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Old 11-11-2017, 06:57 AM   #61
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Plan,if Thompson is purchased ,remove the detroit and install a new john deere that research shows has exceptional power,reliability and fuel economy.

So question,Thompson or Cheoy Lee?

Good question for a whole new thread.

What's wrong with the Detroit?

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Old 11-11-2017, 07:08 AM   #62
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"What's wrong with the Detroit?"

They are no longer advertised with glowing brochures , sent to your home.
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Old 11-11-2017, 07:24 AM   #63
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He does now. What was said and experienced at TF Get together ,stayed at TFGT. Everyone had fun,no animals were harmed!
Not harmed intentionally, but I heard a few died laughing at us......

....... but I dont remember (that's another story) starting any discussions about TF members that weren't there.....
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Old 11-11-2017, 07:25 AM   #64
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I would think twice before removing the Detroit unless it was a blown motor. The payback on an engine swap of an old Thompson Trawler would be decades if the fuel use is the measure.
Maybe live with the Detroit Diesel or find another boat to purchase. You would never recoup the repower costs.
Strongly agree. You can completely rebuild a 6 cylinder Detroit, if needed for the cost of a 200hp outboard.
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Old 11-11-2017, 08:12 AM   #65
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I would think twice before removing the Detroit unless it was a blown motor. The payback on an engine swap of an old Thompson Trawler would be decades if the fuel use is the measure.
Maybe live with the Detroit Diesel or find another boat to purchase. You would never recoup the repower costs.
The fuel hungry DDs simply won't provide the range for what the poster is contemplating. Many happy lowered fuel stories for those who have swapped out DDs. Costly in the short run, yes. If front end money not only decider, I say a good move.
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Old 11-11-2017, 10:47 AM   #66
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Keep the DD or buy a boat w the engine you want.

Like most here I was obsessive about a low burn rate 12 or so years ago. My Willard burns very little fuel but now I know that doubling my fuel burn wouldn’t be a problem at all. A few years ago we almost bought a 36’ boat w a 4-53DD. I think of that boat even now.

And re what sunchaser just said I remember reading here on TF that the difference between furl burn on a DD and a modern diesel is really quite small. Wish I could pull up that thread. The latest tech engine may indeed burn much less but you face not only the very high cost of a new engine but getting that new guy in the boat up and running finished w all it’s sea trials.

On the flip side a lot of people think like Sunchaser and they won’t be buying your boat when it’s time to sell. It would be a bit like selling a wood boat. But flip again and consider the DD boat will cost the same amount less to purchase. So the selling issue could or should be a wash.

For the cost of a JD or Lugger you could buy literally years of fuel.
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Old 11-11-2017, 11:28 AM   #67
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The fuel hungry DDs simply won't provide the range for what the poster is contemplating. Many happy lowered fuel stories for those who have swapped out DDs. Costly in the short run, yes. If front end money not only decider, I say a good move.
I'm curious what facts you have to support that. Hatteras LRC owners and hundreds of commercial user would disagree. Are you aware of the variety of DD engines used in real trawlers as well as passagemakers back in the day?
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Old 11-11-2017, 12:09 PM   #68
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I'm curious what facts you have to support that. Hatteras LRC owners and hundreds of commercial user would disagree. Are you aware of the variety of DD engines used in real trawlers as well as passagemakers back in the day?
Ok, I am attaching three manufacturer's data sheets, one for a NA Detroit 6-71 another for a Cummins 6BT 210 hp engine and the third for a Cummins QSB 330. The first two produce about he same wot power and the Cummins 210 at least is a popular trawler engine.

Looking at the N55 injector DD engine which would be appropriate for a 40' trawler, it burns 4 gph while producing 60 hp (as well as I can read the curve), again a reasonable displacement speed hp for a 40' trawler. Now look at the Cummins 210. It produces 60 hp while burning 4 gph, the same as the DD.

The two engines match well at 160 hp both burning about 9.5 gph.

The Cummins 6BT is a generation behind current and the DD is at least two generations behind. FWIW the current generation Cummins QSB does better, burning a bit less than 3.5 gph to make 60 hp, probably due to the more precise, clean burning injection system.

So the best you can do to beat a DD is with a modern, common rail QSB and even then the real difference is about a half a gph.

There are other good reasons to repower a DD based trawler, but fuel consumption isn't one of the better ones.

David
Attached Files
File Type: pdf DD NA 671 datasheet.pdf (454.5 KB, 14 views)
File Type: pdf Cummins-220 Performance Curve.pdf (303.6 KB, 155 views)
File Type: pdf Cummins QSB 330 specs.pdf (43.5 KB, 15 views)
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Old 11-11-2017, 12:59 PM   #69
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David,
That’s about what I remember .. thanks.
I think 16% is more useful than 1/2 gph. 1/2 gph w my 37hp engine would be a huge difference.

I think the biggest downer for the DD is noise. But for what a new engine would cost one could sound insulate until the DD could barely be heard.

DD’s are old but still hard to beat. I could use a 2-53 in my Willard but w a two cyl engine smooth would be near impossible. I assume they had a 180 degree crank.
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Old 11-11-2017, 01:20 PM   #70
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ok Iam totally new.Looking at 2 trawlers,one Thompson 47 ft and a Cheoy
lee LRC 45 ft.
Plan,if Thompson is purchased ,remove the detroit and install a new john deere that research shows has exceptional power,reliability and fuel economy.1400 gal of fuel on board so good distance could be accomplished.
The Cheoy Lee is pretty much turn key with two Cats 3208 ....the plan once deciding which boat is to travel from Ft MEyers along the coast ,thinking 50 miles offshore,to Newfoundland,up to Greenland,over to Iceland,then onto Denmark .Family live there and have not seen them for a bit.So question,Thompson or Cheoy Lee?Look forward to the debate
Why would you replace the Detroit?
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Old 11-11-2017, 02:05 PM   #71
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Only reason I can see to replace the DD is you don't like the leaks or noise. There is noway in hell this would make sense in Thompson trawler. Very limited resale value in a not so popular hull that hasn't been manufactured in a couple of decades. I like Thompsons (some) but if he needs range...buy a different boat or add tankage. Payback on this project would maybe make sense after about 10,000 hrs of running.
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Old 11-11-2017, 02:24 PM   #72
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Ok, I am attaching three manufacturer's data sheets, one for a NA Detroit 6-71 another for a Cummins 6BT 210 hp engine and the third for a Cummins QSB 330. The first two produce about he same wot power and the Cummins 210 at least is a popular trawler engine.

Looking at the N55 injector DD engine which would be appropriate for a 40' trawler, it burns 4 gph while producing 60 hp (as well as I can read the curve), again a reasonable displacement speed hp for a 40' trawler. Now look at the Cummins 210. It produces 60 hp while burning 4 gph, the same as the DD.

The two engines match well at 160 hp both burning about 9.5 gph.

The Cummins 6BT is a generation behind current and the DD is at least two generations behind. FWIW the current generation Cummins QSB does better, burning a bit less than 3.5 gph to make 60 hp, probably due to the more precise, clean burning injection system.

So the best you can do to beat a DD is with a modern, common rail QSB and even then the real difference is about a half a gph.

There are other good reasons to repower a DD based trawler, but fuel consumption isn't one of the better ones.

David
Thanks David, needless to say, I think that's a great post!

As for "10,000 hr payback", I think a zero may have got left off.
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Old 11-12-2017, 07:30 AM   #73
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The hassle with DD is they need to operate at above 60%% power to be efficient.

60% power at the operating RPM , not at full power full rated RPM.

The 71 series can be operated safely at 1200, to 1500RPM so a prop change , instead of an engine change might be as effective for fuel burn , and $20,000 , $50,000 cheaper than a new engine.

Our 6-71 boat cruises easily at 7K (50ft LWL) at 1200RPM -3GPH , and the noise level is minor.
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Old 11-12-2017, 09:22 AM   #74
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DD 2 cycle lovers are alive and well. But to keep stirring the pot ---

The real tests started 40+ years ago, long before EPA restrictions, in the genset business where 24/7 operation clearly showed 2 cycle units to have greater fuel burn and lesser life vs the 4 cycle engines of the time.

By the 1980s you couldn't give a new DD genset or irrigation pump away except for casual users. The same followed for off road use. Why haul inefficient dead iron around when you could be hauling payload? Another tell, anybody been pushing DD gensets in the 40 kW (or any) range for larger yachts during the last half century?

Recently I've had contacts with larger yacht owners where fuel savings amounted to verifiable 30% savings after swap outs. One is finishing planning replacements for twin 16V92s with fuel saving projections in the 30% range. One planing 25 knot vessel removed 8V92s and saved around 6,000 pounds which muddied the waters on his fuel savings (he gained about 3 knots he says) which easily approached 25%.

But don't believe me and you shouldn't. Ask a prolific boating swap out guy like Tony Athens as to what his happy clients say.

Now back to the transatlantic question. If your heart and wallet are set on vessel with DDs, yes replace them with proven fuel sipping JDs or similar and gain range and reliability. The great overall improvements and new horizons allowable by tossing out half century old DD mythology has spawned new horizons, and new boats. Which you should probably buy and avoid the wrath of TFites.
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Old 11-12-2017, 12:06 PM   #75
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The Thompson trawler in question isn't going to cross oceans with or without DDs',JDs' or any other power plant except as a stunt.....
We have 8-71s (4) aboard the boat I run. We run each of the 2 gensets 24/7 alternately. The fuel savings from a new cummins or JD genset on a skid (150 KW) is $65,00 give or take. The payback in fuel (and lube) savings would be approx 3-4 years. We have been trying to get the company to do it , they resist. I'm not a hardcore DD fan but I do have yankee frugality. It doesn't make sense in the Thompson ....on any level economically. It makes sense to run the DD or pass on the purchase. I would love to see how the OP REALLY used his past vessels and compare.
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Old 11-12-2017, 12:15 PM   #76
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Why would you replace the Detroit?

For me it would be about noise and smell, and less so about fuel burn. But thats just me.
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Old 11-12-2017, 12:42 PM   #77
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DD 2 cycle lovers are alive and well. But to keep stirring the pot ---
The vast majority of swaps are still done when problems develop with the existing engines. Very few "trawler type boaters" can ever realize net savings by swapping a healthy engine.

I had a friend who started talking about trading cars even though his older vehicle was fine. He wanted me to financially justify it for him based on fuel savings. Wasn't going to ever happen. I told him, "if you want a new car go buy it and stop talking about it, but don't come to me looking for justification." At $2.50 per gallon, spending $20,000, takes saving 8000 gallons which for most drivers is 25 years or so of savings.

Now, when marine engines need major rebuilds is the time to consider rebuilding or replacing. That then depends on your usage as well as just what you'd prefer to have.
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Old 11-12-2017, 12:51 PM   #78
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I've done more due diligence at the prodding of some on here and realize a rebuild is definitely the way to go.
Ill buy the kit clean &paint all parts in need . machine ANYTHING that requires it and reassemble to enjoy an efficient and adequate motor.
As far as the Onan goes I can get that resolved easily. Most owners are unaware of some of the safety features onan has and I think I know which failed.
Thanks everyone for advise and conversation. If anyone knows best parts house for Detroit's send me contact information please.
Ill be closing on Thompson tomorrow.
Thx again
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Old 11-12-2017, 01:01 PM   #79
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I was thinking age .not knowing if he's as anal about maintaining but after conversation and replies on here a simple in place rebuild will suffice as time is not an issue.Can't wait to begin the project .
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Old 11-12-2017, 01:09 PM   #80
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Makes complete sense.. Ill rebuild more or less as a preventative maintenance train of thought to eliminate ANY motor issues right off. Rewire reupholster install proper prop and head north... Thanks again
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