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[tonyH]

Good Morning!
Now I've got space and decent plans I've started on the build of the troopship Archangel at 1:72 which gives a length of 1.4 metres, She's a triple screw vessel and while the outer screws will sit close to the hull the centre propshaft will need to be split with two "knuckle" joints to allow a decent depth of keel. Can anyone advise a practical maximum deviation between the shaft section attached to the prop, the lay shaft and the output shaft from the motor?
Many Thanks
TonyH
PS There are a couple of threads on here about the reason for the build, apart from the fact that she's (was!) an attractive ship. 

[Colin Bishop]

Is there any scope for having a shorter centre shaft and mounting the motor above it using a toothed pulley drive connection?

Colin

[tonyH]

Sadly no Colin. The stern keel section is quite fine. Theoretically I can take the motor forward as far as I want to but the optimum practical distance between the prop and the motor would be 40-45 cm to get the motor to an access point under a removeable deckhouse. The plans of the real vessel show that the shaft rises but only by a couple of degrees and if kept straight wouldn't allow for half the pulley diameter plus half the motor diameter.The main driving force would be the outer pair of props so the centre one would be for slow speed cruising only, so not a lot of load.Racing prop and flexi-drive?
Tony

[Colin Bishop]

Yes Tony those LNER ond other ferries were quite narrow gutted with not much room in the after sections. I seem to recall that Nick Brown posted some photos of displaced drivelines in his HMS Glorious topic. Obviously you lose efficiency abut at relatively slow speeds it might not matter too much. I think it's not just the angle but the revs as well as at higher speed there is more likelihood of vibration.

My main worry with a model like that would be stability as those ships were relatively shallow draught and in model form susceptible to basic stability issues and the effect of wind. I thought my Bilsdale paddler with its very full hull form and an extra half added to the draught would be OK would be OK but I still ended up having to stick motorcycle tyre weights to the bottom of the hull!

No doubt you have methods in mind to overcome this.

Colin

[Treble]

Tony , According to my ancient HPC Gears catalogue , 25° is the maximum deflection per coupling.. Also , have you considered a flexible shaft , available from the likes of Prestwich Models ?

[tonyH]

Cheers Treble, I'd forgotten about the HPC "Bible", possibly the best read of the lot for any moving bits in model engineering!!I reckon I can get away with 15 degrees, split between two couplings, without losing the stability in the keel so the 25 is ample. A flexishaft would, of course, be a bit "boy racer" 
   Tony
and thanks Colin!

[John W E]

Hi there Tony


Are you proposing to build this hull plank on frame - if so, you may try this method which I have used in the past where I have had to reduce the height of the keel to virtually nothing to incorporate the prop shaft and drive to keep them parallel to the keel.  The method I used was to insert 2 extra keels between the bulk heads approximately 1 inch either side of the main keel; this in theory maintains the strength of the keel.   If you have a look at the photograph, you will see I used this method on a cargo vessel which I built.   It may be of some help, or, I may be a mile off the mark.


John

[Akira]

One approach that I have used, and it worked very well, was to make up a long shaft u-joint. This can be done a couple of ways. I have taken a Dumas ball joint and cut into two and added a piece of 3/16 brass tue between the ends. I cross pinned the end into the tube. The longer the shaft, the less of an angle.The other way was to take two single knuckle u-joints and insert a shaft between them. Again, the length is adjustable. One could put the motor in the bow if one were so inclined.cheers

[tonyH]

Hi John and Akira and thanks for the input. In fact I'm hoping to use a combination of both your actions so I'm cutting the frames at present (Yes John, plank on frame!) without taking out the centres and mounting temporarily on the keel so I can see 'A ' if and how much reinforcing is needed and 'B' where I can place the motor with a 3 section shaft as you describe Akira. It, along with the wing motors, has to be under a lift-off cabin unit. You'll see from the plan that the baby cabin aft is ideal for the rudder servo etc, the midships one is for the motors. The main one is for the batteries so it should allow all the deck planking (3mm at 1/72) to run straight through without cutting out hatches.As to having the motor in the bow, I suspect that there could be a touch of shaft vibration over 1.4 metres
Tony

[JimG]

You shouldn't get any vibration if you treat it as three separate shorter shafts, each with their own shaft tube and bearings As each shaft tube can be rigidly mounted it should stop any vibrations.
Jim

[tonyH]

Hi Jim,I suppose if one were reeeaaaly classy I could tune the hull to the vibration and play "Rock of Ages" as she went down!
Tony

[tigertiger]

I assume that there is a reason why nobody has suggested a flexi shaft.
Please let me know why a flexi shaft would not be suitable.

[Colin Bishop]

There have been suggestions for a flexishaft!

[tonyH]

Thanks all! Decision made and it's going to be a pair of timing pulleys from HPC (Thanks again Treble for the reminder) This minimises the amount of wood taken from the keel, especially along the length and having used them some years ago I have an idea of the quality and low noise value. When Colin suggested this initially I'd forgotten how small and accurate the HPC system was, so apologies Colin and you were ahead of the game!
Cheers, TonyH

[tigertiger]

oops, I missed those Colin. I must be losing something. Even when I read back I could not see them, until I did a find on page.   I must be getting old