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shaft lengths and prop types

vanfuego

Island Bird
I own an E-41, Island Bird, and recently pulled the shaft and had it inspected. Turns out I need to replace it. The two shops that inspected it both agree its beyond straightening. I decided to have a new one machined and sent the specs to Marine Hardware out of Redmond WA. It seems that the machinist has a different idea of the length of shaft exposed beyond the aft end of the cutlass bearing to the forward edge of the prop than the specs i gave him. According to him the distance should be the width of the shaft making it only one inch. I have no reason to doubt him. The amount of exposed shaft I have with the shaft I am replacing is close to six inches. The total length of this shaft is 53 inches with a standard tapered prop end and a straight coupler end. The shaft I'm replacing had half of the threads cut off and was using a zinc nut as the prop nut. I sent him the prop from the shaft I'm replacing and when he fit it to the standard tapered end it seated further up than normal leading him to believe the prop may have been over bored. My questions, one; what amount of shaft exposed between the cutlass bearing and the prop is standard? Does engine size and gear ratio determine that? and question two; it looks like im going to replace my prop, two blades or three?
 

EGregerson

Member III
prop shaft

I have no expertize is such matters, but it sounds like your old prop assy was prepared by Darryl and his brother Darryl and their cousin Darryl. My prop is close to the cutlass bearing; probably 1". I would think 6" would allow the prop to wobble and bend the shaft. It sounds like your machinist is on the right track. Re: the choice of 2 or 3 blade, will this be fixed or folding? (or feathering)? Depends on what type of sailing (or motoring) u do; there are lots of threads on this subject on this site. good luck
 
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Sven

Seglare
The amount of exposed shaft I have with the shaft I am replacing is close to six inches.

It is the same on Senta II. It looks odd to have the strut that far away but a shorter shaft would not work unless we had a smaller diameter prop. There just wouldn't be enough clearance between the prop and hull. With a 1.25" shaft we're probably ok unless we snag a pot or fishing net.

I don't know what a new strut placed further aft would entail but it is not at the top of our to-do list yet :)


-Sven
 

Greg Ross

Not the newest member
Same Dilemma

I have a Max Prop (feathering) now that has not yet been run. I am inclined to pull the shaft and have it shortened up. The configuration of the Max Prop hub and where the blades are positioned I have the same overhang concern comparitively.
To get clearance for a 14 inch diameter prop on my I-31 Hull I had to remove some material from the centerline of the hull (loads of surplus thickness)
That first season with the 14 inch three blade and nominally over an inch of clearance there did not appear to ever be any hint of cavitation. I believe the rule of thumb for hull clearance is minimum 10% of prop diameter.
The machinists recommendation of one shaft diameter spacing to the berring is optimum, but your hull configuration must dictate.
My existing overhang is contributed to by repowering, larger engine moving the gear box further aft. For the first season I needed the shift aft to contribute to the prop clearance for the 14 inch prop, now with my Max Prop it is perhaps getting out beyond....
Think I should also consider adding a Line Cutter!
 
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