J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Prop Vibration, Slipping Clutch??

I sent my Martec prop in and had it refurbished to the tune of $185. It needed it, but I am still experiencing the following problem; I run the boat in forward at 2500 rpm for example, slow to 1000 rpm for a couple minutes, then when I throttle up again, I get a bad vibration that feels to me like one ear of the prop is not open completely. I sent Martec an email about it and their response was;
"Over the past few years, the slipping clutch (Yanmar engines 10+ years old) problem has come to our attention when we have reconditioned a customer's propeller & upon launch, customer has contacted us to report same problem still occurring after our service."

I sent another email asking if they were saying the vibratition was the slipping clutch, or that the slipping clutch was causing the prop to not open all of the way. They did not respond. I don't believe the clutch is slipping and don't think just slowing down, then speeding up again would cause it to slip. I usually have to go to full throttle until the vibration stops, then back off to the desired speed.

Anyone out there with similar experiences that can shed some light on how to resolve this problem? Is the clutch something that needs to be serviced over time? If so, is it a major job or something that can be managed by a back yard mechanic such as myself?

I have the same problem with my J-30. It is not the clutch (on my boat). It is the prop not opening. Sometimes when I try to accelerate I have a big vibration but if I slow down the revolutions then open the throttle again it usually seems to open up OK. There is a fair amount of play in my prop. Of course there is always some amount of vibratuion with the J-30 engine anyway- even when the prop is competely open.

I've been having similar problems with a newly reconditioned Martec, especially in relation to switching between forward and reverse.

This is a recurring problem and the topic of a previous thread in 2002. Here's what I wrote back then, and read Dyk Luben's reply. With a bad transmission, observing engine RPM is pointless, you need to be concerned with shaft RPM. While the shaft may be turning, it won't turn with enough RPM to drive the boat even at high engine RPM. I'll wager to anyone that their Martec prop is indeed opening. Climb overboard and watch!

Brad Stokes
Senior Member posted 08-08-2002 11:19 AM
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My prop opens easily by hand and when the blades are oriented properly the lower one will hang down by its own weight. Given that data, I knew with absolute certainty that if it spins, it has to open. The condition Bob and Dyk are describing happened to me just after I reinstalled the engine after rebuilding it and I had not adjusted the linkage properly. I would have to rev the engine up around 1500-1800 and it would rumble and abruptly "kerchunk" and churn water at the stern. Initially I thought that was the prop opening, but knowing how loose the prop was I knew there was no reason for it to be closed before that. So I looked at the shaft. When put into gear, it would spin but so slowly that there wasn't enough revolution to drive the boat. I pushed on the linkage lever on the transmission and wham it fully engaged and the shaft started spinning like it should - much faster. I realized the rumbling I heard was gears trying to mesh and the kerchunk I had heard was the transmission popping into gear, not the prop opening. I adjusted the linakge so now when I shift into forward, the boat moves even at low RPMs.
Dyk, Bob, I don't know how tight a brand new or recently rebuilt prop is supposed to be, but a spinning mass generates quite a bit of force. The formula for centripetal force is F=mv^2/r with m=mass of object, v=velocity at a certain radius, and r= radius. A quick check of the numbers will tell you that even at low RPM, there is easily enough force to open your prop. Keep in mind that if it is so tight that it won't open, it shouldn't be able to close either, so when sailing an open prop should be spinning like mad and you can hear and feel that. If you can assure yourself that the prop is opening and closing, the only other variable in the equation is the RPM of the shaft. I can only speak from my own experience and what worked for me but there is no reason I can think of for a clean, properly adjusted prop to not open. It has been designed to open when it revolves. Good luck!

Dyk Luben
unregistered posted 09-13-2002 02:36 PM
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I need to follow up on my propeller situation. After further study, I found that indeed the propeller shaft was spinning too slowly. It was a problem in what I called the transmission, but what the professionals call the reversing gear. The clutch was worn out and no amount of linkage adjustment would correct it. I had a new clutch and seals installed by Mack Boring, and it works perfectly now. So if anyone assumes that their propeller is not opening correctly, don't go buy a new prop like I did, but check first that the clutch is fully engaging

I may not be 100 percent sure that my prop isn't opening all the way - it is pretty hard to look under the boat to see if it is, but I can't believe it is a problem with the reversing gear because when my prop finally does open all the way it drives the boat just fine and has plenty of thrust. And there is a lot of vibration - like something is really out of balance when it doesn't open corectly. I cannot see how a problem with the reversing gear or transmision could be intermitent. I have to believe it is the prop. Sure the centripital force wants to open the prop but the water flowing past the prop wants to close it.

"Ditto for Rhapsody last year"


We had the exact same problem on Rhapsody. Plus, we could not reliably engage transmission from neutral to forward when warmed up. A temporary work around was use 50 weight oil in the transmission to make it through the season last year. We had the transmission rebuilt this winter ($650 at Kiwi Marine in Portsmouth, RI). We looked at doing this ourselves but decided that the tools needed to pull sleeves and line up everything justified using a pro. Mack Boring and the local Yanmar service place both quoted $850 for the rebuild.


Just launched Rhapsody last week. Now there is a solid "Clunk" as the lever is moved from neutral to either forward or reverse. The transmission immediately engages with smooth operation - the prop opens right away. The slipping clutch is definitely a common issue on theses older J/30s.

Bill

[This message has been edited by whk (edited 05-14-2005).]

[This message has been edited by whk (edited 05-14-2005).]

Thanks to everyone for the replies. As it turns out, the problem was indeed the transmission/clutch. I observed the shaft and shift mechanism while the wife shifted into gear and throttled up and found when I pressed on the shift lever, the shaft would speed up and the noise/vibration would stop. Upon closer examination I found that the adjuster and keeper nuts were loose and all it needed was to be properly adjusted and secured. Working great now. I only hope I did not damage the clutch surfaces too severly the last several months while it was out of adjustment.

Jerry,
Same with mine, lots of vibration then once it did engage, it had plenty of thrust and drove the boat just fine. It engaged with a "kerchunk" which I thought was the prop opening. Wrong. The prop was already open, the shaft just wasn't spinning fast enough. Save yourself the expense of a refurbished or replaced prop (which doesn't fix the problem). Trust me. Check your shaft RPM.

Well, I wouldn't go so far as to say that props don't need reconditioning. When I bought my boat, the prop had a huge amount of slop in the fit of the blades, and the blades themselves would touch when closed.

Still, now that it is reconditioned, I think I need to take a close look at the shaft and shift lever while the prop is moving. I'll be very pleased if adjustment of the clutch cable fixes all problems.

I still think I have a prop problem. When I put the shifter into forward or reverse I have plenty of thrust but a lot of vibration - like something is out of balance. If I throttle back and go into reverse for a second then shift back into forward It seems to clear up the problem and the vibration goes away. There isn't a significant change in the amount of thrust, just in the amount of vibration when I do this.