480CE overpropped- what to tell prop shop?

[Nicholas]

I’ve finally managed to get some visibility into my fuel burn numbers and from looking at Tony’s articles on propping the 480CE I can tell I’m overpropped. Looks like I need to reduce the fuel burn for each engine by about 2gph at 2200 RPM. Do ya’ll have a suggestion for how much pitch to have taken out to remedy the situation? They are 4-blade props (photo attached).

Here are my numbers, measured with 4 people on board with gear and supplies for a 3 day trip, full fuel, full water, etc (I only have data from one engine, but I suspect they are the same or similar):

1900 – 12.1 gal/hr
1950 – 12.3 gal/hr
2000 – 13.2 gal/hr
2150 – 15.1 gal/hr
2200 – 15.4-15.8 gal/hr (got two different measurements at different times & conditions)
2300 – 17.7 gal/hr
2350 – 18.3 gal/hr

Topic

[Rob Schepis]

In that your starting post in this thread only had fuel burn data for one engine it’s hard to offer much at this point. The fuel burn data in the initial post was from which engine? do you know?

[Nicholas]

Interestingly, the dock hand said he thought he heard the stbd engine missing. But it’s actually the port that is reading higher on the fuel burn, unless I’m reading my instruments wrong. So go figure…

[Nicholas]

The saga continues

Got the props back. After having them reconned and 1” of pitch taken out I’m now seeing 13.2-13.8gph on one engine and 15gph-15.6gph on the other at 2200. So an improvement but I have no idea why they are so different. I’m seeing a little bit of black smoke out of the stbd engine. The dock hand said he thought he heard the stbd engine missing at idle. I couldn’t hear it. So the question – is it likely that the prop job was “uneven” between the two props, and that’s causing the higher fuel burn and black smoke? Or is it more like that I’ve got a different problem on the stbd engine that is causing the higher fuel burn? Boat seems to run great – I’m not noticing any issues with power, acceleration, noise, etc.

[Rob Schepis]

Nicholas definitely “gets it”… he hasn’t even completed the full delivery run home yet and he’s having her hauled and re-pitched.. He’s destined to make her right one thing at a time. This old Bert is lucky to have a new home.

[Tony Athens]

The only thing you said in this post that says anything of real substance is that you reached 2650 RPM and YOU KNEW there is more to the story————————-You do read very well as that is so important!..I do appreciate that as so many do not…………

We both know that “2650 RPM” really means ZERO on this particular engine engine.. The way the governor & ECM operates is ” different” if that help explain– It’s no one’s fault–It’s the way it is….Even the Cummins engineers do not realize what they did or what the long term ramifications were going to be..

So yes, you have more work to do, which most likely really means “PROP WORK”

It’s all about your GPH between 1800 & 2200 RPM that tells engine loading..

NOTHING, and I mean NOTHING ELSE, matters..

Keep us all in the loop…

Tony

[Nicholas]

Philip wrote:

Usually if you work with the prop shop to adjust for max RPM fully loaded then your mid range fuel burns fall right into place.

Any chance you know what your max rpm was?

The prop shop should be able to tell you what the effective average pitch was even with less than perfect props and use that number to adjust from.

As I’ve learned by countless hours studying articles and posts on this site the 480CE is a bit of a different “beast” for propping. I was able to achieve ~2650 WOT on the initial sea trial but that doesn’t necessarily tell the whole story with these motors.

Interesting comment about them being able to give me the “effective” pitch. I didn’t think to ask about that.

One other complication is that I’m having this done while I’m in the middle of moving my boat up the east coast from FL to the Annapolis area. So I don’t necessarily have lots of time. In addition to the high fuel burn numbers I also noted black soot starting to accumulate on my transom. So I think the best thing to do is to get them reconned, take a little pitch out, get new numbers, and go from there. Will report back how it goes.

[Philip]

Usually if you work with the prop shop to adjust for max RPM fully loaded then your mid range fuel burns fall right into place.

Any chance you know what your max rpm was?

The prop shop should be able to tell you what the effective average pitch was even with less than perfect props and use that number to adjust from.

[Rob Schepis]

His explanation sounds a bit over the top…I’m sure your survey included a check of the props where a straight edge is secured in place and the props are rotated by hand for a visual check of straightness. and I think if you hit a sandbar on your way home at 25 knots you would have noticed!

Be that as it may, your approach seems reasonable all things considered. Hopefully it works out.

[Nicholas]

Just got off the phone with the prop shop guy. He said he had no way to adjust the prop to a BHP target at a given RPM. He could talk in terms of pitch or WOT RPM.

That being said he told me he scanned them and both props were way “out of whack.” He said it looked like someone had hit a sand bar at 25 knots. His recommendation was to simply recon them back to the original 31″ pitch and he thought I’d get at least 200 RPM-worth of improvement just from that.

I told him I was still nervous about it being over-propped because of the early major overhaul that was done by the PO, and i told him I’d much rather err on the side of being under-propped than over-propped. I was tempted to just have it reconned and put them back on and see where we are but then if they need to come off again I’m having to pay for another haul out, prop removal and reinstallation, etc.

Ultimately I told him to go ahead and recon them AND remove 1″ of pitch. It feels kind of like a shot in the dark but I don’t know what else to do given the fact that the “baseline” fuel burn data I have was with prop blades that were severely out of alignment.

[Nicholas]

Ok thanks. I’ll see if the prop shop can work off the BHP numbers. It looked like that thread was for 3 blade props – I don’t suppose it matters that mine are 4 blade? I’m guessing not since we’re talking in terms of power not pitch.

[Rob Schepis]

I would say you could be looking at a 2″ pitch reduction.

In a recent almost identical thread here is what Tony recommended be told to the prop shop

“Tell him you need your props to absorb no more than about 250-260 BHP at 2200 RPM ( about 13 GPH)…Then the rest will take care of itself. Let’s see how good he is…”

Here is the thread:

https://www.sbmar.com/community/topic/prop-pitch-38-tiara-open/

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