Propellors and all that jazz...

The Jackeens · 07 February 2006, 19:36

OK anyone got a useful and easily understood explanation as to how propellors work? Have heard a few slightly differing theories (might have been the fact the theorists were sinking Guinnesses at the time!!!

)

many thanks

missus technophobe

Hugh Jardon · 07 February 2006, 19:44

they rotate and suck you forward

Quote:

Originally Posted by The Jackeens

OK anyone got a useful and easily understood explanation as to how propellors work? Have heard a few slightly differing theories (might have been the fact the theorists were sinking Guinnesses at the time!!!

)

many thanks

missus technophobe

The Jackeens · 07 February 2006, 19:48

Cheers Chris!

I shall relay that to the peeps in question!

Any other offerings?

missus

Dino · 07 February 2006, 19:54

Quote:

Originally Posted by Hugh Jardon

they rotate and suck you forward

surely that's thrusts you forward

Hugh Jardon · 07 February 2006, 19:54

some will say they rotate and push you forward

so basically the question will be whether they suck or push/blow

a propellor in free air uses lift created by the aerofoil shape of the "propellor wing shape" as a force that pulls the propellor forwards.

in a gasturbine engine there is a misture of suck and blow with the blow being much more powerful due to the controlled explosion that has occured in the engine.

however in a propellor in the water there is no such explosion creating that effect

as usual it will be interesting to see folks views on what actually happens

in air i know exactly what happens, was my job, but in hydrodynamics i am not sure if the same principals apply

Dino · 07 February 2006, 20:08

Quote:

Originally Posted by Hugh Jardon

some will say they rotate and push you forward

so basically the question will be whether they suck or push/blow

a propellor in free air uses lift created by the aerofoil shape of the "propellor wing shape" as a force that pulls the propellor forwards.

in a gasturbine engine there is a misture of suck and blow with the blow being much more powerful due to the controlled explosion that has occured in the engine.

however in a propellor in the water there is no such explosion creating that effect

as usual it will be interesting to see folks views on what actually happens

in air i know exactly what happens, was my job, but in hydrodynamics i am not sure if the same principals apply

No,lost me on the first line!!

Dino · 07 February 2006, 20:14

Hugh
By the way,the cutting of the transducer lead seems to have worked,or lets say it appears to be,I haven't tried it on the water yet

Pete7 · 07 February 2006, 20:19

Quote:

Originally Posted by The Jackeens

missus technophobe

She has done it again, looked what happened when she asked how a jet worked

Pete

Props for girls

.

Hugh Jardon · 07 February 2006, 20:34

oh

haha, hope it will be all ok for you

i have cut the mushroom off of my garmin

well cut the bnc connector off rather than mucking around making much larger holes in the aframe. but is only coax so will be fine putting back together

Quote:

Originally Posted by Dino

Hugh
By the way,the cutting of the transducer lead seems to have worked,or lets say it appears to be,I haven't tried it on the water yet

Nasher · 07 February 2006, 20:40

I think props push the water away from the boat, the boat then moves because of the equal and opposite force generated, hence the need for a thrust washer.

Nasher.

Srellom · 07 February 2006, 20:44

Quote:

Originally Posted by The Jackeens

OK anyone got a useful and easily understood explanation as to how propellors work? Have heard a few slightly differing theories (might have been the fact the theorists were sinking Guinnesses at the time!!!

)

many thanks

missus technophobe

Is this a serious question or have I inadvertently joined a knitting forum?

randski · 07 February 2006, 20:54

Quote:

Originally Posted by Srellom

Is this a serious question or have I inadvertently joined a knitting forum?

Knit one Pearl one

Steve Waters · 07 February 2006, 21:33

The more I read the more I am assured I have joined a bunch of mad people. I've just been reading abvout the Doggers on Portsdown and now just to prove how I go forward (slowly looking for dry land) I discover it's best if I (k) nit one pearl one. I checked the Smilies and I thought this was appropriate

! If it doesn't turn in to a bannana then I was right about the Doggers.................
PS I went out out yesterday with the missus and we went out and came back without scraping the bottom; mind you I did notice the missus looking over my shoulder quite a lot at the depth gauge .......

Steve Waters
The depth of H2O goes all over the place...............

Oh!! NICE BANNANA!!

Hugh Jardon · 07 February 2006, 21:41

there is a knitting forum and a radio forum that i have joined recently and they are treeeeeeeeeemmmmmmmmmmmmmenddddddddouuuuuuuuuuuuss ssss fun, lots of wit and the like,

i think this is the perfect thread to hijack and send off on a few tangents as all this tosh was discussed on the jet thread some weeks back, similar principals apply i think

Hey steve from winch, are you going down the doggers on monday?

it does help to be a bit mad to be on here from time to time also

Quote:

Originally Posted by Srellom

Is this a serious question or have I inadvertently joined a knitting forum?

IanE · 07 February 2006, 22:48

Who has a link on his site

HTH

Ian

Jimbob · 08 February 2006, 12:24

i think this is correct

Props come in many different configurations from 2 to 5 blades, with the primary aim of providing propulsion in both forward and reverse (astern) directions. The propeller is design for primarily forward motion, as such is not as efficient in the reverse direction.

Propellers can be right hand and left hand, for example a right hand prop turns clockwise looking from the back of the boat.

The propeller in simple terms screws its way through the water, like a screw being screwed into a piece of wood, in a perfect world the forward movement of the propeller, know as PITCH, would be for example on a 19inch pitched prop in one rotation of the propeller be forward 19 inches. However there is an element of SLIP which means the propeller does not move forward by the pitch, this is the ADVANCE.

PITCH- how far you would travel in the perfect world in one rotation of the propeller
ADVANCE- is the amount of forward movement taking into account the water SLIP

Propellers are designed to reduce the cativation, this in simple terms is bubbles that form on the blades, this also reduces the efficacy of a propeller

Paddlewheel effect – this is noticeable at low speeds, it is always there but at high speeds it is minimal compared with the forward motion of high speed. Basically a propeller will act as a paddle, for example a RH (Right Hand) prop in reverse will tend to pull the boat to port. Yachts take advantage of this when mooring, e.g. one way this will help mooring, the other it will force the boat from the jetty.

Matt · 08 February 2006, 12:53

Nope. Madmat.

Quote:

Originally Posted by IanE

Who has a link on his site

HTH

Ian

The Jackeens · 08 February 2006, 19:29

Some helpful replies thank you!

Like the link Pete!!!

missus