Prop Problems

[gerrysailing]

Hi

I own a Beneteau 36CC fitted with a 28hp Yanmar Engine, the performance going astern is hopeless, it simply has no power or manoverability, has anyone else experienced this problem? could it be a wrong prop fitted or wrong gearbox ratio?

Regards

Gerry

 

[Paul Mermelstein]

To help you answer the question, we need to know a few things.

Have you either had a diver check out the prop (engine off, of course) or haul out the boat and examine it yourself or with help?

Are there any weird noises or vibration in reverse that is different from forward?

Does your boat do ok in forward?

In reverse, can you get any thrust and speed at all? If so, what speed are you doing at 2000 rpm out in the open?

What type of prop is it (fixed, folding, or feathering)? If folding or feathering, what manufacturer?

How old is the prop? How has it been maintained?

Give us a little more, please.

 

[gerrysailing]

Hi Paul

The boat is out of the water at the moment, there are no problems with the prop, the boat will meet its max speed in forward approx 6-7knots with no vibrations etc

In reverse it has no power at all, i can put in reverse while still attached to the pontoon and can physically pull the boat forward against the prop

In the open at full revs it will eventually pick up speed after say a minuet or so, but the max speed would not be more than 2 knots

The prop is fixed 12inch 3 blade and is in perfect condition, I have owned the boat for three years and have always had the problem, the answer I believe lies in the spec of the prop or the gearbox ratio in reverse

Regards

Gerry

 

[Philip_Oceanis 361]

The prop is 12 inch? Do you mean the diameter? This is far too small. On my Beneteau Oceanis 361 (same hull as the Beneteau 36cc) I have the factory fitted 2-blade fixed 16 diameter X 11 pitch propeller and it's very good for both astern and forward (OK with its disadvantages when meeting rough seas and the luck of smoothness of a 3rd blade of course).
I know that the factory fitted 3-blade fixed propeller must be 16X10.
So I guess you have a very small propeller or something wrong with the reverse gear.
You can check the gear box by moving the lever for astern (at idle rpm) and checking the shaft's rotation. If there's not resistance at the shaft and you can stop the rotation (if any) with your hand it means that the gear is not really engaged. I have similar but luckily small problem with forward movement. I have to wait 2-3 seconds for the gear to engage before pushing the lever forward otherwise the gear box will be just spinning.

 

[Ron20324]

Hi Paul

The prop is fixed 12inch 3 blade and is in perfect condition, I have owned the boat for three years and have always had the problem, the answer I believe lies in the spec of the prop or the gearbox ratio in reverse.Gerry

Gerry, the prop diameter is a circle that encompasses all the blade tips. The Syselios site shows a 15x 10 or 15 x 11 for the Yanmar 3gm30. No wonder you're not going anywhere.