Paddlewheels: How to choose the right size/model

[kno3]

Hello!

I would like to know how to choose the right size and type of side paddlewheels for a given MODEL hull length. Is there a rule to go by? I am planning to build a model boat of my own design, starting from the steam engine (which I already have), then designing a hull to fit it, and the appropriate paddlewheels.

The questions I can think of are:

1. Fixed paddles or feathering paddles?
2. How many paddles per wheel?
3. What wheel diameter?
4. Where to mount them on the hull? Middle / towards bow / stern
5. How deep should the paddle go? Completely submerged or not?

My hull would be around 40-55 cm long.

Thanks for any hints!

[Eddy Matthews]

A difficult question to answer, as (as far as I know), there aren't any hard and fast rules.....

But my feelings are as follows:

#1. Fixed paddles on boats used in rivers with a lot of debris - floating treetrunks etc. Also fixed wheels on boats which were purely designed to be a very basic and cheap method of transporting goods - African vessels and a lot of the Australian ones. Feathering wheels where only used to a large extent in the UK and Europe - There are exceptions to that, but it's a reasonable generalisation.

#2. Depends on the size of the wheel and the power of the engine, but 8 floats is the normal minimum, going up to 30 or 40 on some of the really large wheels!

#3. Early vessels with slow revving engines generally used very large diameter wheels, as engines improved, the wheels became smaller in diameter. Large passenger vessels had smaller wheels than tugs for example, at least compared to their length/beam. A typical sized paddlewheel on an 80 foot tug would be about the same size as the wheel on a 250-300 paddle steamer.

#4.Early vessels tended to have the paddlewheels towards the bow, the wheels slowly moved back to the midship position as they developed. This was probably because early boilers where inefficient and needed to be placed centrally in the hull besause of the size needed to get the required steam generation, as boilers and engines became more efficient, the engine was placed more amidships with the boiler forward or aft of it.

#5. The bottom paddle blade (float) needs to be fully submerged for maximum efficiency.

Anyway, that's my two penneth worth.... 

Regards
Eddy

[mjt60a]

Have a look at this site - http://www.ivorbittle.co.uk/8.%20Paddle%20wheel/Front%20page%20for%20section%208.htm -
two of my models can be seen here, the PBM paddler (first pic) has six floats per wheel, the tug has eight (feathering rods are for show, the floats are fixed in place) They are similar in size and weight though the tug is a little shorter and wider and both have similar motor and battery setup.
What surprised me is that the PBM model is much faster, about 3 times as fast as the tug and the reason seems to be (at least partly) that the wheels on the tug 'clear the water away faster than it can flow back into the wheel' - which I think is what Ivor Bittle is explaining on his site.
The tug works well up to about half throttle but any more results in lots of bubbles and no extra speed.
Soon as I get some time, which will be over the christmas period, I'm going to try to make a pair of six-float wheels to try on it...

[kno3]

Thanks, that's a good start.

Mick, your observation is very interesting. I will read that website.

[Dinosaursoupman]

Something else to consider in answer to question 4 is the bow wave pattern as it progresses down the length of the hull. You don't want to place the wheel in the trough of the wave; at slower speed the paddlewheel will end up digging deep into the water placing a greater load upon it. Secondly, you don't want to put it at the crest of the wave either. At slower speeds the wheel will barely reach the waterline. You want to place the wheel in an area where the amount the wheel enters the water will be equal at most speeds.

Randy

[kno3]

And how can I know where the high/low of the bow wave will be without having the hull?

[Dinosaursoupman]

Make a mock-up of the hull that will sit in the water at the appropriate waterline and give it a shove in the pool/lake/pond/? As you have stated, you're starting with the engine and planning on building a hull to fit it. I would suggest making a test hull in which you can place your machinery and see how the water responds to it. From the results of the test you could determine if the machinery is in the right place. Otherwise you can make adjustments. Once you have everything working correctly then all other questions will answer themselves; "How big of a wheel", "where do I place the wheel". At this point you can build a permanent hull.

Randy

[kno3]

I'd like to be able to evaluate several hull shapes. So building mock-up hulls is not an option. That would take as long as building it properly.

Reading on the ivorbillte.co.uk site I saw that he made a paddlewheel with only 5 paddles, because he considers that many paddles decrease performance. I have found his explanations interesting, so I might do the same, a wheel with 5 or 6, depending which is easier to build up.

What I still don't know is how big to make each paddle. Forgot to add this one to the list of questions.

[mjt60a]

How I made mine - http://www.btinternet.com/~mjt60a/models/paddlewheel01.html
How 'Barrie' made his - http://www.paddleducks.co.uk/smf/index.php?topic=3673.0
In the Model Boats magazine articles, the author made them with a solid disc inboard and frames on the outside only, with a meccano wheel bolted to the inside (between wheel and hull), they also work well enough according to the article....