Prop shaft seals

Just an update on my Simrit seal arrangements.This is the arrangement on the U Class - ORP Dzik:


You can just see the Simrit seal on the port side shaft.
A ball race is fitted just under the Simrit seal.
You can also see the connectors for the universal joints.
All fairly crude but quite easy to make and works well.

@HERMANN,
Where can be found those magnets like in the picture?. I think they can be used into a lots of aplication don"t You think?.
REGARDS
MARIUS

There must be someone brilliant here that can give me a wiring schematic drawing to convert my Graupner MC-19 to use a 75MHz radio module?
I'm desperately wanting to convert.
Thank you,
Giovanni

Hi Giovanni,
Sounds like a question for John Robinson,put a post on his page.
nigele.

Hello everyone,

(especially Marius and tarheel to answer your questlions)

@Marius: The magnets I have used for the magnetic rudder couplers were samples I had got from a dealer on who had been on a model exhibition selling various electronic components, tools and so on... This had been more than 10 years ago (you can see it by the coin on the photograph for size comparison, a former DM, since 2002 we have the EURO).
Meanwhile you can buy powerful magnets in various sizes for example from ebay (look for "Neodym magnets") for almost reasonable prices. But note: for applications where they are exposed to water you shall protect them from water contact by some moulding (e.g. epoxy glue) because if their nickel plating is injured (fine cracks in the surface) the magnet material beneath the plating will start to corrode rapidly.

@tarheel: Efficiency is a question of running speed, whether the friction of the seal or the "water friction" of a wet running rotor is more lossy. For higher rpm speed a conventional shaft seal will have less losses in comparison to a wet running motor. A wet running rotor is stirring the water around and those water whirls (that do not help for propulsion)cause losses as well.
But the real advantage of the wet running motor is the tightness, there is no leakage at all even at extreme diving depths.

Kind regards
Hermann

I've just been referring Dave from Model Boats Mayhem onto this thread and I just realise that all the shaft sealing solutions are a bit "home brewed".

Can anyone recommend a commercially available "off the shelf" shaft seal system??

@HERMANN,

Thank You Very Much for the answer and Information.
I think these type of transmission can be used especially for the small Sub,where the friction is low,due to the small diameter of the shaft,and from heare,the small angular speed,and the propeller speed is also low!.
Is only My opinion.

MARIUS

I have just had a quick look at the Engel website and all they seem to offer is the Simmering oil seal. Good, yes but was hoping to see a housing to make it more "off the shelf".

David

Just a word on how to fit "Simrit" type oil seals.

As an oil seal they are designed to fit into a machined inset i.e the outer circumference is a push fit into the housing.

You can fit them this way but you can also use the "sandwich" method I showed earlier or I have even heard of them being glued onto the outside of the WTC. The main consideration are to not use up too much of your valuable WTC space (length mainly). I have found them to be very low maintenance items - they seem to last for years.

I have always used a ball race bearing immediately behind the seal and I think that this is a good idea to keep the shaft well aligned.

Don't forget that you will also need some form of "thrust bearing" to take up the thrust of going into forwards or reverse. I use Collets fixed onto the shaft with grub screws. (Aircraft people use them a lot, so available from these sources.)

I have standardized on 4mm stainless steel shafts for everything (prop shafts, push rods etc.)

David

like the idea of the magnet linkages

They do look good for a lot of different reasons:

- quick to connect linkages
- completely water tight shaft seals (deep diving?)

Having said that I haven't tried any yet.

David

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very nice. just finished making mine for the gato.

fingers crossed they work :)

timgarrod wrote:very nice. just finished making mine for the gato.

fingers crossed they work :)

If I can help with any specifics, just shout out.

David

Lovely work, David!

David

Whilst not at the sophistication of 'merriman' I thought I would add some notes on some tests on my prototype ideas, though all based on others ideas.
Using a standard 4mm shaft I opted for a 4x9x3 seal from Simply Bearings @ £2.55 each. As I was already using M10 brass machine screws for the ball race housing I simply bored a 9mm x 3mm recess in the screw head. However, for simplicity I decided to use the screw as a plain brass bearing as the speed is low due to a 9:1 reduction belt drive. Also the M10 is about the right size to fit into a length of hose pipe to do a pressusre test using mains water. Much higher pressure than the 1m or so max depth I'm envisaging.






The 2 x M3 tapped holes are intended for a keeper plate, but due to enthusiasm I drilled right through, they should be blind. Also, I think in the actual boat I will reverse the seal so the head is on the outside and probably not bother with a keeper as the pressure will keep it in. In fact even with mains water pressure and a simple 9mm driled hole the seal is a tight fit and showed no inclination to come out. Simply bearings can supply a 4x8x3 seal but it has an outer metal body and is a lot more expensive (£8) so I'm sticking with the 4x9x3 I think.

I was intending to use the same seals for the control rods, but the friction is quite high so I then decided to test the design based on silicon tubing thats been discussed.
Again I used an M10 machine screw as the body, but used 2mm ID x 0.225mm wall brass tube as a guide for the nominal 2mm control rods (actually 1.75mm). I tried 2 sizes of silicon tube 1.5mm ID x 0.5mm thick and 1.5mm ID x 0.75mm thick both from Advanced Fluid Solutions. I decided against the thinner wall as it seemd to stretch more and I was worried about it tearing.


The guide tube is simply soft soldered into the M10 screw, it was a bit loose for glue. The length of free tubing providing the actual seal was about 3mm, but back in the hosepipe test it showed no signs of leakage so thats my seal designs sorted!
For the actual boat I intend to use an M6 machine screw as the body, again with the head on the outside.

As an aside, rather than various sealing compounds to seal the bolts into the WTC end caps I intend to use M6 & M10 Dowty seals (bonded washers) as they are designed for high pressure and are reasonably cheap, about £0.30 from Advanced Fluid Solutions. Thats one of the reasons I decided to have the machine screw heads on the outside as I can simply put a Dowty seal between the head and the end cap.

I've mentioined the suppliers where I got my supplies from but I'm sure there are others and folks wil have their own favourates.

Thanks for a very elegant take on sealing issues.

Those Dowty seals are new to me and I bought some (M8 ones) to try out:



They look very good. Better than slathering silicone rubber on and better than rubber washers. They will presumably seal at up to hydraulic system pressures. Although I hope it never comes to that!

Thanks for sharing.

David