Looking for Fuel Consumption Info

[DeepSeaDan]

I recently purchased a Chris Craft Catalina 281 with twin 305's. Anyone have an idea of average fuel consumption at cruise?
Thanks,

[FraidNot]

I'm researching similar questions for 38 footers - they seems to suck 100 litres at 22kts (ish) with 2 x 300hp installed.
You might be looking at 2/3 that with 2 x 230hp motors and a much lighter hull ?
I did see one post with the 281 with 350's and 90L/hr at cruise.
And another at 60L/hr.

[u4ea32]

Gas engines burn 1 gallon per hour for each 10 HP generated (not rated engine power, but the amount of power you are actually using at the time).

Once fully on a plane, running at low angle of attack (about 3 degrees), planing boats have surprisingly level resistance curves: the faster you go, the less hull is in the water. Therefore, the best economy once fully planing is simply the speed you are going when the engine is turning the RPMs where it makes maximum torque (also, the RPMs where the engine is the most efficient at converting fuel to HP). For typical gasoline V8 engines, that's 3500 RPMs.

28 feet with twin small block V8s: you will probably be able to fully plane, so your best cruise speed will probably be at 3500 RPMs.

Let's say your boat goes 30 knots flat out, engines turning 4500 RPMs (They should turn about 5000, but its not a new boat, right? so its probably full of gear, lots of things have absorbed water so weight is higher, the bottom and props are not so smooth, etc). Your engines will be burning something like 25 gallons per hour each, so you'll be getting something like 30 knots/50 gallons per hour = 3/5 of a nautical mile per gallon.

You will burn close to this at any planing speed. But near 3500 RPMs, you will get about 10 to 20% better efficiency, so you should approach 4/5 of a mile per gallon. This is very typical for planing power boats.

[sdowney717]

50 gallons per hour ?
Then 50 times 4 is $200 per hour so in 5 hours of boating at cruise speed you have burned up $1000.00

that is likely 2 1/2 hours out and 2 1/2 hours back to the dock costs you $1000
How many times can you afford to do that?

Outrageous
Back in the 60's all the way till just a few years ago, fuel costs were perhaps affordable, now power boats are unreasonable unless you have money to burn.

[FraidNot]

25 gal total for both engines combined

[DeepSeaDan]

Thanks to All for the input. This fall I'm seeing numbers closer to 8-12 gph, but that has been on relatively short trips with variable RPMs and guests on board. In the spring, I'll top off the tanks and use GPS to get more exact consumption rates.

[flfishing]

good day here some info i run across hope this helps cc 281

The floscans don't work well below 2000 rpms. It flucuates up and down. I am not sure but it may be the gas filling up the carb bowl then when the float stops the flow the gph drops.

Floscan says flucuations may happen at low speeds but the total gallons used will still be correct. Not sure exactly why.

I did 2 different test runs:

#1
2000 rpms/11 mph/4 gal. each engine. 8 total gph.
2500 rpms/17.2 mph/6 gal. each engine. 12 total gph.
3200 rpms/23 mph/9 gal. port & 11 gal. stb. 20 total gph.

WOT was 4000 rpms port and 4200 rpms stb./ 28.5 mph
18 gph port & 22 gph stb. 40 gph total.

Winds were ~ 15 mph at my port bow.
Total miles 8.3
Average speed 10.7 mph
46 minutes
Max speed 28.5
Total gal. used 7.1

[flfishing]

#2
2800 rpm/ 8 gph each engine/20 mph
We idled to get out of Contrand Bayou and back to dock and ran several different speeds but none for too long except the run back. We ran 20 mph due to rain.

Total miles 8.8
60 minutes
Max speed 20.3
Average speed 8.8

I had the bottom cleaned/painted and the props refurbed 3 weeks ago.

[GordMay]

Greetings and welcome aboard the CF, flfishing.

Thanks for sharing that specific information.

[u4ea32]

So, tabulating the data from flfishing:


RPMs MPH GPH MPG
2000 11.0 8 1.375
2500 17.2 12 1.433333333
2800 20.0 16 1.25
3200 23.0 20 1.15


So it looks like your engine's torque peak (and therefore peak efficiency at converting fuel) is about 2500 RPMs. This is typical of engines tuned for torque. High performance engines have higher RPMs for peak torque.

[DeepSeaDan]

Thanks again to All for the data, analysis and explainations. I'm very happy to hear that my consumption rates were "in the ballpark" with others. The news, however, means that the boat will stay on the inland "Chain O Lakes" instead of moving to Lake Michigan. If I want it up in Door County or Macinaw, it will be more efficient to put her on a trailer and move her up there.

[David M]

You can also go to the engine manufacturers website and look up what is called the engines Specific Fuel Consumption.

[flfishing]

Originally Posted by DeepSeaDan

Thanks again to All for the data, analysis and explainations. I'm very happy to hear that my consumption rates were "in the ballpark" with others. The news, however, means that the boat will stay on the inland "Chain O Lakes" instead of moving to Lake Michigan. If I want it up in Door County or Macinaw, it will be more efficient to put her on a trailer and move her up there.

that is what i do with mine brought it up from south fl at 50 mph behind my truck i got 16 mpg the 281 is no speed demon at over 8000 pounds dry i rented a trailer since then i got my own trailer and thats were she sits
the beam being all most 11 ft i have spent the last three years setting it up
hope to do some cruising and fishing this winter from what i have found so far and seen they are fine built vessel with plenty of room good luck to you dan

[djambalawa]

Originally Posted by sdowney717

Outrageous....now power boats are unreasonable unless you have money to burn.

Not sure if thats a fair generalization.. this "power boat" burns 0.7 gallons per hour at 6 knots...

1990 Legacy Yachts Legacy 32 MKII Power New and Used Boats for

I do agree in regards to semi-planing or planing large power boats though... crazy.. don't know why anyone would want to run one...

[flfishing]

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here is a pic of 6 not vessel powered buy 471 diesel i was on glade it had the haul it did note the anchor line 15 foot plus seas