shaft size

[KWKloeber]

J

Here's an exchange with SLube about that.  I agree that, given all other equal, the ptfe isn't needed in this application (no lubrication necessary) if one carried both types. A prior email said that they are basically the same, minus the ptfe.

Ken,

Our part number 91003 is our super Lube® Silicone Dielectric Grease and part number 82003 is our Anti-Corrosion Gel. I have listed some differences.

The grease is much thicker than the gel.
The grease uses silicone oil as its base oil, whereas the gel uses a blend of mineral oil and PAO oil.

There is a higher concentration of anti-corrosion additives in the gel.

The gel has been tested and approved by Thermo-King for their electrical connectors on refrigerated trailers to reduce road salt corrosion and fretting. (see attached link)
http://www.super-lube.com/files/pdfs/Connector_Gel.pdf


http://www.super-lube.com/files/pdfs/Technical_Data_Sheet_Engine_Treatment_w_PTFE.pdf
Use our Super Lube® Engine Treatment, 20320 at a ratio of 4 to 1.
For a standard engine oil and filter change which requires 5 quarts of oil, use 4 quarts of the recommended motor oil and 1 quart of Super Lube® Engine Treatment.

I have attached a few links for your review.
http://www.super-lube.com/files/pdfs/Technical_Data_Sheet_Silicone_Dielectric_Grease.pdf
http://www.super-lube.com/files/pdfs/Technical_Data_Sheet_Anti-Corrosion_&_Connector_Gel.pdf
http://www.super-lube.com/files/pdfs/Technical_Data_Sheet_Silicone_Lubricating_Grease.pd
http://www.super-lube.com/files/pdfs/engine_treatment_technical_bulletin.pdf

Regards,
Kevin Wall
Operations Manager

I wonder whether the grease is better lasting underwater?  Although, as I tried to explain (probably not well) I think it may be moot because the anti-corrosiveness really resides in the minute voids and neither should get "washed away" out of there.  The grease might work better on the "bolt application" as RC describes.  dunno.

[J_Sail]

Ken,
In one of your posts you referred to SuperLube as being the same as Tef-Gel. That suggests you were referring to Super Lube Multi-Purpose Synthetic Grease, which is not listed in the email from Kevin Wall. His email listed their Silicon Dielectric grease, which does not only doesn't contain PTFE, it has an entirely different base. For use in blocking galvanic corrosion between dissimilar materials (such as a stainless bolt thru a zinc or aluminum fitting), you want either Tef-Gel or Super Lube's Synthetic grease. Both the PTFE particles and the synthetic base help maintain the protective coating and help seal out moisture. Their silicone dielectric grease probably won't perform as well. I'm surprised they didn't list it in their email to you. Besides, silicone should be avoided where not needed, due to its tendency to creep long distances, contaminating other surfaces, and later interfere with epoxy, finish, and sealant adhesion.

****
BTW everyone - greases labelled as "dielectric" as still fine on electric connections; as Ken stated before, they get squeezed thin enough for the microscopic peaks of the metal to poke through the grease and make a fine connection. Dielectric refers to the fact that the grease in bulk form won't short out adjacent contacts or breach an insulator. Similarly, some greases labeled as "conductive" such as DeoxIT, are not really conductive at all; they just rely on the same phenomenon of being squeezed thin enough to allow the contacts to touch on a microscopic scale.

Jeremy

[KWKloeber]

Jeremy

I had discussed the multi-purpose synthetic in an earlier email w/ them.
However, the datasheet omission was my fault.

His datasheet links were dead, so I copied over the new URLs.  But I mixed up the silicone with the synthetic .  MEA CULPA.

http://www.super-lube.com/files/pdfs/Technical_Data_Sheet_Multi_Purpose_Grease.pdf



-ken

[KWKloeber]

Jeremy:

from another sailor.... 

I use Ox-Gard anti-oxidant compound which is electrically conductive (formulated with zinc) on both anode and shaft contact surfaces. To isolate the stainless screws as much as possible from the anode, I place a plastic washer between the spring washer (under the head of the screw) and the anode, and put a few wraps of PTFE plumbing tape over the length of the screw before inserting the screws and tightening. (Both Ox-Gard and PTFE tape are available at Home Depot, and the plastic washers usually come with the anode)[/i]

I have never used GB Ox-Guard, have you?
Any thoughts?

-ken

[J_Sail]

The short answer is that it for the purposes of preserving the zinc surface where it contacts the prop shaft and mounting bolts, Ox-Gard is probably no better or worse than any grease that adequately blocks water from contacting the zinc in the interface area. For reasons I may address in a longer post later, the small amount of powdered zinc and graphite contained in the grease is unlikely to make a difference.  So feel free to use it, just don't expect it to perform any better than a grease that is not metal-filled.

For other uses involving electrical contacts, the graphite and zinc are unlikely to improve connection quality. In some cases (high voltages or sensitive hi-impedance circuits), the graphite and zinc can actually be detrimental.  The net of it all, is that for most uses, non-metallic greases are best; for many of the applications where metal filling sounds inviting, it is actually useless or potentially even detrimental.

Like I said, I will try to write up something more thorough later.

Regarding using a plastic washer and PTFE tape to isolate the Stainless Steel bolts from the zinc - once there is any electrical contact at all (which there will be regardless of your measures), you have formed the electrical corrosion cell.  All you can do then is try to control how much of the S/S surface is exposed to the water and what surface of the zinc performs the protection. The PTFE tape may seal some area of the S/S from seawater and thereby reduce the electrical current flow from it thru the water (that's what consumes the zinc).  The washer will not do anything at all (other than potentially reduce the effectiveness of the lock washer). The only way an insulating washer helps is if it prevents ALL electrical contact between the two dissimilar metals, which isn't going to happen when the threads cut thru the tape and make intimate contact with the zinc elsewhere. So, maybe PTFE tape seals out water over a larger area of the S/S bolt for longer than grease, maybe not.  Only an experiment can tell us.

In the end, the zinc is there to sacrifice itself to protect the prop shaft. So long as there is any electrical connection left between the zinc and the shaft it will do its job. So, unless the zinc erodes so badly as to lose all electrical connection to the shaft (or wobble and become unbalanced), I can't see why it matters. 

Disclaimer - I am an electrical engineer (with special knowledge of contact lubes), but very limited experience with the deterioration pattern and rate of prop zincs, so I defer to folks such as MaineSail and others who have changed out zillions of them.

[KWKloeber]

Thanks Jeremy.

I understand all you are saying -- the point of current flow if the whole thing is submerged is key.

What I don't really understand (not a metallurgical engineer) what's the interaction between the anode and s/s bolts/nuts?

I would **think** it would be similar to having good contact between the s/s shaft and the anode?  How are the bolts different than the shaft?  i.e., what's the galvanic transfer going on (if they are not completely isolated from the anode.)  And, I guess. what's the difference anyway?  -- if the anode gets that bad -- screw the bolts -- I'm gonna cut them in half w/ an angle grinder.)

-k