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[jgs43]

I am currently recovering a second hand kit which had been just started by the previous owner. Since the graupner motors are no longer available I need to work out what I require to achieve the correct paddle rotation speed for this model. I can access geared motors and suitable nylon gears etc to effect almost any reduction ratio. My problem is that I require to know what the paddle rotation speed should be so that I can then calculate the various options that might be suitable. Would anyone be able to provide, at least, an estimate of the recommended paddle rotation speed for this boat. I intend using the graupner paddles supplied with the kit as Clyde Model Boats appear to be having problems in obtaining some parts for their excellent alternative units.

[john44]

Have you had a chat to Kim at Clyde model boats he supplied me with geared motors ond gears,
All I had to do is drill the gear centres to the correct size.


John

[Colin Bishop]

The reprint article on his model of Waverley by Sandy Cousins in the 2012 special issue of Model Boats included the calculations below which you may find helpful. Richard Webb's Bournemouth Queen paddler used a conventional brushed motor and a reduction of 10:1

It does seem to be important that water cannot build up inside the paddle box.

Colin

****************

 Paddle Drive
I connected the Como 432G multi ratio pile gear unit with its RE 385, 6v-15v motor (free speed on 12v, 12600 rpm, 0.25A) using 6v with a 6:1 reduction. This is a neat wee unit about half the cost of the Monoperm pile. This gave about 140 rpm in a bath trial, cavitating of course because there was no forward sailing. The motor drew 1 amp and became hot.

Consulting helpful Como, I changedto 12v, drawing 0.5 amp with a cool motor. My excellent neat wee reversing speed control was made and kindly supplied by Tony Stott.
While the ship's paddles run at about 45-50 rpm for 15 knots service speed (on her trials she did 18.5 knots at 56 rpm) I reckoned with my float fulcrum radius giving a circumference of 250mm I should want a scale appearance speed of about 1 knot maximum. So what rpm should I need?

1 knot = 0.5 m/sec
Scale speed for 15 knots;
Ship knots = (15/66) x 0.5 = 0.092 M/sec scale
With no slip, (0.92/0.25) x 60 = 221 rpm
Circumference of paddle circle = 250mm. Therefore, 1 rev moves 0.250 M with no slip.

I did some experimenting in the pond to settle the gearing reduction to achieve a real looking model speed. With a pile gearing of 5 x 4 = 20:1, I got 350 rpm (dry), 300 rpm in the water with a model speed of about 0.7 M/sec. Quite a lot of water was being lifted into the tunnel.
I changed the gearing to 3 x 4 = 12:1 reduction. The model speed increased only marginally. The paddle seemed to be digging the water rather than pushing it back. Water was still lifting into the tunnel and falling out of the fan.

I cut away the aft side of the tunnel and part of the bottom of the inside of the paddle box up to the first porthole to allow the water to eject from the paddle.
The speed increased, practically no water came out the fan and I had a good bubbling wake, all at about 300 rpm.

At 300 rpm the no slip speed would be 300 x 0.25 = 75 M/min.
Actual model speed 60 M/min.
Therefore, propulsion efficiency (60/75) = 0.80
Therefore slip 20%

A fork coupling enclosed in a foam disc links the motor pile output to the drive shaft. The motor is mounted on a bracket (supplied) over the 2 - 6v, 3 A/Hr batteries secured in the canoe.
When the paddles and drive shaft were first assembled the shaft could barely be turned by hand. I set up a power drill drive, and with everything oiled, started it at slow speed. With some trepidation I watched and listened. I half expected a crunch as the paddles disintegrated into a tangle of brass and wire. Surprise, surprise, nothing happened, so after about ten minutes I increased the speed by stages until in half an hour I was up to 200 rpm. With bags of confidence I went for my dinner and on my return found the drive shaft could be spun by my fingers as all the bearings - 37 in all - had eased.
 

[Danny]

I read that 200 - 300 rpm was a good speed for the Glasgow, so geared mine for 300 on the basis that you can always slow them down with the throttle, but you can't speed them up past full!
I went for independent drives which gives far better steering, especially at low speed or in small water areas.
Make sure you do the paddle box mod (strip of plastic attached to the inner inside of the box and slots over the deck bulkhead (?) (the boat edge which sticks up into the box) otherwise it will ship a lot of water into the boat.
I also saw that Ken had converted the plastic rivets on the paddle wheels to M3 screws and locknuts.  On my first trial three of the rivets went to Davy Jones so I followed Ken and also converted.  When painted black they are hardly noticeable (except to rivet counters :).  No problems since!  (I also read that a drop of superglue on the ends cured the problem)??
I think the paddles and the towhook benefit from black paint, it makes them look less 'toylike' than the Graupner red plastic.
Have fun.