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sparrowcycles

Lister ld2 propeller

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Hi folks, I'm not sure if this is the best section to ask this in but I'm about to fit a lister Ld2 in a 30ft boat that currently has a bmc 1.5 in it. I'm pretty certain it'll need a new propeller, I'm just wondering if anyone has a good guess of what size I should aim to get. 

 

It has an LM100 mechanical gearbox and looks to have no reduction box. 

 

Thanks! 

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On 17/10/2020 at 20:54, sparrowcycles said:

Hi folks, I'm not sure if this is the best section to ask this in but I'm about to fit a lister Ld2 in a 30ft boat that currently has a bmc 1.5 in it. I'm pretty certain it'll need a new propeller, I'm just wondering if anyone has a good guess of what size I should aim to get. 

 

It has an LM100 mechanical gearbox and looks to have no reduction box. 

 

Thanks! 

And whether left or right handed. 

 

At 7hp an LD2 is going to be a lot less powerful than the BMC 1.5.

Edited by David Mack

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11 hours ago, OptedOut said:

Do you have an image of the gearbox you can post to confirm the presence or lack of a reduction box?

 

Hope this info helps.

 

http://listerparts.co.uk/LM100.html

 

Thanks, I can confirm the lack of a reduction box, the output shaft is at the same level as the crank, no drop at all. 

 

Have measured the existing prop today and its approx 18", so much too big! 

 

I'm thinking that between 12" and 14" would do it. 

2 hours ago, David Mack said:

And whether left or right handed. 

 

At 7hp an LD2 is going to be a lot less powerful than the BMC 1.5.

It looks to be right handed, the crank turns clockwise when looking from the stern/gearbox end to forward. 

 

 

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Based on my 17th edition 'Motor Boat and Yachting,' manual.

 

LD2 is 7hp at 1800 rpm.   That suits about a 10 in diameter prop direct driven.

 

With a 30 ft boat  the theoretical top whack is  about 5 kts.  Allow for plenty of slip,  assuming this is for canal work, so work out the pitch based on water through the prop at  10 kts, and at 1800 rpm you will need a pitch about 9 or 10 inches. 

 That also gives a sensible pitch to diameter ratio for a displacement boat.

 

With so little power I would be inclined to under prop, so you can at least get all available horses,  so start with a 10 in diameter by 9 in pitch 3 blade.  Keep the shaft size down to minimise the boss diameter.

 

If you want 12 or 14 inches (don't we all!)  you need a reduction box.

 

 It is not going to go like with a BMC though!

 

  Caveat.  Your boat and engine are  very close to the edge of the plotted diameter to power   and pitch to speed curves.  

 

N

 

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24 minutes ago, BEngo said:

Based on my 17th edition 'Motor Boat and Yachting,' manual.

 

LD2 is 7hp at 1800 rpm.   That suits about a 10 in diameter prop direct driven.

 

With a 30 ft boat  the theoretical top whack is  about 5 kts.  Allow for plenty of slip,  assuming this is for canal work, so work out the pitch based on water through the prop at  10 kts, and at 1800 rpm you will need a pitch about 9 or 10 inches. 

 That also gives a sensible pitch to diameter ratio for a displacement boat.

 

With so little power I would be inclined to under prop, so you can at least get all available horses,  so start with a 10 in diameter by 9 in pitch 3 blade.  Keep the shaft size down to minimise the boss diameter.

 

If you want 12 or 14 inches (don't we all!)  you need a reduction box.

 

 It is not going to go like with a BMC though!

 

  Caveat.  Your boat and engine are  very close to the edge of the plotted diameter to power   and pitch to speed curves.  

 

N

 

Thanks for your reply, I think I'll start looking for a 10" prop then! 

It was grossly overpowered with the bmc and as this is for my mum I feel she would rather a slower boat with less twitchy steering while under power! 

 

Many thanks! S

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49 minutes ago, Tracy D'arth said:

But is it a left or right hand prop you need? I'm not sure.

As it turns clockwise in forward when viewed from aft then I'm thinking it is a right hand prop. 

 

The engine plate does say 7hp at 1450rpm, I'm not sure it that will make a difference compared to the. 1800rpm quoted by BEngo

1 hour ago, BEngo said:

 

 

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Cutting the delivery speed by 350 rpm has noticeable effect.  There is still  only 7 hp, so you cannot increase the expected speed but the power is there at a little lower revs, so you could increase the diameter a little and the pitch correspondingly. 

The graphs have lines close together at these sorts of sizes, but I think that 11 in x 10 or 11 in would be a good revised starting point.  Keep the diameter up, for good stopping.

 

It is indeed a right hand prop that is needed for a shaft with clockwise rotation from the rear.

 

A good way to remember propellor rotation hands is to use your own. Hold a hand out palm down, fingers curled abit and thumb out at right angles. The fingeRs point in the  direction of the Rotation  of the blades, the thuMb points in the direction of the boat's expected Motion.

 

N

PS.  I assume that the LD does not have a big  alternator bolted to it?  They consume significant power and that will affect the prop size that the engine can handle whilst charging.

N

Edited by BEngo
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43 minutes ago, BEngo said:

Cutting the delivery speed by 350 rpm has noticeable effect.  There is still  only 7 hp, so you cannot increase the expected speed but the power is there at a little lower revs, so you could increase the diameter a little and the pitch correspondingly. 

The graphs have lines close together at these sorts of sizes, but I think that 11 in x 10 or 11 in would be a good revised starting point.  Keep the diameter up, for good stopping.

 

It is indeed a right hand prop that is needed for a shaft with clockwise rotation from the rear.

 

A good way to remember propellor rotation hands is to use your own. Hold a hand out palm down, fingers curled abit and thumb out at right angles. The fingeRs point in the  direction of the Rotation  of the blades, the thuMb points in the direction of the boat's expected Motion.

 

N

PS.  I assume that the LD does not have a big  alternator bolted to it?  They consume significant power and that will affect the prop size that the engine can handle whilst charging.

N

Thanks again, I really appreciate your help and clear explanations! 

That is a great rule of thumb (love the wordplay too) I shall use it for sure. 

I think I have found a 10.5" x 9" RH so that should be perfect. 

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