2 stroke versus 4 stroke

[cimotusa]

Our own RT Firefly made a wonderful suggestion in another thread, a sticky thread covering the many steps involved in a successful boat search and acquisition. This thread will remain open for all to contribute however I do request we limit our contributions to the topic of locating and purchasing a boat.

Let's see what we can come up with folks.

All: question regarding 2 stroke-vs- 4 stroke engines. Is a 4 stroke engine more fuel efficient and environmentally friendly than a 2 stroke engine? I read somewhere that 2 stroke engines my be more difficult to get repaired in the future ( 2 yrs or 10 yrs) for these reasons. We plan on using the trawler for expeditionary exploring.
Fuel being a major cost factor in life-cycle management, currently looking at caterpillar or Cummings 4 stroke engines. Not sure if I’m headed in the right direction.
My husband and I are not diesel maintainers.
Thanks in advance for all the answers. Patti

 

[Baker]

All: question regarding 2 stroke-vs- 4 stroke engines. Is a 4 stroke engine more fuel efficient and environmentally friendly than a 2 stroke engine? I read somewhere that 2 stroke engines my be more difficult to get repaired in the future ( 2 yrs or 10 yrs) for these reasons. We plan on using the trawler for expeditionary exploring.
Fuel being a major cost factor in life-cycle management, currently looking at caterpillar or Cummings 4 stroke engines. Not sure if I’m headed in the right direction.
My husband and I are not diesel maintainers.
Thanks in advance for all the answers. Patti

I think this may not be the right place to be asking this question. It would be good in the "General" area or "Power Systems". But I will answer here and consider moving it later. The only manufactuer of 2 stroke diesels is Detroit...as far as I know. And they do burn more fuel although nominally at lower power settings. As far as "getting repaired", Detroits are likely the most prolific engine in the world. And their "modular" blueprint makes parts interchangeble across the entire line. So parts and people to work on them should be around for quite some time. If I found a boat that I really liked with 671NA in it that are operated in a displacement mode, I would not hesitate as those engines will last forever in that application. NOW if I found the same boat with those 4 stroke Cummins you speak of, I would go with the Cummins.

 

[Comodave]

Detroits are a great and bad engine at the same time. We had 6v53s in a previous boat. They do leak oil so we kept diapers under them all the time. They are a bit more noisy but it is a throaty noise so it does sound good, not an annoying whine noise. They do blow oil and the engine room can get an oily mist all over. There is a fix for that filters the oil mist so that issue can be easily fixed. Those are the bad things about Detroits. The good things are they are everywhere. Mechanics are available everywhere. Almost any diesel mechanic can work on them. Parts are everywhere and are relatively cheap. They run forever unless they are turboed and aftercooled and run hard all the time. Overall I would pick Detroits over Volvos. However I would choose Cummins over almost any other diesel.

 

[Ken E.]

Detroits are a great and bad engine at the same time. We had 6v53s in a previous boat. They do leak oil so we kept diapers under them all the time. They are a bit more noisy but it is a throaty noise so it does sound good, not an annoying whine noise. They do blow oil and the engine room can get an oily mist all over. There is a fix for that filters the oil mist so that issue can be easily fixed. Those are the bad things about Detroits. The good things are they are everywhere. Mechanics are available everywhere. Almost any diesel mechanic can work on them. Parts are everywhere and are relatively cheap. They run forever unless they are turboed and aftercooled and run hard all the time. Overall I would pick Detroits over Volvos. However I would choose Cummins over almost any other diesel.

+1 What Dave said. I've also had Detroits and it really is a love/hate relationship. Realize that 2-cycle Detroits were designed in the 1930's but are still a marvel with the interchangability of parts. But they are somewhat hard to live with, with the oil leaks and engine noise. More modern engines, especially Cummins, IMO, would be a better choice.

 

[DavidM]

Here we go again- the fuel economy debate goes on, and on. Fuel consumption for a trawler is one of the lower cost components. Depreciation, maintenance, slippage are usually all higher. Only if you are using the boat for several hundred hours each year does fuel economy become an issue and even then the differences are small.

A DD makes about 16-17 hp per gpm of fuel at moderate rpms. A modern Cummins makes 18-19 hp per gph, a difference of about 10%. That difference is way, way down on the list of boat operating costs, maybe $300 per year when using it for 300 hours annually.

David

 

[Comodave]

Right, I had no issue with fuel consumption in the boat with Detroits. It was fairly efficient and the difference in fuel burn was almost insignificant.

 

[Baker]

Here we go again- the fuel economy debate goes on, and on. Fuel consumption for a trawler is one of the lower cost components. Depreciation, maintenance, slippage are usually all higher. Only if you are using the boat for several hundred hours each year does fuel economy become an issue and even then the differences are small.

A DD makes about 16-17 hp per gpm of fuel at moderate rpms. A modern Cummins makes 18-19 hp per gph, a difference of about 10%. That difference is way, way down on the list of boat operating costs, maybe $300 per year when using it for 300 hours annually.

David

I don't think anyone is disagreeing with you!!!.....

 

[ranger58sb]

We plan on using the trawler for expeditionary exploring.

My husband and I are not diesel maintainers.

Thanks for your service.

For that scenario, you will have to become diesel maintainers.

There are classes, and other ways to get hands-on instruction, practice, etc. Plus books and videos and so forth.

-Chris

 

[twistedtree]

Here we go again- the fuel economy debate goes on, and on. Fuel consumption for a trawler is one of the lower cost components. Depreciation, maintenance, slippage are usually all higher. Only if you are using the boat for several hundred hours each year does fuel economy become an issue and even then the differences are small.

A DD makes about 16-17 hp per gpm of fuel at moderate rpms. A modern Cummins makes 18-19 hp per gph, a difference of about 10%. That difference is way, way down on the list of boat operating costs, maybe $300 per year when using it for 300 hours annually.

David

Agreed, but the stink and the noise would be deal killers for me since that's a constant annoyance, at least to me.


Also just to clarify, Detroits are the most common 2-stroke diesels that "were" built. They haven't built 2-strokes is decades.

 

[jleonard]

question regarding 2 stroke-vs- 4 stroke engines. Is a 4 stroke engine more fuel efficient and environmentally friendly than a 2 stroke engine? I

In direct answer to these questions, YES a 4 stroke engine is more efficient, but as stated above, probably not significant in a trawler application.

YES a 4 stroke diesel is more environmentally friendly. Those 2 cycle Detroits are no longer made because they couldn't meet emission requirements.
(they have/had other advantages, but clean burning wasn't one)

 

[fgarriso]

3406 CATs for ever.

In my HO they are the most reliable and durable diesels built.

Stay away from the ACERTs

 

[Bendit]

3406 CATs for ever.

In my HO they are the most reliable and durable diesels built.

Stay away from the ACERTs

I have one so I hope you’re right. 16 years so far...

 

[PPandE]

I ran Detroit 671TI's (450hp each) for over twenty years in our 41' Hatteras Sport Fish with never a hiccup. Even after extended periods of disuse they would fire right off. Smoke like the proverbial freight train for the first half hour but ran they did. I hated the smoke and oil mist in the engine room. Walker Air Seps help but they don't completely solve the problem. Seems that they run a very high crankcase pressure that makes them the darling of the mud moving industry by keeping the dirt out but as seals age they leak, blowing mist into the engine room. I also found that they had a narrow window of peak efficiency on the power curve. When run for extended periods at the sweet spot on the tach they were remarkably efficient. Otherwise not so much. I always thought that they were better suited for buses or bulldozers than boats.

 

[Pete Meisinger]

I think you need to redo your budget. Here is a quick snapshot of my expenses, not dollars but highest to lowest.

1) Dockage and storage, including transient fees
2) Insurance, including towing
3) Incidentals like new lines, fenders, hoses, clamps, dock stuff, varnish and paint.
4) New toys (this can fall anywhere on the list, it always changes)
5) Sometimes higher on the list, paid repairs like prop balancing, shaft alignment, genny problems
6) Maintenance, Oil changes, filters, etc.
7) Fuel

Even if you add a few items above #7, which you probably will, Fuel still remains at or near the bottom. Stop worrying about fuel, especially these days, we might actually see diesel at around a buck a gallon!

pete

 

[Lepke]

Large ship engines are all 2 cycle that I know of. They are much more efficient than 4 cycle. And they burn MDO at about 1/2 the price of #2 diesel. But they're not made in sizes for boats.
Cummings and older Caterpillars are great engines. Newer Cats are bad enough that Cat withdrew from the large truck market about 2010. In mining and marine they get a lot closer care. Recreational Cats are usually better than smaller engines, but not much. I wouldn't buy a propulsion engine that didn't have changeable sleeves.

I've had my say about Detroits many times. MY biggest issue is reliability, not fuel usage or pollution. I would consider a boat without Detroits, but it would be a hard decision.