Propeller has Fallen Off!

[Allan M]

Hi, I went to shift my boat back to her permanent marina berth yesterday and nothing happened when I engaged forward gear ( I reverse into my berth so as to drive straight out)! After checking all the obvious things on board and finding nothing, a quick dive underneath revealed a naked shaft. I have a Yanmar 3HM35 engine with a SD20 Saildrive which until recently had what I believe to be an Alco folding prop on the shaft. 6 months ago the boat was out of the water for antifouling and Saildrive anode replacement which required removal of the prop to allow the older style one piece anode to be removed. The hub of the Alco prop is held onto the splined shaft with a main nut and a threaded allen type locking nut screwed into the end of the shaft. There is no tabbed washer or pin to prevent the whole assembly working loose. When I replaced the prop I don't recall using Loctite on the locking nut but it seems crazy to have to rely on Loctite to prevent a propeller falling off. On reading my Saildrive manual I have come across a caution for installing the Alco propeller along with a diagram. The somewhat unclear diagram shows a required 'B' dimension of 0.5mm - 1.5mm between the main nut and what I assume is the end of the shaft and there is a warning that if the measured dimension is less than 0.5mm a prop drop will occur!! Given that the main nut is down inside the prop hub and requires a special thin walled box spanner to extract it, I don't know how to achieve this feat and I don't understand the reasoning for it. I am hoping that a diver will find the prop sitting in the mud under the boat this afternoon and with a huge amount of luck the nuts may even still be in the hub restrained by the folding blades of the propeller. Does anyone out there have experience of a similar setup to mine and an explanation of the warning in the SD20 Saildrive manual (page 18).

[sapient sue]

Allan

My sympathies for your situation and I hope the diver finds your prop - expensive items they sure are.

We do not have the same system as you so can't answer you question - but we had the prop fall off when electrolysis affected the split pin holding the propellor bolt in place. Unfortunately we were anchored out and despite several scuba tanks and swimming search grids we never did find the prop. Trust you have better luck.

Sue

[Hudson Force]

Like sapient sue, I can also do no more than wish you luck. Once many years ago I shifted into reverse and my prop with the entire shaft attached was propelled from my vessel. If it's any comfort, you're not alone! 'wish you the best!

[Ex-Calif]

It seems we have a couple of prop drops a year around her. Sucks and sympathies.

If you don't find the prop send me a PM and we might be able to work a deal. I have my original folding prop somewhere after I upgraded to a Max prop...

[Tellie]

I have the SD20s on boat as well. Though I haven't had this issue I remember it being discussed here on the forum several times. It seems that losing props on the SD20 is not all that uncommon.

[Tayana42]

No where near the OP but I've heard that in Wilmington, CA (LA inner harbor) there has been a rash of props stolen off the boat in the water by divers. One boat owner caught a diver with his boat hook. The diver claimed he had the wrong boat.

[ryon]

Originally Posted by Tayana42

No where near the OP but I've heard that in Wilmington, CA (LA inner harbor) there has been a rash of props stolen off the boat in the water by divers. One boat owner caught a diver with his boat hook. The diver claimed he had the wrong boat.

Great catch! Hope he put the guy's head on a pike as a trophy.

[Allan M]

A miracle has happened in Nelson New Zealand! My diver mate found the propeller under the boat, with 6 inches of visibility and just the tip of a blade sticking out of the mud. Also the shaft nut and lock nut were still trapped in the hub by the prop blades. I have pulled the prop apart and all seems to be in order, i.e. no damage, stripped threads etc. I will have to pull the boat out of the water to inspect the shaft and re install the prop. which I will get a professional to do in case there is something I omitted to do last time! I will post any additional information I discover about possible causes etc. Thanks to everyone for their interest and sympathetic comments.

[Tayana42]

Nice to hear that miracles do happen once in a while. Mazel Tov!


Sent from my iPad using Tapatalk

[D&D]

Great to hear you recovered the prop!

We hav Yanmar saildrives, but (like sapient sue) our only prop drop was due to electrolysis...and that's an unhappy experience we very sincerely hope NOT to repeat...

[bizzy]

same thing happened on a boat in the cook islands ,,,,,found the prop ,nut,washer AND the split pin ,,,hope you have the same luck

[Cadence]

Originally Posted by Allan M

Hi, I went to shift my boat back to her permanent marina berth yesterday and nothing happened when I engaged forward gear ( I reverse into my berth so as to drive straight out)! After checking all the obvious things on board and finding nothing, a quick dive underneath revealed a naked shaft. I have a Yanmar 3HM35 engine with a SD20 Saildrive which until recently had what I believe to be an Alco folding prop on the shaft. 6 months ago the boat was out of the water for antifouling and Saildrive anode replacement which required removal of the prop to allow the older style one piece anode to be removed. The hub of the Alco prop is held onto the splined shaft with a main nut and a threaded allen type locking nut screwed into the end of the shaft. There is no tabbed washer or pin to prevent the whole assembly working loose. When I replaced the prop I don't recall using Loctite on the locking nut but it seems crazy to have to rely on Loctite to prevent a propeller falling off. On reading my Saildrive manual I have come across a caution for installing the Alco propeller along with a diagram. The somewhat unclear diagram shows a required 'B' dimension of 0.5mm - 1.5mm between the main nut and what I assume is the end of the shaft and there is a warning that if the measured dimension is less than 0.5mm a prop drop will occur!! Given that the main nut is down inside the prop hub and requires a special thin walled box spanner to extract it, I don't know how to achieve this feat and I don't understand the reasoning for it. I am hoping that a diver will find the prop sitting in the mud under the boat this afternoon and with a huge amount of luck the nuts may even still be in the hub restrained by the folding blades of the propeller. Does anyone out there have experience of a similar setup to mine and an explanation of the warning in the SD20 Saildrive manual (page 18).

Grats on getting it back. Given the nut is in the hub I'm guessing there is no cotter pin. Is there a chance there should have been something like a Delron washer between the nut and the prop. to insulate the nut from the props reverse tough?

[JPA Cate]

AllanM,

May such good fortune attend you always! Good on your diver mate!

Ann

[MBWhite]

Story for another time but I also lost a prop once due to the nut coming off. I suspect that if I ever have a system that did not have a cotter pin I'd at least figure out a way to drill the nut so I could use safety wire at least.

And congrats on finding your prop!

[Allan M]

Cadence is on the right track! Apparently most of these props have long since fallen off and the ones that remain attached were modified with an extra spacer which I have ordered at a cost of NZ$89. I haven't yet heard a technical explanation for how the spacer works but am prepared to give it a go! The cost made me wince a bit but I had a full blown seizure when I asked the price for a replacement shaft nut, thinking that I might carry a spare on board - NZ$200