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[carl]

Hi,
I have almost completed a scratch-bulit model of P&O's first post-war liner - Himalaya. I have chosen a scale which is probably wierd for model ships, being 1:87, but it fits nicely with appropriate dock scenery and other models (railways, cars, etc) when it is to be displayed statically. It is a working, floating R/C model first and foremost. I have built a number of scale models before, but nothing quite this size. The all up weight of the of the model when ballasted to the correct waterline is around 40kgs. In the water, this weight causes significant ingress of water through the prop shafts, and I probably need to pack the shatfs with grease ( or some similar enviromentally friendly substance). Normal oil is only partially effective. Any clues on how I can force grease in the prop tubes? There are oiler extensions soldered to the tubes, but I'm not sure how I can get grease into the shafts using these. I have tried removing the prop shafts from the tubes, filling the tubes as best as I can, but inserting the prop shafts just pushes the grease back out.
I would welcome any advice.

Thanks,
Carl.

[Colin Bishop]

Do you have a decent seal in the form of a thrust washer on the shaft in front of the prop which bears directly on the end of the shaft tube? When the model is going ahead this should prevent water ingress to a considerable degree. You will have to expect a certain amount of water getting in though and it's best to contain this if you can by building some sort of box or dam under the inboard ends of the prop tubes which makes it easier to remove and stops it slopping around in the bottom of the model. Even fit a bilge pump in such a big model perhaps? With properly fitting shafts in the tube bushes the amount of water getting in should be manageable unless you spend a lot of time going astern.

You could also try a sealing washer on the inboard end of the shaft with a cylindrical spring over the shaft tensioned against the motor coupling to keep it against the end of the tube.

It's not the weight of the model specifically that is causing the problem but the depth of the shafts where they emerge from the hull, the further down, the more pressure there is. Full size yachts and motorboats with conventional shaft drives get over the problem by using a 'stuffing box' which surrounds the shaft with compressible material which is periodically tightened - but you still get a bit of water coming in.

Colin

[DickyD]

Carl, if you have lube tubes on the shafts, fix a short length of polythene or silicone tubine to them and then use a syringe to insert the grease into the tube.

This is best done with the motor running and when the motor starts to slow down stop applying the grease.

Too much grease is not good.

Syringe which can also be obtained from the chemist for medicinal application.

http://www.kingslynnmodelshop.co.uk/p579/Model_Craft_-_Plastic_Syringe_5ml_x3%28On_Order%29/product_info.html

Silicone grease, seems expensive but a little goes a long way. I have 18 boats using this grease and I still have some left in the tube.

Robbe Shaft Lubricant
Ideal for lubrication of stern tubes,prevents water from seeping in
Extremely water resistant
Wide temperature range from -10°C to +120°C (14°F - 248°F)
Special additive reduce friction and wear to a minimum
Protects against corrosion
Suitable for plain and rolling bearings
Water-classification WiGKO rating
Part No: R5557

Price: £8.99 (Including VAT at 20%)
Euros: €9.94 (Inc VAT) / US Dollars: US$12.21 (Tax Free)
http://www.cornwallmodelboats.co.uk/acatalog/prop_shaft_accessories.html

[malcolmfrary]

I have tried removing the prop shafts from the tubes, filling the tubes as best as I can, but inserting the prop shafts just pushes the grease back out.

Applying a finger to the inner end of the tube while inserting the shaft will stop the grease being shoved out.  Having two washers at the outer end with a neoprene O ring (plumbing dept) between them will help retain some grease at the outer end.  A thrust bearing at the inner end is a good idea as well, if only to stop the prop trying to walk the shaft out in reverse.

[dickyp]

Could someone advise please

When copling the motor shaft to the M4 prop shaft it is pulling the coupling apart

Should the 2 nuts be treated as lock nuts against the prop shaft or should one be against the coupling and one against the prop shaft

How far should the M4 shaft be inside the coupling

Thanks in anticipation

[craftysod]

Dickyp,
insert innershaft into propshaft,make sure you have locknut against propeller or locktite otherwise by by prop.
Other end of propshaft inside the hull,put on you washer then nut,make sure shaft runs freely.
Screw on coupling,if the coupling screws on far enough to meet nut,wthout the inner shaft touching the join in the coupling and stop it flexing,slacken off the nut to make tight fit against coupling.
If the coupling screws on too far,you will need another nut to screw against coupling,to make a locknut
Hope that makes sense
Mark

[Colin Bishop]

At the propeller end the nut needs to act as a lock nut on the prop. There should then be a thrust washer between the locknut and the end of the tube. Push the prop against the end of the tube and you will then see how much is sticking out of the inner end of the tube and how much of it is threaded as opposed to plain shaft.

Slide a thrust washer onto the inner end of the shaft against the tube. Now you will need to mount the second nut and then the coupling itself. As with the propeller, the nut needs to act as a locknut on the coupling. The question is now whether you can screw on the locknut and coupling far enough on the inner end of the shaft so that there is no significant longitudinal movement on the shaft except a fractional amount to allow the shaft to rotate. If when you have screwed on the coupling as far as it will go and tightened the locknut against it you still have some bare shaft showing at the inner end you will need to make up a spacer to take up the slack.

Colin