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[npomeroy]

This arrangement causes slight lateral movement in the shafts, so they gyrate around the fulcrum at the hole in the ply.
Reading elsewhere, it seems the universal joint must be perfectly aligned (i.e. motor aligned to shaft). I didn't know this and thought these joints were to allow for lack of alignment. Apparently it is correct to used 2 joints in series. My prop shaft casings are 150 mm which seems to be the shortest available so no room for this. Must I fine tune the alignment or is there a better connector? the shafts are 3 and 4mm. Relatively low rpm tug boat with 55mm props.


Also... I was intending to add a second brace point for the shafts, but the wobble would put a strain on it. On the other hand it's no good just letting the shafts wobble - it would put a strain on the exit seal at the hull casing.

prop drive by Nelson Pomeroy, on Flickr

[roycv]

For the last couple of years I have abandoned the u/j centre section and use a thick walled flexible tubing cut into 2 inch lengths.  I fit it straight from hot water and the tubing aligns nicely.  Very quiet as well.
The metal joint similar to yours I used many (many) years ago and I got convinced at the time it was causing radio interference, I maybe wrong here but I never use them now.
My choice is the Huco brass ends with the tubing in between.
Might be a problem for you in NZ but the tubing should be easy.
Roy

[tonyH]

Hi Nelson,
I assume that this is the Damen, in which case I'd suggest that you're starting in the wrong place, i.e. the middle. Personally, I'd fit the Kort pointy shafts and nozzles in place so that the props, shafts and motors line up and then worry about the hole in the ply. You can always enlarge that, juggle the shaft tube with wedges, bits of cardboard, whatever and only lock the shaft tube in place with a bit of fibreglass once you get a smooth system. To be honest, with a 6" shaft you don't really need it but...........
Have fun,
TonyH

[npomeroy]

For the last couple of years I have abandoned the u/j centre section and use a thick walled flexible tubing cut into 2 inch lengths.  I fit it straight from hot water and the tubing aligns nicely.  Very quiet as well.
The metal joint similar to yours I used many (many) years ago and I got convinced at the time it was causing radio interference, I maybe wrong here but I never use them now.
My choice is the Huco brass ends with the tubing in between.
Might be a problem for you in NZ but the tubing should be easy.
Roy

Hi Roy.  Thanks for the comments. I hadn't heard of Huco parts but see they are readily available here through electronics/engineering suppliers. Do you mean the simple bushes, in order to fatten the shafts for a larger plastic tube? There are many types of plastic tube. I may look at silicone fuel tubing, but it does not react to heating. Also silicone retains its flexibility.

[npomeroy]

Hi Nelson,
I assume that this is the Damen, in which case I'd suggest that you're starting in the wrong place, i.e. the middle. Personally, I'd fit the Kort pointy shafts and nozzles in place so that the props, shafts and motors line up and then worry about the hole in the ply. You can always enlarge that, juggle the shaft tube with wedges, bits of cardboard, whatever and only lock the shaft tube in place with a bit of fibreglass once you get a smooth system. To be honest, with a 6" shaft you don't really need it but...........
Have fun,
TonyH

Hi Tony.  I already started at the prop end and the korts have had their positions fixed, so it all already lines up - in terms of the motor shaft locations. But the motor alignment is clearly not perfect (quite difficult to perfect). As said above I may go to silicone tube. The trouble is the motor shafts are 3mm and the prop shafts 4mm. Ideally I'd fatten the motor shafts to match. They have a near-half thickness flatten which makes it dodgy to add a sleeve. I may se if I can bore out some 4mm tube to fit over them, and also file flat onto some 3mm rod to fill the flat.

[roycv]

Hi the Huco brass couplings have a good lined surface for gripping tubing. 
A friend gave me a couple of feet of what looks like a 3mm wall silicon tubing.  It is a tight fit onto the Huco ends.  They do not slip and I have several boats so fitted.
 I would guess they are good for about 50 watts of power.
Regards
Roy

[NickelBelter]

You can shorten those stuffing tubes with a tubing cutter and a punch to carefully remove the bearing from the cut-off end. 

[MPT]

Can you just move the motors back and add another universal joint

[npomeroy]

Can you just move the motors back and add another universal joint

Yes maybe...  There is enough length on the ply mounting plate to do this.  And I happen to have a spare 5 to 5mm UJ bought by mistake - could get another.
Alternatively, I could try and perfect the motor alignment - I can see they are degree or so out.

[Geoff]

If you have enough room I would suggest you use a double Huco coupling. This changes the flexible connection into a constant velocity joint which picks up virtually any miss alignment in any plane.


Cheers


Geoff