Understanding final prop pitch

[bwells]

I did a search in the prop forum and did not find a thread that answered my question completely but I did gain a lot from the posts. I started a list of props using final pitch and arranging them fro smallest to largest in the 2-3" final pitch range. I noticed that, say, an X447 and an X642 were real close (differing by 5/100ths) and assumed these two would act nearly the same. I thought this may be a great way to select a prop when deciding to prop up (or down) and decided to throw in a couple 3 blades. I was surprised to see that an X447 and an X447/3 have the same final pitch, not sure why, just guessed it would be different. I thought I was on to something until then. Is the final pitch a guideline for prop selection or something else? What do most people do for selection other than trial and error or what others have run, although the later seems safer and less expensive?

[Fluid]

You have to consider both diameter and pitch, otherwise you will get into trouble fast. In your example, while they have similar pitch, the x447 could easily overheat a boat which ran an x642 because the diameter contributes more to the load. Once you understand how Octura lables their props it is easier to understand:

x447 means a 47mm diameter with a 1.4 pitch ratio (the x4 means 1.4). You take the diameter and multiply it by 1.4 to get the pitch.
x447 = 47 mm x 1.4 = 66 mm pitch
x642 = 42 mm x 1.6 = 67 mm
x647 = 47 mm x 1.6 = 75 mm
The number of blades has nothing to do with pitch.

When propping up, it is often best to stay with a similar diameter and add pitch. If you can't find a prop with the pitch you want in the same diameter, go up in diameter but watch the temps. The best strategy is often to copy what others have used with a similar setup, but be careful. Some folks say they use a certain prop - but don't tell you it overheated all their stuff....


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[dana]

x447 vs. x642. yes the pitch is similar, but diameter is quite different. a small v hull for instance wouldnt do well with such a large diameter prop like the x447 in my opinion cause it would just cause the boat to roll from the huge prop, so maybe the x642 would be better. smaller diameter means less roll while still retaining a good pitch. i usually consider the size of my hull and choose the diameter first. then depending on the motor, choose what pitch i want.

[dana]

You have to consider both diameter and pitch, otherwise you will get into trouble fast. In your example, while they have similar pitch, the x447 could easily overheat a boat which ran an x642 because the diameter contributes more to the load. Once you understand how Octura lables their props it is easier to understand:

x447 means a 47mm diameter with a 1.4 pitch ratio (the x4 means 1.4). You take the diameter and multiply it by 1.4 to get the pitch.
x447 = 47 mm x 1.4 = 66 mm pitch
x642 = 42 mm x 1.6 = 67 mm
x647 = 47 mm x 1.6 = 75 mm
The number of blades has nothing to do with pitch.

When propping up, it is often best to stay with a similar diameter and add pitch. If you can't find a prop with the pitch you want in the same diameter, go up in diameter but watch the temps. The best strategy is often to copy what others have used with a similar setup, but be careful. Some folks say they use a certain prop - but don't tell you it overheated all their stuff....


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what he said^

[bwells]

Thank you Dana and Fluid! I sure had the final pitch hosed up, I was thinking it was a way to categorize each prop in relation to pitch and diameter. I was looking at trying an X448 as a step up from an X642, not a good choice whereas a 1742 would be the next step with a 1.7 ratio, I think. I'll make a note to increase pitch before diameter. Thanks again.