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phasing out of fossil fuels - programme

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31 minutes ago, ditchcrawler said:

As I have often said, I wonder how many of these boats with the higher Hp engines actually get those Hp out of the propellers

As I have been saying a lot are over propped and can't get anywhere near the headline figure.

My widebeam has 23kw or did before I upped the voltage so it could be more and its been sufficient for canals and rivers around me

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Could anyone explain in a nutshell what the problem is with getting power to the propellers?

 

Are people putting too-large motors with too-small props?

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16 minutes ago, jetzi said:

Could anyone explain in a nutshell what the problem is with getting power to the propellers?

 

Are people putting too-large motors with too-small props?

Large engines with props that are to large, which means that the engine doesn't get into its maximum power band. Over proping is common as itt reduces fuel consumption and makes for quiet cruising.  Remember most canal boats stay on canals so never a problem. Electric motors like mine create maximum torque all the way from zero to maximum rpm, so very flat torque line in acceleration. Diesels don't do that 

Edited by peterboat

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3 minutes ago, peterboat said:

Large engines with props that are to large, which means that the engine doesn't get into its maximum power band. Over proping is common as itt reduces fuel consumption and makes for quiet cruising.  Remember most canal boats stay on canals so never a problem 

And some are the other way and will hit max revs as fast as you can push the lever forward without a great load on the engine

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1 minute ago, ditchcrawler said:

And some are the other way and will hit max revs as fast as you can push the lever forward without a great load on the engine

True my first boat was an ex hire boat and under propped which I sorted, my next 2 boats were way over propped 

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12 minutes ago, peterboat said:

True my first boat was an ex hire boat and under propped which I sorted, my next 2 boats were way over propped 

I think the old Canal Time were a good example of it, engine reving like billyo and going nowhere fast

  • Greenie 1

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39 minutes ago, ditchcrawler said:

I think the old Canal Time were a good example of it, engine reving like billyo and going nowhere fast

I think a lot of hire boats are/were the same,  bigger profits on diesel on return plus less likely to be speeding?

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1 hour ago, jetzi said:

Could anyone explain in a nutshell what the problem is with getting power to the propellers?

 

Are people putting too-large motors with too-small props?

It's a balance between blade area (BAR) & pitch, BAR transmits power, pitch defines its gearing, too coarse a pitch and boat will accelerate too quickly when first engaged, so BAR then has to be smaller to attain very near max engine speed. Correct pitch is then followed by correct BAR to absorb max power, best if it can be achieved with standard 55% BAR (larger dia props turn slower to minimise cavitation) if a larger diameter won't fit then a bigger than 55% will be needed to give a wider blade in a smaller dia, or go for 4 blades (not always ideal)

Over propping does give lower cruising revs but engine is overloaded at higher revs and will overfuel with black smoke. 

It's affected by other things but those are the basics as related to me by Crowther Props, sadly no longer operating. 

 

Tin hat on

4 minutes ago, peterboat said:

I think a lot of hire boats are/were the same,  bigger profits on diesel on return plus less likely to be speeding?

Better for engine life to be lightly loaded than overloaded. 

Edited by nb Innisfree

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8 minutes ago, peterboat said:

I think a lot of hire boats are/were the same,  bigger profits on diesel on return plus less likely to be speeding?

My ex-hire boat had a 3:1 gearbox so the hirers 'going by the noise' (revs) thought they were going fast.

 

 

  • Greenie 1

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All the above may well be true for a typical diesel powered narrow boat. But why does an electric one need need a 20kW peak power motor?

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8 hours ago, nb Innisfree said:

It's a balance between blade area (BAR) & pitch, BAR transmits power, pitch defines its gearing, too coarse a pitch and boat will accelerate too quickly when first engaged, so BAR then has to be smaller to attain very near max engine speed. Correct pitch is then followed by correct BAR to absorb max power, best if it can be achieved with standard 55% BAR (larger dia props turn slower to minimise cavitation) if a larger diameter won't fit then a bigger than 55% will be needed to give a wider blade in a smaller dia, or go for 4 blades (not always ideal)

Over propping does give lower cruising revs but engine is overloaded at higher revs and will overfuel with black smoke. 

It's affected by other things but those are the basics as related to me by Crowther Props, sadly no longer operating. 

 

Tin hat on

Better for engine life to be lightly loaded than overloaded. 

Diesel engines are better worked than not

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