Motor Change

I have a 1979 Main ship trawler 34'. The boat originally had a Perkins 160. I have found a ford-leihman 120 would this be a good replacement engine

Why not repair the Perkins? A swap out can get complicated as motor mounts and different transmissions come into play. And you are 100% positive the Lehman is in good working order?

The old motor was not in the boat when I bought it,the Lehman was rebuilt three yes ago, open for all ideas thanks

Put a higher powered Cummins or Yanmar and cruise in the mid to upper teens. There are many out there that have done it. Not cheap though.

We had a 1981 Mainship with the Perkins it worked well with the hull. I think you'd regret the 120 with the lower hp since it is a semi planing hull. We had friends that re-powered to 200 hp. The boat could move if needed. Ask the question on the Mainship owners group. This wouldn't be the first 34 to be repowered.

Larry I've heard the same. I talked to one owner that repowered w a 200hp Volvo and loved it.

This is one trawler that I'll not be sing'in songs about powering w small engines because the Mainship 34 is basically a planing hull. And it seems to be light enough to step out.

"Put a higher powered Cummins or Yanmar and cruise in the mid to upper teens."

And at about 20+GPH for the fun of making big waves.

Most trawler folks seem to prefer 2 GPH at 7K to 20 GPH at 17K

Not to mention that you give up a totally reliable engine for one dependent on electronics and a turbocharger. The Yanmar turbo being a bad design as to the raw water injection location which allows salt water to splash into the turbo on shutdown.

I had a Mainship and repowered it with a 270 HP Cummins. Best thing the boat ever had. MUCH more economical then the Perkins and it sold within ONE WEEK when it was time.
The Lehman 120 is not enough power. nTrust me I went thru this.
New power, new boat. Go with at least 200 horsepower. The Cummins 210/220 is perfect for the Mainship and it can handle more if you can.
Peoplw want power and economy. You won't get both with a 120 Lehman. You'll make a dog out of a good boat. It will wallow more in a following sea, and won't get you thru inlets like Barnegat when you need to.
Just my opinion but I have the experience with this particular boat.

FF said:

"Put a higher powered Cummins or Yanmar and cruise in the mid to upper teens."

And at about 20+GPH for the fun of making big waves.

Most trawler folks seem to prefer 2 GPH at 7K to 20 GPH at 17K

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Not quite FF. my 240hp Yanmar burned 13gph at WOT and about 6-7 at cruise...2800rpm. That Would push this boat in the low to mid teens. So you would end up with approx 2mpg in a 34ft planing boat. Some would call that efficient....just a fraction less mpg than your 7k at 2gph. So the penalty for speed is quite small and is made up with time.

Now your numbers match my current boat....but that is twin Cummins 330hp in a 23000lb boat.

With my Cummins 270 I could fast cruise at 15 but usually cruised at 11.5-12 knots (1900 rpm)and got about 2.4 nmpg which is the same as I got with the original Perkins 160 at 8.5 knots.
When I throttled back to 8.5 knots (1500 rpm) I got close to 3.5 nmpg.
And yes at that rpm the engine temp was where it was supposed to be (coolant and egt).

2mpg versus 3.5mpg

3000 miles cruising the AICW each year

1500 gal fuel at $4 = $6000 vs 857 gal fuel at $4 = $3428

$2500 fuel diff for some liveaboards/cruisers is a chunk and fuel is not a stable commodity.

while nice to have the speed...if you aren't going to use it...I'd probably go with a smaller engine in many boats and save even more...

But the idea of the correct /better size engine in a 34 Mainship as Jay pointed out could really help in resale.

psneeld said:

But the idea of the correct /better size engine in a 34 Mainship as Jay pointed out could really help in resale.

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Jay hits the mark on most if not all things.

I have an affinity for the Lehman diesels, perfer smaller engines for several reasons, and am a hull speed kind of guy. But Jay's advice needs serious consideration.

Here is my take, tempered by recent threads on boatdiesel:

The Cummins 6BT, 210 hp engine is rock solid and can easily put out 150-180 hp long term. That much power should push a 34 to 13-14 kts. The 6BT has no aftercooler which is a + and a -. The plus is that you don't have an aftercooler to worry about. The minus is that an aftercooler improves efficiency. The other downside is that for some reason 6BT remans are difficult to obtain and often cost more than the higher hp version.

Probably the best choice then is the factory remanned 6BT 270 hp version. You get a little better efficiency with the jacket water cooled aftercooler, but since it is jacket water cooled and not sea water you don't get all of the maintenance problems that go with it. One of these should cost in the upper teens.

The 6BT 270 can put out 200 hp reliably and will push the boat to about 15 kts while burning 11 gph.

Somewhere in my files I have data on a Cummins 270 repower of the 34. If the OP would email me with his address, I will dig it out and send.

David

Substantial HP increases require that someone at least look at the engine beds, shaft and bearings, rudder and steering gear, exhaust, ventilation, and the cooling system. Of course you will also probably need a new propeller.

Thanks,my email is dale.robins@rocket mail.com

My Cummins 270 powered old MAinship hit 18.5 knots at WOT (2630 rpm).
That was with a 1.5 tranny and the original 20 x 21 4 blade prop. I also did some keel fairing and hull reinforcement inside to stop vibration..it is necessary in those boats if you go for more than 210 hp.
Those boats get squirrelly at 16 knots (I called it chine walking in an old thread but lets not get hung up again with terminolgy in this thread).
I could cruise at 15.5 all day and still be within Cummins specs for 100% running. That was the reason I chose the 270 to be able to get to that edge.

The 6BT 210 repowered old Mainships can hit just about 14.5 - 15 knots and can cruise about 12 full time.
I helped several Mainshippers repower with Cummins 6BT or 6BTA engines.
If you go at 210 hp you can keep your exhaust, raw water, fuel line size shaft size and tranny if you insist but a new one is better for long term reliability (the BW is marginal at that HP)

The 270 requires upsizing the above.

PS I didn't use the power most of the time, however there were several summer evenings that Block Island called my name when I got to the marina but I knew I couldn't make it there for the sunset unless I put the hammer down. At that point, screw the fuel economy, I want to be anchored with a cocktail in my hand watching the sunset.

jleonard said:

PS I didn't use the power most of the time, however there were several summer evenings that Block Island called my name when I got to the marina but I knew I couldn't make it there for the sunset unless I put the hammer down. At that point, screw the fuel economy, I want to be anchored with a cocktail in my hand watching the sunset.

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I can relate to that sentiment. Some things in life are priceless. Not being late to your favorite sunset is one of them.

psneeld said:

2mpg versus 3.5mpg

3000 miles cruising the AICW each year

1500 gal fuel at $4 = $6000 vs 857 gal fuel at $4 = $3428

$2500 fuel diff for some liveaboards/cruisers is a chunk and fuel is not a stable commodity.

while nice to have the speed...if you aren't going to use it...I'd probably go with a smaller engine in many boats and save even more...

But the idea of the correct /better size engine in a 34 Mainship as Jay pointed out could really help in resale.

Click to expand...

First off, you forgot the .4 in Mr. Leonard's example...if that is what you were using. I'll make it simple and not sure if the math works but .4 represents 20% in this case. Take 20% off of your $6000 dollars and you are at $4800.

So that is $1400 dollars more in a year(than your slowboater) and you covered at least a 1000 more miles!!!...again....all a matter of what YOU consider efficient! Efficiency has different values to different people....and it is not always the cheapest.

cpseudonym said:

i can relate to that sentiment. Some things in life are priceless. Not being late to your favorite sunset is one of them.

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amen!!!!

Baker said:

First off, you forgot the .4 in Mr. Leonard's example...if that is what you were using. I'll make it simple and not sure if the math works but .4 represents 20% in this case. Take 20% off of your $6000 dollars and you are at $4800.

So that is $1400 dollars more in a year(than your slowboater) and you covered at least a 1000 more miles!!!...again....all a matter of what YOU consider efficient! Efficiency has different values to different people....and it is not always the cheapest.

Click to expand...

I wasn't...just showing the difference in 2.0 versus 3.5 NMPG...

I almost never consider mpg. Unless it's for cars.
Speaking of cars I may buy a very nice one today.

for some of us it is one of many planning tools...I hate to limit my nav abilities...