Losing power

[Brickwoman]

Hi, I'm very new to this so please be kind!  I have a Bukh DV10 engine in the rear of a little 33 ft pinder and have noticed that it has started losing power when driving for over 20-30 mins, the first couple of times I thought it was something around my prop so I stuck it in reverse and hey presto we were off again full power, then power slowly dropped off again, I checked the prop, there was nothing on it and it span by hand freely. Following this I has a look at the prop shaft while in drive and noticed there was a top hat shaped bush on the bearing closest to the engine (would this be the thrust bearing?) and it was spinning with the shaft initially then intermittently stopping.  Anyone have any ideas? I've been looking for a diagram of the bearing arrangement to no avail.  I'm going to take a closer look next weekend as I ran out of light once we were home but was hoping to go armed with some experienced knowledge. 

[dmr]

You most likely have leaves on the prop, so when you stop they fall off which is why you find nothing round the prop.

This really is a genuine and significant issue at this time of the year.

As you found, a bit of reverse sorts things out.

 

Can we have a photo of the bearing thingy please?

[nicknorman]

Yes the leaves get caught on the leading edge of the propeller, totally ruining the shape and making the propeller inefficient. If you go into neutral and then a nudge of reverse, the leaves fall off. But likely the process will need to be repeated 1/2 mile later if you are cruising under trees.

[David Mack]

Yup. I had got to leaves by half way down your post.

The spinning top hat thing is almost certainly something unrelated.

[magnetman]

 

It is also possible to lose power on a small engine like that if a large amount of electricity is being drawn from the battery and the alternator is trying to keep up. 

 

Most likely to be leaves. There are a lot of them about right now. 

[Brickwoman]

Thanks so much, that's really reassuring. I can take a picture of of the bearing next time I'm aboard but that sounds like it may be it, there were a lot of leaves! Also I do remember thinking the water turbulence was changing a bit when the power dropped but wasn't sure if I was imagining it. 

[MtB]

1 hour ago, Brickwoman said:

Also I do remember thinking the water turbulence was changing a bit when the power dropped but wasn't sure if I was imagining it. 

 

Quite the reverse. Keeping an eye open for changes in the pattern and appearance of the prop wash is a great way of knowing when leaves are building up on the blades. 

 

 

[cuthound]

14 hours ago, Brickwoman said:

Thanks so much, that's really reassuring. I can take a picture of of the bearing next time I'm aboard but that sounds like it may be it, there were a lot of leaves! Also I do remember thinking the water turbulence was changing a bit when the power dropped but wasn't sure if I was imagining it. 

 

With a clear prop the wash should be almost straight back from the prop, when the prop is fouled by leaves or worse, the wash is diffused, wider and often to one side.

[dmr]

Learning what the prop wash does is really useful. Its not just leaves but you can also detect small prop fouls like plastic bags and maybe throw them off with a bit of reverse.

Note that when you are in shallow water, or initially accelerating, that the prop wash will also "go bad" as the prop is shifting extra water without moving the boat forward at the correct speed. Getting a good clean prop wash generally suggests that you are driving the boat at a good speed.

[IanD]

1 hour ago, cuthound said:

 

With a clear prop the wash should be almost straight back from the prop, when the prop is fouled by leaves or worse, the wash is diffused, wider and often to one side.

Also noisier, with electric drive this is more obvious even for a small foul.

[beerbeerbeerbeerbeer]

50 minutes ago, dmr said:

Getting a good clean prop wash generally suggests that you are driving the boat at a good speed.

Yes, and this time of year it can be an arduous task 

and just have you’ve started a nice run you’ve got to slow for a moored boat, 🤬

 

😃

[Brickwoman]

That's really interesting thank you, it was going past the moored boats that it really started dropping off until I was almost at a standstill, I guess the art is finding the speed at which the leaves get washed off without having to constantly reverse but without creating a 2 foot bow wave! ;-))  

[ditchcrawler]

3 hours ago, Brickwoman said:

That's really interesting thank you, it was going past the moored boats that it really started dropping off until I was almost at a standstill, I guess the art is finding the speed at which the leaves get washed off without having to constantly reverse but without creating a 2 foot bow wave! ;-))  

I wish you luck on that quest 🥰