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Gearbox ratio and propeller pitch


IanD

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I have been using and maintaining Lister diesel engines on & off for over 55 years and I do not know it all and re the HR2M I am learning its foibles.

 

Ed If fact I know very little about engines

No-one knows it all, but some know less than others and are patently slow learners!

 

I learnt most of what I know by listening to other people, rather than by sticking my fingers in my ears and going "blah blah blah".

Edited by nicknorman
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Sorry gents/ladies, there are reasons for my post re nicknorman, he appears to make it his business to criticise my posts and has I have good reason to believe attempted to get me remove from the forum or sanction, he appears to have encouraged other to do the same hence my use of the word cohorts.

 

I have asked Admin to split the thread as it is away from the OP's original post

 

I thank you for your posts and i would regret but understand if you do not post further

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I don't have any photos to hand unfortunately. The governor is in the gear casing between the engine and the gearbox and has a lever and rod connected to the fuel pump rack. The speed control connects to a spring that pulls on the rack

 

Richard

 

If my grey cell is working setting X on the throttle (speed control) will produce Y rpm.

 

As the prop is RPM sensitive and its output is related; then for the aim of the test the actual MPH of the hull will indicate a greater or lower thrust between the original and the new. ed All other conditions being equal

Edited by Graham.m
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If my grey cell is working setting X on the throttle (speed control) will produce Y rpm..

 

Up to the maximum power of the engine, yes. And depending on the load, the engine will use more or less fuel - this is what the governor is doing

 

Richard

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Up to the maximum power of the engine, yes. And depending on the load, the engine will use more or less fuel - this is what the governor is doing

 

Richard

 

Thanks Richard that is what I thought would happen when I muted the test. Fuel efficiency is not the measure for the test thrust is. The forward thrust of the new prop has been reasonably queried because of the shape of the rear of the blades. I happen to have the figures for the old prop and just wish to compare the two forward thrusts. Not sure what it will tell me in the end smile.png the real test would be the new against another with the new front profile but a stand rear profile, not likely to happen.

Edited by Graham.m
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Sorry gents/ladies, there are reasons for my post re nicknorman, he appears to make it his business to criticise my posts and has I have good reason to believe attempted to get me remove from the forum or sanction, he appears to have encouraged other to do the same hence my use of the word cohorts.

 

I've just spent the last 10 mins composing a long PM to you regarding your comment about me attempting to get you removed from the forum - which is something I absolutely refute by the way, although there is more to it than that. However I was unable to send the PM as you have blocked me. Please would you un-block at least so I can send you this one message, I think (hope) it would help the situation.
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I have nothing to add to the conversation but I am enjoying a fascinating discussion. I'm looking forward to Graham's "sea trials" and hope they will demonstrate just how different the Axiom is.

 

I trust you'll be conducting tests in reverse as well as forward Graham biggrin.png

 

Welcome, I have already done a couple of small tests astern smile.png It is going to take some getting used to, with all the cautioning about being gentle I mucked up reversing into my berth, something I normally do with reasonable success, but the wind was not being kind either. Where I would have given a burst of full astern I was being very tentative. Also I reversed her a couple of hundred metres at the boat yard no wind and gently, she went straight and seemed to respond to the tiller. But I need to get somewhere with no boats so I can see what will happen if I open the throttle astern smile.png

 

And yes they astern test will get reported. I will take some months thought :)

Edited by Graham.m
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If my grey cell is working setting X on the throttle (speed control) will produce Y rpm.

 

As the prop is RPM sensitive and its output is related; then for the aim of the test the actual MPH of the hull will indicate a greater or lower thrust between the original and the new. ed All other conditions being equal

Graham, this only work with one propeller, if you test two different propellers, at the same rpm to see the speed at that point, the speed is the resulting thrust power, if the engine turn out more or less power you will not see, unless you get the same max rpm at WOT or WOP wide open pump :-) and measure the speed at that point, if the power lever gave set power or fuel delivery, it would work, if you test two different propellers at partial throttle at specific rpm, you see the result of pitch in first hand and efficiency in other hand. but will not be able to measure efficiency with out a torque meter or a fuel flow meter.

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Graham, this only work with one propeller, if you test two different propellers, at the same rpm to see the speed at that point, the speed is the resulting thrust power, if the engine turn out more or less power you will not see, unless you get the same max rpm at WOT or WOP wide open pump :-) and measure the speed at that point, if the power lever gave set power or fuel delivery, it would work, if you test two different propellers at partial throttle at specific rpm, you see the result of pitch in first hand and efficiency in other hand. but will not be able to measure efficiency with out a torque meter or a fuel flow meter.

 

I agree, the object of the test in my mind is to see if at X rpm the props give as expected different thrusts ( speeds) to see if there is a marked difference. Now if what I am understanding is correct the throttle (speed stick) can be viewed as an RPM setter. Thus from initial tests, not carefully set-up, the indication is the new prop is giving the same thrust (speed) as the old at the same throttle setting (rpm?), the engine response indicates (noise) that it is doing it at a lighter load as the engine is running more freely.

 

Now the real test will be when I can measure rpm whilst doing the test and see if the engine is actually running at the rpm the throttle setting suggests.

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As I travel along the T&M my speed can vary by three quarters of a MPH without touching the speed wheel.

Yes that is one of the problems. Luckily I have a stretch of good water not far from where I moor. As the nearest winding hole is 1/2 hour away it will be do test 1, reverse, test 2 reverse etc then winding hole repeat the other way. So the astern will get a good test as well.

 

Thanks for the thought

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To conduct this comparison test with extreme accuracy Graham.m will need a canoe sterned boat like an old a ships lifeboat, identical at both ends, with two power plants and transmissions at each end of the boat, identical engines in identical states of tune, identical gearboxes, identical shaft resistances, with his old propeller on one end and the Axiom prop on tother. All manner of tests and fun could be had. With identical throttle openings and both in fore gear a tug of war between the two props could be conducted to try and bust the boat apart, and also both engines In astern gear in an attempt to squeeze the boat and shorten its length. Prop thrust comparison tests in all directions could be conducted by tethering the boat to the bank with string and a spring balance between. All tests would need to be conducted in perfectly calm conditions '-0 on the Beaufort scale', in perfectly still water of equal depth for both props and equal distance from the bank. It is of paramount importance that all these tests are carried out at night under the balmy light of a full moon in the early hours of the misty morn of April 1st between the hours of 12.01am and 2.03.1/2 am. Hope this helps.closedeyes.gif

 

I have included a deliberate mistake.

Edited by bizzard
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To conduct this comparison test with extreme accuracy Graham.m will need a canoe sterned boat like an old a ships lifeboat, identical at both ends, with two power plants and transmissions at each end of the boat, identical engines in identical states of tune, identical gearboxes, identical shaft resistances, with his old propeller on one end and the Axiom prop on tother. All manner of tests and fun could be had. With identical throttle openings and both in fore gear a tug of war between the two props could be conducted to try and bust the boat apart, and also both engines In astern gear in an attempt to squeeze the boat and shorten its length. Prop thrust comparison tests in all directions could be conducted by tethering the boat to the bank with string and a spring balance between. All tests would need to be conducted in perfectly calm conditions '-0 on the Beaufort scale', in perfectly still water of equal depth for both props and equal distance from the bank. It is of paramount importance that all these tests are carried out at night under the balmy light of a full moon in the early hours of the misty morn of April 1st between the hours of 12.01am and 2.03.1/2 am. Hope this helps.closedeyes.gif

 

I have included a deliberate mistake.

This is a serious discussion, no room for muckin' about...

I have included a deliberate mistake.

Different drag of each prop when they are idling?

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I once read this true account on the back page of the Beezer comic, that the ship Great Britain which is now in dock in Bristol had it's propeller fall off in mid Atlantic whilst on its way to Australia. It hove to whilst the ships carpenter constructed an new wooden one. This was lowered over the stern on a tackle with men swimming, diving and gamboling about in the water from a ships boat, struggled to fix it on. This splendid effort took over a week or two to complete and apparently there was not much difference in performance between the original iron prop and the wooden one.


Forward and reverse gear selection wrong way round.

Not sure, kindly explain more fully please. Don't forget this is a serious thread so we must be exact.

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To conduct this comparison test

 

:) Think you have miss the main point of the tests :)

 

The real way truly would be to use Durham University's water tunnel

I once read this true account on the back page of the

 

The earliest practical prop I can find record of was a wooden, which performed well and lasted quite a while

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I don't yet understand what you are.aiming to gain with your comments about fuel flow and engine speed.

 

Obviously at a fixed engine speed and load there will be a given fuel flow, and with a prop on the shaft, a thrust.

 

The issue is however with an alternate prop that does not allow any comparable data.

 

It would make much more sense to adjust the engine speed to give a certain thrust (either measuring static pull, or speed over a known stretch and or open water) and measure the fuel flow at that point, perhaps repeating at a number of thrust values.

 

Recording the engine speed would allow that to be included in the results, but is largely erroneous in terms of boat performance, unless perhaps there was an issue with nvh/noise at certain rpm.

 

Daniel

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I am sorry you do not understand. Your post confuses/puzzles me so if you could explain I will hopefully be able to explain

 

You write "Obviously at a fixed engine speed and load there will be a given fuel flow, and with a prop on the shaft, a thrust." Now that puzzles me, could you explain what you mean as posts from Dalslandia and RLWP suggests that the fuel flow is not control by the shall we say throttle, that controls the governor which controls the engine RPM and will vary the fuel feed dependant on load. My understanding is that load could be affected by variations in a number of things, possibly even the amount of suspended solids in the water, the depth etc. However perhaps they were wrong.

 

Your write "It would make much more sense to adjust the engine speed to give a certain thrust (either measuring static pull, or speed over a known stretch and or open water) and measure the fuel flow at that point, perhaps repeating at a number of thrust values." I am sorry fuel use is not one of the objectives of the tests. I think you have misunderstood, Perhaps I am misunderstanding.

 

You write "Recording the engine speed would allow that to be included in the results, but is largely erroneous in terms of boat performance, unless perhaps there was an issue with nvh/noise at certain rpm." I am trying to understand what you mean here bearing in mind the objective of the test is to test how prop X is pushing the boat through the water on this particular boat. As I understand it the rate of rotation is directly related to the thrust the propeller produces and to the speed the vessel attains. Therefore surely it is relevant where the output of a propeller is being tested to see what speed will be attained at certain RPM? Also how is engine RPM erroneous in terms of boat performance, in this case speed?

 

 

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Daniel did say "Obviously at a fixed engine speed and load there will be a given fuel flow, and with a prop on the shaft, a thrust."

 

When comparing propellors, a plot of engine speed with water speed probably won't give much useful information. (I'd expect the greater pitch prop. to give a greater water speed in all cases in which the desired engine speed can be reached.)

 

I think Daniel is suggesting plotting fuel consumption against bollard pull.

 

Basically, there are too many variables!

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Daniel did say "Obviously at a fixed engine speed and load there will be a given fuel flow, and with a prop on the shaft, a thrust."

 

When comparing propellors, a plot of engine speed with water speed probably won't give much useful information. (I'd expect the greater pitch prop. to give a greater water speed in all cases in which the desired engine speed can be reached.)

 

I think Daniel is suggesting plotting fuel consumption against bollard pull.

 

Basically, there are too many variables!

 

Thank you Iain. There are so many variables that in the end the only true way to test the prop is in a water-tunnel where all the variables can be contained. However that does not take account of how the prop handle/deals with the way the water flows around the hull in both deep water and shallow. As for the bollard pull while it is very spectacular with white water flying everywhere how does that show how the prop performs in a flowing stream of water as it moves the boat through the water. Additionally they are invariably performed in shallow water where the prop finds it difficult to pull water from under the hull, in fact I believe spectacular and fun but not allowing the prop to perform as it should do.

 

The starting point for these test is that I have figures and information from tests done with the old prop. So to compare to those figures the tests need to be done the same way in as near as I can the same conditions.

 

There is no way these test can come up with scientific figures, there is not the test equipments available nor the time and money. The aim is to see on the water if the new prop performs equally or better when compared with the old and does it meet the speed parameters given to Axiom as part of the design criteria.

 

Simply overall is the boat better for having it or worse.

 

Now maybe some will say that is not good enough or he is wasting his time. I have no wish to be a purist, I spent too much of my time in labs measuring and testing to the nth degree , this is a leisure pastime a hobby even for pleasure. Sorry I am getting feed up with hole pickers not that I think you are smile.png

Edited by Graham.m
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Daniel did say "Obviously at a fixed engine speed and load there will be a given fuel flow, and with a prop on the shaft, a thrust."

 

When comparing propellers, a plot of engine speed with water speed probably won't give much useful information.

 

I think Daniel is suggesting plotting fuel consumption against bollard pull [or speed over known/repeatable stretch].

 

 

Basically that.

 

Daniel

 

 

 

There are so many variables that in the end the only true way to test the prop is in a water-tunnel where all the variables can be contained. However that does not take account of how the prop handle/deals with the way the water flows around the hull in both deep water and shallow.

 

Some laboratory testing would be fantastic if you could get the time on the equipment, and enough time to work out and then validate some reasonable assumptions/simplifications/scaling. It would perhaps even work out cheaper, depending on what level of equipment you deemed suitable, and if you could get a good price on drydock/slip/cranage.

 

You could (would) model the hull as part of the test, assuming that was the aim, as well as modeling the floor of the canal, and or water surface. You do the whole lot full scale in a large hydrodynamic testing pool if someone would lend you one.....

 

Bollard pull would be very crude, and highly unlikely to be meaning full below a slow cruising speed of say 2mph. However a lot of boats spend a lot of time a 2mph, including most of the time you are maneuvering, as which point there would be no 'white water' anywhere to be seen. Certainly I agree that if you where aiming to test performance representative of a 4-5mph hull speed using a static test would be meaningless.

 

 

Daniel

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