Thanks for the advice M Turpin (don't know any more than that), I am with you on that, I worked out that I actually needed about 500 mm length. So will thread the one end (actually less thread than the one supplied) then fit - measure - measure then cut.

Sidley70 - I think I would have been tempted to remove the old shaft (the outer tube) and fit a new one. I suppose it depends on how well the original is fitted. Having removed one many years ago from a boat. My method was to have a reasonable size piece of steel drill and tap to the size of the old prop shaft, fit to shaft - this holds the piece at the end of the shaft - the basically give it a bash with a hammer - now in my case it came loose and then by swapping round and bashing from the inside, I got the shaft free enough to clamp a mole wrench on and 'wiggle' it out. Not very scientific, but it worked for me - no guarantees though.

Good Luck

Hi Andy
I have been working on a barn find old Sea Queen kit in very poor condition. The restoration required fitting a 5mm prop shaft as the old shaft supplied was a little short, I ordered a new 5mm shaft 19inches long from Model Boat Bits uk and when I tried to fit it it would not fit. Not realising the old shaft was 3/16inch. I had to ream the bushes to take the new shaft of 5mm. this proved a little difficult as the shaft was already fitted. I finally did it and everything works as expected. Fitting the motor which is a 700 ?. The shaft was 1/4 inch diameter. Boring out the brass insert did not leave much meat and I am hoping it does does not let go under power. So far so good. I hope there is some info there that you can use.
Regards Sid

I suggest you thread the end of the 600mm bar and don't cut it to length first, so hopefully not, but if it does go wrong you can just cut the end off and start again. I always do the most complicated job on a piece of work so if it does go wrong you haven't wasted any time on other processes.

Obtained a length of Stainless Steel 600 mm long 5 mm diameter (it is slightly greater diameter than the Raboesch bearings), used 400 wet and dry - couple (or three) rubs - check - repeat, actually it took some time but now fits, only one end, as the prop end fits the bearing. Still have to put a thread on it, will take mturpin's advice.

I only actually needed a shaft about 60 mm longer than the Raboesch.

One thing I forgot to mention is the fact that when I decided to up size to a 5 mm shaft, and the Raboesch maintenance free, is that the outer tube did fit the pre-made hole in the keel but there was no movement for adjustment. Making that hole larger was one of the most difficult bits up to now. Had to make - what I would call a prop shaft hole enlarger - bit of a bodge but it worked.

Go for it, but be very careful when sizing the shaft and bearing fit, use very fine 1000 wet and dry until a slight interference/push fit is achieved. and for the M5 thread make sure you open the die to its max on first cut using lots of quality cutting oil and then finally finish to size gradually closing the die to it neutral size, it also helps if the die is new as Silver Steel is quite hard in its natural state. (sorry if this was teaching Granny to suck eggs)

Based on what has been said, what I have done is order a length of 5 mm SS longer than required. Only problem that I have is that there appears to be (based on a 300 mm length) is that the SS and the Raboesch bearings are supposed to be 5 mm diameter, but either the bearing is less than 5 mm or the steel is greater than 5 mm. So the SS will likely need reducing slightly (very slightly) in diameter, and once cut to length a M5 tread on the prop end. This will mean that there would not be two couplings.

Will let people know how it goes once SS arrives and it gets 'modified'.......

I'll second that MT 👍 I'm gradually replacing all old and 'suspect' shafts with silver steel. Bought a small stock of 1m lengths of 1,2,3,4mm diameters from Conrad here. Checking with a micrometer the tolerances seem better;

Andy, your best going for 5mm silver steel as it will be more likely to be a better size and will run true. Not sure what the total length is of the shaft but your not limited to the normal 13" lengths as its available in 1 mtr lengths from a good steel stockist.

Heartily agree Rex 👍
Two such couplings in series is a guarantee for misalignment and high vibration potential 🤔 which wouldn't do the 'posh' bearings much good! 😡
I would move the motor. Bon chance, Doug 😎

What is the KV of your motor and how many volts do you intend to use?
The theory is that this is how it should be done and in practice I Have done this setup with Huco type couplings which turned over very smoothly but they could not handle the high revs ie14.000
The Radio Active couplings are first class but again I have experienced some balance issues and vibration with them.
I worry slightly that the length of 2 couplings together is somewhat long but I may be totally wrong. All you can do is to try it I shall follow with interest

When I get piece of 5mm SS, will take some pics.

Any chance of some pics and a mock up of what you are intending