Mainship performance

I am new owner to Mainship 2006 34 trawler with twin Yanmar 240’s. I see recommended wot to be 3400 rpm cruise max 80% which is about 2700 rpm. Top rpm I am getting is 3000 rpm with 2 aboard half tank of fuel and water. I am curious if this is the way Mainship propped the boat or perhaps the owner has changed out the props at some time. I see different opinions on overpropping as far as greater efficiency at lower speeds vs overloading at higher speeds. I also have seen posts claiming 3000 rpm to be the top rpm from other owners. I do at times find “The need for speed “ but to get this boat over the hump I need to be at 2800 rpm with tabs down which is 93%. I also am getting barely 16knots at wot. I have seen claims for more speed with this power option. Engines have only 900 hours and have been well maintained. I don’t think it is a power loss issue. I had the bottom cleaned recently as well. Before I have the props re-pitched I was hoping for some feed back.

From my experience with the single engine 34T and reports from other twin owners, Mainship props their boats reasonably. Mine hit 3,400 at wot. FWIW Yanmar rated wot for the single 6LY and the 4LH which you have is 3,300.

So yours is low. Several causes: 1) The throttle isn't opening all of the way- adjust the throttle linkage. 2) The bottom or prop is fouled adding more drag- clean the prop/bottom. 3) And rarely, the engine isn't performing right due to airside after cooler fouling, turbo dragging or ????

Don't continue to run it until you fix it, except at under 2,000 rpm. Running it fast even to 2,700 rpm puts more load on the engine than it was designed to take and will wear it out quickly.

David

These are fine engines for Mainship. They like a slow dance 8-10 knts 2200-2800.
Slow is nice and thats what she likes...Not a go fast boat.

My 2006 MS with twin 240s spins up to 3300rpm and has a top end speed of 16-17 knots. Your lower rpm number could be a problem and the prop may need an adj. Your top end speed is all you will get with this boat/engines! The engines sounds and seems to run best in the 2200 to 2400 range. From what I am reading 2000 may be a little low. It's a 10 kt boat!

Sometimes WOT rpm is calculated in neutral. In gear should never reach that. Need to look up the specs and see if that's the case.

DavidM said:

From my experience with the single engine 34T and reports from other twin owners, Mainship props their boats reasonably. Mine hit 3,400 at wot. FWIW Yanmar rated wot for the single 6LY and the 4LH which you have is 3,300.

So yours is low. Several causes: 1) The throttle isn't opening all of the way- adjust the throttle linkage. 2) The bottom or prop is fouled adding more drag- clean the prop/bottom. 3) And rarely, the engine isn't performing right due to airside after cooler fouling, turbo dragging or ????

Don't continue to run it until you fix it, except at under 2,000 rpm. Running it fast even to 2,700 rpm puts more load on the engine than it was designed to take and will wear it out quickly.

David

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I would also ask if the OP is getting sooting at the higher RPM.

Mine (on a 400, not a 34T) spin up to 3350 WOT, when the props and hull are clean. I run them at around 1900 rpm (8ish knots) 75% of the time and about 2,800 rpm (14 to 15 knots) about 25% of the time. Tabs all the way down when running at the faster speed.


I've done a ton of reading on this and spoken with quite few mechanics about it. Consensus (if there is one) is that I'm not doing any harm to the motors. Many say that under loading is a bigger issue.


There are times I want to run faster, notably on gulf stream crossings. Yes, it burns more fuel, but I really don't care.


Run the boat how you like to run it. It's your boat after all.

My 390 with twin 230s spins up to 3300rpm, both in neutral or under load. WOT is almost 19 over the ground.

Ihave twin yanmar 4lha-stp 240 hp in my 2003 Mainship Pilot 34. I would hit WOT 3,175 RPM. I had the valves adjusted at 1,200 hrs and that helped me get furll WOT @ 3,300 which is the rated RPM for this motor and boat.

16 knots isn't trawler speed. You need to slow down to 7 knots

The boat has been hauled mildly fouled bottom. I am having the 1000 service performed over the winter. Will report on performance in the spring. In addition the tachometers are off 100-200 rpms from 1000 to 2000 rpm.

I agree especially when the crew is starting to turn green.

Roger L said:

The boat has been hauled mildly fouled bottom. I am having the 1000 service performed over the winter. Will report on performance in the spring. In addition the tachometers are off 100-200 rpms from 1000 to 2000 rpm.

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Well, that pretty well explains it. If your tachs are reading 10% low then the 3,000 rpm you noted is really 3,300 rpm. That a little bottom growth explains it all.

David