J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Martec Folding Prop

I HAVE A YANMAR 2 GM AND THE PROP TAKES ITS TIME OPENING UP IN FOWARD.
1,500-1,800 RPM'S. ITS JUST BEEN RE-BUILT BY MARTEC. DOES ANYONE ELSE HAVE THIS ISSUE??

If you've got some way on when you start the prop spinning, this is pretty common with many of the folding props. On thing worth trying is to spin, at say 1200 rpm, for a moment, in reverse, to help the prop open, then back to low RPM, pop through neutural, and into forward, and then bringing up the revs, fairly quickly. This will often get the prop open when it might otherwise be inclined to stay shut.

- David

Martec says it should open at 600 RPM's?? Just pop open??
The boat moves foward under low RPM's,but with little power and then it rumbles at the shaft at higher RPM's(1,800) and finally opens up and powers out.
Does your boat do this??

Martec said my old hub was too soft to recondition, so I just bought a new prop. It is worse than the old one. I tested it this weekend and at 2000 rpm, it would sometimes take 10 seconds to open out even though I greased it with teflon superlube. I think I may have just wasted $500.

Mine wouldn't open at all in foreward unless first opened in reverse and then popped into foreward. Then I had martec rebuild it and balance the shaft. Now it works without a hitch.

I had the same problem. Its not the prop. Its the transmission. I found that my linkage to the transmission needed adjusting, very simple fix. I had the engine in high revolution but the transmission wasn't fully engaged and the shaft was rotating very very slowly. So slow that you'll think the prop isnt opening. Open the engine compartment and watch your shaft when someone puts it into gear. You'll see what I mean. By adjusting the linkage so that there is more throw on the shift lever at the transmission, it will fully engage into gear as soon as you shift into forward and the shaft will spin quickly right away. The prop will open even at idle.

also check for barnacles

I tested it last night and the shaft spins rapidly when the engine is at 2000 rpm, so I believe the transmission linkage is OK. Still the prop won't pop open for several seconds. It's brand new so no barnacles. I dove on it to check for fouling. What am I missing? Martec says trans problems....

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!

My shaft spins quickly. I agree that when static, the blades open and close easily. When dynamic, the rotating hub imparts torque loading on each blade. I suspect the blades bind.