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Author Topic: How do you power the prop in a sub model?  (Read 3558 times)


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How do you power the prop in a sub model?
« on: November 30, 2007, 05:22:17 PM »

Hello chaps + chapesses.

Just wondering what mechanism(s) is/are used to get the shaft out of the pressure hull/waterproof box in the model subs, and onto the prop, without letting water in?

I've seen a couple of pictures of strange black fittings in a couple of the build threads, but not sure what they are or how they work.

Am I also right in thinking it's normal to cover the terminals of the battery in resin, and then let it get wet, as it's not in the pressure tube?

Many thanks



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Re: How do you power the prop in a sub model?
« Reply #1 on: December 01, 2007, 04:51:15 AM »

Basically a short stuffing tube out of the WTC would work.
I have been seeing rubber "O" rings being used to allow three or more shafts to
pass through the WTC end. Power, rudder, and dive planes...
The rods then connect to fixed control or propeller shafts in the boat.

The black rubber boots work ok, but I typically find that my WTC holds water really well.  ::)

Browse through the "Cabal" reports by David Merriman and posted by U812 on the
Sub Pirates forum...


 Oh, bummer they just shifted the info to paid members only...


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Re: How do you power the prop in a sub model?
« Reply #2 on: December 01, 2007, 08:30:34 AM »

There's an article in this months MMI on converting Revell's Gato class sub to fully working model that might be of interest.



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Re: How do you power the prop in a sub model?
« Reply #3 on: December 01, 2007, 01:35:04 PM »

There are a few ways of sealing a shaft to prevent water ingress.

You can stuff the tube with grease. Many kit manufacturers do this like Robbe. Unfortunately water pressure tends to force the grease out, plus it eventually emulsifies with the water. Therefore this method is really only suitable for subs that operate in shallow waters (i.e. a couple of feet), plus you have the unpleasant chore of regularly filling the tubes with fresh grease.

You can fit an o-ring, with some form of adjustment to squeeze it up onto the shaft (like a compression joint). This works well, but an o-ring isn't really designed for dynamic shaft sealing, therefore the profile of the o-ring is not optimal and the result is greater friction. In practice this isn't as big an issue as people think.

You can fit a small oil seal or cup seal. These are available for shaft sizes down to 3mm diameter. This is the most professional solution, as the seal is optimised for dynamic shaft sealing and presents minimal friction. At the same time the seal will squeeze tighter around the shaft as the boat dives deeper by nature of it's design. The trade name for these small oil seals is 'Simmerring', and they're made my a company called Freudenberg.

Here is an image of a shaft set-up for a model submarine-

Another method is to fit a small piece of silicone tubing over the end of the stern tube. The space between the stern tube and the propshaft should be filled with silicone grease. This is a cheap and cheerful way of sealing the shaft, but it is very effective and handy for those who don't have access to a workshop to make a glanded fitting.

Other methods include using a magnetic coupling (Neodymium magnets) and running the motor in the wet, the latter method is popular with smaller models, but it can result in reduced motor life and I'm not a fan of this method personally.

All seals need to be greased. For this I use silicone grease, as it doesn't harm the seals and doesn't emulsify in water.

Ready made units are readily available from various places, and represent good value for money-



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Re: How do you power the prop in a sub model?
« Reply #4 on: December 05, 2007, 07:10:28 AM »

When i had my old Darnell T boat, I had standard propshafts running through the WTC, these were syringe filled with warm vaseline & the "dry" end in the WTC was coated in silicone. If you leave the silicone to go off before moving the shaft you get a top seal.
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