Propshaft Leak

[Paul GodfreyParticipant @paulgodfrey14946]

Hi folks,

 

I’ve been reading with interest the thread ‘Propshaft’ started by Leslie Cook on 23rd Feb, which is going to prove to be very useful indeed as this problem has reared it’s head on the second outing of my Dutch Courage.

 

On it’s first sailing a few days ago (an hours duration or so), there was about a teaspoon of water beneath the port propshaft tube, which I was very happy with. Even better, there was nothing under the starboard tube.

 

Today, however, a different story. Whilst still no water from the starboard tube, around 2 – 3 egg cups full had come from the port tube, and this in around 30 mins. They were both adjusted exactly the same (about 1mm end play), but even reducing that on the problematic tube/shaft has made no difference. Does this sound like a defect in the tube/shaft?

 

I like the sound of the rubber washer/o-ring with a brass thrust washer solution, but It’s going to be very difficult to remove the propellers due to the Kort nozzles (and the fact I used a tiny drop of superglue to ensure they didn’t come loose!!). Of course, the shafts/props cannot be withdrawn backwards now, as the rudders cannot be removed.

 

Where can I get a selection of neoprine washers / o-rings / brass washers etc?  – somewhere like B&Q ?

 

Paul

Edited By Paul Godfrey on 26/04/2009 17:33:32

[Paul GodfreyParticipant @paulgodfrey14946]

This topic AGAIN!!

[ashley needhamParticipant @ashleyneedham69188]

Paul. You will be jolly lucky to get anything other than bog standard washers etc from any big DIY store. I have a set of “Maughn wad punches”   basically a set of punches that produce a hole, in varying sizes obviously. I use them to produce washers out of various materials, such as rubber (inner tubes)  nylon (plastic milk bottles, ok I know its  not exactly nylon but close enough for thrust washers). getting just a couple of very small `o` rings might be a problem. I was going to suggest a few places but they usually come as sets in different sizes. Is there any shaft sticking out bare as it were at the inner end? I was thinking that a trick might be to use some small silicone tube stretched over the tube and of such a size as to be a sliding or better fit on the inner shaft, a bit of vaseline would ensure lubrication. It would act a bit like the bellows on a submarine rod gland  ???  Ashley

[Paul TParticipant @pault84577]

Paul

A few questions:

Is the seal between the shaft and the hull still intact?

Does the shaft suffer from vibration i.e. is it slightly out of line?

Have you fitted contra rotating props and if so which way does the port shaft rotate as the thread on the end of the shaft might be pumping water up the tube.(Archimedes spiral)

Paul

 

[Paul GodfreyParticipant @paulgodfrey14946]

Ashley, unfortunately there’s no bare shaft at the inner end. Mistake number 143 (ish!) was to mount the motors too near the propshafts, something I couldn’t rectify later on as I had built, and mounted with copious P38 filler, a battery box to hold the two 6v batteries, virtually touching the motors to get it as central in the boat as possible.

 

Paul, the shaft/hull seal is solid & leak-free, plenty of epoxy followed when dry by plenty of P38 to give a good seal.

 

It is more than possible that the motor is slightly offset. When running the motors individually, however, they both sound the same, ie the port side is no noisier.

 

 The props are contra rotating, and the port rotates clockwise. Therefore, when going forward, the thread would pump water away from the tube. Of course, when reversing, the opposite would happen, and here’s the thing – after trying to minimise the end-play earlier, a test in the bath initially seemed successful, but after going into reverse, water started to come in. However, water continued to come in even when going forward (and in fact when the props weren’t moving, but only an occassional drip).

 

I have now managed to remove the shaft from its tube, but before doing so, I was able to wiggle it about very slightly! Defect? Wear already?! I had lubricated the shafts with hypoid oil (car gearboxes & differentials), as thicker than machine oil, but thinner than grease. maybe this was mistake 144!!

 

The tube was, of course, full of water, so maybe the silicon grease is the way to go – I’m not worried about a bit more drag as I’m only using about half the available power, and the boat’s fitted with two 6v 12ah lead batteries.

 

Paul

[Paul TParticipant @pault84577]

Paul

 

Now that it is out of the tube check the shaft against the straight edge of a steel rule to look for any bends, kinks etc.

I agree that using a small slug of silicon grease at the prop end of the shaft might solve the problem.

 

Good luck 

 

Paul

 

[Glynn GuestParticipant @glynnguest59245]

Paul,

        You mention 1 mm of end play but does the thrust washer (assuming you have fitted one) actually press against the lower tube bearing when going ahead?  If it does then little, if any, water ought to enter a reasonably good shaft/bearing fit.

As for the amount of end play, I try to achieve the minimum possible.  Ideally I can’t  see the play just feel it when gently pushing and pulling on the prop.

Filling the tubes with oil, rather than just coating the shafts, is another way to slow the ingress of water. That why I try to fit an oiling tube to shafts.

GlynnGuest

[Paul GodfreyParticipant @paulgodfrey14946]

Thanks Ashley, Paul & Glynn for your replies.

 

I’ll put a dollop of grease down the tube from the inner end, then push the shaft in from the inside (after checking it for straightness) whilst plugging the outer end with my finger until the grease or shaft pushes it away. That should give it a good coating.

 

Glynn, no thrust washers were included in the kit, and I didn’t think to fit any (no previous experience!). Therefore, the nuts which lock against the prop and the coupling rub directly against the bearings at each end of the tube. I can see that fitting a washer at the rear should further help to prevent water ingress.

 

Paul

[Mike DavidsonParticipant @mikedavidson22772]

   Silly question No1…………..   Are the inboard ends of your prop tubes above the water line.?…………Doh !………………..   If that doesn’t stop it, go to your model shop and buy minimum quantity of silicone fuel pipe for a diesel engine . Chop off 2-3mm ensuring that the end is exactly square push it onto the prop shaft, and slide it along until gentle contact is made with the tube and the thrust washer. If you have any end play(you should have a little) it will be taken up and cushioned by the silicone tube washer,  any oil in the system will work its way down to make the joint friction free and watertight.

   Silly question No 2…………  Have the swans got a black line around High Water Mark ?.. If yes, you have used too much oil. Rename your model Torry Canyon buy napalm.

 p.s. the fuel pipe should have an internal diameter of 4mm, or the same as your prop shaft    Radio spares stock a large range of O rings which could be just what you want.  If you find what you want on line, select the data sheet for the item you are interested in ,then ask radiospares if they are prepared to deal with you. Helpful tip, your local TV shop owner probably has an RS account.p.p.s. R.S. also do an ace range of brass gearwheels, and brass stock, which is quite expensive   Also, B & Q do a  nice range of metal rods / tubesand bars which a scratch modeller can turn into anything in amongst  which, they have glass fibre rods and tubes which can give you a nasty range of splinters, and are excellent for adding strength to a hulland acting as a conduit for your radio control wiring. by the way, you say you are using two hefty lead acid batteries, and it occurred to me that your ESC could be being asked to do too much at low revs,it will be washing off quite a lot of power generating quite a lot of heat, check it out….Mike…D

Edited By Mike Davidson on 27/04/2009 20:48:41

[Paul GodfreyParticipant @paulgodfrey14946]

Hi Mike

 

The inboard ends of the tubes are indeed below the waterline, but the outboard ends are above (wondered why the boats performance was, at best, sluggish . . . . . . . . ).

 

 Thanks for all the useful info. The fuel tube suggestion is top-notch – I’ll certainly give that a go. Do you think this tube will be long-lasting and leak-free? The birdlife who also occupy the lake will demand an answer!

 

P.s. Have you, or anyone else, heard of Hanna Stainless Steel propshafts? They sound pretty good to me!

 

http://www.scalehobbies.net/id24.html

 

Paul

Edited By Paul Godfrey on 27/04/2009 21:58:12

[Mike DavidsonParticipant @mikedavidson22772]

Well Paul I use a lot of that silicone tubing in my modelling, not only does it make excedingly goodwashers, but a length of 10 inches pushed onto my glasses frame goes round the back of my head and stops the perishing things from falling off. I also use it to go from my boiler to production steam engines I make on my lathe it is good stuff. did you note that I said radiospares do a nice line in O rings, I’ve got loads that i use as washers in my engines where steam might leak under pressure, but going back to your answer, I need to ensure that the propeller end of the propshaft should be well below the waterline, and the motor end of the tube should be well above waterline otherways water will pour in. This goes for all shafts, propeller and rudder. the grease and oil are just finishing touchesto eliminate archimedian screw effects inside the tube. I have just discovered a new modelling material, old steradent tubes from my false teeth bath, they take four  3300ma/H Ni-M-H rechargeable batteries, and I use two tubes to make an 8.4 volt battery pack with a Tamya connector on so the pack will fit all my models and my grandson’s model car. I have also made a connector with a Tamya female connector so the packs simply plug into my battery charger. I can also take a spare charged pack with me to the pond and get two outings for the price of one.

                 Lots of good tips for you in there Paul, can I help you in any other way ?

………………………………………..Good Sailing………………………………….Mike Davidson…………………

Edited By Mike Davidson on 29/04/2009 20:27:21

[Peter FitnessParticipant @peterfitness34857]

Paul, there have been some very good replies to your questions here, and I am adding my 2 cents worth. I make all my own shaft assemblies, and use the thrust washers and O rings mentioned. I also silver solder a grease tube into the prop tube, and fill the whole thing with outboard motor grease. I know that some people believe that grease can cause excessive friction, adding unnecessary load to the motor, but my personal view is that the added load is negligible, especially in the case of slow moving vessels. It may be quite different in high speed boats, I don’t know as I don’t have any.

 

The photo below shows one of my home made assemblies. The grease tube can be seen, and alongside is the cap which is filled with grease then pushed on to the grease tube, thus forcing grease down into the prop tube. I can honestly say that I have never had a problem with water ingress since using this method, regardless of the position of the tube inside the hull, relative to water level.

 

Peter.

[Rick DevonshireParticipant @rickdevonshire]

Have you thought of filling the propshaft with a light grease? You can use a syringe to do this before inseting the shaft. Alternatively if you solder a short length of brass tube into the propshaft tube near the top (inboard end) you can pump in grease periodically during use. I recently obtained some light silicon greas form my local cycle shop.

[Paul GodfreyParticipant @paulgodfrey14946]

Thanks again Mike, and to Peter & Rick for your comments.

 

Fortunately I dont have the need for Steradent tablets just yet (although it’s only a matter of time I suppose..), but I do wear glasses . . . . . .

 

With Dutch Courage, the tubes/shafts are horizontal in the boat, and are about 1.5 inches below the waterline.

 

With the shafts removed, I did decide to pump grease inside them as suggested (I had a spare ‘pet syringe’, used for administering medicine to small animals / birds. No needle of course, just a small tapered plastic nozzle which can be dipped into the grease pot, and the grease sucked out. The nozzle is a perfect fit in the tube, and the grease can then be pushed in). With a fair amount inside the tubes, the shafts were pushed back in with the rear ends blocked, causing the grease to be forced up the shaft.

 

With the shafts in place, I used a 3mm piece of the silicon tube over the shaft as suggested, before fitting the props. 

 

Initial bath testing was very successful, with no sign of any water ingress. The true test will be a long sailing session at the lake, but I feel optomistic, and much happier knowing the tubes are full of grease, not a light oil. As you say, Peter, the drag is only slight, and a small price to pay for peace of mind. I will definately modify the tube on my next boat to allow for additional grease to be pumped in.

 

I’ll report again in due course.

 

Thanks again to everyone who’s responded so far.

 

Paul

Edited By Paul Godfrey on 30/04/2009 21:23:38

[Peter FitnessParticipant @peterfitness34857]

Paul, I also use a small syringe, given to me by our friendly local vet, to fill the prop tube initially, then top up via the cap which is also filled with the syringe.

 

Peter.

[Mike DavidsonParticipant @mikedavidson22772]

 Paul, I wish to eliminate any mis understanding, when I said inboard end of the propshaft, I meant the bit that comes into the engine room. Outboard is like in outboard motor, so the prop shaft penetrates the hull whilst going from inboard to outboard because that’s where the propellers are. try to achieve a good bit of propshaftabove the floor of your engine roomwhich should be well above the waterlinemaking it very difficult for water to invade your space. On your boat plans, the waterline should be quite well marked as should the propshaft . As far as I am concerned, the only way for water to get in now is by capilliary action which can be eliminated by a smear of silicone greasewhich would introduce surface tension. There is one thing that I use, unfortunately I cannot name a supplier or a reference number for it, but I use silicone oil which we use at work to lubricate silcone rubber seals where they rub against metal surfaces, which is pretty much what I advised doing with the model diesel fuel pipe. Thinking a little more about that solution, when the assembly is complete, and you put the model in the water, as soon as the prop starts to turn, it will be thrusting the model forward and that thrust will be through the fuel tube washer compressing it against thestern end of the propshafthelping the seal even more.You know Monty Python’s lot had it absolutely right didn’t they ? Always look on the bright side…….Mike…..D

[Paul GodfreyParticipant @paulgodfrey14946]

No misunderstanding Mike, the inboard ends of the tubes/shafts are below the waterline, and this is exactly how it is on the plans. The tubes cannot be angled any differently, i.e. raised up inside the boat, as the outboard ends have to pass through the ‘Y’ frames, and be parallel with the Kort nozzles, which face directly backwards (not angled).

 

Not had a chance to sail this weekend, as the wife & I have been away, but hopefully will be able to test out the newly-greased tubes/shafts on Wednesday. Fingers crossed!!

 

Paul

[Paul GodfreyParticipant @paulgodfrey14946]

Had an hours sailing at the lake today, and pleased to say not a single drop of water in the boat.

 

Whats interesting is that the boat is actually FASTER with the tubes packed full of grease, than it was with oil in them. Maybe I didn’t have enough oil in them in the first place, or perhaps it seeped out, but now there won’t be any leakage into the lake, which of course is a good thing.

 

I will definately use grease in any future boats!

 

Paul

[Colin BishopModerator @colinbishop34627]

Good news Paul!

 

Colin

[Mike DavidsonParticipant @mikedavidson22772]

PaulI have just enjoyed a couple of days off, and when I got back, I find that a whole sackfull of mail has landed in my inbox, I am just a little intrigued to read that your propshafts are roughly horizontal, and below water line, Blinding Flash of Light !Nothing is guaranteed to let the water in better. The propeller end should be below the waterline, and the motor end should be an inch or so above the waterline, so you would have to push the boat down almost until water came over the gunwhalesfor there to be enough pressure to push water through the propshaft into the boat, this is a fundamental principle of boat design. The same criteria should be true of your rudder shafts,the servo end should be nearly an inch above waterlevel, and there should be no otherhull penetration for other devices , just to give you an idea, the Royal Navy submarines I work on don’t have the old style periscopes any longer as the old ones needed an optical tube coming into the very centre of the ship, nowadays, they have non hull penetrating periscopes or peep sticks which are a telescopic stainless mast that is raised remotely, and this mast has a television camera mounted on the top…..Clever eh ?

Going back to your problem, I think reluctantly that the best route for you  to go is to remove the propshafts, and to drill new conduits for them through your P38. This will enable you to align the propshafts at an angle of about 40 degrees slope down from the motorsand absolutely in line with the ships head, and I think from that point, you will have no further leakage problems. Finally, I should measure the whole lot carefully to ensure that your props will reach the water, because it’s a devil of a job to fit an extension to a propshaft with its own sealing and alignment problems, just remember the craftsman’s motto, “Measure twice and cut once “, then, you’ll get it right, It is a subject that justifies a great deal of thought and strict attention to detail. judging by your previous letters, I guess you might even need to buy a couple of slightly longer propshafts…………..Good luck my friend, I’ve been there too, and it hurt.

[Colin BishopModerator @colinbishop34627]

If you are building a scale boat then it will be frequently the case that the inboard end of the shafts will be below the waterline. There are all sorts of reasons why it may not be possible to angle the shafts so that they exit above the waterline from compromising scale appearance to the motors ending up above deck level!

 

Grease/oil in the tube plus a sealing washer at the outboard end is usually quite sufficient to restrict water ingress to a few drops per session which poses no practical problems. In full size yachts it is considered normal for some leakage to occur and it is part of the daily routine of the yacht to deal with it. Model boats draw a few inches of water at most so there is no appreciable pressure forcing the water inboard.

 

As has been stated previously, the screw thread on the shaft when going astern can tend to “pump” water up the tube, especially if there is a bit of play in the nuts holding the shaft in place at each end but boats spend comparatively little time going astern so, again it should not lead to major problems.

 

A small amount of water ingress is normal and is not a major problem. It can usually be mopped up with a bit of tissue on a stick if necessary.

 

Colin

[Peter FitnessParticipant @peterfitness34857]

Mike, I don’t believe it would be necessary for Paul to undertake such radical surgery on his boat, as he has already said that he has had no problem after an hour’s sailing.

 

I must confess I’m a little puzzled by your statement that having the inboard end of the prop shaft above the waterline is a fundamental principle of boat design. Are you referring to full size practice, or only models? It would seem to me, from my, somewhat limited, knowledge, that most large vessels have their engines, and therefore their propshafts, well below water level. In fact, their propshafts are virtually horizontal. I know that many small boats have angled propshafts, due to size limitations.

 

I can only reiterate what I said in an earlier post, using a grease filled prop tube with neoprene o-rings at each end, I have never had a problem with water ingress.

 

Peter.

 

The photo referred to in the earlier post was accidentally deleted from my albums, and is shown below to illustrate my point.

Edited By Peter Fitness on 16/05/2009 00:39:14

[Paul GodfreyParticipant @paulgodfrey14946]

Hi all

 

. . . . . and just to prove the point, here’s a photo of the part of the plan showing the motor & propshaft layout.

 

 

 

The Kort Nozzle and tube support brackets dictate the angle of the propshafts, which are in fact more like 2 inches below the waterline.

 

I will definately add a greasing tube to my next model, possibly with a grease nipple fitted to this, so a good dollop can be easily injected.

 

Paul

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