Mainship 34 Fuel Burn Rate

Hey guys,

We're going to charter a Mainship 34 out of Anacortes this fall. I Started doing some planning and was unsure about the fuel burn rate we should expect. Please chime in if you can offer some advise. It has a 330hp Cummins with a cruising speed of 8 knots at 2800rpm.

Thanks

8 knots and 2800 rpm does not sound right. I think one of the numbers is incorrect.

As jleonard noted, one or maybe both of your numbers is incorrect.

But in any case, here are a couple of data points from our 2006 Mainship 34T with the Yanmar 370 engine. The fuel burn and speed numbers will be close for the Cummins engine, but the rpm numbers will be lower for the Cummins by about 10%.

1,700 rpm, 3 gph, 7 kts
2,800 rpm, 12 gph, 12 kts

FWIW those are the best two points to operate that boat at. The 7 kt speed is near displacement speed and gives you good fuel economy. The 12 kt speed is a bit over the hump and any faster is loading the engine too much IMO.

And also FWIW the Cummins QSB 330 hp engine is rated at 330 hp at 2,800 rpm. I wouldn't cruise it any faster than 2,500, but I won't tell; it is between you and the owner.

David

I have 50', a 250 hp Cummins and cruise at 1200 rpm, 7-8 knots.

This might help ... from archived 2007 Mainship website:
Mainship Trawler Charters

Click on the engine type below the fuel efficiency overview to get more details.

jleonard said:

8 knots and 2800 rpm does not sound right. I think one of the numbers is incorrect.

Click to expand...

Yep....2800RPMs on a 330hp 6BTA is redline! and will be burning about 16gph I would imagine.

Can this fuel burn rate be correct

I am a newbie to trawlers, but am under contract on a 2009 Mainship 34 Fly bridge Trawler with single Yanmar 380HP. During Sea-trial last Monday the surveyor had the owner advance to full throttle, with full fuel, half full fresh & Blackwater tanks. We had three on board and a clean hull.

At WOT, the boat ran about 14.9 knots, and the Yanmar digital display indicated we were at 99% load, and fuel rate was 19.0 gal./hr. I didn't record the RPM but hopefully it will be in the pending surveyors report.

I don't plan to run WOT, but that is higher fuel rate than I imagined for a single engine.

Does this rate seem accurate?

19-20 gph at WOT sounds about right for a 375 hp fiesel. But 15 kts sounds a bit slow for a 34 footer. I would think that 14-15 kts would be 70% load/ cruise speed, and closer to 20 kts at WOT. But hopefully folks with more experience with either the yanmar or the mainship will chime in.

You've had a knowledgeable mechanic survey the engine?

Peter

boiler81 said:

I am a newbie to trawlers, but am under contract on a 2009 Mainship 34 Fly bridge Trawler with single Yanmar 380HP. During Sea-trial last Monday the surveyor had the owner advance to full throttle, with full fuel, half full fresh & Blackwater tanks. We had three on board and a clean hull.



At WOT, the boat ran about 14.9 knots, and the Yanmar digital display indicated we were at 99% load, and fuel rate was 19.0 gal./hr. I didn't record the RPM but hopefully it will be in the pending surveyors report.



I don't plan to run WOT, but that is higher fuel rate than I imagined for a single engine.



Does this rate seem accurate?

Click to expand...

Bang on. You can get performance charts for that engine that give this info here https://www.yanmar.com/marine/product/engines/6ly2a-stp/

Jeff F said:

Bang on. You can get performance charts for that engine that give this info here https://www.yanmar.com/marine/product/engines/6ly2a-stp/

Click to expand...

Does 15 kts WOT for a 34 footer sound right? Seriously, honest question. Feels a bit slow, but I really don't know.

Peter

mvweebles said:

Does 15 kts WOT for a 34 footer sound right? Seriously, honest question. Feels a bit slow, but I really don't know.

Peter

Click to expand...

I'm sure others with sisterships will chime in on speed. I thought the question was on fuel consumption.

The original 34 like I had would go 15 knots at half that hp, but the later 34 Trawler is a lot more boat, beamier and I'm sure heavier.

Thank all for the great info.
My Yanmar is the 6LY3-UTP, which according to Yanmar charts Jeff F pointed me to, it should burn 17.5 gph @ WOT. Also we did have some current on the Sea-trial, so perhaps it affected speed more than I anticipated.
However, it all seems to point to some inconsistency with my indicated fuel burn.

boiler81 said:

However, it all seems to point to some inconsistency with my indicated fuel burn.

Click to expand...

The chart I'm looking at shows 70 l/hr, or 18.5 gph. Look closely and you'll see the primary graduations are metric. Sorry for pointing at the wrong model above.

We're within 5% here... I'm not sure it's realistic to expect any closer match between the specs and a brief real world spot observation.

Mainship 350 burn rate

My Mainship350 1999 single Caterpillar 300 hp
1400 rpm 8 Knots 1.5GPH

jleonard said:

8 knots and 2800 rpm does not sound right. I think one of the numbers is incorrect.

Click to expand...

Mine has the more common Yanmar 6LYA and I can report an avg of 2.5 MPG over 1,000 mi. I estimate 75% of that is at about 1700 RPM and 8 MPH. 25% at about 2,800 RPM and 13 MPH. Operation between those two makes no sense on our MS 34HT.
Excuse the non-nautical units but our cruising in inland... Great Lakes, canals and rivers where most of the guides and charts are reported in miles... it works well for our use.

That hull is short and fat. SO it does not move through the water very well. Mainship builds boats from the inside out. Meaning the hull is somewhat of an afterthought and the main emphasis is on interior volume.

See attached. Not the same engine, but should be relatively close to what you can expect.