What could have happened?... Transmission?...

[sv.antea]

well, I left few things out. When shifted into forward the shaft would turn, but only slowly and not much change with RPM, like beyond slipping, only light friction carrying it along. Sometimes it would pop in and out the gear. I think it's a variation on my old problem.
As to my own problem with the ZF10, the idle is set plenty low. The crash engage happens even with the coupler disconnected, but recently I found that if I shift fairly quickly from reverse to forward, it engages normally. I have not tried that yet with the shaft disconnected. Plan on it, though. I have read and reread the gearbox shop manual in anticipation of having to rebuild my new used gearbox. I actually rebuilt the old one in 1984 and it worked beautifully for 26 years and vaguely remembered the measurements, calculations and shimming required, so both the OP and my problems may be related to wear and resulting change of clearances.
My previous post on the subject elicited response from someone, who had same problem with the Hurth not shifting into forward. The person had the transmission later rebuilt by a well recommended shop and now the transmission goes in forward but does the alarming crash engage into both fwd and reverse. It's a mystery, but I suspect it is related to the clearances and shims.

[Snowpetrel]

Have you disengaged the morse cable and checked it by moving the gearbox lever fully by hand into fwd, neutral and reverse? Sometimes it is just an adjustment or morse issue.

[GILow]

After the OP’s description of slowly turning prop shaft I am voting for hydraulic gearbox pressure issues. Check oil in trans for being either low or badly polluted. Guessing the latter.

[StuM]

Originally Posted by GILow

After the OP’s description of slowly turning prop shaft I am voting for hydraulic gearbox pressure issues. Check oil in trans for being either low or badly polluted. Guessing the latter.

The OP has not described a slow turning prop. The discussion has got confused because s.v.antea has started describing his own problems with his Hurth gearbox - rather than sticking with the OP's problem.

[sv.antea]

Yup, sorry about apparent hijacking the thread, after all we don't know the brand / type of gearbox OP has. Or did I miss that? But if it is Hurth/ZF, the symptoms are similar to my experience and has been discussed on CF in few threads already. If Hurth/ZF, I recommend doing a search for "no forward" or "not going into forward". The above mentioned disconnecting the linkage and shifting by hand would be telling experiment, but may be frustrated if the problem is intermittent. Try repeated shifting into fwd at the dock?

[GILow]

Originally Posted by StuM

The OP has not described a slow turning prop. The discussion has got confused because s.v.antea has started describing his own problems with his Hurth gearbox - rather than sticking with the OP's problem.

Oops!

I blame my phone.

And old age.

And possibly the government.

[Suijin]

Originally Posted by StuM

The OP has not described a slow turning prop. The discussion has got confused because s.v.antea has started describing his own problems with his Hurth gearbox - rather than sticking with the OP's problem.

Stu I think “moves very slowly in forward” can reasonably be interpreted as a slow turning prop.

Personally I’m highly skeptical of it being a problem with the prop feathering correctly into forward. Marine growth is not going to prevent that as the forces are considerable.

I vote for it being the transmission. The fact that the OP didn’t even mention what kind he has leads me to suspect the fluid is low or spent at the very least. If it’s a Hurth ZF leaking seal at the linkage is fairly common.

[out42]

Work down the chain. Put it in reverse and forward at the dock - does it engage either or both ways with a clunk and does the shaft pick up appropriately? If not, cable adjustment or lever slippage or coupler slip may be there. Then check the oil. Enough? Clean? No burnt smell?.

With it in gear, turn the shaft by hand both ways to check freedom.

All of that OK and the prop not locked somehow by debris, then it's gearbox out, I fear.

[tml]

A Max Prop can cause the boat to go forward though the engine is in hard reverse. This happens when the blades only partially reverse when the transmission is shifted. This can be caused by external blockage of a piece of zinc or I suppose barnacles. It can also be caused if internal stop pins fail.
I have used Max Props for 35 plus years and continue to be a fan. The irony is that Max Props are so reliable that I was convinced it had to be my new Yanmar engine.
This only happened once but caused considerable excitement as the faster the engine turned in reverse the faster forward we went. The answer is to go to neutral and do your best to slow the boat with a line to dock etc.
Max Prop was very helpful in sorting out my problem.
Which Max Prop do you have?
TML

[barnakiel]

Maybe you caught a plastic bag round the prop?


b.

[Mike Banks]

I think you picked up a piece of rope around the prop while reversing--and you have probably now damaged your gearbox clutch.

That is the bad news.

Now maybe--just maybe--your gearbox linkages are out of adjustment, or your controls are not properly engaging them. In that case a bit of penetrating spray lube, followed by dismantling and cleaning and greasing, then some readjusting and un-jamming of and clogged-up control cables not moving freely, might help.

I think you may have to fix your gearbox clutch though--which means taking out the gearbox and fixing it properly. Check the gearbox oil--if it smells a bit burned--that is what you have done by revving it when something was obviously wrong. I know--I did the same thing--in my case driftwood jamming the propeller.

[chris95040]

Originally Posted by FabioC

For completeness, I should add that I have a Max Prop, but I do not think that was the issue.

uh... why not?

[captlloyd]

Originally Posted by Jim Cate

If a shaft drive, visual observation of the shaft whilst in fwd gear and not moving properly will show whether it is prop malfunction or slippage in the tranny.
Jim

X2. Jim suggests a simple test that will narrow down the possibilities quickly. And there are a lot of possibilities.

[waterman46]

Originally Posted by Jim Cate

If a shaft drive, visual observation of the shaft whilst in fwd gear and not moving properly will show whether it is prop malfunction or slippage in the tranny.
Jim

Yes, and it would help to know what sounds OP hears as he operates the shifting mechanism, whether it be single lever or dual. My Hurth gives a satisfying CLUNK when it goes into gear. I also know that it does sometimes start to turn the shaft, slowly, even before it makes that sound. I suspect OP's control mechanism may need adjustment, and possibly has come a bit loose as well, giving the erratic results mentioned.


I remember one evening in windy Oyster Cove CA when the boat across the fairway from us was trying to get into his berth. He was shooting back and forth, and his wild manoevering made it look as if he was completely clueless as to how to get into his slip. The skipper looked panicked, so I offered to help and he foolishly accepted, but then I was totally embarrassed to find I had the same problem he did, probably worse since I was over-confident that I could help him and I really gunned it to try to overcome the wind forces. Turned out he had no forward gear at all so I had a minor crash or two before we got enough good folks on the docks to throw lines to.

[CapnCrunch]

I had a very similar problem with an older power boat that had inboard engines with velvet drive trannys. It turned out that the hub in the flex plate had come loose, allowing the engine to spin freely, but would still "catch" and engage the tranny intermittantly.