r21ec noisy cavitation or what

[bjp447]

First I know the subject has been beat to death, but I need idea's from a different angle.
The boat is a 2012 R21EC, 30ym3 yanmar. Boat always runs fine, no noise other than usual engine noise. Oil good in engine and marine gear, little shaft vibration. I had 5 batteries, 2 grp25 house and start behind engine. 3 grp 27, one on port side , 2 center under lazerette. These appeared to be added later due to sloppy install. Grp 27 weigh 53 lbs each.
I have never used the AC, the grp 27 were basically dead so when I was doing some work on the boat both center rear batteries were pulled. Don't need them don't want them. In pulling the boat out of the marina , rpms approx 1100, gave it a little throttle and got this loud, horrendous noise like the marine gear was eating itself. Took it out of gear , put it back in gear went out no problems. Same issue next day, than next day at 2800 rpm. Only change was 110 lbs out of the lazerette. Got 110 lbs of lead , put it where the batteries were in the lazerette, noise gone(so far).
The boat trim changed slightly with the 110lb weight loss, I gained almost a kt in speed and my WOT went from 3400 to 3600. We were thinking cavitation, but also that the area has no vertical support and the weight has been sitting there for 6 - 8 years, maybe did something to cause vibration. Pulled the boat - prop fine, anodes good and tight, nothing loose underneath, bearings good.
I don't know how to check for cavitation, so if someone has a way let me know. My next try will be to remove the 110lb weigh and temporarily stiffen that area with braces to eliminate something vibrating. Any and all thoughts appreciated.
The folks on this forum have helped me alot with this boat. Special thanks to Dennis in NJ and Larry in Mass

 

[Capt’nKarl]

Very interesting issue. You checked the transmission fluid level with the batteries removed? Have the checked the steering connection accessed through the opening in the lazaret? Also check the brackets that hold the fuel tank in place. I had a 2009 21EC and had an issue with the tank brackets and the steering connection. I can’t imagine the noise being from cavitation. It’ll be interesting to see what you discover being the cause.
Karl

 

[bjp447]

Karl Thanks will check this week. Removed 58 lbs of weight, left 52. Ran boat at all RPM's for 2 hours - no issues. will remove rest of weight will try and recreate noise, than follow your suggestion. Just had boat sanded and bottom painted, 2 days ago. Bottom wasn't bad but could make a difference. I don't want the noise to go away, I want to find it and fix it.

 

[ohioan55]

Hope you solve this issue.

 

[bob daily]

The weight of the batteries would be less than another person on board. I had a similar situation and was the transmission oil level when checked on trailer it was fine, but was a little low when in the water due to angle of boat. When you power up (increased RPM's) the angle of the boat increased causing the oil to be low. Add a little and your problem should go away. Bob

 

[bjp447]

The weight of the batteries would be less than another person on board. I had a similar situation and was the transmission oil level when checked on trailer it was fine, but was a little low when in the water due to angle of boat. When you power up (increased RPM's) the angle of the boat increased causing the oil to be low. Add a little and your problem should go away. Bob

As a follow up - I finally got around to dealing with the Gearbox oil. When I pumped it out it was a light slate Grey. Could be moisture. Putting a magnet in it attracted no metal fuzz, Oil felt , Oily. Have put it in a jar to see if there is a water separation, and have sent a sample to Blackstone for analysis . Bought the boat mid year 2016, fluids were ""suppose"" to have been changed but who knows. If they were gearbox oil has been in there for 3.5 years, maybe 50 hrs, if not could be 8 years old.
Back to Bobs thoughts. The gearbox takes .3 liters 30W (or 10W30 depending on who you talk to) that is a bit over 10 oz.
When I drained the gearbox I took out about 16 oz of fluid. I put 16 oz of 30W back in. so the gearbox was overfull to begin with, this should have negated the trim issue. I have not taken the 50lbs of weight I have where the batteries were back out but will this week to see if the vibration returns. There has been no noise since I put the weights where the batteries were. I am still thinking it is a structure vibration. Electrical systems don't have a monopoly on gremlins!

 

[Capt’nKarl]

On a 3YM30 engine the transmission oil capacity is 300 ml of a premium 30 weight non-detergent oil ( alittle more than 10 ounces). The transmission uses a splash lubrication system so the oil needs to be non-detergent. I’ve heard strange sounds cruising on my 21 but always contributed it to water cavitation under the hull.

 

[MassTug]

I also have a Ranger 21 and I sometimes get the noise that you're describing. I have the batteries in the back for the air conditioning just like you and it doesn't seem to make a difference. It seems to happen at wide open throttle and I've just chalked it up to cavitation. I think it's just the noise that the boat makes. I did the same thing and checked all the fluids as well as the propeller and shaft.

 

[bob daily]

Does this noise happen when you slowly bring the boat up to full speed, or when you slam the throttle to WOT? The theory of weight distribution doesn't make any sense to me as I previously posted. I find that most of my problems/wounds are self inflicted! Going from 0 to 9 MPH in 60 seconds kind of defeats the design of the R-21 and will make it more prone to cavitation and undue were on the gear box. Any way hope you find the cause and let us slower sailor know the outcome. Bob

 

[bjp447]

Does this noise happen when you slowly bring the boat up to full speed, or when you slam the throttle to WOT? The theory of weight distribution doesn't make any sense to me as I previously posted. I find that most of my problems/wounds are self inflicted! Going from 0 to 9 MPH in 60 seconds kind of defeats the design of the R-21 and will make it more prone to cavitation and undue were on the gear box. Any way hope you find the cause and let us slower sailor know the outcome. Bob

To answer your question - let me backstory briefly. I don't use the AC and do not have electric at the slip. Pulled 2 of the 3 batteries in the steer for the room. Ok, pulled out of my slip, no wake zone, got about 50 ft and the racket seemed like something was getting destroyed. Than it went away. Pulled to the ramp to look underneath and started again. Docked boat to think about it. Pulled out the following day , noise started in again, scary!!! Had my friend stand in the swim platform to bring the stern down - noise went away, than started again. Finally got 50lbs of lead (sailboat ballast). Put it were the batteries were and have not heard a peep since. As stated I just changed the gear oil, added an extra 5+ oz. instead of 10 oz (.3 liters). next will remove those weights and see what happens. I suspect the fiberglass over 8 years formed to the 50 + Lbs of batteries and Something is now vibrating with the weights gone. Mind you I am not complaining I think the boat knows I like to work on it.