How to calclate prop pitch?

D

Dalliance

Well-Known Member
Joined
28 Jul 2005
Messages
246
Location
East Coast
Visit site
I've got a virtually new (19hrs running time) Volvo 14" 3-blade prop in my workshop but I don't know it's pitch which makes selling it a little difficult. How can I calculate the pitch? Probably blindinglyeasy but my A-level maths was a LONG time ago.
 
Most props have the size and pitch stamped on the propellor somewhere? I assume you have looked?

Donald
 
Heres a shot make all measurements in inches.
Draw a line in pencil across the widest part of one blade.
Measure the distance from the centre of the prop to this line (Use it as the radius r in this formula 2 x 3.142 x r ( ie 2pyeR )
Measure the length of the line and divide the result of the previous calculation by it. write this number down.
Lay prop on on its back on a table and assuming that the back of the blade touces the table where the line is, measure the distance from the other end of the line to the table.
Multiply this by the number you wrote down and that should give you an approximation of the pitch.

Its far easier to do than to explain

Julian
 
I've just tried this method with my new 11 x 9 prop, and get an answer of 8.62 - never heard of this method before but it seems to work very well.
What if you made a huge jelly and then screwed the prop through it, turning it one complete revolution? Maybe not....
 
[ QUOTE ]
I've just tried this method

[/ QUOTE ] It is not clear from Parglena's post if you should measure to the centre of the line or the ends of the line.

It should be to the ends of the line but when you come to measure the length of the line really it should be the length of the arc between the two ends.
 
[ QUOTE ]
[ QUOTE ]
I've just tried this method

[/ QUOTE ] It is not clear from Parglena's post if you should measure to the centre of the line or the ends of the line.

It should be to the ends of the line but when you come to measure the length of the line really it should be the length of the arc between the two ends.

[/ QUOTE ]

Agreed on the arc I was treating it as basic and assuming a relatively flat blade.

Ill try to clarify but its not easy
The measurement you need for the final one is the distance the one blade moves through the water.
If you look at the end of the blade with it on a horizontal surface and imagine a right angle triangle with the hypotanuse (the long side) along the line that has been drawn across the blade what you need is the vertical dimension.

AsI said its difficult to explain.........


julian
 
Thanks to one and all - great help. No, the pitch isn't stamed on the prop so I've had to use Parglena's method which was easier done than explained. No doubt the offending item will be available on EBay very soon!!
BW
Mark
 
You must log in or register to reply here.

Share this page

Top