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Propeller Flies Off in Reverse

Jul 27, 2011
Bavaria 38E Alamitos Bay
On Christmas Day 2013 backing our Bavaria 38E out of its slip I punched it in reverse, then lost backward (and forward) thrust quickly thereafter. Nearly side-wise now in the fairway, we blew up against the rip-rap within a few minutes and had to be pulled off by a rescue boat and ushered back into the slip. Diving on the Yanmar SD31 saildrive, our 16" x 13" LH 2B (fixed) aluminum propeller was gone; the 8 mm SS retaining bolt sheared at the end of the spline shaft. The prop evidently hit the hull starboard of the center line abaft the saildrive leg whence it came. The bolt was replaced (new) in 2006. A week prior I had had the boat out of the water for a bottom paint job and had taken off the prop for cleaning, and put it back on using that same bolt. Could the torque applied to the bolt when taking off the propeller have weakened it to the point of failing on strong reverse thrust after it was reinstalled? Or, might there be another "unseen" problem at work here?
Jan 28, 2008
Bavaria 47 Tenerife, Canary Islands
Did you use Loctite when you refitted the bolt?

[Later] Just re-read the OP. Looks like you didn't, and relied on too much torque.


Feb 18, 2010
Bavaria Ocean 40 CC Forked River
I think Nigel is correct on the LocTite. The Bavaria (actually Volvo) propeller cone issue is usually one of loctite + torque vs only torque. I have a Kiwi prop now with a slightly different attachment method but when I had a fixed 3 blade I always carried an spare prop, spare cone, and spare bolt. The cone issue I've heard many many times and when you loose one you loose the cone and the prop. I hope you can retrieve it from the slip bottom. Good luck.
Jul 27, 2011
Bavaria 38E Alamitos Bay
When I installed the propeller assembly in 2006, I applied red loctite to the threads for the retaining bolt. As I said, that prop has been on the boat for now 5+ years. However, it took a bit of torque to "break" the loctite seal when I removed it. I could actually see the cap head twisting a bit as the bolt shaft remained tight until it broke free. On replacing that same day, I applied the blue loctite (Tite'N) by mistake, and torqued the bolt down pretty good as it was going back into the water soon after reassembly. I have not had a chance yet to haul the boat to see if there is electrolysis damage of the bolt.

There's no finding the parts in the murky, muddy water near the slip. I'll be getting a replacement prop assembly new. For people carrying spare assemblies, I recommend in addition to the cone and propeller a few replacement bolts as they are not that easy to find locally. However, McMaster-Carr evidently carries them.
Dec 16, 2006
Hunter 25.5 Cayuga Lake, NY
I could actually see the cap head twisting a bit as the bolt shaft remained tight until it broke free.
This is where your failure started. What you witnessed was the bolt starting to shear. Unfortunately the loctite gave way before the shear completed.

I would offer a reward for that prop around your marina, might be fun to watch :-D.
Last edited:
Jul 27, 2011
Bavaria 38E Alamitos Bay
Thanks. I think I will now that you mention it. A whole new assembly will cost over $300; but I'm going to need a spare now anyway, clearly.