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Banging noise under sail, small(er) speed under power ?

Jul 26, 2015
42
Watkins 29 Ft. Lauderdale
Just purchased an 1987 O'Day 302 3 weeks ago.
1st question:
First time I took it sailing, I had 20 knot winds. With only the jib I was doing 6.5 knots.
Exhilarating, but when boat speed surpassed 5 knots, a banging noise can be heard under the hull ....
I do not hear the noise while under power.... (shaft bearing or prop?)
2nd question:
Why is my power speed limited to 5.5 knots? Is it the prop? I assumed most boats do 6.5 knots under power. 1 knot is not a big difference, but it became an issue as I crossed FL on the canals.
3rd question:
My whole boat rattles when the engine is at idle (500 rpm). As soon as I give it gas, it starts running smoothly without any rattling. Bad shock absorbers would make it rattle all the time, not just at idle.
The bottom is in decent condition, and I don't want to haul it out unless necessary.
I listed all 3 problems because they may be linked...
Any suggestions are greatly appreciated.

Do you have a folding prop? Id look for a bad or loose blade...the banging while undersail could be loose blade banging around down there.. when your sailing, with the engine off, where is your gear selector? In nuetral, forward, or reverse? Id suggest putting it in reverse..
 
May 11, 2015
23
Beneteau 323 Sakonnet, RI
I also put my shift into reverse when sailing to stop the vibration of the rotating prop.
Why does Yanmar suggest leaving in neutral?
Thank you, David
 

troy

.
Sep 30, 2006
7
Chaser 29 San Pedro
Why does Yanmar suggest leaving in neutral?
It can damage the motor and trans. It's common for them to lock into reverse if you sail in reverse gear.......and you will need to start it in reverse in order to shift it out of gear.

I read somewhere that on 'some' Yanmars if you temporarily switch into reverse while sailing and then switch it back into neutral it can stop the shaft from turning. I've also read about guys sailing for 20 years with their engine shifted in reverse without any issues. I think it depends on the specific motor or transmission.
 
Last edited:
Jul 26, 2015
42
Watkins 29 Ft. Lauderdale
It can damage the motor and trans. It's common for them to lock into reverse if you sail in reverse gear.......and you will need to start it in reverse in order to shift it out of gear.

I read somewhere that on 'some' Yanmars if you temporarily switch into reverse while sailing and then switch it back into neutral it can stop the shaft from turning. I've also read about guys sailing for 20 years with their engine shifted in reverse without any issues. I think it depends on the specific motor or transmission.

You know...My boat had Volvo engine and we did it that way for years... but it might not be right for a Yanmar. I was sailing a few weeks ago on a boat with a centerboard....the cable to the board made a horrific sound as we picked up speed on a beam reach... Id also look at your speedo sensor... maybe the wheel isnt turning true and vibrating... you did mention that the boat was slower than expected under power. Im reaching here I know...
 
Jul 7, 2015
22
Hunter 33_77-83 Kemah
Will you engine achieve full rpms, around 3200 in neutral? Is there any vibration at high RPM?
The engine is designed to do this safely and the manual recommends that you do this for 30 to 60 seconds prior to engine shut down to blow out the carbon built up by the low RPM operation associated with a calm docking.
 

jmf

.
Jun 22, 2004
5
S2 9.2C Keyport
I had a similar sound under sail on my Pearson and it was my rudder upper bearing. The bearing was lose and had to be removed from the tube. Once I cleaned and sanded the outside bearing and tube and epoxied it back in the banging sound was gone. Many years ago I posted this banging noise as you did and a fellow Pearson 26 owner said it was the rudder bearing and he was correct.

I now have an S2 9.2 with a Yanmar 2GM. For the past 15+ years I always but it in reverse while under sail or the prop will spin. In spite of what Yanmar says, and this in my opinion, this cannot be good for the transmission. The transmission will make a banging noise, from my experience under power, if it is low on transmission fluid or if the transmission fluid is old. On my Yanmar 2GM , my transmission fluid is the same as the engine oil, 30 weight. I have always used Shell Rotella T.

Hope it's something simple good luck!
 
Nov 12, 2016
9
O'Day 302 Sarasota
I usually tun it at 2800 rpm. My current fuel lever does not allow me to go above 2900 rpm ...
I called West by North, and I was told my prop is too big in diameter and pitch...
 
Nov 12, 2016
9
O'Day 302 Sarasota
I appreciate you all for the various solutions.... :) things I would have never thought about ...
 

troy

.
Sep 30, 2006
7
Chaser 29 San Pedro
Our pleasure......being 'overpropped' will also be a potential problem.
 

Jimma

.
Nov 14, 2016
2
Pearson P33-2 Rockland
Could the noise be something rolling around in your aft cabin/quarter berth?