electric boat propeller

[Exatem]

I will be pessimistic but I see several complications.
I try to explain why reconnecting to my previous post of "over and under the waves".

the resistance to the motion of a boat depends essentially on two causes, regardless of type or size.
- friction resistance caused by water friction against the surface of the hull and dependent on the number of reynolds.
- wave resistance generated by surface waves.
to these factors then they associate other less influential.
It is worth noting that friction resistance increases as speed increases, therefore it is necessary to seek for the required displacement and the desired speed, the forms of hull that will lead to the least waste of power.
the forms that the carena can assume are basically two, round or corner.
the round hull, called “dislocating”, with the increase of the speed reaches a wave resistance greater than that of friction and is therefore preferable for medium/low speed (sailing boat case).
the edge hull called “planant”, reached a certain speed has a resistance of friction that exceeds the wave.
there is then a third option given by the hull “semiplanante” or “semidislocante” also called “deep-v” but that at us now does not interest.
as already mentioned, the resistances to the motion are also dependent on the wave resistance that is given by the difference between the pressures in the prodier zone directed from prora to stern and the pressures of the poppiera zone that have resulted opposite.
the wave resistance of a ship depends on the speed, length, shape of the hull, i.e. the angle of penetration of the water lines, the distribution of the volume in the longitudinal sense.
with the name of "resisting resistance" means the sum between the wave resistance (indicated with rw) and the resistance of skiing or resistance of the vortices, resulting in the formation of vortices created by the famine itself and the "appendici". (indicated with rv).
the "exhaust appendixes" are: the thymones, the propellers, the roll fins and, in general, all the components of the ship immersed in the water but external to the hull that cause an additional resistance to advancement.
to determine the total resistance to rt advancement (which is not possible despite the continuous studies in the matter mathematically compute for the many and complex variables in play), we use experimental methods through the "shipping ship".
the total resistance of a scale model that meets in progress (this measurements are repeated for various speeds, so as to obtain diagrams in which the resistance is represented according to speed).
with the data thus obtained, the friction resistance of the model is calculated at various speeds.
the friction resistance, thus calculated, is subtracted from the total resistance of the model measured with the tests of trailer obtaining in this way the residual resistance of the model.
the data thus obtained are related to the real ship using the principles of mechanical similarities.
It is shown that, obtaining the relationship between the length of the real ship (ln) and the length of the model (lm) the residual resistance of the ship to the true (rrn) is obtained by multiplying the residual resistance of the model (rrm) by that high ratio to the cube.
the friction resistance of the ship is calculated in natural size (rf). the total resistance of the ship is given by the sum of the resistors so calculated.
residual resistance, above a certain speed, is above all wave resistance (rw), modest to low ranges but, which varies with the cube of speed.
the rw can be reduced by applying to the prora of the ship an appendix called "bulb", which assumes different forms, depending on the type of ship to which it is applied.

the only way to reduce the resistance value of vortices is to limit the number of famine appendixes, to draw them so that they are as far as possible hydrodynamic.

Therefore, I return to repeat, the big problem is the efficiency of a system that is born already penalized by the nautical characteristics of the hull itself.
a sailboat, equipped with drift, will significantly disturb the flow that invests the generator penalizing it further.
I'm not talking about worsening the maximum speed of the boat, but the efficiency of the generator.

 

[rbaffigo]

but I am warning a gadget that could potentially pull me out 2 kw, even if it had to make only 1 kw no matter is always so much compared to other systems, (heolic and solar) and compared to the consumption of a boat of 10 m.

However, it seems to me that he is wandering here: I opened a discussion to have advice on how to draw a propeller, I didn't ask for reviews on my system.. .
apart from the welcome and short comments the only one who centered the speech (thanks for the precious advice) was drag.

thank you, excuse the clarification

♪

 

[Exatem]

but I am warning a gadget that could potentially pull me out 2 kw, even if it had to make only 1 kw no matter is always so much compared to other systems, (heolic and solar) and compared to the consumption of a boat of 10 m.

However, it seems to me that he is wandering here: I opened a discussion to have advice on how to draw a propeller, I didn't ask for reviews on my system.. .
apart from the welcome and short comments the only one who centered the speech (thanks for the precious advice) was drag.

thank you, excuse the clarification

♪

clarification of a par of ciufoli.
If you disturb the fact that you take inspiration from your idea to discuss also interaction between the hull and the helix, how you behave a hull in water, what are the causes of poor performance etc. etc.. maybe you do not understand the spirit of the forum.
In any case I am the moderator of this area and as such, intervening in this 3ad, I did not go on trampling private gates.
However I will look good from now on, since it probably disturbs you the fact that it did not express enthusiasm for the same, from losing more time in tips or suggestions.

Take care.

As regards the competence of dragon, I think I have hoped for his intervention. I know his culture on the subject and I appreciate it among my friends. but if you read his post again, it seemed to me enough to agree with what I expressed.
Perhaps my then are not just divagations. . .

 

[rbaffigo]

Good morning.
Perhaps last night I was a little rude and I apologize, criticism and doubts (especially if relevant) help to avoid taking chants.

But allow me to reformulate my question:
what software can I use to design and experiment virtually this my propeller, perhaps evaluating the effect of the disorders listed by you?

 

[Drag]

what characteristic of the propeller is the curvature?

I mean the shape of the average profile line, which can be straight or curved. see:http://it.wikipedia.org/wiki/profilo_alareorhttp://www.aero.polimi.it/~auteri/bacheca_fluido/apx_g.pdfas an indicative reference

can you estimate, how and with what approximation the number of turns that will make the propeller used as turbine according to the applied couple?

what you mean, given the characteristics electric motor, torque (power) turns,
built propeller, you want to know, how will it go in terms of turns when you use it as a turbine?

what software I can use to design

find something on the internet for a fee

Virtually experiment with my propeller, perhaps even evaluating the effect of the disorders listed by you?

............... I see hard in faidatè

greetings

 

[Fulvio Romano]

............... I see hard in faidatè

cfd is hard. ..but perhaps by making rapid prototyping some propellers varying the parameters, and by doing the tests in the house attaching it to an electric motor and putting a pitot of forward, perhaps some curve of yields according to the parameters that did not completely flow into the air you should be able to pull out.

Am I right or am I silly?

 

[Fulvio Romano]

@drag
doubt atroce... how do the propellers scale?
is worth the buckingam theorem as for the carenes (resistance that goes with the cube of linear relationships), or, as I imagine, something more complex?

 

[Drag]

doubt atroce... how do the propellers scale?

it is necessary to consider that kt coeff. of moment kq and performance are function:
Geometric similarities
Guidance Section
position
number of reynolds
by weber
by mach for water
by mach for metal
of fade
Cavitation index
coeff. of scrap
just for conventional propellers.
the values of these parameters in scale and real must be equal in order to compare the results obtained.

greetings

 

[rbaffigo]

thanks for the links,

citation
"what do you mean, given the characteristics electric motor, torque (power) turns,
built propeller, you want to know, how will it go in terms of turns when you use it as a turbine? "

exact, I know the performance of the engine/drive/battery system because I have factory data, and I can adjust the negative torque applied to the propeller because I use a drive in 4 quadrants, I would like to be able to estimate the charge amperes according to the used propeller and the speed of the boat.
you could insert an arbitrary factor of loss due to turbulence and inclination of the axis, and maybe when finally I will be at sea verify and correct with experimental data....

I found this sympathetic "program", I think it can be useful or at least fun, what do you think? Can you insert known propellers to verify its reliability?
http://www.mh-aerotools.de/airfoils/javaprop.htmabout paid software: Something like "propcad"?

Thanks soon

♪

 

[Drag]

I would like to be able to estimate the charging ampers according to the used propeller and boat speed

I don't think you can do that. There's too many unknowns at stake.

I found this funny "program"

is not good for the calculation of naval propellers

about paid software: Something like "propcad"?

you are a solution.

 

[rbaffigo]

in javaprop instructions say that by putting the water density instead of the air one can be used for marine propellers... Why do you say it's not okay?

 

[PaoloColombani]

qui I found an interesting document that deals with modeling of propellers and prototyping of the experimental model. there is also an interesting image of propeller mounted on electric motor for the test in tub. at the bottom of the document there is also the complete code of openprop v1.0 in version of scripting for rhino,
at this link is the main page of openprop with the most recent but written versions for matlab.

 

[athlon]

hello to all, I repeat the discussion to indicate that next summer there will be a traveling event from Liguria to Tuscany made by electric boats of various kinds , one of the themes that will be tested on the field is also the regen, using the propeller as "generator" in case of strong wind or in case of need to reduce speed (e.g. towing fishing)

 

[rbaffigo]

Thanks for the information, I really hope to be in the water for the next summer.
Is there any contact with the organization of this event?

good holidays and good new year to all.

roberto

p.s. I designed the propeller with javaprop using a symmetric profile made with javafoil and I am making it in steel and carbon.

 

[athlon]

as contact you can ask me.
both for the event of this summer (if you find some lenders) and for the championship electrosolar boats

 

[rbaffigo]

Hello, do you already have an electric boat?
Is there an association?

Thank you.

rbaffigo