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[magnetman]

I meant anti ventilation plates. 

[Tony Brooks]

10 minutes ago, magnetman said:

I meant anti ventilation plates. 

 

Of course you did. The trouble is that those who know the difference between cavitation and ventilation on props are not as numerous who think both are the same thing.

[MtB]

24 minutes ago, Tony Brooks said:

 

Of course you did. The trouble is that those who know the difference between cavitation and ventilation on props are not as numerous who think both are the same thing.

 

 

I'd imagine with a cavitation problem, welding on anti-ventilation plates would make no difference or could make it worse, if anything. 

[Tony Brooks]

18 minutes ago, MtB said:

 

 

I'd imagine with a cavitation problem, welding on anti-ventilation plates would make no difference or could make it worse, if anything. 

 

I agree, but not sure how it could make things worse because cavitation air/gas bubbles are caused by the prop itself making low pressure areas, not drawing air down from the surface.

[MtB]

47 minutes ago, Tony Brooks said:

 

I agree, but not sure how it could make things worse because cavitation air/gas bubbles are caused by the prop itself making low pressure areas, not drawing air down from the surface.

 

 

I was thinking they might marginally further restrict the flow of water into the prop, making cavitation slightly worse.

 

 

[Tony Brooks]

4 minutes ago, MtB said:

 

 

I was thinking they might marginally further restrict the flow of water into the prop, making cavitation slightly worse.

 

 

 

That is certainly a possibility, but if it restricted much I think it would ventilate because that means water would have been drawing down from the surface.

[Derek R.]

Well I'll show my further ignorance by asking; What is an anti-ventilation plate, and how does it differ from an anti-cavitation plate?

Where is it fitted, what does it do?

The correction needs an explanation. (At least for me it would appear).

[BEngo]

Ventilation is when air is drawn down from the surface into the propellor, spoiling  its thrust.

 

Cavitation is when the pressure at the front face of the propellor blades is low enough for tiny steam bubbles to form ( boiling )   in spots.  When the bubbles collapse there is often damage to the propellor, and a lot of underwater noise.

 

Anti ventilation plates  as seen on many converted butties e.g. Renown, stop air drawing down and are a substitute for the motors counter plate.

 

Anti cavitation plates do not exist.  Cavitation is dealt with by extra immersion and careful propulsion system design

 

 

N

Edited Tuesday at 07:29 by BEngo

[Derek R.]

https://www.boatingbasicsonline.com/boat-propeller-cavitation-vs-ventilation/

[magnetman]

The motorised former horse Boat I owned briefly had anti ventilation plates. 

 

The Raven butty had a very similar arrangement but I don't think it had the flanged edges so if you fell in at the wrong time it would cut you in half. 

 

This was the Boat I had:

 

 

 

https://www.nationalhistoricships.org.uk/sites/default/files/data/nrhv/vessels/2087_ORIANNE_5.jpg

 

 

Edited Tuesday at 08:20 by magnetman

[IanM]

41 minutes ago, magnetman said:

The motorised former horse Boat I owned briefly had anti ventilation plates. 

 

The Raven butty had a very similar arrangement but I don't think it had the flanged edges so if you fell in at the wrong time it would cut you in half. 

 

This was the Boat I had:

 

 

 

https://www.nationalhistoricships.org.uk/sites/default/files/data/nrhv/vessels/2087_ORIANNE_5.jpg

 

 

 

Enlarged picture of Raven from the other end to my previous picture showing the plates being discussed.  Actually it looks to be more of a single plate as it wraps around the stern but whatever 

 

[Ray T]

On 16/04/2024 at 08:18, BEngo said:

Ventilation is when air is drawn down from the surface into the propellor, spoiling  its thrust.

 

Cavitation is when the pressure at the front face of the propellor blades is low enough for tiny steam bubbles to form ( boiling )   in spots.  When the bubbles collapse there is often damage to the propellor, and a lot of underwater noise.

 

Anti ventilation plates  as seen on many converted butties e.g. Renown, stop air drawing down and are a substitute for the motors counter plate.

 

Anti cavitation plates do not exist.  Cavitation is dealt with by extra immersion and careful propulsion system design

 

 

N

Photo from here: http://nurser.co.uk/index.html

Edited Wednesday at 09:39 by Ray T