What’s my props’ pitch?

[BoatingBeginner]

I know that props are usually stamped 16x22, 18x20, etc, to denote their diameter and pitch, but I can’t find any such markings on mine.

They are three-bladed, 19.5” in diameter (roughly – could be 19” or 20” it was difficult to measure accurately), and have the following numbers stamped around on the fronts:

Port

11938PP
GB8760
12654PP

Starboard

11937PP
GB8761
12953PP

I’m also a bit concerned as to why none of the numbers are the same on both props (I double-checked all the ‘6’s and ‘9’s in the light of my dyslexia!). Some of them could be consecutive maker’s serial numbers, but none of them tally with the measured diameter.

The props are in excellent condition and all the numbers are clearly stamped.

Any suggestions, folks?

 

[neil_s]

My prop has no markings but I managed to calculate the pitch. Use a small protractor to measure the angle the blade makes with the plane of its rotation. I did this simply by holding the protractor at the very tip of the blade and 'sighting' across the prop.

Pitch = Pi x Prop diameter x tan (blade angle)

It sounds a bit hit or miss, but I got an answer that agreed to the inch with Propcalc!

Neil

 

[BoatingBeginner]

Thanks very much for that - that's just the sort of simple formula I was after. I've just found Propcalc, and come up with a figure (well, a recommendation telling me my props are too small), so it'll be interesting to see how they compare...

 

[Cheekybrat]

Have you actually removed the props? the actual size may well be hidden by the retaining nuts, if you remove the nuts the size should be there
Nick Heath

 

[BoatingBeginner]

Do you know - I hadn't thought of that - the hub aft is covered by a bronze boss cap. I couldn't believe there could be any more numbers.

Now to remove the boss cap (right word?)...