Lister SL3 drivetrain configuration

[Bennyf]

I'm hoping someone with much more experience than me can assist!

 

 

When I built my 51' narrowboat (13 tonnes) I installed a 1961 Lister SL3, which came with a 1:1 gearbox attached and a 18" dia x 16 4 blade prop.

 

Due to really poor going, black smoke and constant weed around the prop I replaced this with a 15" dia x 12" 3 blade.

 

This has improved things somewhat, but progress underway is generally between 1.5kts and at a push 2.5kts.

 

Is anyone able to recommend an alternative configuration for the gearbox and or prop that could enable progress of around 4kts with 5+ possible under load?

 

Many thanks Benn

 

 

 

 

[David Mack]

I would say both blades are too big for a 1:1 drive. 

Bunging a few numbers into Vicprop suggests around 12.5 in x 7 in 3 blade.

Putting the same data with a 2:1 box produces something much closer to your original 18 x 16.

Edited September 19, 2021 by David Mack

[Tracy D'arth]

Try using this calculator,

 

https://vicprop.com/displacement_size_new.php

 

It gives good results for narrowboats.  You need to know the HP of the engine and the waterline length of the hull.

[Tony Brooks]

I was about to post the same.

[Bennyf]

Thanks all. I should have said that I used the calculator before I approached FAL propellers for a 12" prop. They suggested the 14" so that I would not have to run at near max rpm to achieve a decent speed. 

 

I was at the River Wey festival this weekend and was amazed by the single, twin and triple cylinder engines seemingly speeding along at just tickover. That really started to make me think about my drivetrain and what could be improved.

Is there merit in a smaller prop with a 1:1 box spinning 'quickly' or a larger one with. 2:1 box spinning more slowly? My gut feel is the latter, but I'm open to suggestions.

 

Thanks!

[David Mack]

Egg whisk running at high speed will propel you well enough at steady speed, but will be less good at getting the boat moving and stopping it. A larger slower running prop will stop the boat better, but not in a straight line.

Can you fit a reduction box to the back of your current setup?

[Bennyf]

Thanks. I can add a reduction box. The boat is traditional in layout, so in the words of my other half: 'the engine has its own bedroom in the middle of the boat', although that statement is normally preceded with 'why does'. L

 

[Bee]

As others have said.  I think if you specified a brand new engine you would be recommended to use a 2:1 reduction and a bigger prop - 18" sounds about right and 16" pitch for a slowish motor with a reduction is likely to work too. Each revolution is going to grab a big bucketful of water and push it out the back and with really basic physics that is a good shove. With much the same awful physics a small prop will grab something akin to a 2 litre pop bottle's worth and the shove that produces  is not much with a heavy boat even going at twice the speed. (I failed 'O' level physics by the way - dunno why)