Propeller Replacement

BeforeAfter_Prop
Left is old propeller with crack to the left of the (A), Right is the new propeller

One of the things the surveyor noticed when we purchased Zia (our Morgan 38) was a crack on the hub of the propeller.  It looked like it had been there a long time and the previous owner said he was unaware of it.

While she was hauled out at Schooner Creek, we ordered and installed a new propeller.

Above is a photo of the old propeller (left) with a crack (A).  We were told by the propeller shop that if the previous installer lubricated the propeller shaft and tightened the nut too tight, you could see this kind of cracking.   Lesson: don’t lubricate the shaft and don’t over tighten.

We also replaced the old Zinc, which was in good shape still, with the newer style of Zinc (B) which is mounted at the end of the shaft.  The old Zinc is the collar-like thing bolted to the shaft just to the right of (A) in the photo above.

We were very happy with the propeller shop Sheffield Marine Propeller.  They know their stuff and were reasonably priced compared to the super cheap internet shops.  We wanted to use a local shop for support since we had near zero experience with propellers.

The new prop, like the old, was a bronze 3 blade fixed propeller, 16X11 RH, for a 1-1/4″ shaft.  It cost $583 and we picked it up at their shop in Portland.

If you are new to propellers, the ’16’ is the propellers overall diameter.  The ’11’ is the ‘pitch’ of the propeller.  Pitch is “the distance a propeller would move in one revolution if it were moving through a soft solid like a screw through wood”.

 

PropellerPitch
Graphical representation of propeller pitch

 

 

Finally, the ‘RH’ means it’s right handed, which has to do with the direction the shaft turns to go forward.

The optimal value for all of these factors can be determined by the boat’s hull shape, the engine, and the transmission.  Mix these variables in with a some voodoo, formulas and a bunch of experience and out pops a propeller specification.

In my case, I got on the excellent Morgan 38 owner’s site (morgan38.org) and found out that for my engine and transmission, this was the originally recommended propeller.

Our Engine:  Perkins 4-108

Our Transmission: Hurth HBW150-1.9R

Propeller sizes are usually stamped on the hub of the propeller.

Old Propeller with '16 RH 11' stamped onto the hub.  Notice crack under the lettering.
Old Propeller with ’16 RH 11′ stamped onto the hub. Notice crack under the lettering.

 

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