Paddle wheels

[ongolo]

If I would be any closer to you guys, I would not post this for fear of being forcefully admitted to a mental hospital, however I recon I am safe.

I know that a propeller is more efficient than a paddle wheel while propelling a boat, but as a power take-off to drive a generator, water maker and fridge compressor, the paddle wheel will be much more efficient. The paddle wheel would also need no underwater seals, thrust bearings, stainless shaft etc and it could be driven by a car gear box allowing a selectable transmission raio as required.

So I am considering (not to say that I will do it) to design a system so that one day, when I older and things are more readily forgiven due to senilty, I might just do it.

Actually, there is a practical reason insofar, that where I like to go, it might not be possible to take the boat out to do maitenance on the prop/sterntube.

Cleaning, painting and replacing the anodes could be done by careening of the steel hull.

So does anybody here have an idea how to calculate the optimum size, number of blades, revs and slip of a paddle wheel for a 80 HP motor?

Sorry for the problem, but it is no use telling me to read this or that book, I will not have access to it.

My oldest book is H.B.Whites NAVAL ARCHITECTURE , second edition 1878 (I think) and it does not say anything about paddles.

thanks and regards ongolo

PS, If you reply soon, I will be able to read your post, if you take longer... well the asylum might not have Internet. ))


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[Dave1258]

I presume you mean fitting some sort of paddle wheel over the side of your boat, well both sides to form means of generating electricity, surely solar power or wind energy would be more efficient? when you add paddles gearboxes, drive shafts etc, Just think of the weight added to your craft!


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[ongolo]

Thanks, but weight is hardly a consideration, that I think could be the same in the end. Even if it would add a few 100kg, that would not worry me at 22 ton displacement and a long keel.

You should try and see the whole picture, advantages and disadvantages.

Solar has its problems so has wind power, the question is the size, width and revs of the system. Where would I find the info?

regards ongolo



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[LORDNELSON]

If you type "paddle wheels" into Google I think you will find some links to paddle wheel enthusiasts

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[ongolo]

Lordnelson,

Thanks, I thought I am the only nutcase.

regards ongolo


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[john_morris_uk]

I heard a story once that there is some sort of international law or convention saying that if you have paddle wheels on eiher side of a craft, you MUST have them on the same shaft. I had been having a conversation wih a Naval Architect saying how manoeverable a paddle ship must be when you reverse one paddle against the other - until he pointed out that it also tends to maneovre the ship to the inverted position!

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[Jacket]

Eh? How's it do that then?

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[richardandtracy]

A paddle wheel is really an undershoot water wheel, with a disadvantage that you're less certain about the mass flow rate as there are no sides or base to the flow. I would reckon that the free edge effect would add at least 10% to the affected mass when putting power in to the water, and at least 10% less when taking power out.

Now, I've seen a 10 hp undershoot water wheel. It was a mere 15ft diameter and 2ft wide. Is your vessel really big enough for two of these? From my readings, the old Mississippi steam boats with their stern paddles were in the 80-100 hp region, and their paddle wheels were rather large - size proportionately increased relative to the 10 hp water wheel (15ft dia, approx 20ft wide).

I haven't any data on waterwheels, as most of the reference books I've got were written in the 20th century (and those that weren't, relate to machining rather than power generation) - but 'waterwheels' may give you another useful search term.

If you do do it, let us know on the forum, it'd be interesting to see.

Regards

Richard.


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[ongolo]

I have puzzled over he statement "inverted position" and I do not believe this.

from a mechanical point, there is no reason why it should, but you are right that one could just about turn on the spot if they run in opposite directions.

Thanks for stimulating thought.


regards ongolo


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[ongolo]

Richard,

Thanks 80 -100 Hp is already something. As far as size, width and diam. is concerned, the revs or the flow rate of the water MUST paly a role.

As a kid in Germany, I remember on the elbriver there were paddle steamers, which are still operating. I have been on them, but although to a kid everything is huge, I dont remember them that big.

The Missispi steamer were early steam engine and I guess very slow reving.

I am going to research this. Food is ready got to stop first. Ponder some more.

I would approach it something like a prop calculation, slip being the question really.

regards ongolo


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[richardandtracy]

I agree that slip and water velocity must play a role.

Just remember though, if going for a higher speed design, that paddle wheels can probably cavitate rather more easily than a fully submerged prop as each paddle will entrain more air under the water. If the cavitation gets bad enough, you won't get any thrust from the centres of the paddles at all because the water won't have time to push the air out of the way before the paddle's back out of the water.

As a slightly sideways way of looking at it, a tank track with paddles attached would be better than a wheel. The lower part of the track at nominal water level, and the upper part completely clear. This way a higher proportion of the thrust will be in the horizontal direction, giving a greater efficiency (assuming the track doesn't absorb too much power).

Then, if you're really inventive you boat could be amphibious and self releasing when grounded using the tracks..
Oh dear. I've been watching too much 'Scrapheap Challenge'. It's time for a lie down.

Regards

Richard.


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[PuffTheMagicDragon]

Are you sure this guy's a naval architect? IF paddle wheels try to put the boat in an "inverted position", then surely a propellor would tend to roll the boat over?
When I was little I remember that the Royal Navy had a huge - at least to my eyes - tugboat that had paddles on either side. Called COMMANDER if I remember correctly. I used to be fascinated waching it turning 180 degrees in its own length while churning up Dockyard Creek to a peculiar shade of light green; the eddies would remain visible on the surface for a long time.
Apparently nobody had told her that she shouldn't work in that configuration. ;>)


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[PeteMcK]

RN had a few diesel electric paddle tugs- Director Class - built in the 50s primarily for working under aircraft carrier overhangs. The paddles could be manoeuvered independently which, admittedly, was unusual.

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[Starspinner]

The P.S. Waverley is still sailing every summer round the UK. Contact via INFO@waverlyexcursions.co.uk Happy madness.

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