Mercury tdi diesels 3+ mpg ?

[Geebert]

These engines seem more popular over seas than here, but im dying to know how they'd work in a 31 bertram.
Seems like the perfect power plant, if you can handle having electronic diesels.
Up to 370hp, lighter than gas big blocks, can turn 4200rpm, dimensionally smaller than big blocks.
Found this on YouTube,
https://youtu.be/fVyXdNC-R20.
Don't know what boat it is, but he says its a ray hunt design, 335hp mercury tdi (aka VW marine) 36ft,11ft beam, 7ton. The fuel burn he's claiming is,
2900rpm
30lph
23kts
Thats 3.3mpg!
Iv read of a couple other repowers with these engines, and they're all claiming excellent fuel burn numbers. Does anyone know of a 31 with these?

[scenarioL113]

I am no authority on the subject but it does resemble a Ray Hunt Design. Modern technology can def get more out of engines than old technology.

They look cool and are twin turbos. They look super expensive but probably work very well. I am not a huge fan of v8 Diesels but that is probably more of a personal bias from certain model Powerstrokes and some other common v8s that were dogged bc of CARB emissions etc...

I guess they are Volkswagen base engines???

I dont know what their cruise RPM is but if it is anywhere around 3000RPM then they are doing very good on fuel and better than any competition in that dept. Again I have no idea what their cruise is bc WOT is 4200. That leaves a pretty big gap on where the cruise RPM may fall...

I also think the 30LPH is EACH engine

https://samerwebapp01apncus01.azureedge ... _tier3.pdf

[Geebert]

Aaaaahhhh! I could smack myself for overlooking that!!
I bet you're right, thats probably 30lph for each engine.
Thats much more plausible and far less exciting than i had in mind. Thanks for catching that.

[Geebert]

Yanmar also has a 370 v8 that i haven't seen anyone use. Its a little heavier and doesn't spin as fast, but id love to hear performance and economy from either of these engines in a 31

[Tony Meola]

Mercury has been fooling around with the diesel market for a few years. At one point they had an agreement with Cummins. They were using Cummins for their engines. I heard rumors that the stern drives they tied the diesels too were not surviving and after a few years Cummins moved on.

I think the issue in the US is that the big named diesel manufactures have the market tied up. The other issue who is going to work on them. I looked at the dealers for my area. They are all Mercruiser mechanics but I did not see on that I would trust with a diesel engine. So service is a big issue. If they are serious to make a dent in the US market they will need to look for a diesel shop who is willing to take on the line without having to work on Outboards and gas inboards.

Not sure who they are using for their engines now.

[Carl]

How great is the fuel economy if the motors do not last.

Not saying they will not, but when diesel and gas motor designs are combined, the pros and cons of each become blurred.

[Yannis]

I’m waiting for Bob Lico to comment on these motors and I’m expecting his verdict to be rather negative...

[Amberjack]

This fuel efficiency discussion begs the question of why anyone needs 740 hp on a Bertram 31? Amberjack is moderately overpowered with 630 hp and Carl pointed out sometime ago 240-280 hp is probably the optimum power range. Also not to forget Bob Lico who says anything over 26 knots on open ocean is asking for and will find trouble.

[Tony Meola]

This fuel efficiency discussion begs the question of why anyone needs 740 hp on a Bertram 31? Amberjack is moderately overpowered with 630 hp and Carl pointed out sometime ago 240-280 hp is probably the optimum power range. Also not to forget Bob Lico who says anything over 26 knots on open ocean is asking for and will find trouble.

Are you sure Bob said that? He must have been having a bad day when he posted that.

The 31 set up from the factory will have a tendency to chine walk and drop the bow at higher speeds. I would say once you get up around 35 knots give or take. What Bob did to defeat that tendency was change the prop angle and shift weight. That allows the boat to run at higher speeds without getting squirrely.

[Ironworker]

I spoke to a fellow 31 owner who repowered with used Volvo KAMD 42 engines. He said he got 2.5 mpg! Thats pretty damn impressive to me.

[Geebert]

This fuel efficiency discussion begs the question of why anyone needs 740 hp on a Bertram 31? Amberjack is moderately overpowered with 630 hp and Carl pointed out sometime ago 240-280 hp is probably the optimum power range. Also not to forget Bob Lico who says anything over 26 knots on open ocean is asking for and will find trouble.

You wouldnt have to use the370s. The same engine is offered in 335hp, and v6 in 270hp. I guess what the question realy was, in the search for the perfect power plant, has anyone considered or tried these?

[Geebert]

I’m waiting for Bob Lico to comment on these motors and I’m expecting his verdict to be rather negative...

I too would love to hear Bob's opinion, but are you expecting negatively because its bob ? Or because they're high reving, light weight, computer VW engines ?

[Yannis]

Exactly Geebert, all of the above.

By the way, us here in europe, don't you think we would be much more inclined to use european made VW and BMW motors?
Instead of american or japanese, and recently asiatic hyundai, that most of us do? They would probably be cheaper, easy on parts, the networks and mechanics already exist, etc, etc. However the marinized versions of both these car manufacturers didn't sell. Only some mercedes truck engines made it, out of mostly used trucks, mainly for slow moving single engine fishing caiques that have been custom marinized by individual fishermen.

Yes, also because it’sBob, lol!!

[Carl]

I too would love to hear Bob's opinion, but are you expecting negatively because its bob ? Or because they're high reving, light weight, computer VW engines ?

You left out having an inherently weaker V-8 Crank plus using Aluminum heads.



Yanmar proved lighter, higher revving diesels with lots of Aluminum parts "can" work in the marine environment.

But how many going down that route have not faired so well? Knowing whats proven to succeed and known to fail makes me reluctant to be the guinea pig testing a new design based around designs that have failed. I know I'd advocate against being the testing base to any friend of mine. Well, that is unless done as a test trial where something goes wrong the factory sends their guys down to remedy immediately at no cost. But I do not see that being the case and even still with such a short season here, how much time does one waste with a motor or motors out of service.

Some members here are more knowledgeable about the specifics with even more passion in trying to stop a friend from perhaps making a very expensive mistake.


All that said, I hope these VW powerplants work out for those that buy them.

[scenarioL113]

Exactly Geebert, all of the above.

By the way, us here in europe, don't you think we would be much more inclined to use european made VW and BMW motors?
Instead of american or japanese

How about Perkins? I think they are made in the UK? Dont know much about Perkins but I have NOT heard anything bad about them and parts are prob very available worldwide

There is a 31 for sale now with Perkins claiming 2.3 MPG @ 22knots and those engines are prob 20yr old technology.

There is another one with Nanni/Toyota engines reporting big cruise numbers but not sure of burn rate.

Obviously in Europe it is much more important to maximaize fuel economy. (it is important to me too bc I am a cheapo)

[Yannis]

Nanni have a good reputation. There are boat builders that install them, such as Rhea Marine.
Perkins are well known , I have no idea how they perform, or what service and parts network they provide, though.
For much larger engines we use MAN but these are big ones , not for us... Also Scania.
There’s also Iveco that I know are used by Greek fishermen, therefore they should be trust worthy.

Whoever has a mechanical engine holds on tight to them because when replacement time comes there will only exist computer common rail ones due to emissions. The problem here is that because the fuel, any fuel, is transported ten times to reach the remote destinations (islands, mountainous regions etc), there is always the fear of condensation. If you have a common rail motor and water goes through your traps or filters you can kiss your summer good bye, if not anything more serious than that.

[Tony Meola]

I believe Brewster used to have Perkins in his 31 and he ran the hell out of that boat. I don't think he ever sat at the dock for long. Parts would be the only issue with Perkins.

[Amberjack]

Are you sure Bob said that? He must have been having a bad day when he posted that.

The 31 set up from the factory will have a tendency to chine walk and drop the bow at higher speeds. I would say once you get up around 35 knots give or take. What Bob did to defeat that tendency was change the prop angle and shift weight. That allows the boat to run at higher speeds without getting squirrely.

Well, he did say something vaguely similar, but he was talking about center console boats with outboards at higher speeds. Tony you are right and I misquoted Bob.

"you cannot take a fishing cc at 60 in the ocean even on glass days because on the ninth gentle roller the boat will go into a flight like a ski jump and will come crashing down.you will wear that steering wheel TRUST ME. the atlantic ocean is a monster ready to swollen up the unsuspected big shot triple outboard CC ,28 knots is maximum cruise maybe 30 but fuel economy will drop."