Please Help

[Bertoni]

Hi. Sorry for being a complete novice. I know absolutely nothing about boats and anything associated.

I am a student and im required to design a folding yacht propeller.This info is given:

Engine power (inboard 4 cylinder diesel) - 31kw at 3000rpm
Gear ratio between engine and propeller - 2.94:1
Max diameter - 457mm
Max yacht speed - 6 knots
Yacht mass - 12ton
Length of water line - 10.4m
Expected propeller slip at cruise speed - 10%
Blades must fold automatically when steel shaft not driven.
Means of manufacture of blades - CNC machining.

I have no idea where to start, what calculations to use to work out anything!!
Whats more is : i must show calculations showing how the pitch of my blades was designed on(dont know whats that),and a components list, shaft strength calculations (diameter) for it 2.8m long.

I have to draw all components of the propeller that fits onto the shaft.

Help me please...

[SailDesign]

Bertoni,
Either your prof is doing something wrong, you missed too many classes , or this is a pure research project. If you are being asked to design a propeller without even knowing what "pitch" is.... Like being asked to design an aeroplane without knowing about foils.
Anyhoo, start here
http://www.olds.com.au/marine/terminology.html
for an explanation of terms.

Good Luck,
Steve

[Bertoni]

Thanks alot for the link.
Basically it is a research project.Im studying towards a Mechanical Engineering degree, so its a very broad field. We were not taught anything to do with props, but basic radial and fluid mechanics equations i know.

Thanks..

[Bertoni]

Any links ets specifically on folding propellers?

[Bertoni]

And with that info, do any of you guys know how to work out the necassary blade shape and area. I reckon i should use the 2 blade concept, what do you think?

Thanks

[Kreso]

I have not enough time to calculate your task, but I would like to recommend a very good book which could helps you : "Propeller Handbook The Complete Reference for Choosing, Installing and Understanding Boat Propellers" Dave Gerr ,International Marine, check on www.amazon.com. coast 14$.
Regards
Kreso

[Kreso]

I´ve just read your message again and noticed that you give: max. speed of 6 knots, and 10% slip, I checked in "Propeller Handbook" Dave Gerr and I´ve found that for 6 kn. speed percent of slip is 45% so ....

[Tim B]

yeah, sounds like a mech. eng. project. any idea of the yacht's resistance? at least then you would know the required force. You'll need something more than basic fluids equations for this one though, if it is to be done properly.

The number of blades is largely down to how easy it is to fold them (backwards remember) without sacrificing efficiency.

Good Luck,

Tim B.

[Bertoni]

Originally Posted by Kreso

I have not enough time to calculate your task, but I would like to recommend a very good book which could helps you : "Propeller Handbook The Complete Reference for Choosing, Installing and Understanding Boat Propellers" Dave Gerr ,International Marine, check on www.amazon.com. coast 14$.
Regards
Kreso

If you are ever very bored, please work it out

Really dont have time to order books as well, dont have a credit card yet.Just need links........

[Dutch Peter]

Here you can get an idea of how the propeller should look like, and maybe you find some guidance on how to design.

http://www.bestmarineimports.com/Tristream.html
http://www.australpropeller.com/sailboat.htm
http://marinep1.bluehill.com/foldingprops.htm
http://www.sillette.co.uk/first.htm
http://www.flexofold.dk/technical_specifications.htm
http://www.maxprop.net/max-prop-in-pictures.html

Good luck

[Dutch Peter]

Originally Posted by Kreso

I´ve just read your message again and noticed that you give: max. speed of 6 knots, and 10% slip, I checked in "Propeller Handbook" Dave Gerr and I´ve found that for 6 kn. speed percent of slip is 45% so ....

I think the idea is to work with the data given by the professor, although maybe not correct, that'is the assignment!


<Bertoni>
You could ofcourse mention it in your paper!

[Kreso]

Here is online propcalc.

http://www.surfbaud.co.uk/download.php?view.5