Engine revs dropped

[Miker]

Returning from Conwy I was on the engine and the revs suddenly dropped from 3000 to 2000. Increasing the throttle didn't help. I checked to see that the throttle cable wasn't fouled and motored on. When the wind picked up I turned the engine off and sailed. Later, when I restarted the engine it was back to normal. Any ideas, please, as to what the problem could have been. On a previous sail I had run out of diesel and had to use some diesel from a reserve can, but I had motored a good few miles since then.
Could I have stirred up some muck from the bottom of the tank - the diesel in the tank looks OK - or got something around the prop?


<hr width=100% size=1>

 

[Chris_Stannard]

Sudden rev drop is often due to something, usually a plastic bag, fouling the screw. It can also happen if you sail through a patch of heavy weed. A burst of astern often cures the problem. but is sounds as though whatever was fouling your screw came off naturally.
I expect this to happen once or twice a season and am rarley disappointed

<hr width=100% size=1>Chris Stannard

 

[bedouin]

Could be some form of fuel starvation - e.g. the filter is getting clogged up and limiting the rate at which fuel can flow to the engine.

<hr width=100% size=1>

 

[tcm]

Yes i wd agree. I have had fuelly starving problem and the symptoms are very gradual over some miles, not instant.

Also note that you will always pick fuel off the bottom of the tank, not the top - it doesn't sip it like someone drinking a cup of tea, it is like someone drinking from a straw. But of course if there are bits in there then they will be more concentrated as the tank empties.

<hr width=100% size=1>

 

[Avocet]

You might have a partially blocked fuel tank breather. If the air can't get into the tank to replace the fuel being sucked out, a partial vacuum will build up and start starving the engine of fuel. When you switch off or throttle back, the tank will slowly fill with air again. If it does it again, just try taking the fuel filler cap off WHILE IT'S DOING IT. If you hear a rush of air and the engine picks up again, that was the problem.

<hr width=100% size=1>

 

[Miker]

Thanks everyone for your helpful replies.

Went down to the boat this weekend. Diesel looks clear. Breather tube not blocked up, so I will assume that something was around the prop.

<hr width=100% size=1>

 

[tynesman]

I had a simular problem last year,nearly took the boat apart trying to fix it, but the simple anser was raw water pipe intake was partly blocked causing symptons like fuel starvation.
The restricted water intake causes the engine to surge as it is starves of water.
Blasted fresh water down through the intake hole of the water filters for about five minutes,problem solved!
I now blast out filters as above every month to make sure they are clear.

Happy sailing

Tynesman

<hr width=100% size=1>