There's talk of a new type of prop!!!!

[Amicus]

So, wass all the chatter about a revolutionary new propeller then, anybody got the dirty.....?....then.

[ditch paddler]

Has any one read the Waterways World article on this topic yet if so what are your thoughts?

Edited November 17, 2008 by ditch paddler

[carlt]

Has any one read the Waterways World article on this topic yet if so what are your thoughts?

Dog with a bone alert!!

[Amicus]

'ard 'ats an' safety boots please

[RLWP]

Has any one read the Waterways World article on this topic yet if so what are your thoughts?

 

Yes, I have.

 

Richard

[Theo]

I wasn't going to comment on any technical aspects as it is not quite fair to to form any kind of opinion simply off a photographic image, but as others have done so, well why not..

 

The new type seems to have a constant curvature of the blades from centre to circumference, it is always regarded as a first principle of propellers in any medium that the pitch must change and in fact increase towards the axis of the prop. the idea being that for any given rotational speed the actual speed of different points will vary quite considerably from fast at the tips of the blades to much slower closer to the axis..

 

The varying pitch of the blades should compensate for this effect, any 'point' in the water passing through the prop should do so at the same speed regardless of position, another way to think of it is the classic example of it cutting through cheese, the cut it makes should have a constant thickness.. The new type would produce very different water speeds at different places and I suspect it would make a real mess of a lump of cheese..

 

To add a bit more complexity the pitch should not only vary along the radius of the prop, it must also vary along the 'width' of the blade, the idea being that the 'point' in the water should accelerate smoothly as it passes the width of the blade.

 

Narrowboat have a particular problem as they need to have a reasonable performance in reverse.. If you look at a ships propeller or one designed for a speedboat they have a very unsymmetrical shape with an exaggerated trailing edge and much greater curves to the pitch, all this is done to attain the maximum possible efficiency in a single direction.. One of those props would barely work at all in reverse, so our props have evolved to give a reasonable performance when stopping and going backwards..

 

Just to repeat, may comments are very un-scientific but that large parallel and constant radius of the blades I suspect would not work very well at all in reverse. Anyway I look forward to seeing some independent evaluation, in a way I hope all my words prove to be a load of rubbish but I doubt it somehow.

What you are saying, John, is that the pitch of the blade should remain constant from tip inwards. Pitch is defined as the distance moved in one rotation so the angle has to change from small at the periphery to large at the boss.

 

Nick

[Woollymishka]

Hi everyone

If you lay your hands on the this months edition of Waterways World there is a 2 page item on the Axiom prop - really interesting and they are based in Northants

I think I might be joining the band "I want one" though @ £690 upwards ........!!!!!! ??????

Tim

[ditchcrawler]

Yes there is a new prop called Axiom on the scene i wondered how long it would be before it got talked about.

I have a Axiom fitted to my boat and have been involved in some of the early trials for the new design all i can say is keep your ear to the ground and your eyes on waterways world.

 

 

My Axiom is a 3 blade type and yes it is very clever, its like fitting abs.

I mentioned this to a sailing friend today and his immediate reply was Kiwi Props, well it is very similar except the Kiwi feathers, but the blade shape looks very similar. http://www.kiwiprops.co.nz/philosophy.html