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Old 09-29-2018, 12:11 PM   #1
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Mainship 40 Trawler Expedition Engines consumption

Hello all Ladies and Gentlemen,

First excuse me please about my broken English cause I'm French.

I go here because in France there is no forum about Mainship.

We just have bought "Dakoota" (this is a Mainship Trawler 40 Expedition built
in 2007).

As you know in France Gazoline (Diesel) is very expensive (1,70 euro for 1 liter, note: 1 euro = 1,1608 US $)
and I have some questions about Engine consumption.

Engines model is: Yanmar 6BY260 x2 (There are 2 Engines: 2x260 CV)
CV (Chevaux)=HP (Horse Power)
Now my questions:

1. I suppose cruiser speed is 8 knots (8 nautical miles per 1 hour)
With this speed (8 knots) can you tell me what is the engine consumption?
(Example: 20 liters/hour/engine)

2. But speed (8 knots) is it the best speed for this boat?

3. What is the limit speed of hull?

Thank you very much about your future answers (responses)

Best Regards,

Joel de Binic
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Old 09-29-2018, 12:19 PM   #2
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My estimate is at 8kts, both engines combined would burn about 3 gph, which is about 11 lph. 8kts is about as fast as I would go with that hull with expensive fuel. 7kts would reduce burn rate to estimated 7-8 lph. Generator on would add about 1 lph.

Top speed unknown, depends much on weight of boat and load. Probably around 16-18kts, but that is not practical based on fuel cost, and working the engines hard.
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Old 09-29-2018, 12:55 PM   #3
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Thank you very much about your answer "Ski in NC"

But the mass of Mainship trawler 40 is 10 tons (10 000 Kg) and I maybe think a little more than 11 liter/hour/engine at 8 knots.

I am OK with you cause if v > v (limit speed of hull) consumption is very high and it is not good also for engines.

I think 8 knots is the best cruising speed for many trawlers.

Best regards.

Joel de Binic
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Old 09-29-2018, 01:47 PM   #4
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Joel:


Theoretical hull speed (it is theoretical as it is the speed at which the hull matches the bow wave) of that boat, assuming a 37'waterline is 1.34*sqrt(37) or a little more than 8 kts. Semi displacement hulls take about 2-2.5 hp per thousand pounds of displacement to reach hull speed as a rule of thumb. Your displacement is about 25,000 lbs with fuel, water and passengers. So it takes 50-60 hp. Those engines make about 17 hp per gph at low power. So it burns 50/17 to 60/17 or 3-3.5 gph for both engines.


All of the above is based on rules of thumb, but they should be good to 10-15%.


Those engines will last almost forever at that low power output. But push it to 15 kts and they won't.


So go slow.


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Old 09-30-2018, 03:29 AM   #5
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Hi,


I think your enconomical speed is about 6,5-7,5kn. MS 400 LWL 36' and hull speed is 8kn, but not best economical speed. This is of course relative to each skipper.


My tug LWL is 37' and sped kn /range nm 6.2/2300, 7.4/1640, 8.1/1030

You have an even higher price than here in Finland, which I also like as a high price we have between 1.5 and 1.6 € liters.


Here is an interesting site for MS 400 speed/consuption single yanmar 370hp
http://scyr.org/stellablue/specifications.html#speed


And one reviews

https://www.boats.com/reviews/sea-tr...p-400-trawler/

NBs
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Old 09-30-2018, 09:27 AM   #6
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Joel.

This may give you some idea and help.

https://www.boats.com/reviews/sea-tr.../#.W7DbZHtKgnQ


However there is Mainship Corp. contact info.

You can always email them or call them.


Mainship Corp
(912) 884-9595
(800) 578-0852
www.mainship.com


Cheers Mate.

H.
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Old 10-03-2018, 03:08 AM   #7
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Hello all,
A big thank you for your clear and well-argued answers.
I visited the links that you had indicated. It's really very well explained.
I shall therefore perform fuel consumption tests on the "Mainship" when it will be ready to sail (unfortunately the previous owner died 2 years ago and the boat has not sailed for 2 years).
I think to get a curve giving the consumption "C" (in liters) of the 2 motors according to the speed of rotation "w" ( in turns per minutes) of the engine while studying the effect on the speed (because the speed given by the GPS is the speed compared to the bottom of the sea and not the speed on the surface).
Here in the bay of Saint Brieuc the currents and the winds vary a lot. Thus I will get a function C = f (w) in the vicinity of the hull velocity (of the order of 8 knots).
So I have a lot of work to do to optimize the consumption of 2 engines.

Best regards,

Joel de Binic
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Old 10-03-2018, 06:52 AM   #8
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I have the same boat, but different engines, 4LHA-STP, 4 cylinder vs 6, 240 HP vs 260 (?).


David and Ski have forgotten more about engines than I will ever know, their advice is probably better than mine. But I can tell you what I burn and the speeds I get. I usually run a little faster than 8 knots, more like 8.5, at 1850 RPM, where my boat just "feels" happy. At that speed we burn around 4 GPH combined. When we go "fast" which is about 35% of the time, I run it at 2,850 RPM, which is between 13 and 15.5 knots. A lot has to do with the load and sea state. AT that speed we burn around 13 to 14 GPH.


I ran my boat at WOT for about 5 minutes a few months back, very light load in calm water with little current. It turned 18.7 knots on the GPS.



Hope that helps. I'm not sure how much the different engines would change those numbers.
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Old 10-03-2018, 07:27 AM   #9
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Quote:
Originally Posted by djmarchand View Post
Theoretical hull speed (it is theoretical as it is the speed at which the hull matches the bow wave) of that boat, assuming a 37'waterline is 1.34*sqrt(37) or a little more than 8 kts.

FWIW, I have found it useful to think of that calculation (using 1.34) as "theoretical MAXIMUM hull speed" -- and then to consider Beebe's common advice about using 1.0 (instead of 1.34) to arrive at a more likely "theoretical MOST ECONOMICAL hull speed."

If the boat is 40' OAL and has a waterline length of 37' for example (using the same LWL guess-timate), the latter calculation would suggest approx 6.1 kts would be less expensive.

If I remember right, Beebe actually waffles a bit between 1.0 and 1.2 or some such...

-Chris
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Old 10-03-2018, 08:06 AM   #10
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You might get slightly better fuel economy with the newer Yanmar common rail, small displacement engines in the OP's boat than the older, mechanical Yanmar 4LH engines reported by Doug above. Maybe 5% but no more.


BTW Doug, how did you measure fuel consumption, Flowscans? I am not knocking Doug by saying this, but you can get a pretty good handle on fuel consumption vs rpms by just looking at the manufacturer's prop curve.



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Old 10-03-2018, 08:22 AM   #11
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In owning and operating the MS 400, I can agree with the above.

I'm doing 7 knots at a little over 3 gph, getting about 2.3 mpg. Have a few twin engine friends with the same boat, and get about the same performance at hull speed.
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Old 10-03-2018, 10:42 AM   #12
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No offense taken at all David, I know my figures are not 100% accurate.



I don't have flow scans, but I do keep close track of my fuel burn and my hours. Also, we tend to run at higher speed when we do long days, specifically Gulf Stream crossings, I start at full when we leave and fill up again when we get across. I've had the boat for 5 years now and have used this practice all along. I know it's not as accurate as flow scans, but it does give me a good idea of my boat's fuel burn in the way that I typically run it. It helps me to plan fuel burn for trips, and my guesses are pretty accurate at this point.


Someone else may run their boat differently with different loads in different conditions and get different results. I'm just putting my data up for consideration.
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