5.9 6bta wot

[0025]

Greetings

I have a single-engine 2001 390 Mainship. It's powered by a Cummins 5.9 6 BTA engine. I'm trying to figure out why I can not get to WOT.
WOT is 2800 rpm and I can only get to 2600. I haven't verified the rpm gauges yet, but I will shortly.
I max out at approximately 10 knots with a full load of fuel and water.

The propeller: 26d x 26p 4-Blade Bronze.

I can reach WOT in neutral and the bottom is clean.

Suggestions?

Thanks for your time.

Ron

 

[HopCar]

Too much propeller. Talk to a prop shop about your problem. I bet they can take some pitch out and get you some more RPM.

 

[fgarriso]

Greetings

I have a single-engine 2001 390 Mainship. It's powered by a Cummins 5.9 6 BTA engine. I'm trying to figure out why I can not get to WOT.
WOT is 2800 rpm and I can only get to 2600. I haven't verified the rpm gauges yet, but I will shortly.
I max out at approximately 10 knots with a full load of fuel and water.

The propeller: 26d x 26p 4-Blade Bronze.

I can reach WOT in neutral and the bottom is clean.

Suggestions?

Thanks for your time.



Ron

Take 1-2 in of pitch out of your prop.

 

[High Wire]

Before you do anything check the tachometer accuracy with a photo tach. They are often wrong.

 

[bayview]

I agree talk to a prop shop preferably a propscan shop. A properly tuned prop can improve both performance and RPM.

The propscan shops use computer measurement to adjust the shape of each blade for best performance they just dont adjust pitch. I had some pitch taken out of props and added RPMs but retained speed.

 

[rgano]

Before I took my Mainship 30 Pilot II in to have its prop pitch reduced by two inches to achieve specified WOT RPM, I ensured the turbo air filter was clean and that fuel filters were new. Aside from fuel and water, have you loaded the boat down with other misc weights?

 

[David Burgess]

I for one wouldn’t be concerned, you mentioned your “wooded” down with a full load of fuel and water that rpm at WOT is close enough. Your probably not going to gain any more hull speed if you find that elusive 200rpm that your looking for. I suspect you’ll find it in the mechanical loss of the running gear. Don’t sweat the small stuff. Just enjoy that tough little power plant.
Cheers,
Dave B.

 

[bayview]

Good suggestions about air filter and fuel filters.

Did you ever get proper RPM?

It is common to loose speed and RPM when we add all our stuff but then the props should be adjusted to reflect as used weight.

 

[smitty477]

Greetings

I have a single-engine 2001 390 Mainship. It's powered by a Cummins 5.9 6 BTA engine. I'm trying to figure out why I can not get to WOT.
WOT is 2800 rpm and I can only get to 2600. I haven't verified the rpm gauges yet, but I will shortly.
I max out at approximately 10 knots with a full load of fuel and water.

The propeller: 26d x 26p 4-Blade Bronze.

I can reach WOT in neutral and the bottom is clean.

Suggestions?

Thanks for your time.

Ron

Some things to check:
- are you sure rated RPM is 2800 on your engine
- is your tach accurate
- what exactly is the high idle speed reading (WOT in nuetral)
- is the engine in good tune
- do you have any other symptoms (smoke, vibration, overheat)

 

[ksanders]

I for one wouldn’t be concerned, you mentioned your “wooded” down with a full load of fuel and water that rpm at WOT is close enough. Your probably not going to gain any more hull speed if you find that elusive 200rpm that your looking for. I suspect you’ll find it in the mechanical loss of the running gear. Don’t sweat the small stuff. Just enjoy that tough little power plant.
Cheers,
Dave B.

David, that is extremely dangerous advice.

There have been Many, many 5.96BTA engines ruined due to overloading.
It is a industry wide known issue.

 

[rgano]

That missing 200 RPM was causing my Yanmar 315 to soot up the side (side exhaust) badly. As soon as the prop was fixed, and full spec WOPT RPM returned, I could no longer wipe my red hull with my hand and have it come away BLACK.

 

[firehoser75]

Mostly good advice so far (except the ignore it advice ).
To test for WOT you need:

- most 6BTA have a rating of 2800 RPM, but you should check to be sure.

- a clean bottom and running gear

- have checked tac with a photo tac to ensure the degree of accuracy
- Boat loaded as you will actually use it
- engine well maintained. eg. clean air and fuel filters, aftercooler recently serviced (especially the "air side" clean)
- check that throttle linkage will reach (allow) WOT.

- with engine fully warmed up, you should achieve a minimum of 2800 and the true target should be just over 2900 RPM. At the dock in neutral you should reach over 3000 RPM (only check this momentarily).
See these articles from a marine diesel expert.

https://www.sbmar.com/articles/engine-life-vs-engine-loading/
https://www.sbmar.com/featured-article/understanding-low-power-troubleshooting/

 

[cks]

If you can get to wide-open throttle in neutral, the engine governor is doing its job. If you’re not able to attain wide-open throttle, max engine RPM, in The water underway then your over propped. End of story.

Get the prop we pitched. You want max torque at approximately 3/4 throttle under normal operating conditions. That means wide open throttle, max RPM.

You may not even know it, but your engine is probably lugging somewhat. I would suspect your engine temperature would be higher when you’re over propped.

 

[smitty477]

If you can get to wide-open throttle in neutral, the engine governor is doing its job. If you’re not able to attain wide-open throttle, max engine RPM, in The water underway then your over propped. End of story.

Get the prop we pitched. You want max torque at approximately 3/4 throttle under normal operating conditions. That means wide open throttle, max RPM.

You may not even know it, but your engine is probably lugging somewhat. I would suspect your engine temperature would be higher when you’re over propped.

"If you can get to wide-open throttle in neutral, the engine governor is doing its job."
Please see the post above yours - you need to exceed the rated WOT rpm when in nuetral to make up for governor droop.

 

[Arc]

Fully loaded boat should hit 2800. Do not ignore this problem . 200 under is no good . In addition compare your cruise GPH to Cummins data. That will tell you a lot more.