Engines "Bogged Down"

Taking our Pilot 43 out for the first shakeout run yesterday. After warm up under load at trolling speed, I increased the throttle to 50 % power, then to 100 % power, which at this point the engines (Twin Yanmar 6LY 440's) started to "bog down", never reaching WOT RPM's. Actually reaching about 60 % on port and 70 % on starboard. Oil pressure, water temperature normal. Once back to 50 % power all was OK.

Should I assume a fuel problem? I'm going to check the Racor's and secondary fuel filter's. I was also thinking of running the RPM's at the dock not under load. Good idea?

What would be the best progression of troubleshooting this problem?

Crazy as it may sound, I have never had fuel problems.

Bottom and props clean?
No harm in full rpm at no load for a test but they will probably be oK
One or two fuel tanks?
Do check the filters. air filters and inlets and exhausts.
Both engines though sounds first like props or bottom,

Thanks @bayview. The bottom or fouled props may be it. The boat has been in the water all year at our dock, which is on a canal with brackish water. The drag in the Great South Bay is that you cannot see anything under water.

I'll check the filters, etc, but will also put on the wet suit and take a look.

Thanks again.

Common fuel feed? Any whitish smoke? Sounds like maybe contaminated fuel (possibly water=white exhaust DAMHIKT). It could also be a clogged injector (Black Smoke DAMHIKT either)



Running the engines WOT without load not a great idea IMO, as they could redline very quickly.

When we first bought our 430 with 370hp Yanmars it did the same thing. I replaced both the Racors and Yanmar fuel filters and that fixed it.

You can’t make any assumptions with a dirty bottom. Solve that problem and I’d put money on that fixing your issue.

Having said that, you do do your normal maintenance, right?

Sounds like my boat when we first had her.

Turned out to be a lazy fuel deliverly.

When was last time vessel achieved full rated RPM with current props?

Clean the bottom and props. Can't troubleshoot any of this til bottom and gear are clean.

There is a simple test to differentiate between a dirty bottom and a fuel restriction:

Open both throttles to wot after warming up. Look at the exhaust. A clean exhaust indicates a fuel restriction since you are getting plenty of air and limited fuel the engines run clean. If you see black smoke this is an indication of overfueling due to too much load on the engines caused by a dirty bottom.

Those engines need a clean bottom, with the boat propped to reach 3,500 rpm at wot (phototach checked) and never cruised at higher than 2,800 rpms.

David

StarChaser said:

Running the engines WOT without load not a great idea IMO, as they could redline very quickly.

Click to expand...

There is absolutely nothing wrong with running the engines up to WOT with no load. It will certainly redline...that is the goal or hope. It is one of the steps that should be done when addressing a problem like this.

Like David said, we need to know smoke or no smoke under this conditions and what color smoke if there is some.

Baker said:

There is absolutely nothing wrong with running the engines up to WOT with no load. It will certainly redline...that is the goal or hope. It is one of the steps that should be done when addressing a problem like this.

Click to expand...

This is a standard test done on diesel engines. It doesn't hurt anything. This will tell you if the governor is set correctly. No load WOT rpm is very repeatable since there is no load on the engine.
Sometimes also called "high idle" you should be able to find the specs for your engine.

I was finally able to get the boat out and dive underneath to take a look at the running gear. As suspected, the rudders and props were completely fouled, lined with barnacles, etc. There was no growth on the hull or the trim tabs.

For 20 years I have kept my boats in the water, a canal behind my house, which has brackish water. It is located off of a river. This is the first time I have experienced fouled running gear from winterization.

Thanks for the replies.

Thanks for letting us know