Prop - how to measure?

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woody001

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Hi,

I have a volvo fixed 2 blade prop i wish to sell and put on good old ebay.

The prop is in really good condition, but i believe the buyer will need to know prop pitch?
How do i meaure this?
Also, would there be any other measurements that would help?

Thanks again

Simon
 
The prop size (e.g. 14 X 12) is usually stamped on to the boss somewhere, try looking on the forward face of the boss (i.e. the face facing the front of the boat)
 
Have a good look on the prop for something like 16X12 or 18X10. These numbers are the prop "size"
ie 16" diameter X 12" pitch and 18"dia X 10" pitch.

Failing that it is not that easy to measure the pitch of a prop although a good approximation can be made by measuring the angle of the tips of the blade and the diameter. Pitch is how far the prop will "screw" through the water in one revolution assuming no slip.

So a 16X10 will have a tip angle of approximately 11.25° and an 18X10 a tip angle of approximately 10°. How good are you at measuring angles accurately?

I assume (probably incorrectly) that there is a part number or other markings on the prop. Can you not determine the proper size from those?

As for other information.. Ask yourself what you would need to know before you parted with your beer tokens.......

Shaft size ?????
Shaft taper ??????
Key size ????
Hub length ?????

Probably better if you quote the Volvo part number.

Hope the above helps
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo
 
flip, didnt know there was so much to it.

Yes it help's alot cliff, thats not a part number, have listed on ebay now, i'll just sit back and hope they dont ask, if they do they will have to help!

cheers mate

simon
 
As I have just found out, renewing my props see.

An imperial shaft will have 1:12 taper
and a metric will have 1:10

this is a general rule, not infallible obviously.

There is also blade size.... 52% or 43% DAR (3 blade) or 34% or 23% (2 blade), usual for a sailboat is 43%, so I was told, did not ask about 2 blades as they don't concern my plans.

It is a minefield....
 
[ QUOTE ]
It is a minefield....

[/ QUOTE ] BOOOMMMM!!!
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo
 
I see you've found the right answer but in truth it's not that hard to measure dia (doh!) and pitch.

Simply locate the maximum blade width and measure the amount by which the leading edge is ahead of the trailing edge at that position (arguably the maximum "depth" of the prop blade). Then measure the width of the blade at that position, and the distance from the centre (i.e. radius) of that position. Pitch is then 2 x 3.14 x (radius of max blade width) divided by (max blade width x no. of blades), multiplied by the "depth" at max. blade width.

Perhaps not very clearly explained but if you draw it out on paper it should be obvious.

When I did it the result was spot on - as I subsequently found the pitch stamped on it!

Regards, Mudhook
 
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