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Axiom - Oh Dear...

matty40s

By matty40s
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matty40s Veteran II

matty40s

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hard to believe. have you seen their test results, including the conditions of the test?

I havn't, the owner of the old and incorrect new prop has though. Apparently it's done with smoke and mirrors to replicate the water flow. The Crowther was 40/15, Axion claim 50/50 for their design. I will keep you posted as the new prop goes on and gets tested.

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Dalslandia Rising Star

Dalslandia

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Theodore Theodorsen, https://en.wikipedia.org/wiki/Theodore_Theodorsen made a great work on propellers, during his work, based on others, he extended there work and made it more practical.

 

it calculate what happen far behind the propeller, calculating the optimal efficiency, that can be had at that speed, rpm and power, different curves for different Nr of blades, to that the drag of the blades them self is withdrawn, and the optimal propeller is had, this prop is then adjusted for the wake in front of or behind a body.

 

Not that hard to do.


I havn't, the owner of the old and incorrect new prop has though. Apparently it's done with smoke and mirrors to replicate the water flow. The Crowther was 40/15, Axion claim 50/50 for their design. I will keep you posted as the new prop goes on and gets tested.

 

was does props of same diameter, pitch and blade area? how can they simulate cavitation in thin air?

Edited by Dalslandia
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Geo Rising Star

Geo

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All I can say about the Axiom astern; is that on a windy day having full controllable power astern is very handy and the low propwalk makes close quarters maneuvering a lot easier and safer. Rather than having to use a lot of power to get 15% power astern and the stern walking off to one side or the other..

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Dalslandia Rising Star

Dalslandia

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For those interested of real world tests, http://flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

 

we can see that the standard fixed blade fixed pitch propeller did go 7.5 kts, the fastest was the flexofold with 7.65 so the std prop was probably not optimal.

having 94% Thrust HP (shaft HP * efficiency)

 

The moixa doing 7.1 kts having 84,8% THP of the Std. and 79,9% THP of the best of the tested.

 

In the forward bollard pull test. (2.6:1 gear ratio)

the flexofold and Std pulled 270 and 264 kg, std doing 98% of flexofold

the moixa 213 kg 80,7 -78,9% of the std and flexofold

 

In reverse (3.0:1 gear ratio)

the Moixa pulled 181 kg and the standard 173 kg, here the moixa was 4,6% better.

 

so 4.6% better in astern pull test, but the std was 23,9% better in forward pull.

SO, the std 3 blade don't lost to much in reverse, but the gain in forward is large, and how much time is spent in reverse compered to forward?

 

The Axiom had the shortest stopping time from 6 kts

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Dalslandia Rising Star

Dalslandia

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Surely you mean the Moixa had the shortest stopping time from 6 kts.

 

The prices of some of the propellers on test is an eye opener. We seem to get off quite lightly compared with the salty water boys and girls.

 

Surely you mean the Moixa had the shortest stopping time from 6 kts.

 

The prices of some of the propellers on test is an eye opener. We seem to get off quite lightly compared with the salty water boys and girls.

 

Moixa yes but this was in reverse

 

Those folding and feathering props is expensive, and not a good chose in a canal, it will do an knot or so when sailing if the blade fold away. at least for those with sailboats that know how to rise the sails, and use the wind. not all sailboat users do!

Edited by Dalslandia
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PaulG Experienced

PaulG

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For those interested of real world tests, http://flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

 

we can see that the standard fixed blade fixed pitch propeller did go 7.5 kts, the fastest was the flexofold with 7.65 so the std prop was probably not optimal.

having 94% Thrust HP (shaft HP * efficiency)

 

The moixa doing 7.1 kts having 84,8% THP of the Std. and 79,9% THP of the best of the tested.

 

In the forward bollard pull test. (2.6:1 gear ratio)

the flexofold and Std pulled 270 and 264 kg, std doing 98% of flexofold

the moixa 213 kg 80,7 -78,9% of the std and flexofold

 

In reverse (3.0:1 gear ratio)

the Moixa pulled 181 kg and the standard 173 kg, here the moixa was 4,6% better.

 

so 4.6% better in astern pull test, but the std was 23,9% better in forward pull.

SO, the std 3 blade don't lost to much in reverse, but the gain in forward is large, and how much time is spent in reverse compered to forward?

 

The Axiom had the shortest stopping time from 6 kts

Interesting.

My interpretation of the test results is that the Axiom works better in reverse, which is what you might expect given the symmetrical nature of the design.

However, this appears to be at the expense of forward performance.

In the "bollard pull" test, the standard 38 prop gave a pull of 264 Kg, and the Axiom was 57 Kg less, at 213 Kg.

 

A quck calculation that I ususally get wrong tells me that's about 22% less power.

 

This is seen in the speed tests, where the standard 38 prop produced 7.5 knots and the Axiom 7.10.

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mrsmelly Veteran II

mrsmellyDonate to Canal World

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Interesting.

My interpretation of the test results is that the Axiom works better in reverse, which is what you might expect given the symmetrical nature of the design.

However, this appears to be at the expense of forward performance.

In the "bollard pull" test, the standard 38 prop gave a pull of 264 Kg, and the Axiom was 57 Kg less, at 213 Kg.

 

A quck calculation that I ususally get wrong tells me that's about 22% less power.

 

This is seen in the speed tests, where the standard 38 prop produced 7.5 knots and the Axiom 7.10.

 

Correct. My bro in law said his boat stopped better with the axiom BUT the main reason he changed it was for what he does most and that is going forward and for that it was not so good hence the recent crowther.

 

Tim

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Dalslandia Rising Star

Dalslandia

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Interesting.

My interpretation of the test results is that the Axiom works better in reverse, which is what you might expect given the symmetrical nature of the design.

However, this appears to be at the expense of forward performance.

In the "bollard pull" test, the standard 38 prop gave a pull of 264 Kg, and the Axiom was 57 Kg less, at 213 Kg.

 

A quck calculation that I ususally get wrong tells me that's about 22% less power.

 

This is seen in the speed tests, where the standard 38 prop produced 7.5 knots and the Axiom 7.10.

 

What the paper don't tell us fully is what rpm was reached on the full speed test, so I don't say that or that propeller is so many % better, but the net thrust power.

the one with highest bollard pull have the highest speed, it don't have to be so, but in this case going forward it is so. it is not a fast boat anyway.

 

but fact is going 7.5 kts takes 17,9 % more thrust power, (THP) and 7,65 kts instead of 7.1 takes 25% more thrust power.

Is there any evidence to support the claim about prop walk?

 

yes they measured that in the test too. that's correct

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j04n Collaborator

j04n

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Yes, that one looks totally different to one we had fitted in 2011. The boat did seem to stop better, but felt she was over propped as when we got on a river we could only make about 1900 PRM flat out with a Vetus 42.

Bob

So its your fault the rest of us are now having to suffer under propping! wink.png

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