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

[down the north]

I'm no expert on prop design,

but as I understand it , the rounded end of the blade coupled with minimum pitch at that point and coupled to greatest periferal speed is such that the thrust is equal over the blade from centre to blade tip, however thats not to say that ithe rules cant be changed, so looking at the axiom, I could well see that it would reverse better because theres a whole shedload of thrust now coming from the area at the tips of the blade rather than half way down the blade, and that means more push towards the front of the boat to stop the dam thing !! If the swim sheets actually meet rather than joining on a stern post all the better. Anne , me old dustbin, ( topical) had a little reverse swim ,ie a pull in concave heading for the stern tube, but the swim was only 6ft long as i recall, yes 6 ft, but it stopped on a sixpence, probably still does or would if stuart would chuck all that rubbish out ( jokin stew) and that is 19 HP lister HA2, 23 x 18 , 2 :1 reduction, with the blade set as low as possible on the stern post.

I suppose the only consideration with the axiom is that it will be very 'beefy' to take the thrust over the length of the bats, maybe theres minimal pitch at the tips of the blade,,

its always been known that you get more thrust for HP if you add reduction and wack up the blade size. look at Elstree, ( big woolich) RN powered, 18 at 1000 rpm, 3:1 cant remember the blade size, but only a few more revs from normal , and its the parting of the dead sea all over again !!!

get a load of that !!!!

[Guest TerryL]

Yeah, its called a marine screw and if you've done any boating. You'll know it full of problems. We have spent 15 year developing a true propeller.

Brunel bless him. being the innovator he was. He would have love to see the thrust our propeller produces.

 

Pull your stick out of the mud.

 

The inventor of the marine screw was a Mr Francis pettit smith an English farmer in 1836. His invention was based upon the Archimedes screw 250 BC

 

"Axiom propellers have been fitted to 7 narrow boats (37 ft - 60 ft size range) this summer. Collectively they have clocked up nearly 5000 miles. Propelled by this new, patent pending type of propeller. All of the owners have reported the following improvements to there boats; 1, Steering vastly improved. 2, tiller pulsing reduced. 3, Large reduction in the boats wake. 4, Prop walk is eliminated. 5, Improved fuel efficiency. 6, Vastly improved stopping power. 7, Reversing is predictable, powerful and controllable. 8, Reduction in vibration throughout the boat. 9, Less weed pick up. 10, Easy to steer off tunnel walls."

 

Stick in the mud eh? I wasn't aware my prop was full of problems.

 

1. My boat steers without a propellor, 2. Don't have any pulsing, 3. My boat has the same small wake under sail or power, 4. Propwalk is useful, can be eliminated by putting it in a tube but I can't see how this can eliminate it, 5. Not when I'm sailing, proof? 6. Not on my boat with big prop, would seem this can also be done by designing more reverse thrust at the expense of forward thrust, 7. Reversing is the same for me, 8. Don't get vibration, 9. Don't get weed, 10. Definitely don't get this problem.

 

So if I'm interested how does it work differently and what are you claiming that will make me take my stick out of the mud? You are not exactly selling me the idea yet.

[DaveR]

Gentlemen,

 

All this talk of pitch and blade size is all very good. The idea that stopping in a shorter distance does have its appeal. The Bensham, from full speed (5knots) stops in half a boats length (40 footer = 20 feet) using a standard 17 x 9 on a 28hp Kubota. So I can't see there being too much improvement on that which would make me change.

 

However I spend most of my time going forwards. Any data on that side?

 

Thanks

 

Dave R

[Peter & Maureen H]

Hi All,

 

I'm not surprised this make you stop on a sixpence, drop one of these on the back of a boat and even 'nil rotundum' it would be like throwing a sea anchor out the rear. It's not so much a prop as a three bladed shovel- that's not a criticism, if you've ever paddled a boat with a shovel you know how effective it can be! I'd like to see one of these in a vectoring duct, would be like jet propulsion.

 

By the way, has anyone played with waterjets on a narrowboat? I've seen an idea that seems to use 4 bowthrusters set diagonally under computer control with no rudder at all - all good stuff but it gets a bit too far from real hands on sailing!

 

Actually, I like prop walk, it's one of those things to use just to show you really think you know how to handle a boat, (although sadly on a longish narrowboat it's not as effective as I'd like it to be. Wind has far more effect on the boats behaviour). And springs, breast ropes and suchlike stuff. Most sailors of any description don't fully appreciate the power of a well set rope, or the danger in a badly set one.

 

Sorry - enuf rambling- the picture seems to show a sinusoidal curve across the face of the blade- is that accurate or just an artifact of the rendering? Facts and figures from controlled like for like trials are needed please. And as you've said, these will hopefully be available soon-

 

Cheers,

Peter H

Edited October 14, 2008 by Peter & Maureen H

[dor]

By the way, has anyone played with waterjets on a narrowboat? I've seen an idea that seems to use 4 bowthrusters set diagonally under computer control with no rudder at all - all good stuff but it gets a bit too far from real hands on sailing!

 

Been done. Very expensive. Boat currently at Stourport.

[Peter & Maureen H]

Been done. Very expensive. Boat currently at Stourport.

Any good? Cost/Benefit probably doesn't stack up?

[Timleech]

It looks from the little images just like an axial flow fan.

Being apparently symmetrical it ought to work equally well in either direction, hence the improved stopping/reversing, while a standard prop is optimised (we hope) for forward propulsion as that's what is expected of it. I'll be fairly amazed if these things show a significant improvement in normal forward running (in properly conducted and measured tests) over a standard prop of the same diameter, but maybe in certain conditions it might and 'I await developments with interest'.

 

It looks as though it might be more vulnerable to damage and debris collection than a standard prop design.

 

If you want to see really great stopping/starting, go on an old steamer with a large slow-turning prop.

 

Tim

[Hairy-Neil]

I think Brunel got there first with a similar prop on the SS Great Britain.

 

Isambard Kingdom Brunel. What a berk.

 

IIRC it was the Swedish inventor, John Ericsson who persuaded the great Brunel to change the original design of the Great Britain from paddle wheel to incorporate screw propulsion.

 

The inventor of the marine screw was a Mr Francis pettit smith an English farmer in 1836. His invention was based upon the Archimedes screw 250 BC

 

Sounds to me like the reinvention of the wheel....

[John Orentas]

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.

[ditch paddler]

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.

You could not be more wrong about reverse i have trialed this for 6 months and reverse is amazing (like fitting abs). I dont want to give to much information away as that is down to Axiom and Waterways World all i can say is we carried out a timed stopped from 4 miles per hour with a Marine screw and a Axiom and the Axiom stopped with in a boats length (58ft boat) with no prop walk and nearly halfed the stopping time of the Marine screw.

[Cinimod]

This is something that may be of interest to do when we have our boat taken out to be blacked in about 12 months... does anyone have any idea what the cost is?

 

Both to buy and then to fit... also are there any special considerations in fitting?

[ditch paddler]

Maybe they should try and tow each other backwards in a tug of war and then tie them bow to bow and try it in reverse

I have done this many times at boat clubs on the Nene at there annual rallies, narrowboat tug of war is an event. I dont see that this would be a very fair test as the amount of water and air being moved around would just cause a lot of cavation especially for the Marine screw. Like i said keeping checking Waterways World.

 

This is something that may be of interest to do when we have our boat taken out to be blacked in about 12 months... does anyone have any idea what the cost is?

 

Both to buy and then to fit... also are there any special considerations in fitting?

Read the write up on it and i am sure you will want a narrowboat you can steer more easily,stop quickly and create less wash and movement of moored boats when cruising the system, plus you might well find as i have that you will save a bit in fuel.

[Guest TerryL]

I have done this many times at boat clubs on the Nene at there annual rallies, narrowboat tug of war is an event. I dont see that this would be a very fair test as the amount of water and air being moved around would just cause a lot of cavation especially for the Marine screw. Like i said keeping checking Waterways World.

 

 

Read the write up on it and i am sure you will want a narrowboat you can steer more easily,stop quickly and create less wash and movement of moored boats when cruising the system, plus you might well find as i have that you will save a bit in fuel.

 

How the hell can it create less wash, that's a hull problem?

[John Orentas]

You could not be more wrong about reverse i have trialed this for 6 months and reverse is amazing (like fitting abs). I dont want to give to much information away as that is down to Axiom and Waterways World all i can say is we carried out a timed stopped from 4 miles per hour with a Marine screw and a Axiom and the Axiom stopped with in a boats length (58ft boat) with no prop walk and nearly halfed the stopping time of the Marine screw.

 

 

No wish to be rude Ditchy but you cannot be described as in any way independent.. The design of propellers like so many other things is all about compromise and trading one thing against another.. True it is possible to gain a massive improvement of one aspect of performance but 'sods law' suggests you will loose out in another..

 

I must insist though that there are one or two basic design errors.. Prove me wrong.

[ditch paddler]

How the hell can it create less wash, that's a hull problem?

Hull problem yes you are right-problem being the way the hull goes through the water alter this and you create less wash

[chris w]

I thought that one could not have 2 identities on this Forum. It's blindingly clear to me now that JO and TerryL are the same person. There can't be 2 curmudgeons registered surely?

 

Chris

[ditch paddler]

No wish to be rude Ditchy but you cannot be described as in any way independent.. The design of propellers like so many other things is all about compromise and trading one thing against another.. True it is possible to gain a massive improvement of one aspect of performance but 'sods law' suggests you will loose out in another..

 

I must insist though that there are one or two basic design errors.. Prove me wrong.

Not for me to prove you wrong if there are design errors then Axiom is where you need to point your questions i can only answer for my findings and the way it has altered / improved the handling of my boat.

 

I thought that one could not have 2 identities on this Forum. It's blindingly clear to me now that JO and TerryL are the same person. There can't be 2 curmudgeons registered surely?

 

Chris

Well spotted i had not noticed think you be right especially as last replies with in 2 minutes of each other, i only reporting what i have found while trialing the Axiom in the hope i might be able to relay some of my findings to you guys.

 

No wish to be rude Ditchy but you cannot be described as in any way independent.. The design of propellers like so many other things is all about compromise and trading one thing against another.. True it is possible to gain a massive improvement of one aspect of performance but 'sods law' suggests you will loose out in another..

 

I must insist though that there are one or two basic design errors.. Prove me wrong.

Why can i not be independent i only reporting to you my findings while trialing if you not interested then keep your concrete set opinions (no wish to be rude John) to your self and wait for the true independent (in your eyes) Waterways World to publish there findings.

[Guest TerryL]

Hull problem yes you are right-problem being the way the hull goes through the water alter this and you create less wash

 

 

You mean slow it down? How else can you alter the way it goes through the water?

 

I thought that one could not have 2 identities on this Forum. It's blindingly clear to me now that JO and TerryL are the same person. There can't be 2 curmudgeons registered surely?

 

Chris

 

Bitch! Who's JO?

[Liam]

I thought that one could not have 2 identities on this Forum. It's blindingly clear to me now that JO and TerryL are the same person. There can't be 2 curmudgeons registered surely?

 

Chris

 

The only place that dual identities are allowed is in the Virtual Pub, and that is of course if the Site Crew know about them. Any others which we happen to find will just be deleted.

 

I don't know why you think TerryL and John Orentas are the same people, just because they posted within a few minutes of each other. They have a completely different IP address, never mind on completely different ISP's.

[ditch paddler]

You mean slow it down? How else can you alter the way it goes through the water?

 

 

 

Bitch! Who's JO?

Hard to explain what i mean but i will try - What i have found is with the marine screw as you will know as you increase revs the stern of the boat is pulled down which in trun lifts the bow and as you pass over shallow/deep waters this increases/ decreases but with the Axiom it does not appear to pull the stern down any where near as much and therfore keeps the hull sitting flatter on the water creating less wash.

 

The only place that dual identities are allowed is in the Virtual Pub, and that is of course if the Site Crew know about them. Any others which we happen to find will just be deleted.

 

I don't know why you think TerryL and John Orentas are the same people, just because they posted within a few minutes of each other. They have a completely different IP address, never mind on completely different ISP's.

Ok fair play i appologise.

[Guest TerryL]

The only place that dual identities are allowed is in the Virtual Pub, and that is of course if the Site Crew know about them. Any others which we happen to find will just be deleted.

 

I don't know why you think TerryL and John Orentas are the same people, just because they posted within a few minutes of each other. They have a completely different IP address, never mind on completely different ISP's.

 

Don't you get tired of getting shot down Chris?

[Hairy-Neil]

There can't be 2 curmudgeons registered surely?

 

Chris

 

Jim Shead doesn't list any.....

[Guest TerryL]

Hard to explain what i mean but i will try - What i have found is with the marine screw as you will know as you increase revs the stern of the boat is pulled down which in trun lifts the bow and as you pass over shallow/deep waters this increases/ decreases but with the Axiom it does not appear to pull the stern down any where near as much and therfore keeps the hull sitting flatter on the water creating less wash.

 

 

Ok fair play i appologise.

 

I suppose this will depend on the hull type but it would seem to me that too much power was being used when passing moored boats and I can't see how the hull profile might change that much to make a difference. However, I'm still not clear on how it would do this or the claims and how it works, what are the selling points and how are they justified?

[Chris-B]

Lots snipped to keep the relevant bit

 

Why can i not be independent i only reporting to you my findings while trialing if you not interested then keep your concrete set opinions (no wish to be rude John) to your self and wait for the true independent (in your eyes) Waterways World to publish there findings.

 

 

Whilst I am not going to disagree with the independent status of WW , I know that as a boater and also somebody who is directly involved in the marine industry that what may work well in one set of test conditions does not necessarily work for all boats/people under a wider range of test parameters

 

I for one would like to see some reports from a truly impartial random selection of boat owners who have compared this prop under a wider range of conditions

 

This is not a head in the mud attitude BUT wanting to get a broader spectrum

 

Chris

[chris w]

The only place that dual identities are allowed is in the Virtual Pub, and that is of course if the Site Crew know about them. Any others which we happen to find will just be deleted.

 

I don't know why you think TerryL and John Orentas are the same people, just because they posted within a few minutes of each other. They have a completely different IP address, never mind on completely different ISP's.

 

Liam

 

Have you had a sense of humour bypass?

 

Chris