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Propeller shaft lubrication

Grease or oil

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gecon12/12/2020 09:44:34
310 forum posts
271 photos

I've been thinking again, sorry.

In the 'hints & tips' section, Glynn Guest writes about prop-shaft lubrication. The article is not dated so I was wondering if perhaps oil -as opposed to grease- in the sterntube is no longer 'politically correct' ?

Oil will surely gradually leak out of the sterntube and cause a rainbow-coloured wake astern?

Last winter I bought (together with the Comtesse kit) a tube of dedicated sterntube grease from Krick Ro-Marin. The only boat I've had in the water in recent years is the Comtesse yacht launched this summer so -as usual- I have little experience with this.

When applying the grease to the feed tube with a syringe it does not seem to accept much grease. Perhaps it should be applied while the shaft is turning at low speed?

The drive line has been so little used that it's probably not even been slightly warm so I consider it impossible for any lubricant to have 'left the building'. The grease used is what was recommended in the kit instructions but obviously KRICK grease would be recommended in a KRICK kit. There no info about operating temperature.

In view of the low temperatures involved -low water temp and low speed/short periods of motor use, is it perhaps better to use a thick motoroil?

Or can just I forget about the lubrication issue -due to low temp and short periods of motoring etc and just use the grease as sterntube water-proofing?

Any (inuendo-freesmiley) tips/ideas appreciated. Replies need only be simple : Use the grease. Use the oil or even 'Get a life'! Thanks in advance,

George

Malcolm Frary12/12/2020 09:59:43
944 forum posts

Ask any group of 10 model boaters what they use for shaft lube and you will get at least 10 different answers. If they have working boats, they will all be correct. Much depends on the nature of the model, and the nature of the water being sailed in.

Edited By Malcolm Frary on 12/12/2020 10:02:24

Ray Wood 212/12/2020 10:05:13
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2232 forum posts
777 photos

Hi George,

I've never used grease in any prop shafts, never will ! just a drop of light oil like 3 in 1 before the run

I assume your running stainless shaft in brass or bronze bushes.

Happy Christmas by the way finishing off a ducted fan Jet Provost at the moment

Kind Regards

Ray

Kev.W12/12/2020 10:51:49
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281 forum posts
36 photos

I have just purchased my first 'flexi-shaft' equiped boat & have bought some marine grease for it, I believe that flexi being spun at up to 22,000 rpm will generate temps too hot for light oil.

My other boats with solid shafts are lubed with 5w.40 motor oil ( I always have some handy, because that's what my car uses ) smiley these shafts rotate at much lower rpm.

Prop shaft makers who put lube tubes on their shafts, call them "oilers", so I assume you are meant to use oil.

Edited By Kip Woods on 12/12/2020 10:52:53

Colin Bishop12/12/2020 11:05:14
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4757 forum posts
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Yes, it's always a tricky subject. For example Deans Marine say their bearings are water lubricated at the propeller end and shouldn't be run dry for any length of time but the inboard end can usefully accept a touch of grease.

My personal experience is that stuffing a tube with thick grease can sometimes cause the shaft to bind badly but this can depend on the type of tube. A standard M4 type setup might have an 8mm tube around the 4mm shaft so there is quite a lot of space between the shaft and the tube inside (but this could be less if the tube is thick walled brass!). With a 'slimline' tube the outside diameter may be 6mm so there is much less space between shaft and tube.

So as, Malcolm says, it's horses for courses really.

There are a couple of other points to be considered. Usually the bearings will benefit from some lubrication, maybe water at the bottom end and a bit of grease at the top, but another reason some people stuff the tube with grease is to prevent water entry. If you have a well fitted shaft without any play and with a washer on the prop end then the thrust of the prop against the washer and thence against the tube end will pretty much seal it.. You might get a few drops in if going astern a lot but it shouldn't be anything to worry about.

I mistake I have sometimes seen is for the builder to misfit the shaft so that the bit that sticks out at the stern is threaded. The thread MUST be all outside the boat otherwise not only will it be a loose fit in the bearing but you have created an Archimedean screw which will in one direction act as a pump in forcing water into the tube - not at all what you want.

My current practice is to smear the shaft with water resistant lithium grease with an extra dab on the inboard bearing although I do have some older models which still have motor oil in them and occasionally leave the trail of shame!

Colin

Tim Cooper12/12/2020 13:03:54
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394 forum posts
171 photos

George

I have used both. My older boats use brushed motors and some are geared so the tubes are greased with lithium grease. Recent boats are brushless. On these I have fitted oilers, CMB, sell some plastic fittings that fit around the tube, drill a hole, and fit piece of tubing. I use 3 in 1 oil in these.

My older boats haven't been out this year so I'm thinking they might want some attention by next year, so I might change them over to oilers if I can get to the tube.

Tim

neil howard-pritchard12/12/2020 17:23:23
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1626 forum posts
1061 photos
Posted by Malcolm Frary on 12/12/2020 09:59:43:

Ask any group of 10 model boaters what they use for shaft lube and you will get at least 10 different answers. If they have working boats, they will all be correct. Much depends on the nature of the model, and the nature of the water being sailed in.

Edited By Malcolm Frary on 12/12/2020 10:02:22

Well not to disappoint you Malcolm.........here's the 11th.....

i was given a tin of graphite powder from a printer by a friend some years ago, and he told me to mix it with Vaseline until the Vaseline is black with it, and then pack it into a syringe, and squirt it into the prop tube till full, and them inserting the shaft, twisting it so that the whole tube is full around the shaft, catching all that is pumped back out into the Vaseline tub so as not to waste any........i have used this method for the past 25 years, never had a leak and even being left over winter, never ever had a seized shaft EITHER. ......

gecon13/12/2020 10:47:17
310 forum posts
271 photos

20200824_090219.jpgNow there's variation on the theme!

Many thanks gents for your inputs, very much appreciated. I would not have thought much about the subject had it not been for the greaser/tube support that came with the Comtesse drive train accessory pack. When I saw that, I thought that I'd better prepare to install one in all future projects.

On reflection I suspect that my requiremants are more for stern tube 'sealing' rather than 'oiling'. The motorised yacht's in my 'marina' will be mainly driven by the breeze and only motored for short periods.

The grease that I have bought in looks like thickish vaselin and the german text suggests that it 'hampers water ingress'. part nr. ro5557.

The 3 tube support/greasers all came from Graupner last year, part 2997.6.

I'll try applying gentle syringe pressure while running the motor slowly and see if the grease runs into the sterntube a bit. I have greased the propshafts prior to assembly. Shafts are 4mm and the tubes are 6mm so there's not much space for anything else in there!

Cheers,

George

 

Edited By gecon on 13/12/2020 10:47:54

ashley needham13/12/2020 11:08:27
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6920 forum posts
201 photos

I would connect up the motor to a wattmeter and set the throttle to say 1/2, then start pumping grease in and see what happens to the current consumption.

Just a thought...

Ashley

Tim Cooper13/12/2020 13:01:16
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394 forum posts
171 photos

George

Those oiling fittings look like the ones I buy from CMB. You can get an aerosol can of Lithium based lubricant here, which you could squirt down the filler tube.

Tim

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