outboards, etc.

Lubriplate 130 AA

[japawil]

Originally Posted by fstbttms

I edited my post with the reasoning shortly after the initial post, That's why you didn't see my rant in its entirety at first.

[emoji106]

[SaltyMetals]

I realise the OP 's question related to a standard fixed prop. I have an example for mine which is a Darglow Engineering "Featherstream" feathering 20" 3 blade prop on a 1 3/8" (35mm) shaft with a standard ISO taper and a 10mm key. This is secured with a pair of Nordlock washers and the nut had to be torqued to 45 ft.lbs( 61 Nm/6.22 Kg.m). The instructions for the torque were very specific and important.

When i fitted the prop i used grease on the shaft. A year later i found that there was very slight rotational play of the boss of the prop on the shaft. In fact it was being kept in place from the rotational point of view by the 10mm key, so much so that some wear had developed on sides of the key. I since discovered that using grease on the shaft was a big mistake because the key is not designed to handle this sort of load. After discussions with the tech guys at Darglow Engineering they said very specifically that it had to be a dry fit. So i remounted the prop with a dry fitting, no grease. Problem solved.

[SaltyMetals]

BTW, i should have added that the best way to get a 3 bladed prop off the shaft without damaging it is with a three-legged puller. Maybe some heat and a few blows with a soft hammer if it is really obstinate. For this reason i carry my own puller which fits the prop perfectly.
Andrew

[sinnerman]

This is a VERY good question and it would be nice to see some propeller manufacturers comment on this.

My question on lubrication (although some sort of barrier between the bronze prop and stainless shaft might reduce surface / crevice corrosion between the parts..) is not related to preventing seizing, but rather to assure that the parts mate correctly and that proper torque was applied.

Theoretically, when torqueing threaded parts, it is the stretching of the base material in the threaded area (in this case the prop shaft) when torque is applied that actually secures the propeller.

The torque uses the mechanical advantage of the ramp in the threads (pitch) to convert the torque into an axial force on the shaft stretching the shaft material into the elastic range of the metal.

The metal "pulls back" in the opposite direction thus creating a "clamping force" to retain the propeller on the shaft. The cotter pin holds the nut in position to retain the torque/clamping force.

A lot of people have trouble visualizing this process.

I spent years working with commercial airplanes. Mechanics would argue against the use of lube on threads fearing the parts would "come loose". Critical threads were required to be lubricated (including the base of the nut) before torqueing to prevent "false torque readings" caused by thread friction, galling, contamination of the threads and sliding friction of the nut rubbing on the mating surface of the base material as the nut rotated.

With self-locking nuts (with inserts for example), it was required to measure the "running torque" of the thread before the parts actually mated up and add this value to increase the final torque requirement to compensate for this "false torque".

You want 100% of the torque being applied to stretching the base material and not being lost on thread friction / mating part issues. If not, you are not stretching the material enough and the parts are not properly clamped together.

So in theory, you would want the tapered surfaces of the propeller & shaft to be as smooth as possible, free of burrs, corrosion and lubricated before torqueing to eliminate any binding of the parts while mating up (in addition to lubing the threads and nut / prop shaft / washer surfaces) to assure proper torque).

Here is an article I found which touches lightly on this (as well as mating the prop on the shaft without the keyway / lapping to assure a tight fit..):

https://www.sbmar.com/articles/prope...vs-little-nut/


Long winded. Sorry. Sure there will be differences of opinion. My four cents only...

Cheers

[fstbttms]

Originally Posted by SaltyMetals

BTW, i should have added that the best way to get a 3 bladed prop off the shaft without damaging it is with a three-legged puller.

No, the best way to a 3 bladed prop off without damaging it is with a prop puller, not a gear puller. Right tool for the job and all.

[GordMay]

Originally Posted by sinnerman

This is a VERY good question and it would be nice to see some propeller manufacturers comment on this...

Michigan Wheel implies dry fit [no grease mentioned]:
“Inboard Propeller Installation Procedures” ➥ https://www.miwheel.com/uploads/reso...on_Process.pdf


Most Outboard manufacturers recommend grease.

[seabreez]

Originally Posted by fstbttms

No, the best way to a 3 bladed prop off without damaging it is with a prop puller, not a gear puller. Right tool for the job and all.

I second the motion here. I made mine with three threaded rods and two 2, 1/2 plates. The one behind the prop has a u shape slot ro slide it behind the prop. Then three holes for the threaded rods. Easy to fabricate and cheap enough...