Tea Candle Race - RC Groups
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Oct 22, 2010, 03:13 AM
Registered User

Tea Candle Race

G'day guys,

I'm new to the forums but just thought I'd tell you about my family's tea candle race.
Every year the men folk issue a challenge to build the highest performing race boat powered by a single tea candle. My father and uncles are all machinists of one type or another and the standards are pretty high. This year I have issued a challenge to the reigning champion (Dad) and am confident of my first win.
The rules are simple.

1) The boat is to be propelled by a single tea candle
2) No component of the boat may be commercially availible
3) The winner may not re-use last years vessel

Other than those restrictions, the sky is the limit.

This year I am building a small light weight in-line stirling engine with the hot cylinder over the candle and the cold cylinder inverted with the head thru the hull into the water.

I'm going with a multi-chined hull out of balsa with a split keel amidships to accomodate the cold cylinder heatsync. The rough drawings look good but I'm always open to suggestions
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Oct 22, 2010, 06:35 AM
Mmm, tugs...
patmat2350's Avatar
Sounds like a great challenge! We need pictures....

You'll get a lot of help in the steam forum too:
Oct 22, 2010, 07:35 AM
Capt.Crash's Avatar
Yes...sounds like a lot of fun...got any pics of any of these boats?
Oct 22, 2010, 08:56 PM
Registered User
unfortunately none with me. I'll get hold of Dad and see if he's got any floating around. I'm going to video this years race and throw it up on youtube.
I'll touch my sketches up and post some of them in the near future
Oct 22, 2010, 11:43 PM
Taking care of the pond.
We want pictures.
Oct 23, 2010, 10:08 PM
Registered User
Below is a rough concept drawing of my boat. It's not pretty but it's a reasonable representation of what I'm going for.

I'm a bit concerned with the flywheel being so high but I can't really find a better spot for it. If worst comes to worst though, I'll turn the cylinder head of the cold cylinder into a fin keel and drop some weight lower, it'll increase my drag but it means I can lose the ballast...

Oct 23, 2010, 11:59 PM
Taking care of the pond.
Very interesting.
Oct 24, 2010, 07:53 PM
Mmm, tugs...
patmat2350's Avatar
Why can't the flywheel be on the input side of the reduction gear?
And do you need reduction? Every gear pair is a loss. What sort of speed (rpm) does the motor make? If high speed, a small prop running fast might be more efficient that a big prop running slow with reduction...

And of course you want minimum drag in the water... think of a racing scull (shell), not a deep vee displacement hull...
Oct 24, 2010, 08:20 PM
Registered User
Thanks Patmat,
Lowering the flywheel and taking it aft would work a treat. The hull is flat bottomed after the keel splits. Stirling engines can rev quite high bit have very little torque, especially at low rpm. Ideally I'd have a single cam running between both cylinders but I can't figure a way to do that with the height difference. Does anyone know the optimal prop shaft angle?
Oct 25, 2010, 02:58 AM
Registered User
Sorry for the disjointed English in the previous post, I was at work typing it out on my iphone.
Oct 25, 2010, 08:22 AM
Registered User
tghsmith's Avatar
as this is low power, high rpm set-up, hull drag will be your factor(you won't be getting on plane).. take a look at torpedo boats from the 1890s about as slippery as you can get and still keep the hull in the water.. have the lines of british harbor class boat that might work very well as a starting point, will try to post them later..
Last edited by tghsmith; Oct 25, 2010 at 12:08 PM.
Oct 25, 2010, 08:54 PM
Registered User
Thanks mate, that's brilliant. Funnily enough it looks very similar to what my build drawings came out like. I'm sure I can save myself a lot of time and squilla adjusting that hull to suit my needs instead though.
Oct 26, 2010, 03:11 PM
Registered User
tghsmith's Avatar
as close as you can to a horizontial prop shaft will help(no wasted force pushing the bow up or down) think about placing the cold cyl. in a water cooled jacket inside the hull..
Oct 26, 2010, 07:17 PM
3 Blades to the Wind
Shaun Hendricks's Avatar
I'd probably go for an alpha cycle stirling with the hot cylinder horizontal and the cold inverted and nose touching the water (but not displacing much water, drag can negate the power gains, unless you use a open/flooded compartment for cooling). This would eliminate all the cross cylinder gearing and if you used a toothed pulley as the common crank wheel, you could drive a nice double stern paddlewheel, maybe 3 paddles each side. That would be a very efficient drive train and would run forever on the candle.
Last edited by Shaun Hendricks; Oct 26, 2010 at 07:44 PM.
Oct 26, 2010, 08:59 PM
Registered User
I thought about that but the low down torque needed to drive a paddle wheel just isn't in the stirling. The 'L shaped alpha has always held some appeal but the issue of getting the power to the fluid has always been ugly

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