Yanmar SD60 Max Props Neutral Engine Jarring Knock

[SillyCs]

Happy weekend everyone!

As the title suggests, we have twin yanmar 80s with SD60s and max props. I’ve owned the cat for coming up on a year with no event (w the SDs). I will try to explain in enough detail below so hopefully someone can chime in on what is happening.

Yesterday while under sail or using the other motor as propulsion to gain forward flow (I say this so you understand this is not while sitting stagnant) over the feathering max props there was a loud banging knock coming from the STBD saildrives! (I may get an award there for longest run-on sentence). Anyhow, this banging/knocking happens when engine is on, boat is propelled forward, water is flowing past the max props. The volume of the knocking can be heard easily from anywhere on the boat and cadence of the knocking is about 120 knocks per minute (about the pace of singing ABCDEFG song to a child). It’s violent enough to shake the engine on its mounts!

Troubleshooting - When it happened and when it stopped - all while forward momentum

- If we turn the engine off - the knocking continues until shifting transmission into reverse (normal ops w Maxprops to bring to feather)
- if we shift into forward or reverse while engine on - the knocking stops - only happens in neutral
- SD fluid/oil is at normal levels - no milky or seawater issue
- I do need to swim the prop to verify proper and free movement of the feathering system - but intuition tells me it’s working - and I just greased and serviced weeks ago and they worked fine - and even if it wasn’t - it’s no different than having a fixed pitch - it shouldn’t BANG when in neutral

This tells me when moving forward - in neutral - the maxprops not feathered - so spinning the SD hydrodynamicly (sp?) - it causes this shutter?!? Stumped here.

Hoping one of you may know what this is or could be.

We are continuing on up the east coast from
Brunswick GA to Charleston so will have another 20 hrs or so to see if it continues to happen and further troubleshooting.

Thank you for reading and in advance for your wisdom.

Coy

[clownfishsydney]

It will be the props not feathering, happens when there is some growth on the mechanism. A simple cleaning should fix. Putting into reverse and then neutral normally can fix it temporarily.

[SillyCs]

Thank you Clownfish.

What doesn’t add up is - if the maxprops aren’t feathering - which they shouldn’t feather in neutral - they are spinning same as fixed pitch in that moment - why would a then “fixed pitch prop” cause a jarring banging shuttering?

[EWOL Props]

Difficult one, anyway I'd check if anything is entrapped in the propeller. Also check if prop is steadily attached and tightened to the S-Drive shaft and engine's silent blocks are OK

[donradcliffe]

Since you just serviced the prop, that would be where I would look first.

[SVScooby]

Hey Coy, have you found the solution for this issue yet? We just had the same thing happen on our Gulf Stream crossing today. I thought the engine was going to rock completely off the mounts. We were sailing with no engine on and both were shut off in forward and switched to neutral as Max Prop recommends. After hours of sailing the Starboard Engine did exactly as you described. Not a rattle but way more violent. Thanks Skip

[SillyCs]

Hey there skip!

Wild right? It never came back after this occurrence. Speaking with yanmar tech he said we may have inadvertently had trans in forward - moving along at good clip - had enough hydro force to spin the prop while in gear - diesel being such high compression that when it did rotate on shaft the engine shakes violently - sort of like jump starting I suppose. Anyway, not something I want to try again. Hoping your issue was only temporary.

Can you send me the neutral data from maxprops you mentioned? We were taught - engines off - neutral for a few seconds - then reverse while sailing.

Coy

[SVScooby]

Here is the recommendation from Max props website.

[dksail]

A friend has a Cat with a similar issue, here is his solution…”it is likely an issue with props not feathering properly. Exactly what happened to us last year. I have never had an issue since I started my current procedure last February.

Always kill the engine while running at speed in forward then immediately shift to reverse. Props feather perfectly. Can then shift to neutral and run the engine if you want to cool it down at idle. This always works.”