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Author Topic: Water coming up drive shaft.  (Read 4691 times)

ooyah/2

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Water coming up drive shaft.
« on: September 24, 2010, 08:51:43 PM »

Hi Guys,
I would appreciate some thoughts on how to stop the water coming up the prop shaft of my Bluebird K7.
This is my first attempt at fast electrics, never had this problem on other model boats but then they didn't have the revs off this one..
Prop shaft is 3/16 " St/St running in a 5/16 " o/d tube
Brushless motor 2700 kv,  battery Sub "C"  x 7 -cell x 3700
Prop Graupner Carbon fibre surface drive x 36 mm.
I pack the shaft with fine water proof Lithium grease and on running the grease pumps out of the bearing at the coupling end, doesn't matter if it's L.H. or R.H.
So once the grease is pumped out water gets in, not a lot , but it gets in.
I make  all my own running gear with the exception of the rudder which at the price it wasn't worth making.
You can see the boats performance      http://www.youtube.com/watch?v=mjckMFo6TUE and pics of prop set up.
Thank's
George.





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Tug-Kenny

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Re: Water coming up drive shaft.
« Reply #1 on: September 24, 2010, 09:01:54 PM »


I know nothing about 'Fast boats' but my first reaction was that you have a  1/8  inch gap between the tube and shaft.

Could this be matched up a bit closer perhaps. Also, do you have thrust washers on each end behind the nuts and tightened for a close fit  ?

Just a thought, hope you don't mind

Ken

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derekwarner

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Re: Water coming up drive shaft.
« Reply #2 on: September 24, 2010, 11:22:28 PM »

ooyah/2.....in your lower photograph as shown....there appears to be a small hole drilled @ the 12.00 o-clock position in the prop tube

1. you could consider soldering a short vertical tube to this point & using it as a header tank
2. alternate lubrication is a posibility....rubber grease being an option
3. from the name [Bluebird] & construction  I assume you have rather high shaft speeds
4. you mention "3/16 " St/St running in a 5/16 " o/d tube" ....but what is the actual ID of your prop tube bushes? ....it should be approx 0.001" over your 0.1875" shaft
5. if it is a clockwise rotation prop, you could consider machining a fine anti-clockwise long helical  convolution [say two revolutions] in the length of the prop shaft.... :D ...this should have the effect of pulling the grease in the opposite direction....now I am not suggesting you polute the waterway  :police: .....certain lubricants may just stick the the hull/rudder extremities .....Derek
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Derek Warner

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Tombsy

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Re: Water coming up drive shaft.
« Reply #3 on: September 24, 2010, 11:58:20 PM »


For a 3/16" prop shaft you should be using a 9/32" shaft brass tube glued in the hull and a 1/4" brass tube will slide through it and into the strut.
There will be minimal to no water coming up the shaft with this setup.
For extra insurance I put a piece of fuel tubing over the end of the brass halfway over the flex, it also helps to stop grease flinging.
Keep it greased with marine grease like they use for boat trailer axles.
I use the blue Aquacraft stuff.
The boat looks fantastic  :-))
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ooyah/2

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Re: Water coming up drive shaft.
« Reply #4 on: September 25, 2010, 12:07:10 AM »

Hi Guys
If I can answer both of you in the one post.
The motor has a theoretical speed of 2700 kv, which is 2700 rpm per volt so on 8.4 volts  it's going at approx 22.680 rpm  not including loss due to friction in the bushes.
Bushes are reamed  and shaft is .0005" under size .001" clearance isn't good enough any greater and it rattles.
Brass bushes both end allowing .001 float.but when boat is running the bush at the prop end ( thrust washer ) should stop the ingress of water.

The hole in the shaft  originally there but is now covered over, plate soldered on top. Small header tank tried, the oil/grease still pumps up through the tank and starves the bearing at the motor end, tried it.
5/16" o/d tube with .015" wall leaves .284" less dia of 3/16" shaft leaves .095" which gives a clearance of .0475" per side  so can't go any smaller.
Don't like the sound of rubber grease Derek, grease has to be as light as possible. or oil.
I have considered a helix but as I have a variety of L.H. & R.H. props it wouldn't work.
Don't get me wrong there isn't a lot of water but I like dry boats, it may be something that I will just have to put up with.
Funny thing is my Flash Steamer is churning out approx 15,000 rpm on the bench, probably nearer 10,000 rpm in the water and it doesn't do it on it ( OOYAH  name of steamer.)
Yes Derek it's a Bluebird K7 and it's cracking on at 35 mph. click on to the You- Tube link and have a look at it's performance.
Many thank's for the input .

Regards  George.

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ooyah/2

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Re: Water coming up drive shaft.
« Reply #5 on: September 25, 2010, 12:14:25 AM »

For a 3/16" prop shaft you should be using a 9/32" shaft brass tube glued in the hull and a 1/4" brass tube will slide through it and into the strut.
There will be minimal to no water coming up the shaft with this setup.
For extra insurance I put a piece of fuel tubing over the end of the brass halfway over the flex, it also helps to stop grease flinging.
Keep it greased with marine grease like they use for boat trailer axles.
I use the blue Aquacraft stuff.
The boat looks fantastic  :-))

Sorry Tombsy,,  I missed your reply, It's not a flexi shaft but Round Stainless. the water is minimal but as I posted I don't like water in the boat, I will try a different grease.
This is my first attempt at a fast electric and am very pleased with the result, it's a diversion from my Flash Steamer.
George.
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derekwarner

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Re: Water coming up drive shaft.
« Reply #6 on: September 25, 2010, 02:24:15 AM »

ooyah/2 .....1/2 a thou.....your tolerancing is great....but how do you ensure ZERO eccentricity between the inner & the outer stern tube bushes?

"Bushes are reamed  and shaft is .0005" under size ........ .001" clearance isn't good enough"

In another forum...??? or may have been on Mayhem....someone mentioned using a food grade oil milled from grain......for shaft lubrication which did not polute??????....and another offering was Olive oil  {-) %%  :-))
Does the prop shaft tube suffer from over temperature?
Have you considered water cooling the actual tube?

Derek
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Bunkerbarge

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Re: Water coming up drive shaft.
« Reply #7 on: September 25, 2010, 06:37:33 AM »

George, only a thought as I'm certainly no expert on fast stuff.  Using grease seems to me that the grease is being 'pumped' by the rotation of the shaft and the fact that the grease is sticking to it.  I'd also be a bit concerned about the resistance you are getting from it in such a high peformance set up.  I have a fast electric 'V' model and the guy I bought it off said use the lightest lubricant possible and preferably WD40.  Consequently I would try a light oil that will be 'dragged' around a lot less by the rotating shaft and so may stay in place a bit better.
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HS93 (RIP)

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Re: Water coming up drive shaft.
« Reply #8 on: September 25, 2010, 06:58:48 AM »

 Hi George. for fast boats you do not want grease especially as you only have a small gap between shaft and tube, it will slow it down. what I do is use ballraces I get the ones that have Teflon shields I only use them on the top motor end at the bottom I use glacier or Acteal from   http://www.shgmodels.com/acatalog/   around page 30 and get my ballraces from  http://stores.ebay.co.uk/Dinball_Bearings-parts_W0QQ_fsubZ7867823QQ_scZ1QQ_sidZ42095710QQ_sopZ1QQ_trksidZp4634Q2ec0Q2em322  fast delivery i normally use two at the top and the only lube that is req then is a spot of 3 in one to stop and coating of the tube or shaft if running in salt water as the acetal is lubricated by water,

http://www.modelboatmayhem.co.uk/forum/index.php?topic=6401.0   this may give you an idea how to retro fit

http://www.rcmart.com/catalog/bearing-10pcs-inch-c-108_761.html  the prices are normally for ten and delivery is very fast

Peter
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derekwarner

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Re: Water coming up drive shaft.
« Reply #9 on: September 25, 2010, 07:10:29 AM »

mmmm.... ooyah/2 ......this sounds a good approach from HS93  :-))....I have ZERO experience at these high 20K RPM......or even 5K RPM shaft speed operations........

We also must consider that atmospheric pressure is acting on the surface of the water surrounding the vessel [+ all other bits the world over O0] ......

So lets consider then that the propshaft internal bushing near the motor is subjected to the same pressure but has no surface area to oppose the ingress of the grease then the water....... :embarrassed:.....Derek
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ooyah/2

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Re: Water coming up drive shaft.
« Reply #10 on: September 25, 2010, 11:46:40 AM »

Firstly  DEREK
It's very difficult to get Zero tolerance but you can quite easily get as true running shaft as possible by,
1. When buying brass tube at the Model shop run the piece of tube over the glass counter and check for truth
2. Make the bearings .002 undersize to the inner dia of tube.
3. Assemble the shaft in the bearings and fit them all into the tube, smear some Locktite 601 on the bearings and push them into the tube  and leave for 24 hrs and you will have a good running shaft.
4. Machine the end of the shaft that goes into the taper collet at 45 deg, this allows you to feed the shaft up through the bearings and into the collet.
It works for me.
5.  I dont't think the running temp of the shaft comes into the equation as it's the only thing in the water when the boat is running and the grease coming out of the motor end bearing is lubrication enough.
Secondly  HS93.
It's too late to start digging out the shaft to ball race it, in retrospect if I build another fast electric I will consider ball racing the shaft.
I know that grease isn't recommended but the Lithium Poly is very light and as the boat is running at 35 mph in a straight line I am not looking for any more speed,
Thirdly, Bunkerbarge.
Yes I think you could be correct about the grease sticking to the shaft, but it still puzzles me as to how the water can get into the shaft through the thrust bearing
I find at present that if I grease the shaft using a small syringe I can have an afternoon running, 2-batteries each giving about 12 mins running and the boat is dry,
The next time I bring it out without pre greasing I get a small amount of water up through the shaft
As I have said I know that for Racing Fast Electrics grease is a NO-NO but this K7 is exceeding all my expectations and is fast enough see ----

     http://www.youtube.com/watch?v=mjckMFo6TUE

Thank's for your input.
George.

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martno1fan

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Re: Water coming up drive shaft.
« Reply #11 on: September 25, 2010, 12:50:16 PM »

Fit an auto bailer in the transom then any water getting in will run out as the boat moves forward,when boat stops water cant enter the bailer so no more problems with water in the boat.Incidently when the shaft is turning water shouldnt be drawn up the shaft in fact the oposite happens so my money is on water running up when the boats stopped?.Try the small piece of silicone over tube and shaft it works and doesnt cause enough drag to worry about if you use the right size tubing  ok2.Also as someone said run an oiler instead of grease,use vegetable based oil and it wont hurt the enviorment  ;).
Mart
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ooyah/2

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Re: Water coming up drive shaft.
« Reply #12 on: September 25, 2010, 06:27:36 PM »

Hi Mart,
I don't think that I need an auto bailer as I only get about a tea spoon full of water and as already said the K7 is going fast enough although I will try oil rather than grease.
Your suggestion on the silicone over the tube is sound but the shaft is a straight drive not a flexi.


As  it's a straight running flat out boat I only slow it down to turn it and is very rarely stationary on the water and with my power set up I get about 12 mins run time
When  running as it's a 3 point hydro the shaft is hardly in the water when planing on it's wedges, only when slowed down to turn does the stern go down.
Thank's for your input.
George..
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martno1fan

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Re: Water coming up drive shaft.
« Reply #13 on: September 25, 2010, 10:42:29 PM »

A teaspoon? bloody heck m8 these are boats yaaknow  O0 {-)...just kidding.How about some pics of the boat,is she scratch built or a kit or ready built hull ?.
Mart
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ooyah/2

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Re: Water coming up drive shaft.
« Reply #14 on: September 26, 2010, 12:14:18 AM »

Hi Mart,
I am having a quiet laugh,yes only about a tea spoon full and that's every 2nd outing before re-greasing the shaft I think I will stick in a wad of kitchen towel every run.
The K7 is a 1/12 scale model of D. Campbells ill fated Bluebird that is available from Touchwood Models.
I only bought the Fibre Glass hull and sponsons as I wanted to build it as light as possible.
The full kit is complete with many cast resin fittings which makes it too heavy, so I have managed to keep it under 2 kg all up.
It's fitted with Brushless motor and surface prop, I am pleased with the end result as this is my first venture into Fast Electrics.( 35 mph ) not bad with a grease filled shaft.
I am not a very good boat builder so it was quick and easy to build, machining Steam Engines is my forte.Here are some pics of the boat and the link to You-Tube.
George.
 http://www.youtube.com/watch?v=mjckMFo6TUE















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martno1fan

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Re: Water coming up drive shaft.
« Reply #15 on: September 26, 2010, 08:47:07 AM »

Looks very pretty mate well done,i wouldn't mind building a bigger version for gas engines  ;).I like the last pic very good.Oh for soaking up the water try a tampax they soak up the water much better  O0 lol.Mind you you might have a hard job explaining that one to the missus not to mention the lads down at the lake {-).
Mart
ps get yourself a sharpend and balanced brass or stainless even aluminium prop and you will pick up quite a bit more speed.
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HS93 (RIP)

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Re: Water coming up drive shaft.
« Reply #16 on: September 26, 2010, 11:00:05 AM »

how did you measure the speed at 35mph ?

Peter
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ooyah/2

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Re: Water coming up drive shaft.
« Reply #17 on: September 26, 2010, 08:54:49 PM »

Hi Mart,
Thank's for the advice I will probably get a balanced prop later but at present the carbon Fibre ones are O.K.
Don't know if you have ever seen bluebird jet powered by Ernie Lazenby on you-tube.  www.youtube.com/watch?v=JNBRa3oKit8  I think that this is the link, if not try bluebird k7 ernest lazenby.
As to fitting a gas engine I don't think it would be a problem but a lot of work just for a straight runner and I don't think it would be commercially viable for you to make. You boat hulls are superbe.
Touchwood models make a F/Glass hull at 1/6 th scale.

HS93.

400 ft divide by 8secs = 50 ft/sec x 60 x 60 divide by 5280 =34.09 mph. and verified with a speed gun.  SIMPLES  TCH
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martno1fan

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Re: Water coming up drive shaft.
« Reply #18 on: September 26, 2010, 09:43:05 PM »

Hi yes i wasnt really thinking about selling any just having something to look at and have the odd day on the lake with.Thanks for the compliment about my hulls  ok2.
Ohh yes i have seen the jet powered one a few times before looks awesome.
Mart
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