Am I Over Propped

[Charles Pencinger]

I have a 40′ SeaRay Sundancer with twin QSB 5.9 380 hp.  After an oil change and new filters we did a short sea trial.  Bottom was cleaned and painted in October. The props were new last year and are 21 X 24″ Attached are the results of the seatrial.

Topic

[Charles Pencinger]

Overpropped

Richard, yes we met in Colonial Beach. 

Send me a pm and we can discuss. I also have a question about your camper back.

[email protected] 

1 user thanked author for this post.

Richard Scott

[Richard Scott]

Same issue here

Charles, Did I meet you in Colonial Beach several weeks ago? I had the 2007 40DA and we were discussing props and how these guys helped you. I currently have (P)21×23 and (S)21×22. Cummins QSB 380s. I cruise at 2450 at 80% load, appx 30gph total and 20 mph. Not sure why some of these had the different pitched props. Thinking of dropping both down 2 inches. Most RPM I can make is 3900.

[Charles Pencinger]

Overpropped

Thanks for the insite Steve. I wasn’t cruising at 2800, it was only briefly for measurement purposes.  However, I did get 80% load indicated at that speed. Good advice to keep it under 2700.  I still don’t have the guts to take it over 3000.

[Steve Lewis]

CP,

A couple of things.  The gov will kick in around 3065.  The attached performance doc shows a range of 3065 to 3085.  So the engine will manage itself in that regard.  My 480Ce’s self limit at 2665 and my published range is 2650 – 2700.  We will be testing that again once we launch as we finally had our cylinder heads replaced. We had 2 inches of pitch removed over previous seasons so the new heads will get the benefit of that reduced burn.

Cruising at 2800 is a bit hard on the engine in my opinion.  The same document states, in the fine print, that reduced power should be “at or below 300rpm off rated”.  In your case that is 2700 or lower.  Using linear interpolation I am calculating that you will be on the curve at 2700rpm.  You might consider pulling back 100 to 150 rpm for long cruising legs.

In the end it is a balance of engine longevity and acceptable performance for the owner.  I am over the curve a little.  30gph total should be 2300 for my engines but in heavy cruise trim we burn 30ph @ ~2230rpm.  I will live with that as my EGT is within spec.  I am making a judgement call for our own situation. 

[Charles Pencinger]

Re propped

Got the chance this week to take the boat to Wanchese on the OBX for haul out and prop removal.  the prop shop re machined the props from 21 x 24 to 21 by 22.  (2″ of pitch removed) . the ride home was a little bumpy with a 1′ chop on the Albemarle sound.  However the performance improvement was great.  My cruise rpm is now 2800 and I am slightly below the consumption curve at 15.5 GPH and running at 80% load. I easily reached 3000 RPM which is rated.  I did have one question, is is OK to go beyond 3000 or just leave it alone.  I thought the engine was limited by the electronics.  I was too gun shy to push it any further.

As a reminder, the boat is a 40′ Searay Sundancer with Twin QSB 5.9 380 hp.

[Byron Biggs]

cleaning aftercooler

Thanks for your advice.

Just bought the boat in Sept 2022.  My best guess the a/c’s have not been done since 2015!  Having read your advice for over 2 years in anticipation of moving to a powerboat. I have a mechanic going thru the cooling system (HX, aftercoolers and tranny coolers) and the AC’s to your protocol as we speak.

 

[Tony Athens]

Good advice. 

How long has it been since the aftercooler was properly serviced per my protocol?

[Byron Biggs]

Moving dip out of way for impeller removal

The boat is a 2006 searay 40 sundancer with qsb5,9 380

Need to move dip stick on starboard engine a little out of way to remove impeller.

Tony asked for pics.

Been given advice to just remove dip stick clips and move out of way.  Just wanted to check.

[Steve Lewis]

Byron,

As to your prop shop. What I have found is that you have to tell them exactly what you want, not just give them the data and hope they will come to the same conclusions that you are. When I took my props in for tuning and spoke with the guy that was going to do the work, He spoke in terms of RPM at WOT as opposed to “hey I want to lighten the load in the cruise RPM range” I was hitting the gov at 2665rpm but still burning too much at Cruise. So I instructed them to take 1 inch of pitch out of both, then balance and polish. When I got them back I got just what I asked for. Nicely polished props with the Propscan reports before and after the work showing the change in pitch. That was June of 2021. Once we splashed I found that 1 inch was not enough. So in the winter layup of ’21 – ’22 I did the exact same thing. I got just what I asked for. So we started off with 23×27 now we have 23×25. Hindsight is 20/20. I should have asked for 2 inches the first time. Since I was trying to do something that they are not trained to analyze, I asked for the work and gave them an explanation as to why I was asking. He said, OK. Come back in 2 weeks.

[Tony Athens]

No crystal balls here———————-Post GOOD pictures of what you are attempting to sort out as to your impeller change-out issue.

Props– They may be the best as to shops, but do they know that Cummins wants engine props to reach over minimum rated in all cases?

On electronic it goes like this (a cut and past) :

Propping Cummins Electronic Engines (any rating)

With the introduction of electronic control systems, the load demand on an engine is readily displayed and should be used to determine the appropriate propping of the vessel. An electronically controlled engine is able to determine the load placed upon it by using the inputs of engine speed and fueling required to achieve that engine speed. The load reading is displayed as the percentage of load placed on the engine compared to the full load capability of the engine at any given speed. For example, if an engine can produce 200 HP at 2000 rpm and there is a 100 HP draw upon it at 2000 rpm, it would be at 50 percent load. If the same engine can produce 300 HP at 3000 rpm and there is a 270 HP at 3000 rpm draw on it, the load would be 90 percent.
During transient conditions such as hard acceleration, the engine can be at or near 100 percent load demand at less than rated speed. However, once 100% load is reached at steady state conditions, the engine will no longer be able to increase speed. Therefore, if an engine reaches a steady state 100 percent load before rated speed is achieved, it is over-propped. Conversely, if an engine is able to exceed rated speed, the load percentage will indicate less than 100 percent load at rated speed. The degree of under-propping will determine at what speed above rated speed 100% load is achieved.
Electronic engines have an isochronous governor which limits the maximum speed to a range typically between 50-75 rpm above rated speed. Once an engine reaches the governor, it will no longer advance in speed or power.
Therefore, if a vessel is sufficiently under-propped so that an engine does not reach 100 percent load before the governor, the engine will be limited from producing all its available power. In some applications, it may be necessary to prop the vessel so that the engines are hitting the governor and not at 100 percent load at full throttle. Typically this applies to production vessels, where the first hull has been loaded to a heavy displacement, tested to comply with reaching rated speed, and then unloaded to

[Byron Biggs]

With great trepidation I am going to weigh in here!
My boat (just bought Sept 2022) 2006 searay 40 sundancer express with qsb5.9 380’s
I sent my props to Miller Island Prop shop (supposedly best in Balt Md area) with full Cummins Insite data (fuel burn, load etc) and they came back the same, 21 X 23 but a lot less dings. I thought they might take off an 1″ but no, so when we get back in the water I will find out!

Another question (sorry no pics)?
Trying to change impeller (sherwood pumps) on starboard side but dip stick tube is in the way. Looks like there are two easily removed brackets and then I can move and tie off dip stick by about 3″ to give me room. Hoping not to cause oil leaks???

[Tony Athens]

Tell your prop guy you need not less than 200-225  RPM–

Remember, you  cannot under prop engines like this, you can only over prop them.. 

[Charles Pencinger]

Overpropped

Thanks Tony. I am currently at 21 x 24 4 blade. What size do you recommend?

[Tony Athens]

My take based on your numbers = GROSSLY OVERPOPPED.. If you were not fully loaded when you recorded these numbers then you were GROSSLY OVERPRPPOED X 2

[Charles Pencinger]

Overpropped

Thanks to all for your comments.  Pwroberts: my props are 4 blade 21 x 24 nibrals.  I’m thinking I need to go to 21 x 22.  I’ll probably do that at the next haulout 

[pwrobert]

Similar but different.

My 38 ft Chris Craft Commander with 5.9 6BTA’s Diamond 370’s weighs about 24000 lbs and when the engins were installed in 2019 the suggsted propes were 22 X 22 but to get tony’s specs the were reduced to 22 X20 and all is good reaching 3100 RPM loaded at 31 MPH.  These are 4 blade Nibral’s.

You are 2 ft longer and I would guess similar weight as the old Chris was built way heavier than most. You didn’t say so I’m guessing yours are three bladed.

[Steve Lewis]

CP,

I concur with LL.  I have attached my write up on Propeller Tuning.  Since you have already made your own chart and have the data from the Cummins performance report for the QSB380, skip to step 5 and read up on how to interpret and analyze your data.  By my read of it you are looking at removing at least 2 inches of pitch.

There are atleast 3 other Diesel 40 Dancer owners on the forum.  I am sure they would be happy to chime in and share their own experiences and where they ended up with respect to Prop Dimensions.

My wife and I went through the same process over the last 2 seasons and have settled on being a little over the curve in our own full cruise trim and pretty much right on the curve when we are light and just knockin’ around on weekends.

That vintage of 40 Dancer is a very nice cruising platform.  Once you are dialed in, you will not be setting any speed records but you will be able to cruise confidently until you need to find fuel. We cruised our ’06 gas powered 40 Dancer around the Great Lakes for 3 seasons.  It served us well but I would have liked the extra range that the QSB’s would have given us. 

[Loulouton]

You are overpropped

Hello, I learned from that forum and can tell you that you are over propped.

1/ You should hit 3065 @ WOT

2/ Your fuel consumption curve should be at or below the cummins spec (I would tend to say that slighty above can be consider as OK but clearly you are far above specially at cruising speed)

Adjust your propellers seems a must.

LL  

[Charles Pencinger]

Lets try it this way

		Andiamo	12/7/2023	Cummins
RPM	PORT GPH	STBD GPH	SOG KTS	Specs GPH
600	0.4	0.4	4.4
1000	1.2	1.3	6.8	1.1
1200	1.8	1.8	7.6	1.9
1400	2.9	3	8.2	2.7
2000	10.3	10.3	10.4	6.6
2200	11.7	11.9	15.9	8.4
2400	13.8	13.9	18.4	10.4
2500	14.6	15.1	19.9
2600	16.2	16.4	21	12.7
2800	18.6	18.9	23.4	16
WOT 2870	19.5	19.5	24.1
3000				20.1
Conditions Calm temp 60F full fuel tanks empty water tanks 2 POB	Vessel 2007 SeaRay 40 Sundancer

[Charles Pencinger]

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I’m not sure if the attachment took.

[Author]

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