Redoing a Nordhavn

There is a new 76' Nordhavn in my marina that the owner is ripping out the MTU and putting in a JD. As best I understand it, the MTU was spitting and spewing carbon out the dry stack on initial run from Dana Point to PNW. FRP, awnings, all on deck stuff was a mess. The owner finally got tired of dealing with the offending parties and ordered a new drop in JD, now being installed. Hugh $ involved. Rumor has it the engine was oversized and ran the EGT ran too cool. MTU's answer was run the engine at 80% load as compared to the less than 50% the hull required. The owner is not new to Nordhavn's with a 62' powered by a JD his previous vessel. And the 62's decks etc are clean as a whistle!

As it appears it is not being done under warranty yet the boat is new, can we assume this owner failed to listen to the recommended motor size - thought he knew better, but didn't, so now (embarrassed) does not have the hide to ask for the new engine to be swapped over under warranty?

As best I understand it, Nordhavn and MTU sized the motor for the selected duty, then when problems arose, they*began obfuscating. I have no idea as to final "who is to blame"*solution, other than 3rd hand statements and my own observations. The point to be made is that "perfectly designed" dry stack can be*messy on a new high end yacht. On commercial craft the mess from soot doesn't seem to matter.

Of note, for whatever reason, the engine*was not* able to be properly programmed (TIER II/III) for its dry stack duty. Cummins, Cat and JD claim theirs can - maybe sales BS.

Here*are two*questions for rickB - On the new designs of big yachts with TIER II/III*compliance required, what are the dry stack issues, if any? How many big yachts are wet vs dry?

It seem they could load the engine by adding a gen set/hydraulics off the main engine, changing the prop size/pich/variable, change injectors etc?***Also maybe clean up the exhaust with mufflers.* It seems changing the engine out is a little extreme, but when you can afford a 3 to 4 mil boat what is another mil?*

We had dry exhaust and*changed to wet high rise muffle that combined the raw water and exhaust so what comes out the exhuast is wet, which makes the*eingine room cooler and quieter.* It seems*most of *the long range blue water boats have the*high dry stack exhuast.*

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-- Edited by Phil Fill on Sunday 12th of September 2010 08:12:18 AM

I started boating when I was 12. Built a wood/canvas kayak and I've been messing about in/with boats ever since. I have, however been a serious road biker and ultralight pilot.I remember the early 80s and the pathetic attempts engine manufacturers made to meet emissions standards. Motorcycles were set up so lean they would barely run and they employed little tricks to keep you from adjusting the mixture. Anybody who really cared could file off a limiter and start adjusting but frequently one made things worse as another ragged edge function would go over the deep end. When higher performance exhaust systems were purchased and installed the reduced back pressure would require different jets to be installed to make the things run good. Frequently different needles or slides would be needed instead of jets * * *....it was a nightmare. I think mixture plays an important roll in how diesels run too. The Nordhavn's MTU with it's tier emission requirements may have gone too rich w the wet exhaust and high back pressure. The computer probably said "give her some more fuel * *.. *we've got a load on her". Only it wasn't a load at all. Computers are only as smart as the program and can only respond to the variables they are programed for. Wet exhaust was not in the program on the MTU * *.... apparently. What a shame to waste all that time and money when better knowledge and engineering would make the problem non-existant. Boats and their engines are a complex machine and produced by a small industry that frequently gets things wrong. More complex = more problems. I know start up and warm up w older diesels can/does produce tar like flecks of black unburnt fuel all over the outside of a boat w a dry stack. But to see a prominent builder produce a megabuck yacht with this problem is sad.

Another reason I love my Lehman! Simpler = better!

Reel slowly, Keith!!!!

"Nordhavn and MTU sized the motor for the selected duty,"

The problem , as usual, is folks are not honest in their intended cruise speed.

SURE !

"I want a 10K cruise," then they discover 9K uses half the fuel, and 8K half of that.

The engine ends up running at minor loads .And DIES an early and rapid death.

The folks that dream of high speed cruising SL (sq rt Lwl x more than) 1.15 should at least have a CPP prop factory installed.

The Hunstead and many others are only about $10-15K in the small sizes ( 28 to 36 dia) needed for most "trawlers".

There will allow the engine to be loaded well at lower RPM's and will help with underloading problems.

And prevent the engine from being loaded at all at higher engine speeds because you won't be able to do that without overloading the engine. May as well put a smaller engine in, Prop it correctly and rev the engine up where it belongs. "Cruise prop" is only viable with a variable pitch propeller.

""Cruise prop" is only viable with a variable pitch propeller."

Since most boats will be hauled before a long trip, and most cruising boats have a spare prop , a case could easily be made for an inshore high efficiency cruise prop.

And a std. full speed at full throttle offshore prop for punching into the 6- 12 ft seas , not found inshore in a river or canal.