Propping Question – QSC 540s

[Kraig Kilger]

Hi there. I am hoping to get a little help assessing my current propping arrangement and the extent of further required adjustments. My boat is a 2008 41 Riviera flybridge with QSC 540 HP motors (2600 rated rpm). This is my 3rd season with the boat. I have had the props off twice to be adjusted and will do so again after the season if and as needed. I am in SoCal and have used Wilmington Propeller for prior adjustment and balancing. Props are 5 blade Nibral 23.25 x 26 (no cup). Here are a few data points which I hope are helpful:

– I run the boat fully loaded at around 2200-2230.

– Starboard motor burns about 4% more fuel than the port

– When running the boat in a fully loaded condition through the rpm range up to 2230 or so the port is generally at or a little below the recommended fuel curve while the starboard is generally at or a little higher (perhaps .3-.5 gph above).

– When running light both motors are below the fuel curve at all rpms.

– Even with the boat loaded the motors will make 2675ish rpm. At rated rpm, the port is in the high 80 percent range for load while the starboard is in the low 90 percent range for load. Both motors are burning in the 27-28gph hour range at WOT (above 2600).

– While I do not run at 2400, even with the boat loaded both motors run below the recommended fuel curve.

– As an example, this weekend running with the boat fully loaded at 2200 the port was burning 17.3 gph at 65% load (78% throttle), while the starboard was burning 18.0 gph at 68% load (78% throttle). Pretty typical.

– That same trip when I bumped it up to 2400 to get a reading the port was burning 21.3 gph, while the starboard was burning 22.0 gph (both below the recommended fuel curve).

– So, as a general rule, the boat runs through the rpm range into the 2200’s when fully loaded with the port at or a little below the fuel curve, and with the starboard at or a little above the fuel curve. At higher rpms (where I do not run it) both motors are below the recommended fuel curve, and both will easily spin up above 2600 even when the boat is fully loaded.

So, what do I do? How far off am I from where I want to be and if further adjustment is warranted is the answer further reduction of pitch, or potentially reduction of diameter? Okay to keep it with no cup (any concerns about excessive slippage)? Much thanks.

Topic

[Mike Mason]

Nobody better than Wilmington. You are right where you need to be. Adding cup would give you lift but then you need to reduce pitch. It’s give and take. Enjoy it how it is.

I have been down this road chasing a ghost. Our burn rate is slightly off port vs starboard as well.

[Jen Wren]

Trim

Kraig, I’m in a similar situation with my QSC 540’s. One thing I have found to be help is being certain the boat is trimmed to be perfectly level. The starboard motor always burns a little more fuel but I can get the burn on both motors very close. Anglers are always moving around and sea conditions changing. Keeping an eye on how the boat is riding has helped me.

Gary at Wilmington Propeller does all my prop work and I have all the confidence in the world in him.

[Kraig Kilger]

Thanks Tony. That let’s me relax a little. Props have been balanced and should be in good shape. Regarding the cooling side, I replaced my aftercoolers this spring (one purchased from your shop) as the originals were 10 years old and despite periodic service (including removal 2 years prior by my mechanic) they were starting to show the beginning signs of deterioration. Better safe than sorry. Coincidentally, I’m in the process of installing a fresh water flush system on the boat now. Should be up and running in a week or so.

[Tony Athens]

Kraig,

I read thru this 3 times, looked at the graphs, and if I am going to comment it would go like this………You have done all that needs to be done.. As long as the over all quality of your props are up to spec, I’d just go fishing..

At this point I would spend your efforts of being sure the seawater side on the engine stays in tip top shape, with special attention to aftercooler servicing every 2 years or so if you do not fresh water flush when sitting at the dock. You can 2X that with fresh water flushing.

Tony

[Luke Nelson]

Another thing to look at is do both shaft turn as freely as each other or is one tighter?

[Kraig Kilger]

At the risk of being redundant, I wanted to follow up with a few more specifics regarding current performance as I try to assess next steps, if any, for my props. As a reminder, my question pertains to the extent of required adjustments given that my fuel burn at higher RPMs is well below target, but at my cruising RPM range of around 2200-2230ish, I am typically at around 70% load (+/-) and little over the stated fuel curve at least on my starboard motor (around ½ a GPH). In running the boat this weekend I captured a few additional data points to demonstrate the performance at high RPMs.

– First, both motors easily spin up to 2670+.

– At 2400 rpms, port burned 20.7 gph, and starboard burned 21.7 gph. Fuel curve benchmark is 22.6 gph.

– At 2600 rpms, port burned 24.9 gph at 85% load and 96% throttle, and starboard burned 26.1 gph at 90% load and 96% throttle. Fuel curve benchmark is 28.9 gph.

I know that this is the same question I posed in July, but based on this additional information is there any sense of whether further adjustment is warranted and if so how to approach this with the prop shop? I have no aversion to pulling the props again, but I don’t want to take more out of the props and further reduce performance if it is not warranted. If a “little more” is appropriate, how should I make the request to the prop shop (Wilmington Propellers) so they make the proper adjustment and don’t overdo it? I may have removed all of the pitch than can be removed at this point which may leave me with further reduction of diameter as my only option. I would, for obvious reason$$$$, prefer not to purchase a new set of props.

Any guidance is appreciated. Thanks again!

[Rob Schepis]

Well it really comes down to where you are on that fuel curve at the RPM where you run the boat, that’s what really matters, not so much where she falls at the other RPMs just for testing purposes… So yes some further tweaking would be good. Have you considered another set of props, probably less pitch, with cup? As you said yours might be all tweaked out but I’m sure another set of props don’t come cheap….

[Kraig Kilger]

Thanks for the response Rob. When the boat is fully loaded I’m either (i) fishing and therefore running 2 bait tanks (one in the cockpit and one in the transom) which adds about 1,000 lbs of weight, or (ii) towing a 12 foot rib with the outboard down which adds drag. Either way, I think the boat works a little harder to keep its rear end up on plane and burns a little more fuel.

Wilmington Propeller is the shop in our area that everyone seems to use and I understand they are knowledgeable (I’m sure Tony can weigh in if he has a different recommendation). You mention diameter. Yes, diameter was reduced by .75″ and I may not want to take more off. As for further reduction of pitch, I understand the Nibral has a “memory” and that there may only be so much that can be taken out reliably. It does seem like some cup would be helpful but I guess it depends on how much more pitch can be removed to compensate and still end up with a little less fuel burn.

As a threshold question, how far off of target am I now? Seems I may want to make a modest adjustment, but I’m just not sure how to approach it at this point.

Thanks!

[Rob Schepis]

Well you’ve done your homework and your due diligence in making things right – you are very close if not already there…

You did not post speeds but does seems like the hull likes to go a little faster and is falling off plane at the lower cruise rpm’s…?

No cup at all? Cup in the prop should reduce cavitation and slip and increase prop efficiency. But cup will increase the effective pitch so you cannot do it alone, pitch or diameter must be dialed back. Diameter is already conservative so likely a pitch drop to add some cup would be the way. But if you’ve already “de-pitched” you might not be able to do more.

Are you getting recommendations from a good prop shop(s) in your area?

[Author]

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