Qsb5.9 380

[Rayvonne]

On a previous thread the the discussion of over/underpropt was discussed. On my engines the WOT should be 3000 RPM. I believe I am hitting 2900 trimmed out. I am still working with it to hit the 3000. A mechanic said 2900 should be fine but want to confirm with you guys. I plan to be out this weekend and give her another shot loaded. Is the 2900 sufficient? Thanks in advance!

 

[480ces]

QSB 380 should be propped to see no less than 3000RPM fully loaded and fuelled, 3050 is probably better.

What is your fuel burn from 1800 to WOT in 100 RPM increments?

Have you verified your tachs are accurate by comparing to a phototach on the flywheel?
Edit: I've found the Vesselview to be very accurate if you're reading the digital display, though it doesn't hurt to double check it.

 

[swaterhouse]

I highly suggest you go to sbmar.com website and get the performance curve for your engine and compare it to your results. http://www.sbmar.com/engine-info/cummins-qsb5-9-specifications/

For best health your fuel numbers should be at or below the rated curve and you should EASILY hit the max RPM (which for the 380 looks to be 3065 RPM).

I would also question how good your mechanic is, 2900 RPM on a 380 is most definitely over propped or you have some other issue. If you want an independent free expert opinion post your results on sbmar's forum.

 

[alnav]

Since you don't mention it, what is the condition of the bottom? If not completely clean, especially the running gear, you can easily see numbers quite a bit less than the WOT spec.

 

[Rayvonne]

Thank you guys!! Yeah we have fresh bottom paint 2 weeks old in fresh water. This weekend I'm going to try to get out and run it to see exactly where I'm at. I do have the performance chart and will compare. I should have the trim tabs all the way up... correct?

 

[480ces]

You may need a little tabs for stern lift depending on the hull, drop the tabs a hair and see if speed comes up, rpms come up or fuel burn comes down.

 

[Tman]

I have a 2005 390DA with the same 380's. I re-pitched my props from the stock versions. On the stock props, clean bottom & running gear, I was barely getting 3000 RPM's. I took 1.5" pitch out and now hit 3060 @95% engine load.

Stock props were 21" x 23". Now running with 21" x 21.5"

Lots of performance data if you'd like....just PM me.

Tom

 

[anchors aweigh]

I have the same issue. I hit 2950 on my port and 2970 on my stbd. Fuel burn running at 2600 rpm clean bottom is 15 Gph, 15.4 port. I appreciate the specs. Added note on my boat is a sealift hydraulic platform. I have a light dink and try to weigh/trim correctly.

 

[anchors aweigh]

I have the same issue. I hit 2950 on my port and 2970 on my stbd. Fuel burn running at 2600 rpm clean bottom is 15 Gph, 15.4 port. I appreciate the specs. Added note on my boat is a sealift hydraulic platform. I have a light dink and try to weigh/trim correctly.