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Unusual prop


Boaty Jo

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Helped move an old boat a few years ago which had an unusual propulsion system.

The prop was attached to the big rudder. Known, I think, as a bouteur in french (type of sculling propeller in English?)

I've just come acrross these photos which may be of interest

Crew with Propeller.JPG

bouteur.jpg

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I seem to remember that something similar was added to some Butties when they became motorised.

 

Found it.

 

Discussed previously

 

https://www.buttyhampton.com/undercloth-conversion-2005

 

a146be_4c0763d719f74b5a8d56dd434f3c82db~

 

https://www.canalworld.net/forums/index.php?/topic/96064-hydraulic-pipes/

Edited by Alan de Enfield
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Two things about the prop arrangement in the first post spring to mind. 1) Its vulnerability to damage 2) the way that it would work more like an outboard as the moving water generated by the prop doesn't move over the rudder. In fact I'm wondering if that big rudder anctually does very much other than extending the distance from the stern to the prop to make it more efficient?

Edited by blackrose
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The trip boat at Froghall has a prop mounted in the ellum and driven by a hydraulic motor with the motot connected by pipes to the inboard hydraulic pump.  The prop is within the ellum rather than fitted on the back.

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44 minutes ago, jonesthenuke said:

The raise and lower facility is interesting. Presumably the deeper the water the lower the prop?

 

 

I'd have thought the opposite.

 

When fully loaded the prop will be deeply submerged so can be straight. When running light and drawing only a foot or 18", it needs to be angled down to get any 'bite'. 

 

 

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20 minutes ago, Mike the Boilerman said:

 

I'd have thought the opposite.

 

When fully loaded the prop will be deeply submerged so can be straight. When running light and drawing only a foot or 18", it needs to be angled down to get any 'bite'. 

 

 

A prop should always be running parallel to the water, if the boat is 'unevenly loaded'  then the prop will need the angle adjusting. 

On outboard engines this is done electrically / hydraulically with a 'trim' button, or on smaller OBs by moving a steel pin that the leg rests against.

 

In effect the OP's picture shows an 'outboard' with the ability to adjust the trim (not something normally associated with a tin-slug with the aqua-dynamics of a brick)

 

I know its a picture of the effects of getting the trim wrong with an outboard, but the principle is the same.

 

Image result for boat trimangle vs prop angle

Edited by Alan de Enfield
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7 hours ago, Boaty Jo said:

Helped move an old boat a few years ago which had an unusual propulsion system.

The prop was attached to the big rudder. Known, I think, as a bouteur in french (type of sculling propeller in English?)

I've just come acrross these photos which may be of interest

Crew with Propeller.JPG

bouteur.jpg

Was the boat previously un-motored? That large rudder suggests so

6 hours ago, blackrose said:

the way that it would work more like an outboard as the moving water generated by the prop doesn't move over the rudder. In fact I'm wondering if that big rudder anctually does very much other than extending the distance from the stern to the prop to make it more efficient?

The water action would be completely different - the large rudder may date from horse-drawn days when the boat would be pulled from the bank. With the propeller the boat is pushed by a screw creating turbulence just behind the rudder.

 

It occurs to me as well that all the thrust to push the boat forward is going through the rudder stock! Whereas the rudder trailed the boat it's now pushing it! 

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That will be the “Aster”, the last wooden French Peniche surviving. Originally built as a horse boat. As for UK narrow boats there were many weird and wonderful ways of converting a horse drawn or sailing barge to power, including things like side-board motors in NL etc. 
 

http://www.musee-saintjeandelosne.com/projetasterGB.htm#aster

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6 hours ago, magpie patrick said:

It occurs to me as well that all the thrust to push the boat forward is going through the rudder stock! Whereas the rudder trailed the boat it's now pushing it! 

 

Can't see in the photo, but from the diagram it looks as if the thrust is taken directly on the sternpost, with the propshaft hanging below the rudder (which may have been partly cutaway). Requires a universal joint in the propshaft just behind the sternpost, and that has to be capable of carrying the thrust. How do you keep that properly lubricated?

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11 hours ago, David Mack said:

Requires a universal joint in the propshaft just behind the sternpost, and that has to be capable of carrying the thrust. How do you keep that properly lubricated?

Water lubrication?

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I don’t know but guess that the thrust carries through the u-j and the stern tube to an internal thrust bearing or the gearbox.

 

The u-j would not last long for a variety of reasons (thrust, water, excess angle, single joint only) but would be cheap and easy to change the bearings.

 

I used to watch the Aster cruising backwards and forwards on the Nivernais summit at Baye in the eighties and it seemed to manage OK but needed two people on the bow rudder. As said, many of these motorisation adaptations were rather Heath Robinson.

 

 

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