Axiom Props

[Tony Brooks]

I agree it is not a competely scientific test but it is the closest we have seen to date in that the boats are of the same design and age. I don't know this for a fact but I assume they were picked because they performed similarly in the first place so changing the prop on one would demonstrate a difference logically.

 

I am not saying you have to believe the Axiom sales pitch (there is much I don't understand) but I think there is enough here to take a view that something different is happening with the Axiom prop and it seems to be a good difference. So, either way it is useful to keep an open mind.

 

As for conditions like "more crap on the bottom" well when you get down to that level of objection nothing short of a sterile canal in a laboratory is going to do is it and then I can here someone banging on about chaos theory or such-like.

 

There is however the fact that it is chuffing expensive and I would have to be really sure it was worth it to cough up the difference personally.

 

 

As I say above Tony I agree an open mind is best in both directions so you also need to recognise the possibility that such a design could be producing the claimed results.

 

I find the talk of "scientific evidence" slightly bizarre as even if we had all the necessary data to hand most will probably not understand it so like your Crowther prop that you seem to be able to take on a non-scientific basis as an improvement we have to go buy weight of argument and some demonstration.

 

For my part with the number of articles now and trials that are showing at least reasonable anecdotal evidence of a benefit I have to conclude that something in this new design has merit. Whether this has more merit than a good conventional prop (like the Crowthers) matched to the boat and engine/gearbox combination is another matter as is the price.

 

You are right about most would not understand it, and I probably would not, but some will and they will post their comments. Others will post different comments but most of us can probably apportion the likelihood of who's comments are likely to be the most informed.

 

I thought Newton said something about every force has an equal and opposite reaction so for a prop to propel a boat faster it must develop more "force", yet it seems there is a claim that the Axiom somehow moves less water from under the boat and that seems counter intuitive to me unless the blade area is a lot greater or, in some way the pressure difference across the blade is greater with less water flow. Convention, as I understand it says props can never be 100% efficient because if they were they would produce no thrust and thats why we get prop wash.

 

We need an informed discussion and unfortunately when this thing started, as far as I can tell, the vendors tried to use this forum for marketing in a less than transparent way. The ensuing nastiness caused them to cry off it seems. If they had been open and answered questions several people, including myself may have been more receptive to empirical test results.

 

If (say) the Southampton Institute could produce test tank results the balance of probability is that the results would have had to stand up to peer review and would thus be more reliable than a small number of magazine articles.

 

I also find it interesting that from the great pool of knowledge we have here no-one has apparently had a stab of explaining why the thing does what is claimed.

 

I just await to be convinced, but unfortunately the older you get the more exposed you have been to "magic aids" like Duckham Acoids, battery pills, air gap ignition improver's, the Broquet Rocket and little propellers inserted between the carburettor and manifold to make engines produce more power. There may have been a tiny grain of merit in all these but if they had been revolutionary we would still have them in common use. If an individual is convinced then I say good luck to them but, I for one, will stand back until it can be shown the extra cost is worthwhile in respect of any benefit it gives.

[Timleech]

If (say) the Southampton Institute could produce test tank results the balance of probability is that the results would have had to stand up to peer review and would thus be more reliable than a small number of magazine articles.

 

I also find it interesting that from the great pool of knowledge we have here no-one has apparently had a stab of explaining why the thing does what is claimed.

 

Likewise I won't be fully convinced until I see some *proper* scientific/engineering tests.

I can see why there might well be a real 'improvement' going astern, simply because the thing is symmetrical whereas conventional props are really designed for operation in one direction, and that improvement could be a real benefit for a canal boat.

 

I share the doubts of others about the durability of a fairly sharp-cornered device in a canal environment.

 

The Axiom design might have a larger effective blade area because there is more area near the tips, that also might give some advantage where the max diameter is limited to below the optimum for a given engine/gearbox.

 

I note the WW article refers to something like 'equal phasing' between the two props used, without explanation of what that is supposed to mean. Anyone know?

What ought importantly to be equal for a test such as that described is the load which each prop applies to the engine, so that the hp used is the same for each at a given rpm, and that they are both of similar diameters. That might be what is meant by phasing, but then again how are we supposed to know....

 

Tim

[Arnot]

I just await to be convinced, but unfortunately the older you get the more exposed you have been to "magic aids" like Duckham Acoids, battery pills, air gap ignition improver's, the Broquet Rocket and little propellers inserted between the carburettor and manifold to make engines produce more power. There may have been a tiny grain of merit in all these but if they had been revolutionary we would still have them in common use. If an individual is convinced then I say good luck to them but, I for one, will stand back until it can be shown the extra cost is worthwhile in respect of any benefit it gives.

 

I too spent a little time with Mr Axiom at Crick and looked at the much-vaunted graphs but they didn’t seem to tell me very much either. My suspicion is that the square section of the blades is likely to give slightly more propulsive force and possibly direct it slightly better - but - I suspect this will be at the cost of a greater likelihood of the early onset of cavitation and venting. I may well be wrong though.

 

I was interested in seeing the torque demand curves for the Axiom Prop to see how it would integrate with a hydrostatic drive system but they didn’t seem to have even one. I have to say that without this sort of information it is difficult to design for their propeller. The choice can then only really be made empirically which could be quite expensive…

 

For those who are not sure about it, a torque demand curve shows the torque required to turn a propeller at any given speed and from this you can work out how much engine power it will require and take a good stab at how much propulsion force it will give. From this you can work out approximatley how fast it will need to be turned to propel a given boat at a given speed.

 

I have to say I left their stand both unimpressed and doubtful. Like other posters, I cannot see how a prop change will effect bow wave or if all that is changed is the propeller, it will have any direct impact on a hull “squatting at the stern” but would be quite happy to be convinced otherwise. A lot of the claims seemed to be dubious, irrelevant and unquantifiable and a lot of the important data didn't seem to exist.

 

It’s a shame really, I actually thought that the Axiom Propellers were really nicely made and rather wanted to be convinced that they were an improvement but I wasn't.

 

I have done a lot of work studying propellers recently (largely because almost all manufacturers don't provide enough information) and the more I find out the more I realise just how involved and difficult they are. As it stands, I suspect that the best propeller for a narrow boat may well be a four bladed standard marine prop. They have a better disc area ratio and less slip, both of which lend them to this application. For my part, what I wanted was a propeller that would, without being excessively large in diameter, develop a good thrust at low speeds so that the engine speed could be kept down whilst cruising.

 

Regards

 

Arnot

[churchward]

I too spent a little time with Mr Axiom at Crick and looked at the much-vaunted graphs but they didn’t seem to tell me very much either. My suspicion is that the square section of the blades is likely to give slightly more propulsive force and possibly direct it slightly better - but - I suspect this will be at the cost of a greater likelihood of the early onset of cavitation and venting. I may well be wrong though.

 

I was interested in seeing the torque demand curves for the Axiom Prop to see how it would integrate with a hydrostatic drive system but they didn’t seem to have even one. I have to say that without this sort of information it is difficult to design for their propeller. The choice can then only really be made empirically which could be quite expensive…

 

For those who are not sure about it, a torque demand curve shows the torque required to turn a propeller at any given speed and from this you can work out how much engine power it will require and take a good stab at how much propulsion force it will give. From this you can work out approximatley how fast it will need to be turned to propel a given boat at a given speed.

 

I have to say I left their stand both unimpressed and doubtful. Like other posters, I cannot see how a prop change will effect bow wave or if all that is changed is the propeller, it will have any direct impact on a hull “squatting at the stern” but would be quite happy to be convinced otherwise. A lot of the claims seemed to be dubious, irrelevant and unquantifiable and a lot of the important data didn't seem to exist.

 

It’s a shame really, I actually thought that the Axiom Propellers were really nicely made and rather wanted to be convinced that they were an improvement but I wasn't.

 

I have done a lot of work studying propellers recently (largely because almost all manufacturers don't provide enough information) and the more I find out the more I realise just how involved and difficult they are. As it stands, I suspect that the best propeller for a narrow boat may well be a four bladed standard marine prop. They have a better disc area ratio and less slip, both of which lend them to this application. For my part, what I wanted was a propeller that would, without being excessively large in diameter, develop a good thrust at low speeds so that the engine speed could be kept down whilst cruising.

 

Regards

 

Arnot

It is hard to judge isn't if such shyness in giving information is intended to hide a lack of substance or protect their copyright and patents because they want to reap the benefit of the idea and hard work developing it.

 

For instance Gibbo is hardly likely to tell us publicly (or privately either come to that) how his Smartgauge really works we just have to trust that it does given the products success and recommendation of others. It does work by the way!

[Arnot]

It is hard to judge isn't if such shyness in giving information is intended to hide a lack of substance or protect their copyright and patents because they want to reap the benefit of the idea and hard work developing it.

 

For instance Gibbo is hardly likely to tell us publicly (or privately either come to that) how his Smartgauge really works we just have to trust that it does given the products success and recommendation of others. It does work by the way!

 

Accepted but this isn't magic, it is physics.

 

Even though the mysteries of the machine code embedded in a microcontroller are difficult to download, they can at least be reverse engineered reasonably accurately (although if you are cute enough to do this then you can probably write your own). It doesn't require too much in the way of test equipment to verify the claims of most electronic equipment designers and manufacturers and in the case of Gibbo's equipment, he provides specifications, people buy it and can see that it works! He doesn't have to tell us how...

 

Testing a propeller is a different matter. A test tank and all the necessary instumentation is eye wateringly expensive, almost to the point of being confined to research establishements with close ties to the defense industry. Without comprehensive testing how can a designer of a propeller know that they actually have a better mose trap? And, if they have these test results, why should they withhold them? Verifying the performance of a propeller on a narrow boat seems almost impossible, I really don't see how all the variables can be kept constant while just the propeller is changed.

 

I do have sympathy with Axiom but don't think that they are helping thensleves too much at the moment by not telling us just what their propeller does even if they chose to withhold how it does it. I really do wish them well though.

 

Regards

 

Arnot

[alan_fincher]

I do have sympathy with Axiom but don't think that they are helping thensleves too much at the moment by not telling us just what their propeller does even if they chose to withhold how it does it. I really do wish them well though.

I disagree, I'm afraid.

 

The shoddy attempt to pretend to be someone else to promote it on this forum was bad enough. Denying that was what they were doing, and then having to retract that denial was a complete debacle.

 

I don't actually care how good (or bad) the prop proves to be in practice.

 

I try to only do business with people who are not actively trying to deceive us, so would not consider an Axiom prop based on that principle alone.

[PeterF]

At work when the marketting people ask the engineers and scientists for something great sounding to psh products they ask for PSB - Pseudo Scientific Bull***t.

 

Here is some propellor PSB - please note I have nothing to do with Axiom but in my job I come accross fluid flow a lot and use of comupational fluid modelling and I am just thinking out loud here.

 

In an ideal world, you want all the water leaving the propellor to be travelling perfectly backwards, but in reality the jet exiting the propellor will have some spiral action and will also have some sideways motion so the jet is in the fom of a cone. If you go to the extent of a really bad propellor, mst of the water ejected from the propellor flows sideways away from the propellor in a disc of moving water rather than flowing backwards. The prop is still demanding lots of power to move lots of water about but the boat is not going anywhere. The prop has to suck this water in from somewhere, so it creates a suction in front of the propellor and the boat squats down. A more efficient propellor, but reducing the amount of "wasted flow" may be able to generate more forward thrust from the same shaft power whilst actually moving less water about, because what it does move it moves efficiently and usefully. Therefore, the boat squats less because the propellor is moving less water.

 

As I said PSB but it sounds good and it may have some grain or nugget of truth in it.

[churchward]

Accepted but this isn't magic, it is physics.

 

Even though the mysteries of the machine code embedded in a microcontroller are difficult to download, they can at least be reverse engineered reasonably accurately (although if you are cute enough to do this then you can probably write your own). It doesn't require too much in the way of test equipment to verify the claims of most electronic equipment designers and manufacturers and in the case of Gibbo's equipment, he provides specifications, people buy it and can see that it works! He doesn't have to tell us how...

 

Testing a propeller is a different matter. A test tank and all the necessary instumentation is eye wateringly expensive, almost to the point of being confined to research establishements with close ties to the defense industry. Without comprehensive testing how can a designer of a propeller know that they actually have a better mose trap? And, if they have these test results, why should they withhold them? Verifying the performance of a propeller on a narrow boat seems almost impossible, I really don't see how all the variables can be kept constant while just the propeller is changed.

 

I do have sympathy with Axiom but don't think that they are helping thensleves too much at the moment by not telling us just what their propeller does even if they chose to withhold how it does it. I really do wish them well though.

 

Regards

 

Arnot

 

Are you implying the that Smartgauge is magic and Gibbo a wizard? Well I suppose he is an elektrickery wizard at least.

 

It comes down to the same thing though both cracking Gibbo's code and testing a prop is beyond most peoples means and highly dubious practice at that. So in both cases we are stuck with a choice to believe satisfied customers and what independent info we can gather to decide to buy or don't buy.

 

As I have already said I doubt that if I were to be in the market for a prop at the moment I would be ready to dig deep into my pockets for the funds to buy an Axiom one over a well matched and spec'd conventional one as at the moment the weight of evidence is showing promise but not enough for me to buy.

 

I also agree with Alan in that the memory of how they tried to BS the forum in the past leaves a very poor impression of the company. However, in terms of the actual product then it does seem to have some merit and seems to work well enough as a prop. Whether it is better by far (to justify the price) than a conventional prop is in doubt still but I keep an open mind either way. I will await events with interest particularly whatever Gibbo has to say on fitting and using one on his boat. His input will be very useful I think.

[David Schweizer]

I do not know enough about propeller technology to offer any sort of constructive view on the Axiom's perfomance compared with more conventional propellers, but I do know a bit about verifiable research. The test conducted was so amateur as to be embarassing, one boat was equipped with the new prop whilst an identical boat retained it's conventional prop, they were then both taken on the same journey by different crews who compared notes. It is laughable.

 

To ensure continuity, the same crew should have tested both boats, then the boats should have been docked, the props changed over and the tests re-run, still using the same crew. The report does not state whether the crews knew which prop was on the boat they tested, but in order to avoid any risk of bias (in either direction) this should be kept unidentified until after the results had been declared. Only then could the beginnings of anything approaching a scientificly verifiable test be claimed.

 

One final pedantic point, Axiom claim that the propeller design is a new style which is radically different to conventional propellers. Really?? A chap called I.K.Brunal might disagree, he designed something remarkably similar more than 160 years ago.

 

http://commons.wikimedia.org/wiki/File:SS_...n_propeller.jpg

 

OK it has more blades, but the shape of the Blades?

Edited June 15, 2009 by David Schweizer

[churchward]

I do not know enough about propeller technology to offer any sort of constructive view on the Axiom's perfomance compared with more conventional propellers, but I do know a bit about verifiable research. The test conducted was so amateur as to be embarassing, one boat was equipped with the new prop whilst an identical boat retained it's conventional prop, they were then both taken on the same journey by different crews who compared notes. It is laughable.

 

To ensure continuity, the same crew should have tested both boats, then the boats should have been docked, the props changed over and the tests re-run, still using the same crew. The report does not state whether the crews knew which prop was on the boat they tested, but in order to avoid any risk of bias (in either direction) this should be kept unidentified until after the results had been declared. Only then could the beginnings of anything approaching a scientificly verifiable test be claimed.

 

One final pedantic point, Axiom claim that the propeller design is a new style which is radically different to conventional propellers. Really?? A chap called I.K.Brunal might disagree, he designed something remarkably similar more than 160 years ago.

 

http://commons.wikimedia.org/wiki/File:SS_...n_propeller.jpg

 

OK it has more blades, but the shape of the Blades?

I'll read the article again but I thought they did swap boat crews and boats so they experienced part of the journey on both boat set-ups. Anyway we are talking about a popular magazine article here not a scientific journal

Edited June 15, 2009 by churchward

[David Schweizer]

I'll read the article again but I thought they did swap boat crews and boats so they experienced part of the journey on both boat set-ups. Anyway we are talking about a popular magazine article here not a scientific journal

You are correct the crews did swap over (I missed that when I read it) but the remainder of my argument still applies.

 

Whilst I agree that WW is not a scientific journal, it is a respected magazine which is read by many people. If they declare in favour (or otherwise) about a new product, it could have an impact on the commercial success (or failure) of the product. In this case they appear to be hedging their bets with a luke warm indication of approval.

 

Personally I think it is a lot of money for a fairly insignificant improvment in performance. But then I still cut my lawn with a mechanical lawnmower built in the 1930's, so perhaps I am not the best person to sell an "inovative" design to.

[carlt]

Whilst I agree that WW is not a scientific journal, it is a respected magazine which is read by many people. If they declare in favour (or otherwise) about a new product, it could have an impact on the commercial success (or failure) of the product. In this case they appear to be hedging their bets with a luke warm indication of approval.

Don't the waterway mags declare in favour of everything they review.

 

Even YM are noted for this, as opposed to PBO, even though they're from the same stable.

 

Yesterday's review is tomorrow's advertiser.

[Gibbo]

To ensure continuity, the same crew should have tested both boats

 

The crews did test both boats so that's a huge lump of your argument out the window.

 

.....................but I do know a bit about verifiable research. The test conducted was so amateur as to be embarassing...................

 

How can you make those statements and then follow them with............

 

Axiom claim that the propeller design is a new style which is radically different to conventional propellers. Really?? A chap called I.K.Brunal might disagree, he designed something remarkably similar more than 160 years ago.

 

They are "remarkably similar" because they look, sort of, a little bit like, the same idea? That's hilarious. To me they look completely different. The only similarity I can see is that the edges of the blades are straight! But either way.........

 

Concorde and the Tu144 look "remarkably similar" yet ask any aerospace engineer and they will tell you that they are completely different, use a completely different method of air flow and therefore lift, the wings are much more aerodynamically primitive in the case of the Tu144 and wind tunnel testing will show totally different airflows. In fact the wings are so different that each have a different name to describe the type. All as a result of a very subtle change to the leading edge shape. Yet to someone who knows nothing about aerodynamics they look the same.

 

How about we know nothing (or certainly not enough) about boat screws and therefore looking at a picture and concluding it's the same type of prop because it looks a little bit similar is just naive?

 

This attitude of "It can't work because I don't understand how" is ridicuous in the extreme. Do the people who hold this view really think they know everything?

 

I'm not saying this thing works like a dream, but I'm convinced enough to put one on my boat. And I will be honest about the results. If it's rubbish I will say so.

 

I agree with many posters that the way they tried to introduce the prop to this forum was extremely stupid and certainly did them no favours.

 

Gibbo

 

Don't the waterway mags declare in favour of everything they review.

 

How on earth would that be possible if they're comparing one prop against others and giving scores (in tabulated and graph form) for each performance criteria? It wouldn't be possible would it.

 

Gibbo

[RobinJ]

Some comments which may or may not help!

I can understand the reference to air propellors, since most research has been done on aircraft propellors and it is fairly easy to use a wind tunnel rather than a water tank!

As to squatting at the stern, this is more difficult. Aircraft generally have air going round all sides of the propellor, with possibly some interference from the fuselage, but generally symetrical. Boats particularly sea going ones, often have the propellor shaft at a slight angle, so there might be a tendancy for the thrust not to be horizontal. However the majority of squat is caused by the fact that there is air on the top side which the propellor doesn't affect. Pushing water behind you on the left and the right cnacel any sideways forces except the 'paddle' effect, but pushing water away underneath results in less bouyancy and the boat 'squats'.

Questions; How can a propellor be more efficient and produce less squat, if the only way is to reduce the amount of water drawn from under the boat (which will be less on canals anyway)? If it still manages to push water from the sides this must have to increase (how is that achieved)? Does this not create more 'suck' with moored boats?

[carlt]

How on earth would that be possible if they're comparing one prop against others and giving scores (in tabulated and graph form) for each performance criteria? It wouldn't be possible would it.

By making even 12th, out of 12 no worse than average.

 

Also, as the rag and stick brigade have totally different requirements, of a prop, than narrow boats (get the boat home when there's no wind, moving about in moorings and minimising drag, when the sails are out) it really isn't a worthwhile test, for canal users.

 

I bet the winners were feathering props.

[ChrisPy]

a bit like the "University of St. Andrews" scenario, Gibbo :

Having a historical interest in UofStA as an alumnus please enlighten me - what was all that about?

[ChrisPy]

Here is some propellor PSB - please note I have nothing to do with Axiom but in my job I come accross fluid flow a lot and use of comupational fluid modelling and I am just thinking out loud here.

 

In an ideal world, you want all the water leaving the propellor to be travelling perfectly backwards, but in reality the jet exiting the propellor will have some spiral action and will also have some sideways motion so the jet is in the fom of a cone. If you go to the extent of a really bad propellor, mst of the water ejected from the propellor flows sideways away from the propellor in a disc of moving water rather than flowing backwards. The prop is still demanding lots of power to move lots of water about but the boat is not going anywhere. The prop has to suck this water in from somewhere, so it creates a suction in front of the propellor and the boat squats down. A more efficient propellor, but reducing the amount of "wasted flow" may be able to generate more forward thrust from the same shaft power whilst actually moving less water about, because what it does move it moves efficiently and usefully. Therefore, the boat squats less because the propellor is moving less water.

 

As I said PSB but it sounds good and it may have some grain or nugget of truth in it.

I can actually live with most of that PSB.

 

We can assume that the ideal prop thrust is a parallel jet of non-rotating water. A smaller, faster rotating prop probably has less tendency to twist the water stream. A duct or nozzle will discourage sideways flow away from the periieter of the prop.

 

The conventional design of standard propellors is common for most "displacement-speed" vessels including leisure craft, fishing boats, traditional cargo vessels, tugs and ships. That design is unlikely to be ideal for narrowboats which have peculiar operating requirements. We are not too concerned about efficiency per se, but we are concerned about limiting wash in shallow and narrow channels at optimum speeds. It might be interesting to test how a ducted propellor (in a tunnel or jet tube or in a nozzle, as used on modern tugs) would work on a narrowboat.

 

What seems to set the axiom apart is that the blades are not twisted, so that the pitch actually increases with the distance from the hub. The obvious consequence is that the tube of water leaving the prop is travelling faster on the outside and slower on the inside. Maybe that in some way achieves the PSB criteria?

 

I thought that type of technology died with Brunel, but obviously not. Maybe he was actually the Leonardo of his age.

[Arnot]

Are you implying the that Smartgauge is magic and Gibbo a wizard? Well I suppose he is an elektrickery wizard at least.

 

"Any sufficiently advanced magic is indistinguishable from technology." (Terry Pratchett)

 

Seriously though, I look forward to hearing what gibbo has to say when he has tried the Axiom.

 

Although he has no axe to grind, I'm sure it will be goodly sharp if necessary!

 

Regards

 

Arnot

 

PS for those who want their mind boggled, can I reccomend the "Propeller Handbook" by Dave Gerr, it explains quite a lot and revises your maths at the same time.

[PaulG]

Having a historical interest in UofStA as an alumnus please enlighten me - what was all that about?

 

See this thread for enlightenment!

[ChrisPy]

See this thread for enlightenment!

blimey!

when I was there our prof of civil engineering was making studies of non-uniform fluids, using ................. wait for it .................. blood as the test medium.

[Gibbo]

"Any sufficiently advanced magic is indistinguishable from technology." (Terry Pratchett)

 

No matter how many times I looked at that I still thought you'd written it the other way round and attributed it to the wrong man.

 

Gibbo

[WotEver]

No matter how many times I looked at that I still thought you'd written it the other way round and attributed it to the wrong man.

 

Gibbo

 

Don't forget ACC's fourth law - "For every expert there is an equal and opposite expert." Very pertninent to many threads on here

[Chertsey]

Remember the resounding slagging off and accusations of "snake oil" that the new Axiom propellor got on here from loads of people who'd never seen or tried one?

 

Anyone seen the test results in the May issue of Yatching Monthly? It came in rather well. They thought it was quite good overall. In fact, very good. Apparently the reverse power was extremely good. It got 3rd position out of about 12 on this point (IIRC - I was in the waiting room at hozzie whilst reading it so didn't get chance for a full read).

 

Gibbo

Even though it would appear to be superseded by many of the subsequent posts I will still make the comment that there is no contradiction between being skeptical of something before it is proven and changing your position on seeing evidence.

(Whether there is actually persuasive evidence in this case is clearly a different matter and one into which I will not venture)

[David Schweizer]

Even though it would appear to be superseded by many of the subsequent posts I will still make the comment that there is no contradiction between being skeptical of something before it is proven and changing your position on seeing evidence.

(Whether there is actually persuasive evidence in this case is clearly a different matter and one into which I will not venture)

Agreed. At the moment I am still sceptical, and the tests I have read so far have failed to persuade me that this new prop is a significant improvement on conventional props, and certainly not worth the money. If someone conducts a comprehnsive verified test which has some degree of technical competance, I could be persuaded if it is demonstrated that it gives superior performance, but will I buy one? I doubt it.

[sbillis]

You are all overlooking the fact that Brunel appears to have had the idea first. Check out the propeller fitted to the SS Great Britain and now preserved in Bristol. There are many pictures on varoius web sites.

 

Simon

nb Bulrush