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Old 01-04-2018, 01:38 PM   #1
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Fuel burn for Mainship 430

Greetings,
I just purchased a 2007 MS 430 with twin Yanmar 440 HP diesels and am looking for information about optimal cruising speed. I've looked at the Yanmar specs for RPM and wondered what others in "real world situations" have found. I plan to purchase flow meters next cruising season.
Thanks for the info.
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Old 01-04-2018, 02:54 PM   #2
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I don't know that boat specifically, but I can give you some general advice:

If you want to cruise at planing speeds, get up over the hump which will occur at 12-14 kts and at about 15 kts you will be on a clean plane, or as much of a plane as any semi displacement hull will do. That is the most efficient fast cruising speed.

But make sure that the engine is propped to reach at least 3,400 and preferably 3,500 rpm at wot using a phototach to measure rpm accurately. Then keep the cruising rpm at 2,800 or less. You will be burning 20-25 gph for both engines at that rpm.

If you want to go slow, then the slower you go, the more fuel efficient it will be, at least down to about 6 kts.

David
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Old 01-04-2018, 03:10 PM   #3
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Our 430 has the 370 hp Yanmars. We cruise at 1600 rpm and 8.5 knots. We're using just under 4 gallons per hour. We will occasionally go up to 1800 and 2000 rpm, but since we're retired we can't afford to go much faster, except to briefly blow the carbon out.
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Old 01-04-2018, 05:11 PM   #4
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Thanks, David.
I'm going to stay around 8 kts or so on our way to the Abacos, so 1600 rpm seem to make the most sense.
I'll re post once I get some more definitive numbers with a flowmeter next season.
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Old 01-04-2018, 05:12 PM   #5
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Thanks, David.
I'm going to stay around 8 kts or so on our way to the Abacos, so 1600 rpm seem to make the most sense.
I'll re post once I get some more definitive numbers with a flowmeter next season.
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Old 01-04-2018, 06:52 PM   #6
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Iíll just add that depending on the jump off point, the higher speeds may serve you better fighting the gulf stream. Going slow on the bank has much more merit.
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Old 01-05-2018, 06:22 AM   #7
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Quote:
Originally Posted by jmernest View Post
Greetings,
I just purchased a 2007 MS 430 with twin Yanmar 440 HP diesels and am looking for information about optimal cruising speed. I've looked at the Yanmar specs for RPM and wondered what others in "real world situations" have found. I plan to purchase flow meters next cruising season.
Thanks for the info.

The formula answer: Assuming your waterline length is about 42', I'd guess your best fuel economy will be 6.5 knots or so. (SQRT 42). 7.5-8 kts could likely be acceptable, as long as you stay under 1.34 * (SQRT 42).

I'd guess flow meters won't really give you much better info for slow cruise. May be much more useful for your high cruise speeds, which may be in the area of 15-19 kts (just a WAG).

Until you get flow meters, and once you're on the water, you could compare Yanmar's fuel consumption curves to real world speeds those RPMs give you... with allowances for wind, waves, tides, currents, etc.

-Chris
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Old 01-05-2018, 07:37 AM   #8
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Thanks, David.
I'm going to stay around 8 kts or so on our way to the Abacos, so 1600 rpm seem to make the most sense.
I'll re post once I get some more definitive numbers with a flowmeter next season.
1,600 rpm is where I cruise my boat with a single Yanmar 6LY 370 hp. I make 7+ kts with the single engine driving a 34' boat. Your twin 440s should get you to about 8 at that rpm.

It will be expensive to fit Floscans to twin engines. If you cruise slowly at 8 kts you will never, ever recoup the cost with better fuel savings. In fact since Flowscan accuracy is stated as a percentage of full fuel flow and for diesels you need two flow sensors, the accuracy at 2-3 gph per engine will be very poor. Reading the Yanmar prop fuel curve should be more accurate at that low fuel rate.

David
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Old 01-05-2018, 08:38 AM   #9
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If the OP would post the following data points, I can do a pretty good guess on the various burn rates:

Hull speed (say 7-8kts range) speed and rpm
Planing cruise speed and rpm
Full power speed and rpm
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Old 01-05-2018, 12:02 PM   #10
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If the OP would post the following data points, I can do a pretty good guess on the various burn rates:

Hull speed (say 7-8kts range) speed and rpm
Planing cruise speed and rpm
Full power speed and rpm
Ski- Now you want three points to draw a curve. Chicken!!!

David
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Old 01-05-2018, 12:07 PM   #11
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Codger on this site has 440s in an OA 42. He has added fuel flow meters. You may want to correspond with him for details.
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Old 03-11-2018, 07:46 PM   #12
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I have a MS 430 with twin turbo Yanmar 370hp diesels. With 26/27 props at 1800 RPM my speed over ground is 9 knots, which is pretty much hull speed for a 43’ waterline. My fuel consumption per hour (which includes generator and Espar use) averages 19 LpH or 5 GPH.
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Old 03-12-2018, 04:10 AM   #13
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Ski- Now you want three points to draw a curve. Chicken!!!

David


Excel will give a polynomial equation for the entire dataset
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