Reverse gear seems to work, but actually doesn't!

[julienrobi3]

Hello,
I have an atomic 4 on my C&C 30. I have been sailing it for one year.
The motor works perfectly when it goes forward. The issue is when I need to go backward. It doesnt do anything, or almost anything. When there is no wind and no current, I can move really slowly, less than 1knot. So it doesnt take a lot to lose complete control of the boat!
By reading the manual, I thought that it might have been the reverse gear that needed some adjustment. But it didnt seem to be the problem. The shaft was turning quite fast in reverse, and accelerating when increasing RPM.
So I thought there was a problem with my propeller. When I got it out of the water for the winter, I did some tests and the propeller seemed to turn normally.
So the only thing that I think might be the issue is the type of propeller I have. I know the engine was replaced by an atomic 4 in the past, so could it be that I dot have the right propeller for the type of engine?
Here is the image of my propeller. It is about about 20 cm (8 inches) in diameter.

https://ibb.co/HpBy0Vm (link to image)


This is my first boat, and I even more newbie in the field of mechanics, so I might have missed important things to check in order to find the real problem. So if you have any idea of what could be the issue, I would be really happy to hear your advice!

Thanks a lot !

[Mo]

I have a 12 / 9 on my C&C 30 and it does everything well. It's an old design michigan prop. A 12 /7 would also be a decent prop for that boat. If you were looking around for either I double check the size of the shaft (usually 7/8 inch) unless someone changed it. Check on-line, ebay etc. If buying a new prop buy a 12 inch. The other option is 2 blade props but they don't reverse as well.

With that small prop diameter you have I'd think you'd be doing some higher rpms in forward gear as well and sucking a bit more fuel than you need to be.

[ndutton]

The prop appears to be an Indigo, designed, manufactured and sold by a member of this forum by the same name. I suggest you contact him for the best analysis of your symptom.

Another thought:
Is the engine a direct drive or reduction gear?

[ronstory]

Are you sure the prop is only 8" in diameter? The indigo prop is 10" and I agree with Neil it does look like Tom's prop... but the size would be wrong

Just do a google search for Indigo Electronics.

... and welcome to the forum.

[jbsoukup]

there's no detent in reverse so if you're giving it a lot of throttle you might have to ride the reverse lever (put pressure on it). it makes a distinct sound when engaged and reversing.

[joe_db]

That is an Indigo 10" prop. You are not going all the way into reverse.

[Mo]

there's no detent in reverse so if you're giving it a lot of throttle you might have to ride the reverse lever (put pressure on it). it makes a distinct sound when engaged and reversing.

Agree completely, a video with audio of the boat going into reverse would certainly help.

[Dave Neptune]

To engage reverse you need to hold the clutches in place manually, if you are just moving the handle back and not holding it it will slip.

That's an Indigo prop for sure. I ran one for many many years on my old E-35MKII that I have since sold.

Dave Neptune

[Mo]

C&C 30 is direct drive normally. It wouldn't have a reduction gear unless the engine and step were moved forward with considerable modification to the step in the galley area.

[JOHN COOKSON]

LINKAGE PROLEM?

The first thing I would do is disconnect the shift cable and shift by hand on the trany lever. Check the outer cable cover. It needs to be held down firmly and not move.

ex TRUE GRIT

[julienrobi3]

Thank for all the replies. The diameter is probably my mistake and it would make sense that it is a 10". I live in Canada and my sailboat is currently not easily reachable (cold and snow), so I cannot verify the information just yet.

So if I am not mistaken, I understand from all your answers that my propeller might not be perfect for my engine, yet it might not be the main issue (but I will definitely get in touch with the Indigo guy).

Once the snow melts I will do some more checking according to your replies, and will post a video if I still have issues!

Thanks again everyone. This Afourians community seems really friendly and helpful !

[joe_db]

The Indigo prop is perfect for the engine more or less, it is specifically designed for A4s pushing displacement hulls.
The A4 uses a reduction gear in reverse, but not in forward. There are several things that can go wrong:
1. Lever not moving forward enough to get into forward detent.
2. Lever not moving back enough to fully engage reverse.
3. Internal adjustment issues.
1 and 2 can be fixed with cable adjustments usually.

[Surcouf]

I would add that the understanding if your shaft is spinning as it should, or if your gear is "slipping" when in reverse, is key here. You mentioned earlier that it seems to accelerate when you ramp up the rpm.
- Can you confirm that you keep the same ration "rpm engine" / "rpm shaft" when you hold the shift handle at "idle rpm", and at "higher rpm"? This could be checked with a cheap Harbor F**** speed gun ( I did that to tune the idle speed on mine), depending on the accessibility in your boat of course
- if it is slipping, all the items mentioned by the others on shift cable / gear adjustment apply.
- if it is not slipping, you are back to you prop... first question: how clean is it? after comes the choice of the prop, and I am useless on that

[joe_db]

The Indigo prop has one weak spot - barnacles. In order to not be a huge drag under sail it does not have a lot of blade area. It only takes a few barnacles to really screw it up.

[julienrobi3]

Hello everyone!
So I got to do some tests in order to investigate further my motor problem, and additionnal help from you guys would be really helpful!

So I basically did two things:
1. Test the shaft RPM with a speed gun as mentionned by Surcouf.
2. Look inside the gear box for anything weird.

1. RPM tests
I have tested the RPM at forward and reverse to see if there was some differences. And since the boat is out of the water (so less friction on the prop?) and that I have used a speed gun that I dont really know if it is well calibrated, I dont think we can use the actually absolute numbers, but we can still compare the numbers between them (that is my assumptions, I might totally be wrong about this).
So at mid power and forward, the shaft is at 3000 RPM.
At mid power and reverse, it drops to 900 RPM.
From what I've read, t is normal that the reverse RPM is lower than forward.
But the weird thing occurs when I try to add a more throttle when in reverse.
At some point, the shaft RPM drops almost completely and seems to be at neutral!

2. Opening the gear box
From the previous experiment, I suspected that there was something wrong within the transmission.
So I opened it and played a little bit with the lever to change from forward to neutral to reverse.
I've taken a small video of this:

https://photos.app.goo.gl/KgCshZdJKLfEP6Pr5

Since it is a bit fast, you can pause at different moments to see the positions:
Pause at 3 seconds to see the forward position.
Pause at 6 seconds to see the neutral position.
Pause at 15 seconds to see the reverse position (at that position, I cannot go further with the lever).

So as you can see, there is very little difference between the neutral and reverse position. From other videos of other people, I have seen that the plate fingers could go a lot further than mine.
And actually, the first thing I noticed when I started to play with the lever was that everything seemd to wobble when going from neutral to reverse, even the gear case. And I thought to myself that it probably wasnt normal.

So maybe some elements of the gear are getting loose? and I guess it would make sense that the reverse cannot be engaged properly if everything moves with the lever....
So what do you guys think?
Is there some bolts I should firsst thighten to prevent what is not supposed to move from moving?

Again, thank you very much for your help, this is really appreciated!

Julien