Axiom Propeller

[John C]

I recall seeing on Axiom's website reference to testing done at some eminent institution, (just had a quick look, could'nt find the ref.), publishing that could answer the critcs.

 

In a previous thread I mentioned that props are usually efficient in one direction (rotation), nowhere near as good in the other. I speculated that the forward efficiency was sacrificed a little for better reverse performance, this may account for slightly less forward performance the original poster experienced rather than over propping.

 

The suggestion that the water seems to be less disturbed by movement of the boat, (less wake?), how can the prop have an effect on this? Regardless of type of prop the hull will always displace a mass of water equal to its own, or slightly more as it moves through the water.

 

This argument will only be settled when a set of carefully controlled, repeatable experiments are carried out and results etc. published. If the results are good everyone will buy one the price will come down and I might even be tempted to buy one.

[jonk]

I recall seeing on Axiom's website reference to testing done at some eminent institution, (just had a quick look, could'nt find the ref.), publishing that could answer the critcs.

 

In a previous thread I mentioned that props are usually efficient in one direction (rotation), nowhere near as good in the other. I speculated that the forward efficiency was sacrificed a little for better reverse performance, this may account for slightly less forward performance the original poster experienced rather than over propping.

 

The suggestion that the water seems to be less disturbed by movement of the boat, (less wake?), how can the prop have an effect on this? Regardless of type of prop the hull will always displace a mass of water equal to its own, or slightly more as it moves through the water.

 

This argument will only be settled when a set of carefully controlled, repeatable experiments are carried out and results etc. published. If the results are good everyone will buy one the price will come down and I might even be tempted to buy one.

 

I'm not sure but isn't the total disturbance a combination of bow wave and rear confluence of displaced water plus prop turbulence? If so then could it be that different props have different affects on the shape of the rear disturbance 'waves'? As I say, I'm not sure, but several people have now noted that there IS a difference when using a different prop. - could just be that the new one is better matched though I suppose!

 

John

[WJM]

Doesn't a horse-towed butty make less wash than a motor? The act of throwing water backwards to create forward propulsion adds to the water disturbance. The axiom possibly moves that water more efficiently - throwing less, or throwing more cleanly with greater efficiency.

Edited April 28, 2011 by WJM

[John C]

Hull shape has a big effect on this hence all the research that has been done on hull shape for narrow channels rather than prop design.

 

Slowing down (passing moored boats) reduces water disturbance to a greater or lesser degree, a good way compare hull design. I suspect that reducing prop speed will have alot less effect hence the need to slow down before passing moored boats, not going to tickover as your bow aligns with the bow/stern of the moored boat.

[carlt]

 

What I'm hearing over and over again is "I don't understand how it works, therefore I conclude that it can't" which is an utterly ridiculous attitude.

I understand how it works (materials engineer) but don't understand how it works any better than a properly balanced, high quality, conventional prop.

 

I imagine, if the idea takes off, there will be 'run of the mill' axiom type props providing no advantage, whatsoever, over 'run of the mill' conventional type props and 'top of the range' axiom type props providing no advantage, whatsoever, over 'top of the range' conventional type props.

 

There seems to be some problems with Axiom matching their props to boats, making me wonder if they actually know what they're doing....I may be more impressed if Crowthers produce an Axiom type prop, compare it to one of their own and say it is a step forward, in prop development.

[bottle]

As a totally non qualified person,

 

The Axiom is as good in forward as it is in reverse but to allow this to happen it is not as good in forward as a 'properly designed' normal prop.

 

I know of one boat that had an Axiom, (one of the first) that has had a mark two version fitted, (tweaked design I believe) reason the manufacturer wanted to use the original for display purposes.

 

They were pleased with the first one and first thoughts are that the Mk2 is better.

 

I will still be fitting a Crowther High efficiency prop, when I can afford it.

[Phoenix_V]

I bought a copy of the Yachting Monthly tests, this was mainly looking at folding props butthey did include an axiom and a standard prop.

 

The Axiom did well astern bollard pull 181kg against 173kg standard stopping in 7.7 against 9.3 seconds

propwalk was good too at 9.3% against 13.9%

 

However ahead max speed was 7.1 knots against 7.5 on the standard bollard pull 233kg against 264kg standard

 

I have asked Axiom about this and they say that the competition was overpropped and if they had overpropped they would have done better ahead.

So inconclusive here.

 

Most of the information out there is either very technical or way to simplistic, I have just about got my head around propeller diameter and pitch sizing but propeller area calculations elude me. However I wonder if on our boats often the problem is not propeller area. As I understand it the area of the blades does not matter a lot until you get to the point where you are putting more power in than a given area can cope with and the prop cavitates. This would explain why 2 props of nominally same diameter and pitch perform differently if one has a lower area and fails to take the power?

 

The prop suppliers I have asked to quote me have been unforthcoming on this point I suspect most have a limited range of prop sizes and sell what they have rather than what you need, Crowther have a good reputation but the term "high efficiency" does not seem very specific.

Edited May 2, 2011 by Phoenix_V

[nb Innisfree]

Crowther have a good reputation but the term "high efficiency" does not seem very specific.

 

IMO for "high efficiency" read "correctly sized" Crowthers have a reputation for calculating and manufacturing an optimum sized prop. That's all, no mystique, just experience and an understanding of the basic principles.

[Timleech]

I bought a copy of the Yachting Monthly tests, this was mainly looking at folding props butthey did include an axiom and a standard prop.

 

The Axiom did well astern bollard pull 181kg against 173kg standard stopping in 7.7 against 9.3 seconds

propwalk was good too at 9.3% against 13.9%

 

However ahead max speed was 7.1 knots against 7.5 on the standard bollard pull 233kg against 264kg standard

 

I have asked Axiom about this and they say that the competition was overpropped and if they had overpropped they would have done better ahead.

So inconclusive here.

 

 

 

That doesn't sound right to me. If the competition was overpropped they would get less rpm & less power, my non-expert guess is that it's the other way round and the Axiom was slightly oversize, which might also help them with the reverse pull and stopping because props never seem to transmit full power going astern. I can well believe the Axiom would win astern anyway because the design is more symmetrical than many conventional props.

 

Tim

Edited May 2, 2011 by Timleech

[jonk]

Now that the season is coming to a close, has anyone any experience(s) to add about Axiom props?

 

John

[alan_fincher]

Now that the season is coming to a close, has anyone any experience(s) to add about Axiom props?

 

Fishing season ?

 

Hunting season ?

 

Festive season ?

 

???????????????????

[Theo]

Hmmm

 

I don't thihk I read that blog the same way others might. It seems very confused within itself and the timing of events seems to jump backwards and forwards...

 

They had an Axiom on and were happy.

 

They had a new gearbox fitted, the boat started making noises.

 

They then could no longer duplicate this fault.

 

So they removed the Axiom prop.

 

I think someone might have some diagnostics issues.

 

ISTR that you fitted an Axiom, Gibbo. Or am I misremembering?

 

Doesn't a horse-towed butty make less wash than a motor? The act of throwing water backwards to create forward propulsion adds to the water disturbance. The axiom possibly moves that water more efficiently - throwing less, or throwing more cleanly with greater efficiency.

 

A better prop can't throw less water unless it throws it faster. The forward force comes from the rate of change of momentum of the water being thrown back by the propeller.

 

N

[jonk]

Fishing season ?

 

Hunting season ?

 

Festive season ?

 

???????????????????

 

Silly season of course

 

John

[carlt]

ISTR that you fitted an Axiom, Gibbo. Or am I misremembering?

 

Gibbo hasn't posted here since the "Edit out my mucky joke and I won't post here ever again." incident. .

[mickeyduff]

Can anyone give a price of an Axiom?? as you have to send a query to get any on their site

[David Mack]

Can anyone give a price of an Axiom?? as you have to send a query to get any on their site

"If you have to ask, you can't afford it."

 

Attributed to JP Morgan who apparently said this in response to a question about the cost of owning a yacht. So quite on-topic really!

 

David

Edited October 11, 2011 by David Mack

[mickeyduff]

"If you have to ask, you can't afford it."

 

Attributed to JP Morgan who apparently said this in response to a question about the cost of owning a yacht. So quite on-topic really!

 

David

 

just found out, about £870 for my boat/engine, alot more go's into it then replacing like for like.

 

Crowther about £430

Edited October 11, 2011 by mickeyduff

[rgesner]

I agree that it's probably overpropped, I've always suspected that some of Axiom's claims might be down to a slight overpropping. However a properly set up engine/fuel pump/governor shouldn't 'keep banging fuel in and run black', it should just 'run out of steam' and develop no more revs which is pretty much what has been described.

 

Tim

The practical Sailor magazine test (which are now reproduced on Axiom's web site) provide unbiased evidence that their claims are pretty well substantiated.

[bottle]

Of course it does and that is why Axiom posted it.

 

I doubt they Axiom, would have put it on their site if it said it was crap.

 

ps. they have changed their claims from when the Axiom prop first appeared.

 

Welcome to the forum and have a nice day.

[MtB]

The practical Sailor magazine test (which are now reproduced on Axiom's web site) provide unbiased evidence that their claims are pretty well substantiated.

 

 

And how much advertising do Axiom place in "Practical Sailor"?

 

It's a bit ironic that the 'engine boat' mags fail to publish any good reviews or tests, and it's a sailing mag finally comes up with something positive to say about axiom blades!

 

 

MtB

[Tony Brooks]

Actually WWW came up with SOMETHING positive when they tested the thing. It was the test procedure that was questioned by me and others.

[bizzard]

Actually WWW came up with SOMETHING positive when they tested the thing. It was the test procedure that was questioned by me and others.

What did they do? Carry out a bollard draw bar thrust test using Mr Crowther as the drawbar.

[Tony Brooks]

What did they do? Carry out a bollard draw bar thrust test using Mr Crowther as the drawbar.

 

Had two Alverchurch or Black Prince hire boats and put an Axiom on one and then ran them up and down the cut to assess the claims made. I can not remember if they swapped them over and repeated the comparison. From the article I could see no reference to checking the original non-Axiom prop was actually the correct one for the boat.

 

They (Axiom) now quote draw bar pull tests from a University, Southampton I think.

[dmr]

One reason for the popularity of the notorious Elecsol Batteries was a very positive test review in a caravan magazine (where Elecsol also placed adverts). When a number of complaints were received about Elecsols I believe the magazine admitted that their "test" consisted of reading the publicity material that Elecsol supplied.

 

However I have not seen the Practical Sailor article

 

 

.............Dave

[flatplane8]

I've heard some good reports from someone in our boatyard who has fitted one to wide beam. This was after several conventional props gave them problems. They are expensive, party as they are small/custom production runs, rather than modifying a more standard base prop.

 

I did consider one, then went with a conventional 4 bladed prop from FAL propellers in Scotland. Although it's a bit better all round than our last one, we still have a lot of prop walk and not such great performance astern. So I may revisit axiom props one day If I can get better astern performance.