Prop question: how can you tell pitch? Or if the hub is spun?

[chinewalker]

quote FrankR:

quote Chinewalker:

Sometimes, if I have a propshaft for a similar motor in the pile, I’ll set it up in a vice and mount the prop. If it’s spun, I can turn it by hand with much effort. Often, a badly spun prop will be apparent with a visual inspection.

"Much effort" are the key words here. The 35hp props are supposed to hold 165 ft lbs according to the chart. It’s dang near impossible to apply anywhere near that much torque without the special fixture made for the job.

But, a spun prop will often spin with much less. Other things to look for, a hub that appears off center of the prop casting, evidence of rubbing on the prop casting, rubber bits snaking out of the gap between the hub and casting, etc.

[frankr]

Very true.

[outbdnut2]

The others covered the spun hub thing well – note you cannot see the thin rubber interface.

Now for your pitch question:
Before you go to the trouble of measuring the pitch, look at the prop carefully and you will likely find the diameter and pitch numbers if it is an OEM prop. Look at the aluminum casting on the end of the prop around the edge of the brass hub. You may see numbers in this format: "10 1/2 x 13" which is the diameter and pitch. I’ve also seen these numbers stamped into one of the blades up near the hub. Yo may have to carefully clean some dirt or corrosion off to read it. You may also find the propeller part number, and can look up the pitch. I have a dozen or so props that fit your motor and nearly all of them have the numbers on them.
Dave

[nj-boatbuilder57]

I’ll look again….but haven’t been able to find any numbers anywhere on them.

[outbdnut2]

quote NJ-boatbuilder57:

I’ll look again….but haven’t been able to find any numbers anywhere on them.

Here is a photo showing the numbers. The clarity and font used in the casting has varied from year to year. You may have aftermarket props.

[bill-loveland]

I fell asleep about halfway through, but this guy seems to know his stuff:

https://www.youtube.com/watch?v=Uzv_m_Gm1es

[nj-boatbuilder57]

Yeah….that video was suggested in an earlier thread, and I’m going to give it a try tonight. That guy has a website where you can dump in the numbers and it gives you the pitch. Oddly enough, though, you enter the diameter in inches, everything else in millimeters. Strange.

Bottom line: Looks like some pretty easy trigonometry; I’ll just do the calcs myself. Of course, this will be AFTER I scrub these props & look for stamped numbers!

[Author]

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