First thing is why put any lubricant in the propshaft at all ? Not as obvious as it sounds.

1) To lubricate the bearings. Depends on the bearing type. PTFE, oilite and ball races don't neccesarily need any added lubrication.

2) To keep water out of the shaft and stop it running back up into the boat. By far the most important reason why most people do it.

WD40 is not a lubricant even though it does contain some oil. Over the years I tried a number of oils getting progressively thicker to stop it running out too quickly.

I changed many years ago to a light grease, initially LM, but these days I use a PTFE loaded grease. The one I use was manufactured by Tri-Flow but there are other manufactures.

Contrary to what you may think grease does not cause any more drag than oil in this use ( once it gets warm it melts locally) but a properly loaded shaft will keep water out of a boat for a year or more.

Loading the shaft is performed by removing the shaft then squirting grease up the tube using a bicycle grease gun until full. Then carefully push the shaft back into the tube. Don't forget the paper towel at the end of the tube to collect the surplus grease as it gets squeezed out. Messy but it only needs doing about once a year on fast electrics less often on scale.

Trevor

Ashley perhaps I was not clear the MAIN purpose of filling shafts with grease is to keep water out. Water coming up the shaft is a major problem in a lot of models. The grease does emulsify but this does not stop it keeping the water out.

The majority of people I deal with have moved over from oil to grease. The problem is that people think of grease as thick and sticky resulting in lots of drag. Once you realise this is not the case it becomes a a better option. To be clear I have won many races with motor revs in the 30,000 to 40,000rpm range all with greased shafts.

As you say each to their own and there will always be some situations where oil is the better option.

Trevor

I like a thin silicone grease as it handles water much better than traditional greases and doesn't emulsify anywhere near as quickly.

As Ashley pointed out, this subject has been debated on numerous occasions, and agreement has never been reached. Speaking personally, I use outboard motor grease with excellent results – it's waterproof and does not emulsify, at least, not in my experience. Ashley prefers not to use grease, and who am I to argue with his decision? As in many things it boils down to personal preference, and as such there is no definitive answer.

Peter.

Edited By Peter Fitness on 06/03/2015 21:02:45

If you put an amp meter on the motor and run the shaft out of water with a selection of lubricants you'll find which causes the most resistance. I once used the silicon based grease (mountain bike tube – Halfords) and found I couldn't get a tick over speed. When I checked the amps, it was pulling near 0.5A just to turn the shaft. After de-greasing I tried with 3 in 1 and the power dropped to less than 0.05A. No difference to using nothing. BTW I now use the amp meter to set up the shaft and motor alignment too, as was suggested on a thread here some time back.

I expect with the massive power on the race boats a little bit of resistance in the shaft caused by grease will not be noticed at all. On small boats @ 6V we want all the power available to turn the prop.

It's a question of choice, and to stop water getting up the shaft I use teflon rings.

Aye, Kim

I have read this thread with interest because I have a major problem with water getting into my Vosper fire tender. A bath test suggests that the hull is not leaking and I suspect that water ingress up the prop shaft is largely if not solely to blame. The other culprit may be the rudder shaft. The prop shaft is the type with bearings at either end. I have packed with Lithium grease but, to be honest, most of it gets pushed out as the shaft is inserted. Should I try O rings or some other means of seling the top end of the shaft. Any thoughts or advice would be much appreciated.

I note Trevor's comments that water coming up the shaft is a major problem with a lot of models. Maybe strangely, whilst water ingress is a problem with the Vosper, I have no such problem with my Chris Craft which similarly uses a high speed brushless motor.

Ashley

Thanks for the comments and advice.

By nipped up to, I assume you mean held in place maybe with a collar. I will definitely try that.

I don't quite understand your reference to a water scoop. There is one on the Vosper located aft of the prop and forward of the rudder. It is there to feed the fire montors via a pump.

I have tried to seal the joins between the formers and the skin of the boat with epoxy resin. I should have done this when I first built the hull. Assuming this is working, most of the water appears to be in the area where the prop shaft enters the hull, much less in the rudder shaft area.

Jeremy

While the propshaft is a prime candidate for a leak as mentioned there are others such as the rudder shaft. Don't forget that as well as the shafts the tubes they fit in can leak when they pass through the hull.

The hull can also leak normally this will be along the seams. This can occur on a new hull but a fibre glass hull can develop hairline crack after a collision. A wooden hull left in a loft for many years can develop leaks on along the seams due to shrinkage. A lot of folks who have this problem just give up and line the inside of the hull with fibre glass. Always seems like the wrong thing to do to a wooden hull but it works.

A bath test is always a good place to start but I always load the boat up with weights so they float lower than normal. If you are having difficulty spotting water coming into the hull try putting some coloured toilet tissue in the bottom of the boat. A single drop of water will cause enough discolouration to be easily seen.

Unfortunately some leaks only open up under running conditions due to the vibration and flexing of the hull.

On occassions I have found leaks by filling the boat with water and watching where it comes out. This is an act of desparation as it means emptying everything out of the boat but sometimes it is the only way.

Some boats leak and similar or identical boats run dry for no apparent reason ! Be very gratefull when you get one that runs dry.

Trevor

A cheap seal can be made out of suitable diameter silicone tube – there is an illustration at the bottom of this page, if you scroll down…

**LINK**

Hi Mike, what a great idea. I’ve been making boats for 50 years so I love it when I see something new to me.
My dad made live steam, I wish he had passed that tip on to me.
I’m going to try it in my current build.
Charles.