Freewheeling Prop Noise

[tomgrigsby]

I recently acquired my boat and am not sure what is "normal." When under sail, if the transmission isn't put in reverse, I can hear a ticking as the prop spins. Went below and checked while making about 6 kts and saw the engine actually jiggling up and down at the rear. Haven't noticed any knocking or unusual problems under power. Have a yanmar 3GMD. There is some vibration, but it doesn't seem excessive. At about 2000 rpm engine/shaft combo vibration appears to be about 1/8 inch at the coupling. It had more vibration under power prior to having bottom and prop cleaned btw. Any thoughts?

 

[Fast Ed]

Put the trans in reverse when sailing. This will keep the turning parts from wearing out! You do not want to put the trans in forward due to the possibility of starting the engine.

 

[Don S/V ILLusion]

Locking the prop may reduce the noise ( it will never cause the engine to start) but it sounds like you have bigger issues - the engine shouldn't be moving. Do you know how to inspect your engine mounts?

 

[kloudie1]

Motor moving probably means the prop shaft has a slight bend in it..(could be a badly fitted coupling as well) Make sure everything is tight right now but this fall, when ya take her out of the water, have a list of stuff ready to work through.. remove shaft and straighten or replace. Balance prop, check coupling for trueness and fits, Check Cutless bearing, Check motor mounts,(replace stuff that fails checks) and finally re-assemble and realign the whole train. Not cheap, but once correct, it will stay that way for a LONG time..

 

[Nereussailor]

Hi Tom,
I've posted on this before, but I'll do it again so that your repairs might be less than mine. What year is your H30? It sounds like you have some problems that could cause some serious damage. Do you hear a knocking sound when motoring? Something that sounds like it's coming from near the motor, but not from the motor? Here's what I went through...
There was a knocking sound coming from the engine compartment. it didn't make the sound all the time, only at certain RPM's. mostly lower ones. At first It was quiet, then it got louder. After a couple of weeks of motoring out of the marina and back in, I didn't notice it as much. Then on the trip home across lake Michigan, it gave out.
It started with bad motor mounts, which gave the motor excessive movement and caused the shaft to move around a lot. This caused the shaft seal in the back of the transmission to go out, which caused the transmission fluid to leak out of the transmission, which caused the transmission to go out, which scored the shaft, and the shaft log tube, and messed up the cutless bearing.
It ended up costing around $4000 for everything when all was said and done. My guess is that the motor mounts are original, and need to be replaced. An alignment will have to be done when they replace them. Check the rest of the parts that I mentioned, and don't skimp on replacing something while it's apart. There's no point in going back in a year or two to replace a part.

Dave

 

[tomgrigsby]

Now that I think about it, I did have a loud knocking noise when under power at the dock. I though it was just something vibrating sympathetically to the engine vibe, but after reading about alignments above and all over this site, I think now it is a shaft knock. It got quieter & smoother after I had the prop cleaned. I'll have to listen closely next time out. The boat is a 1979. The motor is from around that period. I have the Yanmar manual, and hopefully it will have specs on the mounts. I also wondered about a slightly bent shaft and alignment issues as noted by the gentlemen above. I do put it in reverse under sail (and am reminded by the noise if I forget). The preceding posts are grim news since I have a 1hr transit to open water, but I certainly appreciate the input. Looks like I will be attempting an in-water alignment. As I understand things, I should disconnect the coupling bolts and move the shaft up/down/port/stbd and then position it and block it in the center of the range. Then adjust the motor mounts to get .001" evenly around the coupling.

 

[jcherubini]

I'm weighing in-- it's a cracked strut (if that boat has one) or a bent shaft. The prop could be out of whack too.

I can't believe you haven't been taking in water if they motor bounces 1/8" up and down under sail! Look at the shaft log/cutless bearing now too.

Leave it go too long and the rear bearings of the motor will go next.

 

[tomgrigsby]

Thanks for the input. I'll be checking all those things and will post results if anything definitive is found. I sure appreciate all the advice. It can be a steep learning curve with all the different things involved with sailing, and this site is a gold mine thanks to all who are willing to share their experience and opinions. Thanks again to all who responded. I feel better prepared and have a plan now to get to the bottom (so to speak) of things!