hub lengths for inboard props?

I must be missing something obvious, but where do you find the hub lengths for inboard props? Are they all a standard length?

 

Have you tried contacting the prop manufacturer or distributor?

There's no big secret about the length of a prop hub. The hub is usually cut off as close as possible to where the blade root fairs into the hub, thus hub lengths vary depending on the blade geometry.

 

Thanks. That's my next call. I couldn't find it published with any of the other prop data, so I assumed it was a standard size.

 

They are sorta-kinda standards, having to do more with power absorbed to shaft diameter to shaft taper to hub material. Generally both shafts and props are designed based on power or torque inputs. For the hub and shaft material there are consistent rules of thumb for taper given a specific power. All of this tends to drive hub size and length to be similar between props designed to absorb a specific power. Which is a good thing for most commercial and commercial fisherman applications. You still should check it, always allowing for push up on the shaft.

 

There is a SAE size chart that prop mfrs follow

 

Like this one:

http://www.pacificmarine.net/engine...ft/sae-specification-j755-propeller-shaft.htm

Or this one:

https://www.techboat.com/Bibliotheque/SAE_ dimension.pdf

 

Yes! That is exactly what I was looking for. I knew that they were tapered to an SAE standard, but I hadn't seen it dimensioned out so clearly. Thank you.

Now all I need to do is figure out how far the blades project behind the hub (rake, shaft angle and so forth) and I'll be set. Goal is to place rudder shaft for appropriate spacing between prop blades and leading edge of rudder. Gerr suggests about .15 x rudder dia.

 

You need to first specify the propeller. They are many designs that will give you different clearances.

 

15% prop dia. Or make sure you can pull the prop without having to remove the rudder