Fuel burn...

Zues boat "It turns on a dime, thanks to standard Zeus electronic steering that adjusts for boat speed to keep everyone safe. Based on my sea trial and discussions with Cabo’s factory captain, the 40 HTX’s best cruising speed, with respect to economy and engine load, is 2,710 rpm, making 32 knots and burning 45.4 gph for a net of 0.71 nm per gallon."
Cabo 40 HTX | Boating Mag

MAN boat burns 63 GPH at 2100 rpms 32 knots

https://yachtforums.com/attachments/c40-pdf.94861

MAN and Cummins both list rated cruise speed at 80% load, those numbers are at 80% load. Cabo modified the mold for Zues boats so they weren't mounted on the V, same hull just different in the tunnels. I've run boats with pods mounted on the V (same angle as the V) and when you turn a little more than a little all of a sudden they hook and the entire boat leans over and cuts a hard turn. How are the numbers hard to understand? Cummins boat 80% load 32 knots, 45 GPH. MAN boat 80% load 32 knots 63 GPH. I've run dozens of those boats in those combinations. I'd actually get 33 knots out of the Zues boat at 45 GPH, and 32 knots at 62 GPH on the MAN boats, on all of them. Cat C12's 700hp would do 30 knots cruise at 58 gph I think it was. It's a direct comparison. It's a direct comparison as one can get, same boat, same setup, same weight (except lighter engine weight). Different props, different reduction, hotter air and water temperature than where you are. 85-90F air temp and 83-86F water temp burns more fuel. Those are the numbers and 100% accurate. There is no data on Post #8, these numbers are for the express with tower, they also did make a flybridge 40' cabo also which would be slower.

With the same or similar power plant they can have a comparable fuel burn at the same rpm or load; it's the nautical miles per hour that will be different.

Because it's doing 32-33 knots at that fuel burn. Better efficiency. NMPG

The difference in fuel burn is because your boat is in the med, cooler water, cooler air, leaner air fuel ratio. Could also be props. That's what the man 800's burn, any set of 800 hp diesels burns 60-65 gph at 80% load. You could always run the cabo slower and get better mileage, like any boat. But yes, the seatrial is accurate. I've done deliveries on at least 20 different 40' Cabo's over the years. For efficiency the Volvo's D12's in the newish Cabo 41's were very fuel efficient for shafts and ran good....... 41' is same boat as 40'.

@ MapishM.
Can you see fuel burn on a screen live ?
In the absence ( which I suspect ) using dry manufacturers graphs with hypothetical prop curve is where the error , the mismatch of your findings and the others on here lies .

To comment on fuel burn one needs live instrumentation.
My MAN 2876 le 401 rated 700 Hp have MMDS so I can see it live .
The numbers I witness are different from the manufacturers graphs flying about online which are let’s face it done on a test bed not in a real boat .Those manufacturers graphs are over optimistic.

This explains your wildly optimistic fuel burn numbers on this thread and others when you quote your numbers .

^
A fuel hose off would trigger some alarm or other .If it doesn’t then simply lack of rpm or some other parameter would be brought to the helms attention.
Coincidentally since you mention injector timing I have had a faulty injector sensor ( the only thing btw in 7 seasons taking them from 480 to 1080 hrs ) .Well you get a sensor error for starters and some of the numbers do alter .Alter enough to make it obvious further investigation is necessary.Also a rpm limit is triggered .I can’t remember exactly which .But noticed for example the EGT s no longer sync d .The affected motor switched to a stored algorithm for its fuelling instead of using live data = some parameters on the screen lost there synchronicity.This is when the sensor alarm is shut off .


So the multiple bits of data fed into the black boxes by the arguable excessive sensors MAN use , then transferred to the screens kinda cover each other .

I don’t think your argument that Capt J s , mine and others sensors are erroneous when we run our boats and happen to flick about through the various pages on our screens ……fuel burn being one , is validated.

If they were as I said the boat tells you either via alarms or you see plane differences in the pairing of the parameters.

For any credibility discussing fuel burn comparisons on boat forums we need like for like independent electronic ( does not matter which the manufacturer has adopted) read from a screen .
I will add the caveat if I may from fully working engine(s) not alarming off .

like this below .


My normal cruise ^ keeping under the 80 % load in the interest of engine longevity.Equates to a 28/29 knot cruise .Or a bit lower with a dirty bottom .
I can’t exactly remember when this pic ^ was taken in the season ? I have seen 80 L early on in the season lightly loaded .So the consumption does vary sometimes.I suspect this pic is later in the season + heavily loaded fluid wise ?


A fast cruise ^ 31-32 knots .



WOT test. Some 3-4 months after it’s annual service / antifoul .
The rated rpm is 2200 . So pretty pleased with that 20 y old MAN 2876 le 401 s @ 700 Hp , in-line 6 s . Tells me the propping is right .No alarms ( touch wood ) the motors are in rude health.

I have sight glasses on my tanks with tape from the previous owner marking them in 1/4 increments.I just casually “ sight “ them during daily checks especially if I plan a long ish trip .Yes agree with you partially years of experience tells me you can’t beat the MK 1 eyeball .With electrotwackery there’s always a lurking suspicion it’s gonna fool you .

But it’s no doubt the best thing , the only way to compare boat fuel burn rates .Well to get any credibility.

It’s not or ever was a case of ignoring yours or anybody else’s post .

It a case of accountability for your outliner consumption figures .
Explaining the real reasons for the differences.

As it is you claim your 16 L V8 s running at or around 1900-2000 rpm ( or what ever ) in a far bigger / heavier boat 56 ft vs theCabo 40 or my 14 m lighter (heavily built granted coming in @ 18 - 20 T depending on fluids carried ) boat with inline 6 s at 40 % less cubes , 2 less pots users the same fuel more or less .It can’t .Worse still burn less fuel typically running .


Assuming my numbers I have posted and Capt J he quoted ( assuming he can read his screens ) are correct .Also if others chime in with there screen data we will collectively form a hierarchy whereby the Hp , the size ( boat + motors ) , drive systems IPs or shafts , Arnesons , jets etc broadly form industry standard order .
So others without “ screen “ fuel burn data can make a meaningful estimation where there boat fits in this general order .

Your calibration must be waaaaaay out .

Your numbers are outliners .

Have you never considered that’s the case ?

pershing 82 after this summer plance mti 52 race boat order but wife 50-60 ft yacht need (don't want to spend a lot of money)
If I can't convince, this topic will be useful. =)

So a 1 M tall tank hold 2700 L ? That feels a bit large in a 56 .
Can you expand on those numbers ? They don’t feel right .

How tall are your tanks and what’s your boats tank arrangements?
Just intrigued by your claimed outliner fuel burn numbers .Let’s get to the bottom of this anomaly.

I mean mine are twin 800 L marked in 1/4s so 200 L between marks .
The tanks guessing are about 1.4 M tall by eye and estimating. The marks 1/4s are about 30 cm + apart .Each tank feeds a motor .So running guzzling 90 L per side @ 80 % or under load I have autonomy of over 8 hrs .

Additionally there’s an optional 600 L “ long range “ tank .This has no sight glass or gauge .Buts it’s connected by cocks / valves to the others so I can top them up . About another approx 4 hrs planing .3 to be safe .

Gents,

The discussion went from boat recommendations to fuel burn so we split the above posts into a new thread.

Precisely as I mentioned and I think you agreed - manufacturers charts with ave prop demand curves cannot be relied upon .Indeed underestimate the real world consumption.
The pics I posted show the load which I use around 80 % to set the cruise rpm .The variability of load I see due to fouling / weight etc I can assure you I am familiar with how diesels work .I see it .Also EGTs on a another page .Having screens and watching changes actually stimulates a greater understanding than otherwise .

It’s still a pity in terms of credibility and comparability of your consumption you cannot access real data from a screen .

Or your consumption figures fitted in the gen norms / patterns of other 56 ftrs with 16 L V 8 s .
10 tons heavier ( near enough 50 % more ) and despite my 23 degree deadrise on a 14 M boat your 17 M must have at least 2x under water surface area planing compared to mine . Bigger engines etc older mech injection .
Mines pretty near the Cabo 40 maybe a 1 M bigger ? .= similar consumption.
Well closer to the Cabo 40 than your DP 56 in terms of consumption.

I just can’t see it like the Cabo 40 being close to your consumption or indeed worse as you claimed ^
For a like for like cruising rpm say typically 1870 , 1900 rpm .It must burn more , possibly @ more “ load“,
We can never see your true load figures .
Mine will travel faster obviously which it does , which improves its gallons / Nm .