3126-TA Low Speed fuel consumption #’s?

I have the 350 hp version. I haven’t seen official consumption #’s for low speed operation. Lowest I’ve seen is 1400 RPM.

My cocktail speed is probably around 1000 rpm, gives me about 8 mph, no wake, and no bow rise, and its quiet, probably the hull speed for this boat.Higher RPM get more wake, not much more speed and more noise. We have been spending a lot of our time at this speed.

Anybody have the expected fuel burn at idle through 1400 RPM?

Do a thorough search. There are several graphs and post related to rpm gpnm etc...
in the Diesel section concerning the 350hp Cat 3126. I know FrankW has posted some numbers, all be it a slightly different engine model I think. GOD bless. JC

Lots of discussion and burn numbers but in 2 years of reading, ive never seem published consumption numbers below 1400 RPM. The CAT burn numbers stop around 1600.

If you have some published numbers from a your search please post.

Here 'ya go:

2400rpm=13.0 gph/engine
2300rpm=11.5
2200rom=10.0
2100rpm= 8.8
2000rpm= 7.5
1900rpm= 6.6

and my personal favorite......1450rpm = 3.0 gph (about the speed your boat is traveling in your photo) There are trawlers that go slower and burn more fuel than that.

All the above numbers are per engine, so double them.

Frank

The above (Copied) was from a post dated June 4 2008. From Frank.
If you want to see it do a search (3126) just on the Diesel section.
Hope this helps. JC

He wants GPH below 1400 rpm if I read correctly, JC...(hope you guys are well!)....and those #'s are for 420hp 3216's.

Caterpillar fuel tables begin at 1200 rpm. 1200 RPM = 1.6GPH/engine
1400 RPM = 2.7GPH/engine

I don't know what you are looking to do with this data, but your boat will probably begin to lift the bow and try to plane at about 1500 rpm and that is where efficiency drops..........but ,I honestly don't know how you can get more efficient 5.4GPH in a boat this size anyway.

Thanks Frank...yes looking for low speed cruise consumption rates. The cat literature I have only goes to 1400 RPM

Not for efficiency, but to answer the question of how much fuel do I have in the tanks. One fuel sender doesn’t work, and they aren’t reliable anyway. The other question is how much fuel should I put in? I don’t trust fuel vent systems to stop filler nozzles either. As the boat is new to me, I’m also trying to correlate what I think I have in the tank, to what the gauge indicates. Old pilot tricks.

For this boat, 950-1000rpm is the quietest smoothest speed to operate at, and trying to account for the fuel burn at the speed. Got to save those manatees ya know.

Of course I’m assuming the indicated RPM is correct, but that’s a whole other thread.

I ran some real world tests with my 3116’s. They are also 350hp.

After accounting for the generator fuel burn, it turned out 1400rpm was the most efficient/fastest speed getting us about 1.5nmpg


I could go slower and burn a little less fuel in the engines but the generator burns 1gph no matter what so it became a time over distance equation.

Noise was the factor keeping me from pushing the throttles up, 1000 RPM was just a nice easy speed, we can talk and enjoy the radio. Wife was happy! There are just a lot of no wake zones around so like I said I have spent a good portion of our time at this speed. I’ll plan 1.5 g/hr per side, 3 gph total at this speed.

When we can get up on plane, I have found just like Frank said 2150-2200 is a very nice high speed cruise at about 21 mph. I’m at the far end of bottom cleanings so I’ll probably pick up a little once cleaned.

Dave,
I’ve got a lot of no wake zones around here too, and my wife likes to cruise at “cocktail speed” during the rare times when boat traffic is light.
Props, loads on the boat, and conditions all make a difference so it’s hard to accurately compare.
With 22 x 21.5 props on my boat:
The no wake zones often mean around 1000 RPM or less. Usually less, more like idle speed with lots of neutral coasting if I’m near any docks or bulkheads. In closer quarters at 1000 RPM I’m still throwing a little wake that would cause tied up boats I pass to rock so I have to do a lot of neutral coasting and just putting one motor in gear at a time for short periods.
It’s all but impossible for me to strictly comply with 5 MPH zones at idle speed and flat water.
Without a fuel flow meter, it’s tough to be really sure, especially since a fill up goes such a long way on this boat, but my best estimate was in line with the 3gph number others have posted at a combination of those slow speeds.
I had flow meters on my old boat and was able to really maximize fuel burn according to conditions by watching them and adjusting RPM and trim accordingly. Much better than I could do by ear.
One of these days I’d like to treat myself to them on this boat, but they are way more expensive for diesels and since the diesels are so much more efficient than gas, I’m not sure there is much cost benefit in it for me as a recreational boater.
My very unscientific gut feeling is that my boat seems to like 1200 RPM for slow cruising. No real difference in noise at that as opposed to less RPM but it usually adds a few MPH, bow stays down, and she seems to glide nicely through the water.
Best overall cruising RPM for my boat seems to be about 2300-2350 according to my tachs (never checked their accuracy). Speed in MPH at that RPM once I get her trimmed properly, is most often anywhere from 22-25.5 depending on wind (windy afternoons are the norm around here), tide, and conditions. I’ve seen slightly worse and slightly better in extreme conditions, but those are rare.
Just yesterday evening I hit an all time high of 26.1 mph running with an incoming tide and a breeze at my back, but it’s the first time I ever saw 26 on my GPS. The wind and water gods were all in synch.
The longest I ran at that cruising RPM continuously for was about 6 hours, and I burned about 25 GPH.
I’ve found that paying a lot more attention to my wake than my bow gets me the best results.
I was always used to giving equal attention to both, but the bow on this boat can really throw you off since it rides so high. Visually, it makes me feel like I need to get the bow down more with the tabs to get her to run more efficiently (more speed at a given RPM), but doing so has the opposite effect.
The bow high effect is more a result of the design shape of the bow on our 410’s.
The 420’s (next generation of our size class) have a sweeping downward bow that eliminates this. I think the Sea Ray designers intentionally addressed this in the newer boats.
At a modest 5’ 11”, I’ve resigned myself to flipping the helm seat pad up to use as a leaning post when running on plane in the channels and bay so I can see over the bow. The only time I can sit when on plane is in the ocean with no other boats or possible hazards close by.
It was tough at first, but now that I’m in to my 2nd season with the boat I’m getting used to the high riding bow.
I’ve thought about a higher seat base, but I’d probably need it to be at least another 6 inches higher to feel comfortable.
That’s a big investment for something that I’m not positive would work out all around.