Spun Prop Hub

[bobreeves]

I could use some expert opinion on a problem I had with my Yamaha 25 4 stroke. About 3 weeks ago I believe my prop hit something (but not certain). All of a sudden I was unable to get on plane - acted like a slipping clutch in a car. I limped along for 10 minutes or so, then tried again and she came right up on plane and behaved normally. Since that time I have re-experienced the same behavior 3 or 4 times and reasonably certain that the prop did not hit anything. I've done the standard test - hold the nut with a wrench and try and turn the prop by hand, and I cannot. Has anyone else had a similar experience - where the rubber hub seems to repair itself or recover? Prop shops I have spoken with say when they go that they go for good and you have to press in a new one.

There are no signs of damage to the prop - no dings or scratches.

I went to my dealer today to purchase a replacement prop. When I originally purchased the boat the prop on the engine had a lot of dings in it, so I asked the dealer to replace it. This engine comes from the factory with a 9 7/8 x 10 1/2 prop. They did not have one in stock, so he put on a 9 7/8 x 11 1/4. Performance seemed fine with this prop - engine rpm 5800 and 28 mph. When I spoke with the dealer today, he suggested I go back to the standard issue prop which he had in stock. He said it was possible that the additional pitch on the prop I was using might have put enough strain on the rubber hub to spin or weaken it. 10 1/2 to 11 1/4 doesn't sound like much to me. I have installed but not tried out the new prop yet - waiting for the temps to go up a bit which is scheduled to happen by the weekend.

Sure would appreciate any opinions on this.

By the way, I was going to have this prop re-hubbed, but my dealer said just bring it in and he would have it replaced free by Yamaha as long as there were no signs of external damage.

Thanx,

Bob

[Flipper]

sounds like a spun hub, if yamaha is going to replace it free go for it . the first number is the diameter of the prop the 2nd is the pitch, the pitch is 1 revolution will take the prop so many inches ie. 15x19 1 revolution it will go 19" just be sure you stay in the operating range of the engine found in your manual. Prop 101: pitch goes up,speed goes up, RPM's goes down, thrust or hole shot goes down-------pitch goes down,speed goes down,RPM's go up, thrust or hole shot is better each pitch change RPM's on average go up or down 200r's. Flipper

[Harry]

Spinning a prop does happen and it acts exactly like what your describing.

I had this happen to me with my 90hp Johnson. No the rubber doesn't repair itself, but re-seats in the hub, until next time. Over time it will happen more and more.

The first time it happened to me I was cutting the wheel too hard and I guess going to fast. The prop must have cavitated and the prop spun too fast and dug back in too hard which made the rubber in the hub slip. RPM's went way up.

I throttled back down and took off again slowly until I reached plane and all was fine. It did it a couple more times until I eventually sold the boat 2 years later. I never did change the prop, and it did it just once since the first time under hard acceleration, and once in a hard turn again.

[bobreeves]

Really appreciate the responses. I believe now that prop cavitating then digging back in probably was the cause in my case too. I have trimmed up too far several times then dug back in.

Thanks guys.

[thunder]

its may just be you caught a bag or a bunch of leaves, i had the same thing happen to me at low tide while duck hunting, I was just about hitting bottom and sucking in the leaves and it would rev like hell and go nowhere. just my 2cents..

[bobreeves]

006
At $35-45 to press in a new one, they ought to make it a little more difficult to spin one, but then again better to error on this side rather than on the other and have to replace a lower unit I suppose.

[bobreeves]

009
My dealer gave me a new original equipment Yamaha prop - 9 7/8 x 10 1/2. I warmed up a bit today, and I was able to try it out. It was clear that I needed more pitch - engine ran 6200 rpm at WOT and top speed dropped. I returned it and he gave me a new 9 7/8 c 11 1/4, which seems perfect for my particular J16 setup. He also refunded my purchase price and will file with Yamaha for warranty replacement, as it was also obvious to him that there was no obvious external damage to my spun prop - not a sign of a ding or scratch anywhere.

Thanx again for all the helpful comments I received on this problem.

[bobreeves]

After much communication, I've concluded that I didn't actually have a spun prop, but rather prop ventilation / cavitation, due probably to a combination of running through weeds and my motor being mounted a bit high. To review, I have a Yamaha 25 4-stroke short shaft mounted on a CMC35 tilt trim. CMC recommends the anti-ventilation plate on the motor be between 1 and 3" above the bottom of the boat. Mine is right at 2", so certainly within spec. Another user with a similar problem indicated lowering his engine just 3/4" completely cured the problem. Unfortunately that is not a trivial operation on my setup. I would either have to drill holes and remount the pivot point on the CMC, or remove and lower the entire unit (plug old holes, drill new ones). I'd like to avoid either of these cures if possible. The problem only happens occasionally and I could really just live with it. Turning Point Propellers sells an aluminum Rascal prop for this motor which they claim specifically addresses this type of problem, so I have ordered and received one. It is a cupped prop - about the only one I could find in aluminum. It is not yet installed, but weather is supposed to progressively get better over the next several days, and I expect to try it out before the end off the weekend.

If anyone has experience with this prop, I would love to hear about it. I very much like their hub system, which is user replaceable should I actually spin one at some point.

I will report back my results once I test this. Turning Point has an exchange program where you can swap out for a different pitch if needed for about $30 (assuming no damage to the prop). I purchased the prop from boatmartusa.com and very pleased with their prices and particularly their service - very prompt responses to questions.